T cell subsets in leprosy lesions: in situ characterization using monoclonal antibodies.

Cryostat sections of dermal lesions from 30 untreated leprosy patients were studied by indirect immunofluorescence using monoclonal antibodies defining T cell subsets and Ia like antigens. Most lymphocytes in leprosy lesions were positive for OKT3 and Ia like antigens indicating thereby the presence of activated T cells. Maximal numbers of these cells were seen in localized paucibacillary tuberculoid leprosy lesions in close association with epithelioid cells. A decline in their numbers was observed over the leprosy spectrum with a marked reduction in disseminated, multi-bacillary, lepromatous leprosy where only scattered OKT3+ cells were visualized. OKT4 and OKT8 positive cells defining T cell subsets, were frequently found within the OKT3+ lymphocytes throughout the leprosy spectrum. The ratio of OKT4+/OKT8+ cells ranged from 1.2 to 5.0 in tuberculoid and from 0.2 to 1.0 in lepromatous lesions. Macrophages in the granulomas stained intensely with anti-Ia antisera. Ia like antigens were expressed to the same degree on macrophages with or without intracellular acid fast bacilli.