Two types of inherited B-cell deficiencies exist. The first type re-sults from lack of differentiation of B-cell precursors into mature B cells. As a result, plasma cells are lacking, and the germinal centers from all lymphatic tissues disappear, leading to a com-plete lack of antibody production against invading bacteria, viruses, and other pathogens. Infants born with this disorder suf-fer from severe infections starting soon after birth. This syndrome is called sex-linked agammaglobulinemia (Bruton’s disease) be-cause all antibodies disappear from the patient’s plasma. B cells in the peripheral blood and the immunoglobulins IgG, IgM, IgA, IgD, and IgE are low or absent. The prevalence of this disorder is approximately 1 case per 100,000 population (Parslow, Stites, Terr & Imboden, 2001).
The second type of B-cell deficiency results from a lack of differentiation of B cells into plasma cells. Only diminished an tibody production occurs with this disorder. Although plasma cells are the most vigorous producers of antibodies, affected pa-tients have normal lymph follicles and many B lymphocytes that produce some antibodies. This syndrome, called hy-pogammaglobulinemia, is a frequently occurring immunode-ficiency. It is also called common variable immunodeficiency (CVID), a term that encompasses a variety of defects ranging from immunoglobulin A (IgA) deficiency, in which only the plasma cells that produce IgA are lacking, to the other extreme, in which there is severe panhypoglobulinemia (general lack of immunoglobulins in the blood).
CVID is the most common primary immunodeficiency seen in adults; it can occur in either gender. Although it can occur at any age, its onset is most often in the second decade of life. The vast majority of patients do not become symptomatic until 15 to 35 years of age. The major immunologic features of CVID in-clude recurrent pyogenic infections, an increased incidence of autoimmune diseases, and a decreased level of total immuno-globulins, with IgG below 250 mg/dL. The B-cell numbers usu-ally remain normal. The etiology of this disorder is unknown and believed to be multifactorial. The prevalence of CVID is about 1 case per 80,000 population in the United States (Tierney, McPhee & Papdakis, 2001).
Infants with sex-linked agammaglobulinemia usually become symptomatic after the natural loss of maternally transmitted im-munoglobulins, which occurs at about 5 to 6 months of age. Symptoms of recurrent pyogenic infections usually occur by 5 to 6 months of age.
More than half of patients with CVID develop pernicious anemia. Lymphoid hyperplasia of the small intestine and spleen and gastric atrophy detected by biopsy of the stomach are com-mon findings. Other autoimmune diseases, such as arthritis and hypothyroidism, frequently develop in patients with CVID. Those who develop late-onset disease also have an increased in-cidence of chronic lung disease, hepatitis, gastric cancer, and malabsorption that results in chronic diarrhea (Porth, 2002). CVID must be distinguished from secondary immunodeficiency diseases caused by protein-losing enteropathy, nephrotic syn-drome, or burns.
Patients with CVID are susceptible to infections with encap-sulated bacteria, such as Haemophilus influenzae, Streptococcuspneumoniae, and Staphylococcus aureus. Frequent respiratory tractinfections typically lead to chronic progressive bronchiectasis and pulmonary failure. Commonly, infection with Giardia lamblia occurs. Opportunistic infections with Pneumocystis carinii, how-ever, are seen only in patients who have a concomitant deficiency in T-cell immunity.
Sex-linked agammaglobulinemia may be diagnosed by the marked deficiency or complete absence of all serum im-munoglobulins. The diagnosis of CVID is based on the history of bacterial infections, quantification of B-cell activity, and re-ported signs and symptoms. The number of B lymphocytes and the total and specific immunoglobulin levels are measured. Total serum globulin level alone is an inadequate measure because a compensatory overproduction of one globulin may mask the loss of a missing globulin or one present in very low amounts. Anti-body titers to confirm successful childhood vaccination are de-termined by specific serologic tests. Previous successful childhood immunization indicates that B cells were functioning adequately earlier in life. If the patient exhibits signs and symp-toms suggestive of pernicious anemia, hemoglobin and hemat-ocrit levels are also obtained.
Patients with primary phagocytic disorders may be treated with intravenous immunoglobulin (IVIG). Those who are receiving adequate treatment with IVIG usually do not require prophy-lactic antibiotics unless they also have chronic respiratory dis-ease. Antimicrobial therapy is prescribed for respiratory infections to prevent complications such as pneumonia, sinusi-tis, and otitis media. Intestinal infestation with G. lamblia is treated with a 10-day course of metronidazole (Flagyl) or a 7-day course of quinacrine hydrochloride (Atabrine) (Parslow et al., 2001). Patients with pernicious anemia receive parenteral
injections of vitamin B12 at monthly intervals. Management may also include physical therapy with postural drainage for patients with chronic lung disease or bronchiectasis (Parslow et al., 2001).