PULMONARY MALACOPLAKIA IN ACQUIRED-IMMUNODEFICIENCY-SYNDROME - AN ULTRASTRUCTURAL-STUDY OF MORPHOGENESIS OF MICHAELIS-GUTMANN BODIES

Malakoplakia is an unusual inflammatory reaction to a variety of infec tions, characterized by the accumulation of macrophages containing the target-like calcospherites, the Michaelis-Gutmann body (MGB). We repo rt three patients with acquired immunodeficiency syndrome with pulmona ry malakoplakia associated with Rhodococcus equi infection; two patien ts were diagnosed at autopsy and one by examination of a transbronchia l biopsy specimen. All three patients had pulmonary bacterial cultures and light and electron microscopic examination. The patients were 33- , 41-, and 43-year old men, human immunodeficiency virus-positive for 2, 6, and 8 years, respectively. The two patients diagnosed at autopsy had cavitary lesions, and the patient diagnosed by biopsy specimen ha d nodular lesions on chest radiographs. Histologically, the lungs had well-circumscribed areas of infiltration with benign macrophages with granular cytoplasm, scattered MGBs, and numerous gram-positive coccoba cilli. Electron microscopic examination showed intracellular coccobaci lli, from 990 x 702 to 972 x 648 mn in diameter, with thick, homogenou s cell walls, trilaminar cytoplasmic membranes, and dense cytoplasm wi th from one to five vacuoles. Electron microscopic studies showed that the bacteria within the pulmonary macrophages had thicker cell walls, less prominent nucleoid areas, and more vacuoles than the bacteria in cultures from the sputum and blood. The mature MGB ultrastructurally had a concentric, trilaminate structure with central mineralized core and was without recognizable bacterial forms. Early MGBs, however, con sisted of a circular, electron-dense core containing bacteria, ultrast ructurally similiar to the R. equi seen in the culture. Pulmonary mala koplakia in patients with the acquired immunodeficiency syndrome might thus represent an acquired macrophage dysfunction of the intracellula r digestion of phagocytized bacteria The bacteria within the macrophag es, however, seemed to have thicker cell walls compared with those in culture, and thus might be protected from enzyme digestion. It seems t hat MGBs are formed around the undigested bacteria as an alternative p athway for bacterial destruction, because R. equi was identified withi n the cores of early MGBs but not the mature or late stage MGBs.