English: Lymph node - Atypical mycobacterial infection (MAI) Impairment of cell-mediated immunity with abnormal macrophage function may interfere with the ability of macrophages to inactivate and kill bacteria and/or eliminate bacterial degradation products. Instead of organizing themselves into compact discrete aggregates to form granulomas, the bacteria-filled macrophages proliferate diffusely forming large sheets of cells. This is what occurs in atypical mycobacterial infections in immunocompromised individuals. The inflammatory response in immunocompetent individuals to atypical mycobacterial infection is usually granulomatous. In this image almost all of the lymphoid tissue is replaced by large histiocytes admixed with a small number of other inflammatory cells..