In situ identification of activated Ta1+ T lymphocytes in human leprosy skin lesions.

Using a monoclonal antibody, anti-Ta1, that identifies antigen-activated T lymphocytes in vitro, we sought to identify activated T lymphocytes in leprosy skin lesions. Greater numbers of Ta1 positive T lymphocytes were observed in tuberculoid leprosy, lepromin skin tests, and reversal reactions as compared with lepromatous leprosy or erythema nodosum leprosum (ENL) (p less than 0.001). With a double-staining technique, we found that the majority of these activated T lymphocytes were of the helper/inducer phenotype. No differences of Ta1 positive lymphocytes were observed in the peripheral blood. The defective cell-mediated immune response in lepromatous and ENL patients correlates with, and may be related to the failure of T-helper/inducer activation or proliferation in the presence of Mycobacterium leprae.