A recombinant Leishmania chagasi antigen that stimulates cellular immune responses in infected mice.

Cellular immune mechanisms resulting in gamma interferon production are critical for protection against visceral leishmaniasis. Antigens stimulating T-cell responses are likely present in the intracellular amastigote form of the parasite, since this is the form found in a mammalian host. To identify T-cell antigens of Leishmania chagasi, the parasite causing South American visceral leishmaniasis, we used a double antibody-T-cell technique to screen an amastigote cDNA library. One cDNA selected (Lcr1) encodes an antigen that stimulated proliferation of splenic T lymphocytes from infected mice that were either resistant (C3H.HeJ) or susceptible (BALB/c) to L. chagasi infection. The Lcr1 cDNA contains four highly divergent 201-bp repeats homologous to the 204-bp repeat of a Trypanosoma cruzi flagellar antigen gene. Results are consistent with a single copy of the Lcr1 gene producing an mRNA of > 10 kb and a protein of > 200 kDa. Recombinant Lcr1, cloned adjacent to polyhistidine and purified on a nickel affinity column, stimulated gamma interferon but not interleukin-4 (IL-4), IL-5, or IL-10 secretion by T-cell-enriched splenocytes from either susceptible or resistant mice during L. chagasi infection. Immunization with Lcr1 partially protected BALB/c mice against challenge with L. chagasi, indicating the utility of the double screening approach in selecting relevant T-cell antigens.