Immune Deficiency
. Deficiencies in immune function may be either inherited or acquired. Inherited immune deficiencies usually reflect the failure of a gene important to the generation or function of immune system components. Some inherited diseases damage a person’s innate immunity by making macrophages incapable of ingesting or breaking down invading organisms. Individuals affected by these diseases are especially susceptible to opportunistic infections—that is, infections by normally harmless organisms that can flourish in a person whose immune system has been weakened. DiGeorge syndrome is an inherited immune disorder in which a person has no thymus and, therefore, cannot produce mature T lymphocytes. People with this disorder can mount only limited humoral immune responses, and their cell-mediated immune responses are severely limited. The most extreme example of a hereditary immune deficiency is severe combined immunodeficiency (SCID). Individuals with this disease completely lack both T and B lym...