Mechanism Of Macrophage Activation And Enhancement Of Leishmanicidal Effect By An Attenuated Leishmania Donovani And A Membrane Protein Of The Same Attenuated Leishmania Strain

Leishmania is a trypanosomatid protozoan that is responsible for the disease leishmaniasis. Promastigote form of pathogenic Leishmania, an intracellular pathogen, delays phagosome maturation and represses normal function of macrophages (MΦs). In the first chapter, attenuated Leishmania strain (ALS) UR6 exposed RAW 264.7 cells showed an enhanced respiratory burst and enhanced production of pro-inflammatory mediators. We observed low parasite burden in ALS primed MΦs when co-infected with PLD, compared to control. In our study, increased co-localization of carboxyfluorescein succinimidyl ester labeled pathogenic L. donovani (PLD) AG83 with Lysosome was found. Moreover, increased co-localization was observed between PLD late phagosomal markers viz. Rab7, LAMP1, Cathepsin D, and V-ATPase which indicate phagosome maturation. It was also observed that V-type and p38 MAPK is the key player in acidification and maturation of phagosome in ALS pre-exposed MΦs. We conclude pre-exposure of MΦs to ALS could potentiate short-term prophylactic response in the host. In the second chapter, bioactivity of a Leishmanial integral membrane glycol-lipoprotein (LIMP) isolated from the attenuated Leishmania donovani UR6 was assessed. LIMP is well capable of inducing the generation of ROS in RAW 264.7 cells. LIMP also capable driving pro-inflammatory cytokine viz. IL-12, TNF-α, and IL-1β expression. The overall expression and nuclear accumulation of p65 subunit of NF-kB after treatment with LIMP were found. LIMP was also found to be activating TLR-2-CD14 axis. In the third chapter, we observe Lipid Bodies (LB) or lipid droplets (LD) generation in L. donovani infected MΦs in a time-dependent manner. The size of LD was also increased along with time. We provide novel insight on the signaling molecules i.e. ERK½, which is responsible for LB accumulation. Alongside ERK1/2, the paracrine action of IL-10 may also important to induce LB generation. Interestingly LPG-deficient UR6 failed to induce LB generation. But inhibition of phagosome maturation drastically stimulates LB accumulation in UR6 infected MΦs. Aspirin treatment in AG83 infected MΦs does not only lowers LD load but also favors phagolysosome biogenesis and correct cytokine balance, hence aspirin could be used as a therapeutic tool to resist parasite growth in the early hour of infection