Leishmania recombinant antigen modulates macrophage effector function facilitating early clearance of intracellular parasites

Background: Immunmodulation combined with chemotherapy has emerged as an alternative to treat infections. The study evaluates immunomodulatory properties of a Leishmania recombinant protein (rA6) in activating macrophages and clearing intracellular parasites. Methods: The rA6 from a previously identified cDNA clone was analyzed for inducing the production of nitric oxide (NO) and reactive oxygen species (ROS) in macrophages, post and prior to infection with promastigotes by Griess method and flow cytometry. Phagocytosis and killing by treated macrophages was evaluated using Staphylococcus aureus as an index organism. Intracellular clearance of PKH67-labeled parasites from treated macrophages was assessed flowcytometrically. Combined effect of rA6 with miltefosine/AmBisome in reducing intracellular amastigotes was examined microscopically. Results: Treatment with rA6 post infection caused increased production of NO with increased number of macrophages producing NO and ROS coupled with enhanced phagocytic and killing capacity. Antigen stimulated macrophages expressed high level of iNOS and TNF-alpha mRNA. It synergized with miltefosine and AmBisome and facilitated early clearance of intracellular amastigotes at sub-optimal drug doses. Conclusion: The study demonstrates immunomodulatory potential of rA6 and presents first evidence on synergism between rA6 and anti-leishmanial drugs, thus placing it as a promising candidate for adjunct therapy.