Resistance to cutaneous leishmaniasis in nude mice injected with L3T4+ T cells but not with Ly-2+ T cells.

The importance of T cells in resistance to infection with the intracellular protozoan parasite Leishmania major is substantiated by the susceptibility to infection of athymic nude mice of both resistant and susceptible strains. However, the relative roles of different T cell subpopulations remain controversial. In order to address this issue, selected L3T4+ Ly-2- or L3T4- Ly-2+ T cell subpopulations from normal mice were adoptively transferred into athymic nude recipients of the same strain, and their capacity to mediate host-protective immunity against infection with L. major promastigotes was determined. In experiments with mice of different inbred strains, reconstitution with L3T4+ Ly-2- cells rendered the nude mice completely resistant to cutaneous leishmaniasis, whereas L3T4- Ly-2+ cells failed to do so. Partial protection in some recipients of large numbers of Ly-2+ cells could be ascribed to contamination of the transferred inoculum with L3T4+ cells. Thus, resistance to L. major infection in reconstituted nude mice can be promoted by L3T4+ T cells in the absence of detectable Ly-2+ T cells.