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INTRODUCTION

Immunodeficiency can occur in any of the four major components of the immune system: (1) B cells (antibody), (2) T cells, (3) complement, and (4) phagocytes. The deficiencies can be either congenital or acquired (Table 68–1). Clinically, recurrent or opportunistic infections are commonly seen. Recurrent infections with pyogenic bacteria (e.g., staphylococci) indicate a B-cell deficiency, whereas recurrent infections with certain fungi, viruses, or protozoa indicate a T-cell deficiency.

TABLE 68–1Important Congenital Immunodeficiencies

CONGENITAL IMMUNODEFICIENCIES

B-Cell Deficiencies

X-Linked Hypogammaglobulinemia (Bruton’s Agammaglobulinemia)

Very low levels of all immunoglobulins (IgG, IgA, IgM, IgD, and IgE) and a virtual absence of B cells are found in young boys; female carriers are immunologically normal. Pre-B cells are present, but they fail to differentiate into B cells. This failure is caused by a mutation in the gene encoding tyrosine kinase, an important signal transduction protein. Cell-mediated immunity is relatively normal. Clinically, recurrent pyogenic bacterial infections (e.g., otitis media, sinusitis, and pneumonia caused by Streptococcus pneumoniae and Haemophilus influenzae) occur in infants at about 6 months of age, when maternal antibody is no longer present in sufficient amount to be protective. Treatment with pooled gamma globulin reduces the number of infections.

Selective Immunoglobulin Deficiencies

IgA deficiency is the most common of these; IgG and IgM deficiencies are rarer. Patients with a deficiency of IgA typically have recurrent sinus ...

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