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 |Favorite Table|Download (.pdf) TABLE 68–1 Important Congenital Immunodeficiencies
|Deficient Component and Name of Disease ||Specific Deficiency ||Molecular Defect ||Clinical Features |
|B cell || || || |
|X-linked (Bruton’s) ||Absence of B cells; very low immunoglobulin (Ig) levels ||Mutant tyrosine kinase ||Recurrent bacterial infections, especially of respiratory tract, caused by pyogenic bacteria such as pneumococci |
|Selective IgA ||Very low IgA levels ||Failure of heavy-chain gene switching ||Recurrent infections, especially of the sinuses and lung, caused by pyogenic bacteria |
|T cell || || || |
|Thymic aplasia (DiGeorge’s) ||Absence of T cells ||Defective development of pharyngeal pouches; not a genetic disease ||Viral, fungal, and protozoal infections; tetany |
|Chronic mucocutaneous candidiasis ||Deficient T-cell response to Candida ||Unknown ||Skin and mucous membrane infections with Candida |
|Combined B and T cell || || || |
|Severe combined immunodeficiency (SCID) ||Deficiency of both B-cell and T-cell function ||Either defective IL-2 receptor, defective recombinases, defective kinases, absence of class II MHC proteins, or ADA or PNP deficiency ||Bacterial, viral, fungal, and protozoal infections |
|Complement || || || |
|Hereditary angioedema ||Deficiency of C1 protease inhibitor ||Too much C3a, C4a, and C5a -generated ||Edema, especially laryngeal edema |
|C3b ||Insufficient C3 ||Unknown ||Pyogenic infections, especially with Staphylococcus aureus |
|C6,7,8 ||Insufficient C6,7,8 ||Unknown ||Neisseria infections |
|Phagocytes || || || |
|Chronic granulomatous disease ||Defective bactericidal activity because no oxidative burst ||Deficient NADPH oxidase activity ||Pyogenic infections, especially with S. aureus and Aspergillus |
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 ...