The pathophysiology of disseminated Mycobacterium avium complex disease in AIDS.

Mycobacterium avium complex (MAC) organisms cause disseminated disease in patients with AIDS. The organisms penetrate the gastrointestinal mucosa by unknown mechanisms and are phagocytosed by macrophages in the lamina propria. These cells cannot kill the organisms, and MAC spreads through the submucosal tissue. Lymphatic drainage transports mycobacteria to abdominal lymph nodes, from which the organisms enter the bloodstream. Hematogenous spread can occur to many sites, but spleen, bone marrow, and liver are the most common. Tissue destruction is rare, and most signs and symptoms of MAC disease are due to elaboration of cytokines. MAC is rarely the direct cause of death but increases the risk for superinfection; death may result from malnutrition or other infections.