Chapter 441. Disorders of Granulocytes

White blood cells, or leukocytes, are part of the innate immune system. They are one of the body’s major defenses in preventing and combating infection. The most common types of leukocytes are lymphocytes, monocytes, and granulocytes. This chapter will deal primarily with granulocytes. These cells are derived from stem cells in the bone marrow and have diverse functions. The most common of the leucocytes is the neutrophil. Deficiency of neutrophils, called neutropenia, is one of the most common hematologic abnormalities during childhood and when severe can result in life-threatening infection.

The absolute neutrophil count and the relative proportions of neutrophils to lymphocytes vary with age. At birth, neutrophils predominate but rapidly decrease during the first few days of life. During infancy, neutrophils comprise approximately 20% to 30% of the circulating white blood cell population. By 5 years of age, neutrophil and lymphocyte counts are equal, and by puberty, adult proportions of approximately 70% are reached.

Neutropenia is defined by an absolute decrease in the absolute number of circulating mature (segmented) and band forms of neutrophils, which can be determined by calculating the absolute neutrophil count (ANC). The ANC is calculated by multiplying the total white blood cells (WBC) obtained from the complete blood count (CBC) by the combined percentage of segmented neutrophils and bands from the differential. The normal resting ANC in the general population ranges between 1500 and 8000 cells/cm3 for Caucasian children over 6 years of age, while 30% of African American children have an ANC as low as 1000 cells/μl. Based on the ANC, neutropenia can be classified as mild (ANC between 1000–1500 cells/μl), moderate (ANC between 500–1000 cells/μl), or severe (ANC < 500 cells/μl). Neutropenia is associated with an increased chance of developing infections. However, only patients with severe neutropenia are likely to develop life-threatening infections.

Patients with neutropenia are most frequently infected with endogenous flora, Staphylococcus aureus, and gram-negative organisms. Susceptibility to bacterial infections varies even in the presence of severe neutropenia. Some patients with chronic neutropenia syndromes with an ANC less than 200 cells do not develop life-threatening infections, while neutropenia induced by immunosuppressive drugs, particularly in conjunction with a malignancy, is associated with higher rates of severe infections, probably due to the additional loss of cellular immunity. Severe neutropenia is associated with skin and soft-tissue infections, gingivitis, stomatitis, pneumonia, and septicemia. However, isolated neutropenia is not associated with an increased risk for parasitic, viral, or fungal infections. Acute neutropenia arises when neutrophils are being employed and production is limited. Chronic neutropenia lasting months to years often evolves from impaired production or excessive splenic sequestration. Neutropenia may commonly occur from factors extrinsic to marrow myeloid cells or less frequently as an acquired disorder of myeloid and stem cells.

Classification of Primary Neutropenias

The inherited disorders of bone marrow production, characterized by selective loss of neutrophil production without accompanying congenital anomalies, are diagnosed by clinical and laboratory features and by genetic testing (Table 441-1).1 Many of the inherited forms of congenital neutropenia fall into a category of chronic disorders with a heterogeneous genetic basis. Neutropenia associated with multifaceted syndromes can now be classified molecularly, which provides a basis for understanding the pathophysiology of the neutropenia.1

Disorders of Granulopoiesis

Reticular dysgenesis (RD) is a very rare form of severe combined immunodeficiency characterized by agammaglobulinemia, lymphopenia, and neutropenia.2-4 Patients with RD usually die shortly after birth from overwhelming sepsis. Bone marrow transplantation is the only available treatment. Examination of the bone marrow from patients with RD reveals absent myeloid precursors with normal erythroid and platelet differentiation. RD is thought to arise from a defect in a common stem cell that affects maturation of myeloid and lymphoid cell lines. However, the defect may be more specific for granulocyte and T lymphocyte development, since some patients with RD have residual functional B lymphocytes and monocytes of host origin following bone marrow transplantation.

Cyclic neutropenia is an autosomal dominant disorder resulting from a mutation in the ELA2 gene encoding for neutrophil elastase.5-8 Peripheral blood neutrophil numbers oscillate with a 21 ± 3 day periodicity, with the nadirs often falling below 200 cells/μl. During the periods of neutropenia, patients often have episodes of fever, malaise, aphthous stomatitis, cervical lymphadenopathy, and gastroenteritis. While episodes may be asymptomatic, life-threatening infections with Clostridiaperfringens and gram-negative organisms are a risk. The diagnosis can be made by monitoring peripheral neutrophil counts three times a week over a 6- to 8-week span. The diagnosis can be confirmed by sequencing the ELA2 gene.7,9 While management is predominantly symptomatic, aggressive use of antibiotics, including coverage for both gram-negative and anaerobic organisms, during infections may be required. Improvement in the neutrophil count occurs with daily granulocyte colony-stimulating factor (G-CSF). Unlike patients with severe congenital neutropenia (SCN), these patients are not at an increased risk for hematologic malignancies.

Chronic benign neutropenia represents a group of disorders that are characterized by absolute neutrophil counts (ANCs) persistently less than 1500 cells/μl. Patients with this disorder are not at an increased risk of developing severe infections but may present with mild to moderate infections of the skin and mucous membrane, including oral ulcers, chronic gingivitis, and chronic periodontitis. Inheritance is autosomal dominant or sporadic, and the management consists of good skin and dental care and expeditious use of antibiotics for infections.

Severe congenital neutropenia and Kostmann disease10,11 are a group of genetic disorders characterized by severe neutropenia, with ANCs persistently below 0.2 × 103 cells/μl and with associated monocytosis and eosinophilia. Affected patients suffer from severe life-threatening bacterial infections beginning in the first few months of life. Examination of the bone marrow reveals an arrest in myeloid differentiation at the promyelocyte or myelocyte stage of development. Approximately 60% of cases of SCN arise from a mutation (autosomal dominant or sporadic) in the ELA2 gene, resulting in an increase in apoptosis of neutrophil precursors in the bone marrow. Additionally, rare cases of autosomal dominant SCN arise from mutations in Gfi1, PRDM5, and PFAAP5, which repress transcription of myeloid genes, including ELA2.12,13 Kostmann disease was the first described (as an autosomal recessive SCN) and results from mutations in the HAX1 gene, which encodes for a mitochondrial protein that protects myeloid precursors from apoptosis.14

A majority of patients, up to 90%, respond to G-CSF, resulting in an increase in peripheral neutrophil counts and reduced rates and severity of infections.15 While their prognosis is greatly improved, they are still at risk for severe bacterial infection, probably due to functional defects in neutrophil function. In addition, they have up to a 40% risk of developing myelodysplasia (MDS) or acute myelogenous leukemia (AML), frequently characterized by monosomy 7 and alterations in expression of the G-CSF receptor.16

Multifaceted Syndromes Accompanied by Neutropenia

Neutropenia arising from complex phenotypes may be classified into disorders of ribosomal dysfunction, metabolism, vesicular transport, and immune function.

Disorders of Ribosomal Dysfunction

Shwachman-Diamond syndrome (SDS) is an autosomal recessive disorder characterized by neutropenia, recurrent infections, exocrine pancreatic insufficiency, short stature, and metaphyseal dysplasia.17 Metaphyseal chondrodysplasia, associated with dwarfism, occurs in approximately 50% of patients, but other skeletal anomalies include rib cage deformities, osteopenia, clinodactyly, kyphosis, supernumerary metatarsals, coxa vara deformity, and syndactyly. SDS usually presents in early infancy due to pancreatic insufficiency with steatorrhea, weight loss, and failure to thrive. While anemia and thrombocytopenia can occur, neutropenia is the most common hematologic manifestation of SDS. Approximately 90% of patients with SDS have an inactivating mutation in the SBDS gene (located on chromosome 7q11), which codes for a protein involved in rRNA maturation.18,19 These patients also have a propensity for monosomy 7–related hematologic disorders, including MDS or AML.

Management of SDS must include the replacement of pancreatic enzymes. G-CSF will raise the absolute neutrophil count into the normal range but should be reserved for persistent neutropenia associated with recurrent bacterial infection. MDS and AML are generally preceded by cytogenetic changes in the bone marrow. Bone marrow transplantation may be curative, but its precise role has not been completely defined.17

Dyskeratosis congenita (DC) is a rare congenital syndrome in which progressive bone marrow failure is associated with the triad of reticulated skin hyperpigmentation, nail dystrophy, and oral leukoplakia.20-22 Common abnormalities include developmental delay, short stature, pulmonary fibrosis, esophageal web, dental carries, hyperkeratosis of the palms and soles, mandibular hypoplasia, and osteoporosis. Inheritance can be X-linked recessive, autosomal dominant, or autosomal recessive. The X-linked recessive form of DC is the most common and most severe and is caused by a mutation in the DKC1 gene coding for dyskerin, a ribosomal RNA processing and telomere maintenance protein. The autosomal dominant form arises from mutations in the telomerase components TERC or TERT.22,23

The hallmark of DC is pancytopenia, with the mean age of onset being 10 years of age. However, 90% of patients have at least a single diminished cell line by 3 years of age, and 50% of patients will develop aplastic anemia. There is an increased incidence of malignancies (9%) in patients with DC. The role of hematopoietic stem cell transplantation is not well defined because of the high prevalence of fatal pulmonary complications, probably due to underlying pulmonary disease.

Disorders of Metabolism

Barth syndrome is a rare X-linked recessive neuromuscular and metabolic disorder characterized by cardiomyopathy, skeletal muscle weakness, and neutropenia and growth retardation. The cardiomyopathy presenting with either biventricular dilatation or left ventricular dysfunction is the most serious complication of this disorder, which is caused by mutations in the TAZ (Tafazzin) gene (located at Xq28), which encodes an enzyme required for cardiolipin synthesis. Cardiolipin is important in maintaining the structure and function of mitochondria. The mechanism of the neutropenia is unknown, but absolute neutrophil counts (ANCs) range between 0.5 to 1.5 × 103 cells/μl. There is no specific treatment for Barth syndrome.24,25 Management is directed by symptoms and the judicious use of antibiotics during infection. Peripheral ANCs will respond to G-CSF. Often, the heart disease and short stature resolve entirely with puberty.

Pearson syndrome is a rare disorder caused by a large deletion in mitochondrial DNA.26,27 Clinical features of Pearson syndrome include failure to thrive; macrocytic sideroblastic anemia; dysfunction of the exocrine pancreas, resulting in malabsorption and chronic diarrhea; lactic acidemia; hepatic dysfunction, which may lead to liver failure; renal disease; and endocrinopathies, such as growth hormone deficiency, hypothyroidism, and hypoparathyroidism. The bone marrow reveals normal cellular numbers, but both erythroid and myeloid demonstrate vacuolization and accelerated apoptosis.

Glycogen storage disease type 1b is an autosomal recessive inborn error in glycogenolysis and gluconeogenesis caused by a defect in the glucose-6-phosphatase complex.28 This disease is characterized by hypoglycemia, hyperlipidemia, hyperuricemia, lactic acidemia, hepatomegaly, nephropathy with renal failure, growth retardation, and recurrent infections. Neutrophils in these patients have a flawed transport system that causes defective mobility and subsequent neutropenia (ANC falling below 0.5 × 103 cells/cm3). The bone marrow in these patients may be either hyper- or hypocellular. Treatment with G-CSF improves the ANC and the risk of infections.29

Disorders of Vesicular Transport

The constellation of autosomal recessive disorders combine neutropenia with partial albinism derived from abnormalities in formation or trafficking of lysosome-related organelles.

Chediak-Higashi syndrome (CHS) is a rare autosomal recessive disorder characterized by partial oculocutaneous albinism in conjunction with neutrophil dysfunction.30 This disorder is frequently associated with recurrent infections; enterocolitis; peripheral neuropathy; easy bruisability with prolonged bleeding times; and hypopigmentation of the skin, hair, and eyes.

CHS is caused by a mutation in the lysosome trafficking regulatory gene (LYST) localized to chromosome 1 (q42-43) resulting in a defect in intracellular trafficking that affects vesicle formation and fusion.31,32 Leukocytes, fibroblasts, platelets, and melanocytes contain large irregular storage and secretory granules. Decreased survival of myeloid precursors in the bone marrow results in moderate neutropenia, with total white blood cell counts of about 2500 cells/μl. Neutrophils contain giant specific and azurophil granules exhibiting diminished bactericidal activity. Ingestion and the respiratory burst remain normal; however, chemotactic activity is decreased, and intracellular killing is diminished due to a slow, inconsistent delivery of dilute amounts of hydrolytic enzymes from the giant granules into the phagosomes. Monocyte and natural killer cell function also is impaired, together resulting in recurrent infections affecting the skin, respiratory tract, and mucous membranes. These infections are caused by both gram-positive and gram-negative bacteria as well as fungi; S. aureus is the most common organism. Despite normal platelet counts, patients with CHS have prolonged bleeding times, which is related to a platelet storage pool abnormality.

Most patients exhibit an accelerated phase caused by a lymphohistiocytic proliferation in the reticuloendothelial systems, which intensifies the already existing neutropenia and leads to pancytopenia.33 The accelerated phase is associated with recurrent bacterial and viral infections and ultimately results in death. The onset of the accelerated phase may be related to the inability to contain and control the Epstein-Barr virus and leads to features that simulate viral-mediated hemophagocytic syndrome.

Oculocutaneous albinism is prominent in chediak-Higashi syndrome (CHS) secondary to melanocyte dysfunction. Patients with this condition have skin that is usually fair, light blond or silvery gray hair, pale retinas, and translucent irises.

Neurological dysfunction frequently appears during the accelerated phase of CHS, commonly associated with gait disturbances, seizures, mental retardation, or dementia later in life; parkinsonism; and peripheral neuropathy. However, spinocerebellar degeneration or movement disorders may be the presenting symptoms of CHS, and parkinsonism or dementia occurs in patients who survive to adulthood.

CHD is often fatal before age 10, usually secondary to overwhelming infection. Those who survive longer are at increased risk of developing lymphomas. Early bone marrow transplantation is preferred therapy, especially if the patient is in the accelerated phase. While a transplant will correct the immune problem and the accelerated phase, it has little effect on the development of neurological sequela, which will frequently become worse with age.

Griscelli syndrome (GS) is a rare autosomal recessive disorder characterized by pigmentary dilution of the skin and hair in association with either hepatosplenomegaly, lymphohistiocytosis, a combined T-cell and B-cell immunodeficiency with an associated hemophagocytic syndrome, or predominantly neurological signs.34,35 They have silver hair with large clumps of pigment in the hair shaft and the accumulation of melanosomes in their melanocytes. Neurological complications include obstructive hydrocephalus, bilateral basal ganglia involvement, hypotonia, encephalopathy, hemiparesis, peripheral facial palsy, spasticity, seizures, and psychomotor retardation.

GS is caused by one of two gene mutations located at band 15q21RAB27A, which encodes for GTP-binding protein, or MYO5A, which codes for myosin Va. Both proteins are involved in pigment granule (melanosome) transport. The two clinical presentations of GS are due to differential expression of RAB27A and MYO5A. MYO5A is expressed in the brain while RAB27A is not, accounting for the absence of neurological involvement with in with RAB27A mutations. All patients with RAB27A mutation have uncontrolled activation of T cells and macrophages and develop hemophagocytic syndrome, which is not seen with MYO5A mutations. Patients with RAB27A mutations can be successfully treated with bone marrow transplantation.

Hermansky-Pudlak syndrome type II (HPSII) is a rare autosomal recessive disease characterized by neutropenia, oculocutaneous albinism, hemorrhagic diathesis as a result of platelet dysfunction, and lysosomal ceroid storage.36,37 Patients are also at risk for developing pulmonary fibrosis and inflammatory colitis. HPSII is caused by mutations in the gene (AP3B1 or HSP2) encoding the beta subunit of the adaptor protein 3 complex. The adaptor protein complex is involved in intracellular vesicle formation and trafficking, and mutations in eight genes (HSP1-8) have been associated with variations of HPS. In HPSII melanocytes, platelets, cytotoxic T-lymphocytes, and natural killer cells are preferentially affected and the neutropenia is associated with diminished levels of neutrophil elastase.

The autosomal recessive disorder p14 deficiency leads to congenital neutropenia, partial albinism, short stature, and B-cell and cytotoxic T-cell deficiencies.38 The p14 protein is required for the proper biogenesis of endosomes and subcellular relocation of mitogen-activated protein kinase signaling to late endosomes.

Cohen syndrome is an autosomal recessive disorder characterized by intermittent isolated neutropenia; nonprogressive mild to severe psychomotor retardation; facial dysmorphism, including high-arched or wave-shaped eyelids, a short philtrum, thick hair, and low hairline; pigmentary retinopathy; joint laxity; and microcephaly.39 The gene (COH1) for Cohen syndrome has been mapped to chromosome 8q22, which codes for a transmembrane protein thought to be involved in intracellular vesicle transport.

Disorders of Immune Function

Cartilage-hair hypoplasia (CHH) is an autosomal recessive disorder characterized by short-limb dwarfism arising from metaphyseal dysplasia, fine hair, immunodeficiency, and increased incidence of cancer.40,41 Neutropenia and lymphopenia occur in approximately one fourth of patients, and they are at particular risk for infections with varicella zoster, Candida species, and Pneumocystis carinii. Physical manifestations of CHH include redundant skin folds around the neck and extremities; fine and sparse hair, including eyebrows; hypopigmentation of the skin; nail dysplasia; notched incisors; microdontia; doubling of lower premolar lingual cusps; hypermobility and hyperflexibility of the joints; and mild platyspondylia and lumbar lordosis of the spine. It arises from mutations in the RMRPG gene on chromosome 9p21-p12, which encodes the RNA component of a ribonuclear protein ribonuclease. Abnormalities of both T-cell function and the humoral immune system have been found. The disorder is associated with moderate to severe neutropenia. Some patients have benefited from G-CSF treatment.

Hyper-IgM syndrome is an immunodeficiency disorder with elevated IgM caused by at least three different genetic defects. The most common form of the disease, X-linked hyper-IgM syndrome (Xq26-27.2), arises from mutations in the gene for CD40 ligand and in 50% of patients is accompanied by neutropenia.42,43 The mechanism of neutropenia is not well understood. Myeloid precursors in the bone marrow express CD40 ligand, and bone marrow examination in these patients reveals maturation arrest at the promyelocyte-myelocyte stage.

CD40 ligand is normally expressed on activated T lymphocytes, macrophages, and dendritic cells. It is necessary for an immunoglobulin class switch. Thus, patients with X-linked hyper-IgM syndrome have normal or elevated IgM with extremely low or absent IgG, IgA, and IgE. These patients also have altered cell-mediated immunity with an increased susceptibility to opportunistic infection and are at increased risk of developing autoimmune disorders and malignancies probably due to altered macrophage and dendritic cell function.

Treatment for the immune deficiency by IgG replacement is necessary. The neutropenia responds to G-CSF. Pneumocystis jirovecii prophylaxis with trimethoprim-sulfamethoxazole is indicated as soon as the diagnosis is established. Neutropenia may also accompany common variable immune deficiency, isolated IgA deficiency, and X-linked agammaglobulinemia.6

Wiskott-Aldrich syndrome is an X-linked genetic disorder with variable expression and in rare cases severe neutropenia.44 Those patients with neutropenia have cellular and humoral immunodeficiency, normal platelet numbers, and recurrent infections. The Wiskott-Aldrich syndrome protein (WASP) is located on Xp11.22-23 and codes for a protein involved in signal transduction between G-protein coupled receptors and the initiation of actin bundling. WASP mutations affect cellular functions such as growth, endocytosis, exocytosis, and cytokinesis. The bone marrow shows trilineage dysplasia with markedly reduced myelopoiesis. The neutropenia responds to G-CSF therapy.

Myelokathexis and Whim Syndrome

Myelokathexis is a rare autosomal dominant disorder characterized by moderate to severe neutropenia accompanied by neutrophil hyperplasia in the bone marrow. There are striking morphological changes in the neutrophils, including cytoplasmic vacuoles, prominent granules, and nuclear hypersegmentation with very thin filaments connecting pyknotic-appearing nuclear lobes.45,46 Recurrent warts and hypogammaglobulinemia often accompany myelokathexis, hence the acronym WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis). This syndrome is now attributable to a defect in the chemokine receptor CXCR-4.47 Observations of these patients have suggested an important role for the ligand stromal derived factor I (SDF-I) in regulating neutrophil migration as well as the trafficking of lymphocytes in hematopoietic progenitors cells. Myeloid cells fail to be mobilized from the bone marrow, where they undergo eventual apoptosis. The neutropenia can often be partially corrected by the use of G-CSF and GM-CSF.

Acquired Neutropenias of Myeloid and Stem Cells

Neutropenia can develop as a result of a variety of conditions.48 Bone marrow failure with neutropenia, associated with anemia and thrombocytopenia, can occur in aplastic anemia, which is thought to arise from altered immune function or from marrow replacement (eg, malignancy). Vitamin B12, folate, and copper deficiency as well as starvation can lead to decreased marrow production of neutrophils. Antibodies directed against neutrophils and several drugs, including chemotherapeutic agents, can induce neutropenia. Overwhelming bacterial sepsis, some viruses, fungi, and protozoal infections can also cause neutropenia. This condition can arise during hemodialysis and leukapheresis. Many of the acquired neutropenias will respond to removal of the offending agent or treatment with recombinant G-CSF.

Immune Neutropenias

Alloimmune neonatal neutropenia is a self-limited condition whereby maternal antineutrophil antibodies (IgG) cross the placenta, resulting in the destruction of the newborn’s neutrophils.49 Maternal antibodies may be the result of an underlying maternal autoimmune condition or may be secondary to direct sensitization to paternally derived fetal neutrophil antigens, in a similar fashion to Rh hemolytic disease. The duration and extent of the neutropenia depends on maternal antibody production, but recovery is usually complete within 6 to 12 weeks. During the neutropenic period, the infant should be watched closely for infection and managed aggressively with appropriate antibiotics for clinical indications.

Autoimmune neutropenia of infancy is a relatively benign condition in which children transiently develop moderate to severe neutropenia secondary to the production of antineutrophil antibodies.50 The age of onset is usually between 5 to 15 months, and the mean duration of neutropenia is 17 months. While the absolute neutrophil counts often fall below 0.5 × 103 cells/μl, life-threatening infections rarely occur. Patients usually present with otitis media, gastroenteritis, tonsillitis, and skin and soft-tissue infections. Approximately one third of the patients show circulating antibodies against neutrophil antigens HNA-1 or HNA-2. G-CSF is the most effective agent at normalizing peripheral neutrophil counts in patients with recurrent fever or infectious complications.

Autoimmune neutropenia arising from the production of antineutrophil antibodies can occur in patients with no underlying autoimmune disorder or can be associated with a variety of autoimmune conditions such as systemic lupus erythematosus, autoimmune hemolytic anemia, immune thrombocytopenia, or thyroiditis. Autoimmune neutropenia in children frequently is associated with immune deficiencies.51 Successful management of the underlying autoimmune disease will often result in normalization of peripheral neutrophil counts. In other instances, G-CSF may be required.

Drug-related neutropenia is common and can occur at any age, although more than 90% of cases occur in adults.52 Drug-induced neutropenia is not always predictable, but when it arises, it may occur by several different mechanisms, including immune-mediated toxic, idiosyncratic, and hypersensitivity reactions. In contrast, cytotoxic chemotherapy predictably affects proliferating myeloid cells by impairing neutrophil production. Therapy of the former causes of neutropenia requires cessation of the responsible drug. Treatment with G-CSF should be employed, but it may not always be effective. The neutropenia accompanying cytotoxic chemotherapy typically occurs 7 to 10 days after administering the drug. It is often accompanied by depressed cellular immunity, thereby predisposing patients to a much greater risk of infection than those disorders associated with the acute onset of isolated neutropenia.

Reticuloendothelial sequestration frequently results in mild to moderate neutropenia often accompanied by platelet and red cell trapping in the spleen, leading to thrombocytopenia and anemia. Splenectomy should be avoided if possible because of the increased risk of infection due to encapsulated bacterial organisms.48

Viral-related neutropenia occurs concurrently or shortly following a viral illness and is secondary to viral antibodies cross-reacting to neutrophil antigens. The neutropenia is usually mild, transient, and of minimal clinical significance. Conditions that result in complement activation, inflammatory disorders, hemodialysis, and extracorporeal membrane oxygenation (ECMO) can also cause neutropenia.53

Neutrophil Production and Kinetics

Like other cells in the circulation, neutrophils originate from pluripotential stem cells in the bone marrow. Depending on environmental influences, these stem cells may give rise to the early progenitors of blood cells. By using an antibody to the cell surface antigen CD34, human pluripotential stem cells can be isolated and employed for human stem cell transplantation. These pluripotential stem cells give rise to more mature stem cells that are committed to either lymphoid or myeloid development. Myelopoiesis begins with about 106stem cells in the bone marrow; these cells undergo both self-renewal and differentiation to produce all the individual types of blood cells. The growth factors such as G-CSF and GM-CSF interact with specific receptors on progenitor cells, giving rise to myeloid precursors through a process of cell division, which is affected by the synthesis of many cytoplasmic components of the neutrophil as well as by expression of the transcription factors that are necessary for myeloid cell differentiation.30 Transcription factors such as PU.1, C/EBPα and ε, and GFi-1 affect myeloid differentiation. The mechanism that determines whether a stem cell simply self-renews or differentiates is probably governed by the different signaling pathways used between cell surface receptors and the nucleus. Cell proliferation and differentiation are also influenced by interleukins in the local hematopoietic microbe environment, which is defined by extracellular matrix proteins in their stromal elements. The colony-stimulating factors often work in synergy with as many as four or five other factors to influence the multiple steps in myelopoiesis. As cells mature, they lose the receptors for most cytokines, especially those that influence early cell development such as stem cell factor. Once the cells have matured, they express receptor for chemokines, which help direct the cells to sites of inflammation. Normally the production rates of the neutrophils equal the destruction rates.

Based on kinetic studies, four cellular components containing myeloid cells are generally recognized: (1) the marrow mitotic compartment; (2) the marrow postmitotic and storage compartment; (3) the vascular compartment, which in turn is divided into the circulating pool and marginating pool; and (4) the tissue compartments.54 Neutrophils survive intervascularly for 6 to 12 hours. In order to maintain a level of circulating neutrophils of 5000/μl, a daily production of 20,000/μl of neutrophils is required. During infections, tissue macrophages, upon activation by invading microbes, release interleukin-1 (IL-1) and tumor necrosis factor (TNF), which activates stromal cells and T lymphocytes to produce additional growth factors. In turn, the early progenitor cells in the normal marrow are then stimulated to proliferate and differentiate. This step markedly shortens the time of maturation of myeloid precursors through the postmitotic pool. Increased numbers of neutrophils can then be released from the marrow storage compartment into the circulation. These same neutrophils can then be primed by either G-CSF or GM-CSF to enhance bactericidal function. The peripheral blood pool of neutrophils migrates via diapedesis into the tissues to ward off bacterial infection. The peripheral blood pool is supported by an immense marrow reserve of identifiable precursors, some undergoing mitosis and others maturing into bands and neutrophils. The proliferation of myeloid cells takes place during the first three stages of neutrophil development (myeloblast, promyelocyte, and myelocyte), and each of these stages usually undergo five divisions. Once the myelocyte stage is reached, the cells terminally differentiate into myelocytes, bands, and neutrophils. Neutrophil maturation is accompanied with changes in the nucleus and with the production of azurophilic primary granules and specific secondary granules. Through the sequential activation of transcription factors, the myelocytes acquire peroxidase-positive azurophil granules in the myelocytes and specific granules. In turn, the formation of the segmented neutrophils takes place through condensation of chromatin, loss of nuclei, and the shape changes of the nucleus, resulting in the characteristic morphometry of the segmented neutrophil.

Neutrophil Function

Neutrophils are the first line of defense against bacterial and fungal infections. About 1011 neutrophils per day are produced.30 Neutrophil responses are initiated as these cells pass through the postcapillary venules and detect low levels of chemokines and other substances released from sites of infection. During infection, the cellular detectors initiate subtle changes in the distribution and activity of surface molecules on both endothelial cells and neutrophils (Fig. 441-1). The initial associations lead to weak neutrophil adherence, as manifested by the rolling of the neutrophils on the endothelium, which is mediated primarily by cell-selectin-carbohydrate interactions. Rolling is characterized by neutrophil adhesion, which is made and broken, thereby allowing neutrophils to move hesitantly along the endothelial surface. The rolling of neutrophils allows for the cells to be more intensely exposed to such factors as TNF or IL-1. This then leads to the induction of qualitative and quantitative changes in the family of β2 integrin adhesion receptors on the neutrophil (eg, the CD11/CD18 group of surface molecules). The activated integrin receptors mediate strong heterotypic adhesion between the neutrophils themselves and the neutrophils and endothelial cells. The neutrophils then flatten onto the postcapillary venule endothelial cells.

The next phase involves loosening the integrin adhesion by mobilizing integrin receptors to the trailing pseudopod of the neutrophil. The neutrophil displaces part of this pseudopod and undergoes conformational changes that allow it to migrate between endothelial junctions into the extravascular tissue. During neutrophil migration, there is a coordinated, complex set of activities, including receptor engagement, signal transduction, and remodeling of the actin microfilaments composing, in part, the cytoskeleton. When the neutrophil reaches the site of infection, it recognizes pathogens by means of Fc immunoglobulin, complement, and toll-like receptors. The neutrophil ingests the microbes that are opsonized (prepared for ingestion) by factors in human serum, which include immunoglobulin G (IgG) and C3, respectively. The opsonins facilitate phagocytosis of microbes into a closed vacuole called a phagosome. As phagocytosis is proceeding, two cellular responses essential for optimal microbicidal activity occur concomitantly—degranulation and activation of the nicotinamide-adenine dinucleotide phosphate (NADPH)–dependent oxidase. Fusion of the neutrophil granule membranes with the phagosome membrane results in the delivery of both components from the azurophil and specific granules. Concomitantly, the assembly and activation of NADPH oxidase at the phagosome membrane occurs. The multicomponent NADPH oxidase generates superoxide (O2-) from molecular oxygen, which then decomposes to hydrogen peroxide (H2O2) and singlet oxygen. In turn, H2O2 can react with (O2-) to form hydroxyl radicals. Myeloperoxidase (found in azurophil granules) can catalyze a reaction that employs H2O2 and chloride ion to create hypochlorous acid (HOCl) in the phagosome. H2O2 in the neutrophil cytoplasm isreduced to H2O2 and O2 by glutathione. The potent oxidants contained within the phagosome can denature bacterial proteins, thereby rendering them susceptible to proteolysis. Additionally, some of the neutrophil proteases are activated by the oxidants. These coordinated events serve to enhance breakdown of pathogens at the site of infection. Following resolution of infection, as inflammation is terminated, neutrophils undergo apoptosis, thus preventing injury to host.

Disorders of Phagocytosis

Neutrophils play a key role in protecting the skin and mucous membranes of the oral cavity, the respiratory tract, and the gastrointestinal tract; they are the first line of defense against bacterial invasion. Neutrophils arrive at sites of inflammation during the critical 2- to 4-hour period after microbial tissue invasion. It is at this juncture that infection must be contained. If not, the infection can spread and potentially disseminate. Patients with the following disorders of neutrophil function have difficulty in containing bacterial infection (Table 441-2).

Specific Granule Deficiency

This is a rare autosomal recessive disorder resulting in an increased susceptibility to severe bacterial infection, characterized by severely diminished production of neutrophil constituents, defective neutrophil chemotaxis, and diminished bactericidal activity. On peripheral blood smears, the nuclei of the neutrophils have a characteristic bilobed morphology. Eosinophil-specific granules exhibit diminished eosinophil-cationic protein, eosinophil-derived neurotoxin, and major basic protein. The disorder arises secondarily to the functional loss of the transcription factors CCAAT/ε or Gfi-1.55,56 Patients are predisposed to infections caused by Staphylococcus aureus and Pseudomonas species. Treatment is supportive.

Leukocyte Adhesion Deficiency (Lad)

This is an autosomal recessive disorder of neutrophil function arising from a deficiency of the beta-2 antigen subunit of the leukocyte adhesion molecule. The disorder is characterized by recurrent bacterial infections and impaired pus formation and wound healing associated with diminished adhesion functions of neutrophils, monocytes, and NK cells.

LAD type I is characterized by marked leukocytosis, ranging from 12,000 to 60,000/mm3. Even in the absence of a specific infection, patients exhibit a diminished expression of abnormal function of the β2 integrin family surface glycoproteins, designated the CD11/CD18 complex. These proteins include LFA-1 (CD11a/CD18), Mac-1 (CD11b/CD18), and p150, 95 (CD11c/CD18), which are expressed on lymphocytes, monocytes/macrophages, neutrophils, and natural killer cells, respectively, and are markedly diminished.57,58 A markedly diminished or absent CD11/CD18 complex accounts for the failure of patients’ neutrophils to adhere to endothelial cells and subsequently migrate to specific sites of infection.

Each of the molecules comprising the CD11/CD18 complex contains an a and a β subunit that is noncovalently associated in an α-β structure. Each of the a chains associates with the same β subunit and is distinguished by its unique α subunit protein structure. Many patients have point mutations that result in a single amino acid substitution in the β2 subunit. The resulting mutations lead to the failure of the expression of the β2 subunit and a failure of the assembly of the α-β subunits on leukocyte membranes.

The leukocytes in patients with the most severe clinical form of LAD express less than 0.3% of the normal amount of β2 integrins, while those patients with the moderate phenotype may express 2% to 7% of normal amounts of β2 integrin molecules. The severe forms of LAD-I suffer from recurrent and chronic or even gangrenous soft-tissue infections generated by bacterial and fungal microorganisms such as Staphylococcus aureus,Pseudomonas species, other gram-negative microorganisms, or Candida species. Patients with a moderate phenotype have fewer and less severe infections. Infectious susceptibility and impaired wound healing are related to diminished or delayed infiltration of neutrophils and monocytes into extravascular inflammatory sites. All patients surviving infancy have profound periodontitis. Delayed separation of the umbilical cord is noted following birth.

LAD-II or congenital disorder of glycosylation type IIc is an autosomal recessive disorder that is associated with growth and mental retardation.59,60 Patients have distinctive dysmorphic features, including microcephaly and a depressed nasal bridge along with seizures and hypotonia, which are related to a defect in fucose metabolism. Laboratory studies reveal decreased neutrophil motility but normal phagocytic activity. Patients lack the red blood cell H antigen, a fucosylated protein, and manifest the Bombay (hh) phenotype. Functionally, the neutrophils from these patients are unable to adhere to E-selectin or cytokine-activated endothelial cells and exhibit an inability to roll on postcapillary venules in vivo. The LAD-II neutrophils express normal levels of CD18 integrins but are deficient in the fucose structure sialyl-Lewis X, which renders the cell unable to roll on activated endothelial cells. The LAD-II defect is secondary to decreased protein fucosylation, which arises from impaired transport of GDP-fucose from cytoplasm to the Golgi lumen.

LAD-III has been described in four patients with recurrent infections, leukocytosis, absent pus formation, and a bleeding disorder.61 It is characterized by a general failure to activate a number of integrins on leukocytes and platelets.

By applying flow-cytometric measurements of surface CD11b on stimulated and unstimulated neutrophils using monoclonal antibodies against CD11b or the unique a chains, the diagnosis of LAD-I may be established. The diagnosis of LAD-II is established by demonstrating the lack the sialyl-Lewis X on neutrophils.

Patients with the severe form of LAD-I should be considered for allogeneic bone marrow transplantation.62 Since only 25% of LAD patients will have a matched sibling donor, other donor sources have been tried, but the toxicity associated with the myeloablative transplant regiments have restricted the more extensive use of alternate donor sources. Patients with moderate LAD can be maintained on prophylactic trimethoprim-sulfamethoxazole. Broad-spectrum antibiotics are indicated for empirical therapy when infection occurs. Since most children with LAD lack a matched sibling donor, gene replacement therapy may be considered in the future. LAD-I is an ideal candidate for this approach, because some improvement in neutrophil function attenuates the severity of the disease.

Some patients with LAD-II respond to oral fucose, which restores the expression of fucosylated sialyl-Lewis X neutrophils and leads to a disappearance of leukocytosis and an attenuation of recurrent bacterial infection.

The severity of repeated infectious complications correlates with the extent of β2 integrin deficiency. Patients with severe deficiency usually die in infancy, whereas patients with moderate deficiency have infrequent life-threatening infections and relatively long survival. The latter patients are chronically afflicted with severe periodontitis.

Hyperimmunoglobulin E Syndrome (Hyper-IgE)

This is a rare autosomal dominant disorder with incomplete penetrance characterized by markedly elevated levels of serum IgE, chronic eczema, recurrent bacterial infections, retention of primary dentition, and a distinctive coarse facial appearance.63-65 The patients are predisposed to bone fractures and manifest hyperextensibility of the joints.

There have been reports of more than 200 cases. Hyper-IgE syndrome occurs in patients from diverse ethnic backgrounds. It does not seem to be more common in any specific population. Both males and females have been affected with variable expression in succeeding generations, suggesting that the disorder is autosomal dominant with incomplete penetrance. The neutrophils and monocytes from patients with hyper-IgE syndrome exhibit a variable chemotactic defect that appears extrinsic to the neutrophil. Several mutations affecting the signaling molecule STAT 3 have been identified in more than 50 familial and sporadic cases of hyper-IgE syndrome.66 STAT 3 plays a pivotal role in embryogenesis and immunomodulation/regulation, including the induction of antigen-specific T-cell tolerance and IL-12 regulation, which may explain the diverse clinical features of the syndrome.

Clinical manifestations of hyper-IgE syndrome may begin in the first 2 months of life and may include a chronic eczematoid rash, which is typically papular and pruritic and involves the face and extensor surfaces of the arms and legs. Skin lesions usually are sharply demarcated and lack surrounding erythema. By school age, there is a history of recurrent skin abscesses, recurrent pneumonias often leading to pneumatoceles, and chronic otitis media. The most common organism isolated in patients with hyper-IgE syndrome is Staphylococcus aureus, but other organisms, including Haemophilusinfluenzae and Escherichia coli, have been documented. Other associated features include coarse facial features, a broad nasal bridge, and facial asymmetry. There is often retention of primary teeth and generalized osteopenia, which can predispose the patients to bone fractures.

Hyper-IgE syndrome needs to be differentiated from atopic dermatitis. In the former disorder, S aureus infections are deep seeded and serious, and respiratory allergy is rare. Atopic dermatitis in characterized by superficial S aureus infections; furthermore, the patients with atopic dermatitis do not have the distinctive anatomic features found in hyper-IgE syndrome.

The patient with hyper-IgE syndrome has serum IgE levels that exceed 2500 IU/ml. These individuals often have abnormally low anamnestic antibody responses and depressed cell-mediated responses to neoantigens. The treatment of hyper-IgE syndrome is predominantly supportive and includes the judicious use of antistaphylococcal antibiotic therapy. Prophylaxis with trimethoprim-sulfamethoxazole can reduce the frequency of recurrent infections. Incision and drainage are required for managing abscesses, including infected pneumatoceles. At times, the neutrophils of patients manifest impaired chemotactic responses. If hyper-IgE is recognized early in life and if the patient is placed on chronic antistaphylococcal antibiotic therapy, the prognosis is good.

Chronic Granulomatous Disease

Chronic granulomatous disease (CGD) is a genetic disorder affecting the function of both neutrophils and monocytes. The phagocytic cells are able to ingest but not kill catalase-positive microorganisms because of an inability to generate antimicrobial oxygen metabolites. CGD arises from mutations involving one of four genes that encode some of the components of the reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase.67,68

The incidence of CGD in the United States is 1 in 200,000 births, based on data from the National Institutes of Allergy and Infections Disease Registry.69 Data from the registry indicate that 86% of patients are male. Of the total number of patients in the registry, 70% have the X-linked recessive form of the disease.

The primary defect in CGD resides in the inability of phagocytes to generate superoxide (O2-) due to the absence of some components of the NADPH oxidase system.68 NADPH oxidase is comprised in part of four key proteins that account for the genetic basis of the disorder. These include a membrane-bound, cytochrome b558; a 47kDa cytosolic protein p47phox(47 phagocyte oxidase protein); and a 67kDa cytosolic protein (p67phox). In turn, cytochrome b558 consists of two heme-containing subunits, p22phox and gp91phox(glycoprotein 91phox). Upon activation of the phagocyte, the cytosolic proteins, along with a low molecular weight guanine triphosphatase Rac2, translocate to the membrane and interact with the cytoplasmic domains of the transmembrane cytochrome b558 to form the active oxidase. Oxidase activity depends on p22phox to maintain the stability of gp91phox. The latter protein is required for electron transport through its binding of NADPH, flavin, and heme.

Approximately 65% of children affected with CGD have a mutation in the CYBB gene, located on the X chromosome, which encodes for gp91phox. The remainder of patients inherit CGD in an autosomal recessive fashion. Mutations in the NCF1 gene, encoding for p47phox, accounts for 25% of cases, while mutations in the genes NCF2 (encoding for p67phox) and CYBA (encoding for p22phox) each account for 5% of cases, respectively.

Mutations in the genes comprising components of the NADPH mentioned above impair the phagocyte’s ability to generate O2- and H2O2 from molecular O2 following phagocytosis. Mutations in genes giving rise to cytochrome b588 affect electron transport from NADPH to flavin and heme prosthetic groups, whereas mutant genes encoding for p47phox and p67phox affect activation of cytochrome b588 by preventing changes in its tertiary structure.

The failure to activate the NADPH oxidase in CGD predisposes the host to infection with catalase-positive microorganisms. Normal neutrophils generate H2O2 in the phagosome and utilize myeloperoxidase, which is delivered into the phagosome from primary granules fusing with the phagosome’s membrane to generate hypochlorous acid from chloride and kill microbes. The H2O2 produced by normal neutrophils can exceed the capacity of catalase, a hydrogen peroxide–catabolizing enzyme of many aerobic microorganisms, including S. aureus, most gram-negative bacteria, and C albicans and Aspergillus species, to kill the offending microorganisms. In contrast, the CGD neutrophils, which cannot produce H2O2, are unable to kill the catalase-positive microorganisms but are able to kill catalase-negative microorganisms, because the microorganisms produce sufficient amounts of H2O2 to result in a microbicidal effect. Catalase-positive microorganisms can survive for long periods in the CGD phagosome. Eventually the bacteria are killed but are not digested properly in macrophages and thereby contribute to the formation of granulomata.

Although the clinical presentations can be quite variable, several features suggest the diagnosis of chronic granulomatous disease (CGD).68 In a patient with recurrent lymphadenitis, CGD should be considered. Additionally, patients with bacterial abscesses affecting the lung, perianal area, liver, and spleen or with manifesting osteomyelitis at multiple sites or in the small bones of the hands and feet should be evaluated for CGD. Patients with a family history of recurrent infections or unusual catalase-positive microbial infections all require clinical evaluation for this disorder.70 The onset of clinical signs and symptoms may occur from early infancy to young adulthood. Although the majority of patients with CGD (76%) are diagnosed before the age of 5 years, approximately 10% are not diagnosed until the second decade of life and on rare occasions even later.

S aureus is the microorganism most commonly affecting CGD patients, although infection with Serratia marcescens, Burkholderia cepacia, Salmonella species, Aspergillus species, and C albicans can also occur. Patients may develop numerous sequelae, including the anemia of chronic disease, lymphadenopathy, hepatosplenomegaly, hypergammaglobulinemia, chronic purulent dermatitis, restrictive lung disease, gingivitis, hydronephrosis, and pyloric outlet obstruction. Chronic inflammation may lead to granuloma formation, and some patients may develop a Crohn disease–like inflammatory bowel process. Leukocytes from patients with CGD have normal glucose-6-phosphate dehydrogenase (G-6-PD) activity; however, a few individuals with apparent CGD have had neutrophils lacking or almost lacking in G-6-PD activity and have been unable to generate NADPH. These patients have red cells that also lack the enzyme; thus, they have chronic hemolysis.

The guanine triphosphatase Rac2 plays an essential role in modulating the activity of NADPH and the actin cytoskeleton in neutrophils. A toddler has been described with a history of a perirectal abscess and subsequent infections that failed to heal properly. His neutrophils had defective chemotaxis and failed to generate O2– upon activation.71,72 Molecular analysis revealed a mutant Rac2 gene that did not bind GTP and behaved as a dominant negative to impair Rac2-mediated activation of the respiratory burst and actin assembly accounted for failure of a patient’s neutrophils to generate O2– and undergo chemotaxis, predisposing the patient to infections.

Several laboratory tests have been used to diagnose CGD.68 Classically, the diagnosis was made by using the nitroblue tetrazolium dye (NBT) test. In patients with CGD, neutrophils, upon activation, fail to reduce the yellow water-soluble tetrazolium dye to an insoluble blue formazan pigment because of the inactivity of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system. This test is nonquantitative and may miss some patients with p47phox deficiency who may have low but insufficient levels of NADPH oxidase activity. Currently, the dihydrorhodamine (DHR) test employs flow cytometry to detect the conversion of DHR to rhodamine upon activation of the neutrophils. Autosomal recessive p22phox, p67phox, p47phox, and gp91phox expression can be determined by Western blot analysis, and individual genetic analysis can be employed to identify the specific genetic mutation to determine the inheritance pattern. When suspected, the prenatal diagnosis can be determined either genetically (DNA analysis following chorionic villous biopsy) or functionally by evaluating neutrophil activation on fetal blood via DHR. Similarly, the female carrier state of X-linked CGD can be determined genetically or functionally by activating neutrophils and establishing whether two populations of neutrophils exist (ie, one that oxidizes DHR and one that does not).

Treatment involves the aggressive use of bactericidal antibiotics and appropriate drainage of abscesses. Cultures must be obtained as soon as infections are suspected. If fever occurs, it is advisable to obtain studies that aid in managing septic episodes, which may include chest and skeletal x-rays or CT scans to ascertain whether pneumonia, osteomyelitis, or liver abscesses are present. Often it is necessary to administer antibiotics for a long period of time. Aspergillus infections require treatment with antifungal agents and, in refractory cases, granulocyte transfusions. Glucocorticoids may be useful in treating patients with antral and urethral obstruction.

Long-term oral prophylaxis with trimethoprim-sulfamethoxazole (5 mg/kg per day of trimethoprim) reduces the number of bacterial infections.68 Itraconazole prophylaxis has reduced the development of fungal infections. Although its mechanism of action remains unclear, interferon-gamma can reduce the number of serious bacterial and fungal infections.73,74

Hematopoietic stem cell transplantation can be curative. It is estimated that engraftment of only 10% to 20% of normal donor phagocytes would significantly reduce the risk of infection. Transplantation at an early age might have the greatest chance of success, but because the clinical severity of the disorder is so variable, transplantation is often performed later in life. Gene therapy utilizing the normal gene for a missing component has been successfully employed in two adult chronic granulomatous disease (CGD) patients and warrants further evaluation.75

The prognosis for patients with CGD is highly variable, with median survival estimated to be between 20 to 25 years. X-linked CGD tends to be more severe than the autosomal recessive forms.

Myeloperoxidase (Mpo) Deficiency

Myeloperoxidase is the most common inherited disorder of neutrophil function and is inherited as an autosomal recessive trait with a prevalence of 1 in 2000.76,77 Myeloperoxidase is found in neutrophil azurophil granules. It catalyzes the conversion of H2O2 and chloride ions into hypochlorous acid, which is a more potent antibacterial agent than H2O2.

The rate of bacterial killing is initially diminished in patients with myeloperoxidase (MPO) deficiency after the ingestion of microorganisms, but normal microbicidal activity is observed at 1 hour after ingesting microorganisms. Thus, the MPO-deficient neutrophil employs an MPO-independent system for killing bacteria that is slower than the MPO-hydrogen-peroxide-halide system, but eventually it is effective in eliminating bacteria.30 MPO neutrophils produce higher H2O2 concentrations than normal, which improves the bactericidal activity of the affected neutrophils. On the other hand, candidacidal activity in MPO-deficient neutrophils is markedly reduced. The genetic mutations in the MPO gene causing this defect have been defined. The primary translation product of the gene is a single-gene peptide that undergoes cotranslational glycosylation in the promyelocyte stage of development. Most patients with MPO deficiency have a missense mutation in the gene that prevents glycosylation and results in the enzyme’s inability to incorporate heme, leading to an inactive enzyme.

MPO deficiency usually is clinically inapparent. Patients rarely may have disseminated Candida, which is usually in conjunction with diabetes mellitus. Acquired partial MPO deficiency has been found in patients with acute myelogenous leukemia and in myelodysplastic syndrome. Deficiency of neutrophil MPO can be identified by histochemical analysis. There is no specific therapy. Prognosis is usually excellent.

Leukocytosis

Leukocytosis is an elevation in the total leukocyte count that is two standard deviations above the mean value for age. The various etiologies of leukocytosis are categorized by the class (Fig. 441-2A) of white blood cell (WBC) that is elevated.78-81

Neutrophilia

Neutrophilia refers to an alteration in the total number of blood neutrophils that is in excess of about 7500/μl in older children and adults. During the first few days of life, the upper limit of normal ranges from 7000 to 13,000/μl. When the child is 1 year of age, the range is 1500 to 8500/μl.82,83

Neutrophils increase in the circulation following disturbances of a normal equilibrium involving neutrophil bone marrow production, egress from the marrow into the circulation, and neutrophil destruction. Neutrophilia may arise by enhanced mobilization into the circulation from either the bone marrow or peripheral blood marginating pool, by reduced egress into tissues, or by expanded progenitor proliferation and terminal differentiation through the myeloid series. Neutrophilia is usually acquired (Fig. 441-2). Both acute and chronic bacteria infections, trauma, and surgery are among the most common causes. Neutrophilia may accompany sickle cell disease, thermal injury, diabetic ketoacidosis, and chronic hemolytic anemias. Several drugs are commonly associated with neutrophilia, including epinephrine, corticosteroids, recombinant human granulocyte colony stimulating factor, and recombinant human granulocyte-macrophage colony stimulating factor. Epinephrine releases neutrophils from the marginating pool to the circulating pool, resulting in neutrophilia. Corticosteroids enhance the release of neutrophils from the marrow and impair their migration from the circulation into tissues. A slower onset of acute neutrophilia can accompany inflammation or infection associated with the generation of endotoxin, tumor necrosis factor, and interleukin-1.

Leukemoid Reaction

Chronic acquired neutrophilia usually accompanies the prolonged administration of glucocorticoids, persistent inflammatory reactions, infection, thyrotoxicosis, and chronic blood loss. Significant neutrophilia has been reported in those with Kawasaki disease, tuberculosis, and persistent inflammatory disease. It is also seen in patients with juvenile rheumatoid arthritis. Chronic moderate neutrophilia follows either functional or surgical asplenia.

Constitutional neutrophilia is present in patients with leukocyte adhesion deficiency, familial myeloproliferative disease, Down syndrome, and an autosomal dominant form of hereditary neutrophilia. When the total leukocyte count is extremely high, it is referred to as a leukemoid reaction. The leukemoid reaction is usually accompanied by increased numbers of myelocytes, metamyelocytes, and bands. Leukemoid reactions usually result in neutrophilia and are commonly associated with septicemia and severe bacterial infections. These reactions can also occur in inflammatory syndromes such as acute rheumatoid arthritis, liver failure, or diabetic acidosis. Tumor infiltration of the bone marrow can also result in the appearance of immature myelocytes in the peripheral blood, along with nucleated red cells. This is termed a leukoerythroblastic reaction.

Monocytes

The average absolute blood monocyte count varies with age and must be considered in making the diagnosis of monocytosis. This condition can be seen in many clinical disorders, including bacterial, fungal, and rickettsial infections (Fig. 441-2B). It may also occur in some forms of severe chronic neutropenia and postsplenectomy states. Chronic inflammation thus stimulates or sustains monocytosis and includes systemic lupus erythematosus, rheumatoid arthritis, and ulcerative colitis. Monocytosis can occur in preleukemic states, chronic myelogenous leukemia, juvenile myelomonocytic leukemia, lymphomas, and occasionally Hodgkin disease. It is also seen in patients recovering from myelosuppressive chemotherapy following drug reactions and as a manifestation of sarcoidosis.84

Lymphocytes

Viral illness is the most common etiology of lymphocytosis.85 It is observed in infectious mononucleosis, cytomegalovirus infection, viral hepatitis, many common viral illnesses, toxoplasmosis, syphilis, tuberculosis, and brucellosis. Severe chronic neutropenia often is accompanied by a relative lymphocytosis. Both thyrotoxicosis and Addison disease will cause lymphocytosis.

Eosinophils

An increase in eosinophils is associated with many diseases.86-88 Eosinophils are similar to neutrophils with respect to size and morphology but can be distinguished by their characteristic reddish brown membrane-bound granules when stained with eosin. Their constituent products include major basic protein (MBP), eosinophil cationic protein (ECP), and eosinophil peroxidase. Eosinophils are associated with many specific disease processes. They are the primary immune response to infestation by helminths and protozoa and mediate mechanisms associated with allergic reactions and asthma. Eosinophils differentiate in the bone marrow from myeloid precursors in response to interleukin 3 (IL 3), IL 5, and granulocyte macrophage colony stimulating factor (GM-CSF), ultimately comprising 2% to 3% of the circulating white blood cell population. Eosinophils remain in the circulation transiently, for 8 to 12 hours, then migrate to and function in tissue sites where they can persist up to 8 to 12 days in the absence of stimulation. The tissue-to-circulation eosinophil ratio is about 100:1, with the colon being the most densely populated site.

In response to allergens and tissue parasites, eosinophils are recruited to the site of inflammation by chemokines such as eotaxin-1 and -2 and leukotriene B4; at this site, they release reactive oxygen species, granular proteins such as elastase, leukotrienes (eg, LTC4, LTE4,), growth factors (eg, PDGF, TGF), and cytokines (eg. MACROBUTTON HtmlResAnchor IL-8, MACROBUTTON HtmlResAnchor IL-13, and TNF). Eosinophilia, more than 200 cells/μl, is associated with parasitic infestation of the intestines, collagen vascular disease, malignancies such as Hodgkin disease, brain tumors, acute myelogenous leukemia, severe eczema, exfoliative dermatitis, and Addison disease, and can occur in response to certain drugs such as penicillins. Eosinophilia can be a manifestation of several gastrointestinal disorders, including eosinophilic gastroenteritis, inflammatory bowel disease, peritoneal dialysis, and chronic hepatitis. It is often observed in primary immunodeficiency syndromes such as hyper-IgE syndrome and Wiskott-Aldrich syndrome.

Hypereosinophilic syndrome is an acquired condition associated with chronic eosinophilia and tissue infiltration without a definable cause. Three criteria for this disorder include (1) eosinophils greater then 1500/μl, (2) signs and symptoms of organ involvement, and (3) diagnoses not explained by other causes. On the other hand, eosinophilic leukemia can be distinguished by signs that indicate a clonal myeloid disease such as anemia, thrombocytopenia, splenomegaly, and the presence of cytogenetic abnormalities in the marrow. In both the hypereosinophilic syndrome and eosinophilic leukemia, life-threatening complications can arise from cardiac damage secondary to eosinophil infiltration and release of granule constituents.

Basophils

Basophils contain large blue or purple granules. Basophilia occurs when basophil counts exceed 100 to 150/μl.89 Basophil counts may rise in chronic myelogenous leukemia, Hodgkin’s disease, hemolytic anemias, ulcerative colitis, varicella, juvenile rheumatoid arthritis, and hypothyroidism. Estrogens and antithyroid medications may also increase the basophil count. An increased number of basophils is commonly associated with hypersensitivity disorders of the IgE-associated “immediate” type.