The term primary immunodeficiency disease denotes disorders resulting from the mostly inherited defects of the immune system. Multiple isolated defects and combined disorders have been described, including humoral immune deficiencies, the severe combined immunodeficiencies, and disorders resulting from phagocytic and complement defects.
The symptoms, signs, and molecular pathophysiology of the major humoral immune deficiencies will be reviewed here, as well as pertinent aspects of the laboratory evaluation and differential diagnosis. An overview of the laboratory abnormalities observed in the different primary humoral immune deficiencies is presented in the table (table 1). General considerations and descriptions of methods used in the evaluation of immune system function are discussed separately. (See "Laboratory evaluation of the immune system".)
PRESENTATION OF HUMORAL IMMUNE DEFICIENCY
Humoral immune deficiency refers to diseases resulting from impaired antibody production, because of either a molecular defect intrinsic to B cells or a failure of interactions between B and T cells . Cellular immunity is largely intact, in contrast to diseases classified as combined immunodeficiencies, despite underlying T cell defects in some of these diseases. (See "Combined immunodeficiencies" and "Severe combined immunodeficiency (SCID): An overview".)
Antibody deficiency characteristically leads to recurrent, often severe, upper and lower respiratory tract infections with encapsulated bacteria (eg, Streptococcus pneumoniae, Haemophilus influenzae) . Children commonly present with recurrent otitis media, sinusitis, and pneumonia. The same is true of adults, although otitis media is less common. Viral infections of the respiratory tract also occur with greater frequency and severity in these patients . Additional infectious diseases may be associated with particular syndromes. (See "Acute otitis media in children: Epidemiology, microbiology, clinical manifestations, and complications", section on 'Risk factors'.)
Common associated findings in children include poor growth and failure to thrive, recurrent fevers, and poor school attendance and performance . Chronic diarrhea is seen in both children and adults . Autoimmune disease is occasionally the presenting feature in adults. Primary humoral immune deficiency should also be considered in patients with nodular lymphoid hyperplasia in the gut or unexplained hepatosplenomegaly.