The most common of the primary immunodeficiency diseases are those that involve inadequate antibody
production. The characteristic presentation of these disorders is recurrent sinopulmonary infections. An arrest in B cell
development at the pre-B cell stage leads to agammaglobulinemia and an insignificant number of B cells. X-linked
agammaglobulinemia is the most common of these developmental arrests while the autosomal recessive
agammaglobulinemias comprise a small minority of the total cases. Likewise, the most common form of the hyper-IgM
syndromes (CD40 ligand deficiency) is X-linked. Of the autosomal recessive forms, CD40 deficiency is basically
identical to the X-linked form in its clinical phenotype where, in addition to inadequate antibody production, there is
defective T cell signaling through the CD40-CD40L interaction. Aside from CD40 deficiency, the other recessive forms
of hyper-IgM syndrome have adequate T cell function. IgA deficiency is the most common and the most benign of the B
cell disorders. Common variable immunodeficiency is diverse in its presentation and clinical course. The pathophysiology
of this disease is multifactorial and frequently ill defined, often making it a diagnosis of exclusion. A working knowledge
of identifiable PIDDs is essential in both recognizing when to suspect immunodeficiency and making a diagnosis.
Keywords: B lymphocyte, antibody, deficiencies, clinical evaluation.
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