Immunization with Live Promastigote Antigen of Leishmania donovani induces Protection against Experimental Visceral Leishmaniasis Infection in BALB/c Mice

Visceral leishmaniasis (VL) also commonly known as kala-azar is a vector borne parasitic disease which is endemic in Indian subcontinent. At present treatment of this disease relies on chemotherapy and no vaccine is available for human use. Since chemotherapy has some side-effects therefore vaccination with long lasting immunity is the major hope to control leishmaniasis. It is presumed that if a vaccine candidate can activate immune system in a similar manner to the natural course of infection, it will be more successful in generating effective immune response. Also it is known from the previous studies that few numbers of parasites are required to be present in host system for the stimulation of appropriate immune response. Based on this approach we performed our present study in which BALB/c mice were immunized with viable low (103) dose of Leishmania donovani promastigotes. Challenge infection (107) was given to all animals after three weeks of last immunization. Mice were euthanized 15 days after immunization and on 90 post infection/challenge day. A remarkable decline in parasite load was noticed in immunized animals as compared to the infected controls after challenge infection as illustrated by the reduction in parasite burden (72%). Immunized animals showed enhanced DTH responses, elevated IgG2a antibody levels and up-regulated levels of IFN-γ and IL-12 over the infected controls which imply the generation of protective immunity. The present study indicates that such whole parasite vaccines are intrinsically safer and holds a promising potential as anti-leishmanial vaccine candidate.