In situ characterization of T lymphocyte subsets in the reactional states of leprosy.

Using monoclonal antibodies and the immunoperoxidase technique, the numbers and distribution of T lymphocyte subsets in the tissues of reactional states of leprosy (six reversal reaction, nine erythema nodosum leprosum (ENL) and two Lucio's reaction) were determined and compared with those found in stable, non-reactional patients (six tuberculoid, two borderline lepromatous and seven lepromatous). The pattern of segregation of the suppressor/cytotoxic phenotype at the periphery of the granuloma was found in both non-reactional tuberculoid lesions and reversal reactions, but was better developed in the former. In ENL and Lucio's reaction, as well as in non-reactional lepromatous tissue, the helper/inducer and suppressor/cytotoxic phenotypes were both admixed with the aggregated histiocytes. However, the helper/suppressor ratio in ENL (2.1 +/- 0.4) was significantly larger than that in non-reactional lepromatous tissue (0.7 +/- 0.4, P less than 0.001). The immature thymocyte antigen OKT6 was found on scattered large non-lymphoid cells, most commonly in tuberculoid and reversal reaction tissues, less commonly in ENL, but only irregularly in non-reactional lepromatous tissue. The peripheral pattern of the suppressor/cytotoxic phenotype may be an immunohistological reflection of a cell-mediated immune response common to both non-reactional tuberculoid and reversal reaction patients. The reversal of the helper/suppressor ratio in ENL as compared to non-reactional lepromatous disease suggests some role for cell-mediated immunity in the pathogenesis of ENL. The OKT6 positive cell is of unknown origin and function.