Differential Immune Responses of Th1 Stimulatory Chimeric Antigens of <i>Leishmania donovani</i> in BALB/c Mice

Visceral leishmaniasis (VL) is the third most severe infectious parasitic disease and is caused by the protozoan parasite <i>Leishmania</i>. To control the spread of the disease in endemic areas where the asymptomatic patients act as reservoirs as well as in nonendemic areas, an effective vaccine is indispensable. In this direction, we have developed three chimeric proteins by the combination of three already known Th1 stimulatory leishmanial antigens, i.e., enolase, aldolase, and triose phosphate isomerase (TPI). The newly developed chimeric proteins, i.e., enolase-aldolase, TPI-enolase, and aldolase-TPI along with BCG as an adjuvant were assessed and compared, examining humoral and cellular adaptive immune responses elicited in BALB/c mice. The three chimeric antigens exhibited differential immune responses shown by differences in Th1 and Th2 cytokine production in <i>ex vivo</i> stimulated splenocytes of immunized mice. It was observed that all three chimeric proteins are more immunogenic than their component proteins. However, while comparing the immune response of the three chimeric proteins, aldolase-TPI exhibited a better immunogenic (Th1-type) response, as evidenced by the highest IFN-γ production, a high IgG2a antibody isotype switching, a high % population of CD8⁺ and CD4⁺ T-cells, and a significantly high expression of <i>iNOS2</i>. Thus, the results suggest the potential of these chimeric antigens as strong immunogens that can be harnessed in vaccine development against VL.