Adjuvant Effect of Leishmania major Promastigotes on the Immune Response of Mice to Ovalbumin

The immune responses of mice immunized with ovalbumin (OVA) together with killed L. major (KLM) promastigotes as adjuvant were studied. Three doses (5 × 107, 1 × 108 and 2 × 108) of KLM combined with OVA (100 mg) were injected into the groups of C57BL/6 mice. BCG and complete Freund’s adjuvant (CFA) were used as control adjuvants. Lymphocyte proliferation and antibody titers were determined, and IFN-g and IL-4 were measured in the supernatants of lymph node cell cultures. Results showed that immunization using OVA mixed with KLM enhanced the in vitro proliferative response of T-cells to the antigen and resulted in the production of increased levels of IFN-g (2800-3700 pg/ml) relative to the mice injected with OVA alone (1750 pg/ml). In the mice receiving OVA + 5 × 107 KLM, the production of IL-4 remained lower (18, 20 pg/ml) than OVA alone (105, 109 pg/ml) and almost was similar to that of observed in mice inoculated with OVA + BCG, leading to high IFN-g/IL-4 ratios. Using higher doses of KLM (1 × 108), the IL-4 responses were of the same magnitude as or higher than the responses of mice inoculated with OVA + CFA. Antibody titers to OVA were also strongly boosted at the highest KLM dose. These findings indicate that KLM may function as an adjuvant, and its dose plays a role in the eventual outcome of the response. Inoculation of the mice with a low dose of KLM (5 × 107) tends to promote a Th1-type response.