In situ characterization of the cellular immune response in American cutaneous leishmaniasis.

American cutaneous leishmaniasis is a spectrum of granulomatous disease caused by related species of an intracellular parasite. The host response in localized cutaneous leishmaniasis (LCL) is effective in that few organisms can be found in tissue lesions. In contrast, diffuse cutaneous leishmaniasis (DCL) patients mount a poor response with numerous parasites present in multiple skin lesions. Immunopathological correlates were sought in LCL and DCL with immunoperoxidase techniques using monoclonal antibodies directed against T lymphocyte subpopulations and interleukin-2 in tissue lesions. Both LCL and DCL granulomas showed a mixture of T lymphocyte subpopulations with the ratio of helper:suppressor phenotypes less than one. This ratio and localization of cells is more similar to the ineffective lepromatous leprosy granuloma than the effective tuberculoid leprosy granuloma. In contrast, interleukin-2 was identified in equivalent numbers of cells in LCL and tuberculoid leprosy, an order of magnitude greater than DCL and lepromatous leprosy lesions. Cells expressing Tac, the receptor for interleukin-2, were present in approximately equal numbers in all disorders. The immunological effectiveness of granulomas appear to related less to the numbers and location of T cell phenotypes than to the functional aspects of these cells, particularly the ability to generate lymphokines.