Immunity to experimental infection with Leishmania major: generation of protective L3T4+ T cell clones recognizing antigen(s) associated with live parasites.

Exacerbation and resolution of lesions induced by Leishmania major promastigotes are, at least in part, the result of the activity of distinct parasite-specific L3T4+ T lymphocytes. The present report describes L. major-specific cloned L3T4+ T lymphocytes capable of transferring substantial protective immunity to normal highly susceptible BALB/c mice. The two protective T cell clones analyzed appear to recognize antigen associated only with live L. major parasites. Therefore, the pattern of antigen reactivity of these protective T cell clones is different from that of the previously described parasite-specific L3T4+ T cells which contribute to exacerbation of disease. The results presented in this report indicate that the two opposite effects of parasite-specific L3T4+ T cells on the disease process could be mediated by functionally similar L3T4+ T cells differing in their antigen specificity.