Clinical and laboratory studies into the pathogenesis of malacoplakia.

Three cases of malacoplakia are described. Electron microscopic studies revealed intact bacteria or bacteria in varying states of degradation within phagolysosomes of the malacoplakic 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 malacoplakia are: (1) infection with an unusual strain of bacteria, (2) an immunological abnormality affecting intracellular killing of organisms, and (3) an abnormality affecting intracellular digestion of organisms. In considering each of the possibilities, we have been unable to detect any unusual strain of infecting organisms in association with malacoplakia, and in vitro studies have revealed normal T lymphocyte response to mitogen 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.