Immunophenotypic analysis of histiocytes involved in AIDS-associated Mycobacterium scrofulaceum infection: similarities with lepromatous lepra.

The present study reports a rare case of systemic M. scrofulaceum infection in an AIDS patient and analyses the inflammatory infiltrate in a lymph node by immunohistochemistry. Special emphasis is put on the histiocytes. The diffuse infiltrate consists mainly of large histiocytes that contain numerous bacilli. These cells display the phenotype of mature histiocytes and in addition coexpress the antigens recognized by RFD7 and RFD9, both markers of different subsets of histiocytes which have been reported to be co-expressed by the infected histiocytes in the infiltrate of lepromatous lepra. Interdigitating reticulum cells are rare as well as T cells which are mainly of the suppressor/cytotoxic type. These findings are similar to those reported for lepromatous lepra and might indicate common deficiencies in T cell-macrophage interactions in both conditions. Superimposed on the diffuse infiltrate of large histiocytes we observed 'monocytic granulomas', the presence of which might be related to a reactional state comparable to erythema nodosum leprosum, a reactional state of lepromatous lepra.