Vaccination against cutaneous leishmaniasis in a murine model. II. Immunologic properties of protective and nonprotective subfractions of soluble promastigote extract.

We have previously demonstrated that BALB/c mice can be protected against a fatal infection with Leishmania major by i.p. immunization with a soluble leishmanial antigen (SLA) preparation in conjunction with the adjuvant, Corynebacterium parvum (CP). In this study, SLA was separated into nine distinct fractions by anion exchange liquid chromatography, and the fractions were analyzed for their ability to stimulate T cells obtained from immunized mice, to be recognized by vaccine-induced antibodies, and to induce protective immunity. While all but one of the fractions were recognized by antibodies from SLA + CP immunized mice, only two fractions (fractions 1 and 9) stimulated lymphocytes to produce macrophage-activating factor and elicited significant delayed-type hypersensitivity in vivo. When mice were immunized with the fractions, only fraction 9 stimulated significant immunity (76% protection in seven experiments). Proteins (accounting for 1.3% of the total in SLA) appear to be responsible for the protection elicited with fraction 9, since protease treatment of this fraction destroyed its immunogenicity. Thus, a partially purified protective protein antigen fraction has been obtained and protection with this fraction correlated with cell-mediated immune responses. However, these results also demonstrate that the ability of leishmanial antigens to be recognized by T cells and produce macrophage-activating factor does not in itself predict whether such molecules will induce immunity, suggesting that protective leishmanial antigens may have additional unique properties.