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Primary immunodeficiency diseases
result from genetic defects affecting the development and/or
the function of immune system components.1-5 They
frequently manifest soon after birth, although some become evident later
in life. Recurrent infections are the hallmark of immunodeficiency syndromes,
with the types of infections reflecting the nature of the defect. Autoimmune
disorders and certain malignancies occur more frequently in individuals
with immunodeficiency diseases.
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Primary immunodeficiency diseases may affect either acquired
immunity, as seen in cellular and humoral deficiency diseases, or
innate immunity, such as seen in deficiencies of the various complement
components and phagocytic cell deficiencies. This chapter reviews representative
immunodeficiency diseases of altered development and function of
T and B cells. These defects have served as experiments of nature
to unravel the complexities of T-cell and B-cell development and
function. T-cell immunodeficiencies resulting from defects affecting
T-cell development and activation are shown in Figure
188-1, and B-cell immunodeficiencies due to abnormalities in
B-cell development and differentiation are shown in Figure
188-2. Diseases of the innate immune system are reviewed in Chapter 187. Disorders of phagocytosis and
other granulocyte disorders including Chediak-Higashi syndrome, cartilage-hair
hypoplasia syndrome, myelokathexis, specific granule deficiency,
leukocyte adhesion deficiency, chronic granulomatous disease and
myeloperoxidase deficiency are discussed in Chapter 442.
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Because of the role of the T lymphocyte in supporting B lymphocyte
function, abnormalities affecting T cells alone or in combination with
B lymphocytes frequently lead to states of combined immunodeficiency,
the severity of which depends on the extent of the T-cell defect. In
contrast to combined immunodeficiency diseases, where both T-cell
and B-cell compartments are affected, T-cell function in isolated B-cell
immunodeficiency syndromes, such as X-linked agammaglobulinemia,
remains intact.
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Severe combined immunodeficiency (SCID) is characterized by the
breakdown of both cellular and humoral adaptive immunity. The reported incidence
is approximately 1 per 100,000.6,7 It is caused
by a heterogeneous group of at least 15 known genetic abnormalities
that result in severe T-cell depletion (or dysfunction) with either
primary ...