ABSTRACT
Recent scientific evidence indicates that distinct patterns of susceptibility in BALB/c mice to Leishmania major infection are attributable to the differential expansion of distinct CD4+ T-cell subsets and their cytokines production. Production of the Th1 cytokine IFN- gamma is associated with resistance, whereas production of the Th2 cytokines IL-4 and IL-10 are associated with extreme susceptibility. The major host immune defense mechanism against Leishmania is activation of macrophages by INF-gamma derived from T cells. The inability of susceptible hosts to mount the immune response necessary to activate macrophage and destroy the parasites may be due to the parasite-specific proteins that are able to suppress the immune system. In the present study, we have semi-purified the excreted antigens of Leishmania major promastigote and amastigote by column chromatography. The isolated fraction showed a potent immunosuppressive activity on normal BALB/c mice lymphocytes stimulated with mitogens. Fifteen microgram of the isolated fraction caused 81% suppression of lymphocyte proliferation. These data may suggest that the parasite by secreting immunosuppressive factor down regulate the immune system and as a result survive in the body