Superoxide Dismutase B1, an Exacerbatory Antigen Elicits Interleukin-10 Production in Murine Leishmania major Infection

Leishmania major (L. major) superoxide dismutase B1 (SODB1) is an important enzyme for parasite survival. Previous studies have shown that SODB1 is highly immunogenic and sera from patients infected with Leishmania react with recombinant SODB1 (rSODB1). In the present study, the protective effect of immunization with recombinant SODB1 (rSODB1) against the infection with Leishmania major was evaluated in a mice model. Three groups of BALB/c mice received rSODB1 mixed with complete Freund’s adjuvant (immunized group), adjuvant (control I) or PBS alone (control II). This protocol was repeated 15 days later. Three weeks after the second booster immunization, four mice from each group were sacrificed to measure in vitro cytokines production by splenocytes; remaining mice were challenged using meta-cyclic promastigotes. Eight weeks later, the infected mice were sacrificed, and their splenocytes were re-stimulated with rSODB1; then, cytokine levels were assayed by the enzyme linked immunosorbent assay (ELISA). Immunization of mice with rSODB1 plus adjuvant elicited high level of IFN-γ, low level of IL-5 production, and a significant increase in IL-10 level, as compared to controls. Post-challenge re-stimulation of splenocytes also showed a polarized TH1 response accompanied by higher levels of IL-10 in immunized mice with rSODB1 plus adjuvant compared to controls. Although immunization with recombinant SODB1 plus adjuvant induced a strong TH1 response, which was identified by high-level IFN-y production, regarding the increase in footpad swelling and lesions size, it could be concluded that immunization with rSODB1 plus adjuvant was not able to provide protection against Leishmania infection in the presence of high level of IL-10 production.