Role of Mycobacterium vaccae in the protection induced by first generation Leishmania vaccine against murine model of leishmaniasis.

Various Leishmania antigens showed to induce protection when used with IL-12 as an adjuvant in an animal model of leishmaniasis. Limitations in using IL-12 justify searching for an appropriate adjuvant to accelerate induction of a Th1-type immune response and protection. In this study, the role of Mycobacterium vaccae as an adjuvant mixed with either autoclaved Leishmania major (ALM) or freeze-thawed-killed L. major (KLM) in increasing protection in susceptible and resistant mice was studied. Nineteen groups of BALB/c and 19 groups of C57BL/6 mice, ten mice per group, were immunized three times in 45 days interval with different doses of either KLM or ALM alone or mixed with either BCG or different doses of M. vaccae. Immunized groups of mice and PBS-injected control group were challenged with 2 x 10(6) promastigotes of L. major at the base of the tail. The evolution of the lesion was monitored, and the size of the lesion was measured and recorded weekly. Anti-Leishmania total IgG Ab was titrated before and after challenge. The results showed that immunization of either susceptible or resistant mice with KLM or ALM mixed with low dose of M. vaccae increased protection defined by significantly smaller ulcer size in immunized mice compared with the PBS-injected control group.