Immunodeficiency

Immunodeficiency (from Latin immunitas — immunity and deficit — deficiency) is a severe pathological condition characterized by a quantitative or functional defect in one or more components of the immune system, resulting in a reduced or complete loss of the body’s ability to resist infections.

Etiology and pathophysiology

Immunodeficiencies are classified as primary or secondary:

• primary (congenital) immunodeficiencies — are rare genetic mutations in which a child is born without the ability to produce T and/or B lymphocytes (for example, severe combined immunodeficiency, selective IgA deficiency);
• secondary (acquired) forms — are much more common. Their principal cause is the effect of external factors on an initially healthy immune system.

The best-known example is human immunodeficiency virus (HIV). This virus specifically infects T-helper cells (CD4+ lymphocytes), the principal regulatory cells that coordinate the entire immune response.

Secondary immunodeficiency also occurs during treatment with immunosuppressants (in organ transplantation) and intensive radiation therapy.

Clinical significance

Clinical manifestations of immunodeficiency include chronic, recurrent infections that are refractory to standard treatment. Patients experience severe pneumonia, intestinal infections, and disseminated fungal infections.

The principal threat associated with immunodeficiencies is the development of opportunistic infections. Pathogens that are harmless to a healthy person (Pneumocystis, fungi of the genus Candida, cytomegalovirus) cause life-threatening visceral lesions in these patients.

Furthermore, immunodeficiency impairs antitumor surveillance, increasing the risk of malignant neoplasms (sarcomas and lymphomas).

Treatment generally requires lifelong replacement therapy (intravenous immunoglobulins, specific antiretroviral therapy) or bone marrow transplantation.