The Host-Protective Effect of Arabinosylated Lipoarabinomannan against Leishmania donovani Infection Is Associated with Restoration of IFN-γ Responsiveness

Visceral leishmaniasis (VL), which is endemic as a major infectious disease in the tropical and subtropical countries, is caused by a protozoan parasite Leishmania donovani. At present, restricted treatment options and lack of vaccines intensify the problem of controlling VL. Therefore, finding a novel immunoprophylactic or therapeutic principle is a pressing need. Here, we report that arabinosylated lipoarabinomannan (Ara-LAM), a TLR2-ligand isolated from Mycobacterium smegmatis, exhibits a strong immunomodulatory property that conferred protection against L. donovani infection. Although, Ara-LAM modulates TLR2 and MAPK signaling, it is not known whether Ara-LAM involves IFN-gamma signaling for effective parasite clearance. Because, it is reported that IFN-gamma signaling, a principle mediator of NO generation and macrophage and Tcell activation, is hampered during leishmanial pathogenesis. Ara-LAM increases IFN-gamma receptor expression and potentiates IFN-gamma receptor signaling through JAK-STAT pathway. Moreover, Ara-LAM reciprocally modulates IRF4 and IRF8 expression and reinstates anti-leishmanial Th1 response that eventuates in significantly reduced parasite load in spleen and liver of L. donovani-infected BALB/c mice. IFN-gamma Ra silencing resulted in the suppression of these host-protective mechanisms affected by Ara-LAM. Thus, Ara-LAM-mediated restoration of IFN-gamma responsiveness is a novel immunomodulatory principle for protection against L. donovani susceptible host.