Clinical and laboratory studies into the pathogenesis of malacoplakia

Three cases of malakoplakia are described. Electron microscopic studies revealed intact bacteria or bacteria in varying states of degradation within phagolysosomes of the malakoplakic macrophages. Michaelis Gutmann bodies arise within the phagolysosomes. These findings suggest that the bacteria incorporated within the phagolysosomes persist as dense amorphous aggregates which later become encrusted with calcium phosphate crystals to form the laminated Michaelis Gutmann bodies. Possible explanations for the unusual macrophage response in malakoplakia are: infection with an unusual strain of bacteria, an immunologic abnormality affecting intracellular killing of organisms, and an abnormality affecting intracellular digestion of organisms. In considering each of the possibilities, not one unusual strain of infecting organisms in association with malakoplakia was detected, and in vitro studies revealed normal T lymphocyte response to a mitogenic agent and normal monocyte bactericidal capacity. According to the history, each patient had reason to have a compromised immune status; in only one, however, was this demonstrated.