Since successful vaccination in VL was associated with an initial mixed Th1/Th2 response after immunization and with challenge infection the response polarized towards Th1 with further boosting of IFN-γ and down regulation of IL-4 [32], we demonstrate, DNA-prime/Protein-boost vaccination strategy significantly induced mixed Th1/Th2 responses after immunization, while L. donovani challenge infection induced significantly strong Th1 biased response compared to other vaccination strategies. This evidence concerns the gene IL4 and infection.