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CHAPTER 14: Immunology

Gita Ram; Soma Jyonouchi

APPROACH TO PRIMARY IMMUNODEFICIENCY

Warning Signs for Immune Deficiency. Consider immune deficiency when two or more of the following are present (data from Jeffrey Modell Foundation).

  • Recurrent otitis (≥8 episodes), sinusitis (≥2 episodes), or pneumonia (≥2 episodes) in 1 year (from Jeffrey Modell Foundation)

  • Two or more invasive infections (meningitis, sepsis, osteomyelitis, etc.)

  • Recurrent deep skin or organ abscesses

  • Infections with unusual or opportunistic organisms

  • Failure to thrive

  • Persistent thrush in mouth or elsewhere on skin after 1 year of age

  • Need for intravenous antibiotics to clear common infections

  • Family history of immunodeficiency

MAJOR CATEGORIES

The major categories of primary immune deficiencies reflect the various arms of the immune system (Tables 14-1 and 14-2).

TABLE 14-1

Classification of Primary Immune Deficiencies

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TABLE 14-1

Classification of Primary Immune Deficiencies
Category Select Conditions
B cell disorders

  • X-linked agammaglobulinemia (XLA)

  • Common variable immune deficiency (CVID)

  • Transient Hypogammaglobulinemia of Infancy (THI)

  • IgA deficiency
Combined B and T cell disorders

  • Severe combined immune deficiency (SCID)

  • 22q11.2 deletion syndrome

  • Wiskott–Aldrich syndrome

  • Ataxia-Telangiectasia
Phagocyte disorders

  • Chronic granulomatous disease (CGD)

  • Leukocyte adhesion deficiency (LAD)

  • Severe congenital neutropenia (SCN)

  • Hyper IgE syndrome
TABLE 14-2

Features and Diagnostic Approach for Primary Immune Deficiencies

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TABLE 14-2

Features and Diagnostic Approach for Primary Immune Deficiencies
General Features Diagnostic Approach
B cell (antibody/humoral) disorders

  • Usually present after 3–6 months of age after maternal antibodies decrease; exception is common variable immunodeficiency (CVID), which can present at any age including adulthood.

  • Predisposition for infections of the upper and lower respiratory tract with encapsulated bacteria (Streptococcus pneumoniae and Haemophilus influenzae). Mycoplasma spp. and Ureaplasma spp. infections can cause pneumonia and destructive septic arthritis. Enterovirus infections (polio, coxsackie, echo virus) can cause chronic diarrhea, meningitis, or fatal disseminated infections in patients with X-linked agammaglobulinemia.

  • The cornerstone of therapy is immunoglobulin replacement therapy to reduce the frequency of infections.

  • Quantitative measures:

    • Serum immunoglobulin levels (IgG, IgA, IgM), flow cytometry

    • B cell enumeration

  • Functional measures:

    • IgG responses to vaccinations—pneumococcal serotype-specific antibodies after pneumococcal conjugate (Prevnar) or polysaccharide (Pneumovax) vaccination, tetanus and diphtheria antibodies after DTaP vaccination
T cell and combined (T and B cell) disorders

  • Present at birth or in early infancy

  • Failure to thrive, chronic diarrhea

  • Develop prolonged and severe respiratory viral infections

  • Predisposition for fungal infections and opportunistic infections such as Pneumocystis jiroveci (formerly Pneumocystis carinii)

  • Association with autoimmune diseases

  • Severe combined immune deficiency (SCID) is characterized by a complete absence of T cells and is fatal in the first year of life without bone marrow transplantation.

  • Milder forms of T cell deficiencies include 22q11.2 deletion syndrome and ataxia-telangiectasia.

  • Quantitative measures:

    • Absolute lymphocyte count (ALC) on CBC with differential (80% of the ALC is comprised of T cells)

    • Flow cytometry for T cell subset enumeration

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