PRIMARY IMMUNODEFICIENCY DISEASES
Primary immunodeficiency diseases (PIDs) are defects of the immune system that are due to genetic abnormali-ties or some failure in normal embryological develop-ment. They are usually apparent at birth or develop shortly thereafter. Approximately 70 PIDs have been described, including those specific for humoral immu-nity (e.g., X-linked agammaglobulinemia, immune globulin [Ig] A deficiency), cellular immunity (e.g., DiGeorge’s syndrome), or both (e.g., severe combined immunodeficiency syndrome).
The treatment of a PID is based on the aspect of the immune system that is lacking. For those with deficien-cies in humoral immunity, the only effective treatment available is antibody replacement (e.g., immune globu-lin) and medical management of infections. For those with deficiencies in cell-mediated immunity, there is no effective pharmacological treatment.
The clinical manifestations of PIDs vary with the as-pect of the immune system affected. In general, because of the role of antibodies in protection against bacterial infections, individuals with deficiencies in humoral im-munity are particularly prone to infections from Strep-tococcus pneumoniae and Haemophilus influenzae. These individuals are also prone to infections of the respira-tory, gastrointestinal, and urinary tracts because of the protective role of IgA in secretions.
Individuals with defects in cellular immunity are prone to fungal, protozoal, and viral infections, such as Candida albicans, cytomegalovirus, and Pneumocystis carinii, since cell-mediated immune responses are the primary defenses against these types of infection. Because of the role of cell-mediated immunity in tumor surveillance, these individuals will also demonstrate an increased incidence of malignancy if they survive long enough.