Late-stage cutaneous leishmaniasis: immunopathology of tuberculoid lesions in skin and lymph nodes.

Strong development of tuberculoid features in the late stage of cutaneous leishmaniasis presents immunopathological, diagnostic and sometimes therapeutic problems. Only two such cases were identified out of 30 late-stage cases of the disease. They were delineated on histological and immunocytological grounds, and found to present higher levels of Leishmania antigen and lower levels of IgG than the weakly tuberculoid cases. One case showed histological and skin test evidence of delayed-type hypersensitivity; the other case (clinically of the relapsing or recidiva variety) lacked such evidence. Here the residual antigen was segregated at the periphery of the lesion. In three late-stage cases for which lymph node biopsies were available there was a stronger tuberculoid response in lymph node or lymphatic than in the skin lesion. In two cases there was caseation. Germinal follicles were notably active. It is suggested that in cutaneous leishmaniasis a strong tuberculoid response may be associated not so much with immune complex formation (as in the majority of lesions) but with sequestration of antigen at a peripheral site or in the lymphatic apparatus.