Seven cases of genito-urinary
malacoplakia were analyzed histologically, ultrastructurally and immunohistochemically in a comparison with two cases of
xanthogranulomatous pyelonephritis. Immunohistochemically, von Hansemann cells and Michaelis-Guttmann bodies, both hallmarks for the diagnosis of
malacoplakia, showed a common antigenicity for enteropathogenic Escherichia coli as cytoplasmic granules of varying sizes. These microscopic manifestations corresponded ultrastructurally to a series of phagolysosomal degradations of coliform bacilli. Serogroups against E. coli OK
antigens, which were positive for malacoplakic cells, were not confined to a particular group. Macrophages of
xanthogranulomatous pyelonephritis did not show the E. coli antigenicity. Antigenicity of
lysozyme and alpha-1-antichymotrypsin on the von Hansemann cells was equivocal, but these
enzymes were strongly positive on macrophages of
xanthogranulomatous pyelonephritis. The macrophages of both
malacoplakia and
xanthogranulomatous pyelonephritis were positive for antihuman macrophage antibody. These results indicate that
malacoplakia depends mainly on
infection by a non-specific strain of enteropathogenic E. coli and may arise from defective digestive
enzyme activity of infiltrating macrophages. Immunohistochemical analysis using
antisera against E. coli OK
antigens,
lysozyme and alpha-1-antichymotrypsin was useful in identifying the prediagnostic stage of
malacoplakia and in differentiating the lesion from
xanthogranulomatous pyelonephritis.