A. Transient physiologic hypogammaglobulinemia occurs in infants between the ages of approximately 3 and 6 months. Although infants are born with adult levels of placen-tally transferred IgG, a low level of IgG results from:
1. The disappearance of maternal antibody, which has a half-life of 22-28 days
2. The infant's low early rate of synthesis of secretable immunoglobulins
B. Congenital agammaglobulinemia (Bruton's disease) is a sex-linked (male) disorder that affects infants between the ages of 5 and 6 months. These patients have an apparently normal thymus and CMI.
1. Clinical features include:
a. Recurrent pyogenic infections b. Digestive tract disorders
2. Cause. The defect that causes Bruton's disease may occur in the transition from pre-B to B cells and involves the loss of a tyrosine kinase gene. The pre-B cells are normal.
3. Diagnosis is made by noting the absence of tonsils (on physical examination), germinal centers (on lymph node biopsy), and B cells (on a peripheral blood smear). Serum immunoglobulin levels of less than 10% also suggest the disease.
4. Treatment. Passive transfer of adult serum immunoglobulin can be administered pro-phylactically to diminish infections.
C. Dysgammaglobulinemia. Patients of varying age present with a selective immunoglobulin class deficiency (i.e., one or more immunoglobulins, but not all).
1. Diagnosis. Most patients have decreased IgA levels, with 1 in 600-800 of these patients having IgA levels of less than 5 mg/dl.
2. Immunologic features include:
a. Loss of mucosal surface protection b. Failure of IgA-bearing cells to differentiate into secreting plasma cells, although their numbers are normal
C. Increased susceptibility to autoimmune diseases
D. Congenital thymic aplasia (DiGeorge syndrome) is characterized by a hypocalcemia, tetany, and an absence of T cells.
1. Cause. DiGeorge syndrome is not hereditary. It is caused by an unknown intrauterine injury to the third and fourth pharyngeal pouches that occurs between the fifth and sixth weeks of gestation.
2. Clinical features a. The thymus and parathyroid glands are not developed.
b. Depressed CMI permits infections caused by opportunistic organisms (e.g., Candida, Pneumocystis, viruses).
C. Patients have apparently normal germinal centers, plasma cells, and serum immunoglobulin.
3. Treatment. These patients usually die early.
b. The transplantation of fetal thymic tissue is experimental and may be complicated by a graft-versus-host reaction.
E. Chronic mucocutaneous candidiasis is a highly specific T cell disorder that is characterized by an absence of immunity to Candida. Patients have apparently normal T cell absolute numbers and functions. Approximately 50% of patients with this disorder also have endocrine dysfunctions (e.g., hypothyroidism).
F. Wiskott-Aldrich syndrome is a sex-linked (male) disorder occurring mainly in children. The syndrome has three main features: thrombocytopenia (manifested by bleeding), eczema, and recurrent infections. An increased incidence of lymphoreticular malignancies or lymphomas may occur.
Immunologic features include:
a. Depressed CMI and a low serum IgM level, but normal IgG and IgA levels b. Poor response to bacterial capsular polysaccharide antigens
2. Cause. The primary defect may be an absence of specific glycoprotein receptors on T cells and platelets.
3. Treatment. Bone marrow transplantation may be effective.
G. Severe combined immunodeficiency disease (SCID) is a rare disorder characterized by a genetic defect in stem cells that results in the absence of the thymus gland and T and B cells. Affected children are extremely susceptible to infections and have a very short life span.
1. Immunologic features. A deficiency in the enzyme adenosine deaminase (ADA)
occurs in 50% of patients. This deficiency results in the accumulation of toxic deoxyadenosine triphosphate (DATP), which inhibits ribonucleotide reductase and prevents DNA synthesis. A mutation in the y chain of the interleukin-2 (IL-2) receptor gene is found in other patients with SCID.
2. Treatment. Gene therapy with the ADA gene is experimental.
H- Chronic granulomatous disease (CGD) results from a genetic defect in the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system in neutrophils. Patients are susceptible to infections by age 2 years, especially by organisms of low virulence.
1. Immunologic features. Neutrophil bactericidal activity (i.e., respiratory burst) is defective because of depressed NADPH oxidase, superoxide dismutase activity and decreased hydrogen peroxide levels.
2. Diagnosis is based on failure of neutrophils and macrophages to reduce a nitroblue tetrazolium dye.
3. Treatment with interferon-y (IFN-y) has been successful.
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