B-CELL
DEFICIENCIES
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).
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