Leishmania major: nature of immunity induced by immunization with a mutagenized avirulent clone of the parasite in mice

A chemically mutagenized avirulent form of Leishmania major was used to immunize BALB/c and C57B1/6 mice against challenge with virulent L. major. Immunity was elicited when the avirulent parasite was injected intravenously or intraperitoneally, but not subcutaneously. In fact, the latter route of immunization sometimes resulted in exacerbation of a subsequent infection with virulent L. major. Mice immunized with avirulent L. major developed upon challenge with virulent L. major cutaneous lesions which were significantly smaller and contained substantially fewer parasites than lesions on control nonimmune animals. Finally, the protection conferred by immunization with avirulent L. major could be adoptively transferred with T cells of the CD4+ lineage but not the CD8+ lineage.