Granuloma-related lesions associated with impaired cell-mediated immunity
Impairment of cell-mediated immunity 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.
Lepromatous leprosy, malakoplakia, atypical mycobacterial infection in severely immunocompromised individuals and Whipples disease are examples of this phenomenon. All of these conditions result from bacterial infection and are characterized by abnormal macrophage function, persistence of bacteria and/or bacterial degradation products within macrophages, and absence of granulomas. Granuloma formation may be seen in Whipple's disease in addition to the non-granulomatous macrophage response.
The inflammatory response in immunocompetent individuals to the bacteria responsible for atypical mycobacterial infection and lepromatous leprosy is usually granulomatous. The bacteria that cause malakoplakia do not usually provoke granulomatous inflammation in immunocompetent individuals. The inflammatory response to the bacteria that cause Whiples disease, in individuals who do not have Whipple’s disease, is not known.
Because of demonstrable abnormalities of macrophage function and the very similar morphologic appearances seen in these conditions it is likely that all four share a closely related pathogenetic pathway.
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