The role of pattern recognition receptors in host cell signaling and phagosome maturation during infection with Leishmania

Leishmaniasis is a devastating group of diseases causing substantial mortality and morbidity throughout the world. Leishmania are obligate intracellular organisms infecting and replicating inside hosts' macrophages; making them ideal to model and understand interactions between host and parasite. Leishmania entry is receptor mediated through engagement of receptors recognizing molecular patterns on parasites surface, such as lipophosphoglycan (LPG). Macrophages have several cell surface receptors recognizing pathogenic organisms, in particular major receptors for Leishmania entry are complement receptor 3 (CR3), mannose receptor (MR), Fc receptor (FcR), and toll-like receptors (TLRs). CR3 recognizes complement, which coats pathogens for clearance by the immune system. While MR is involved in recognizing sugar side chains present on surfaces of pathogens leading to phagocytosis by macrophages. The Fc Receptor (FcR), not technically a pattern recognition receptor like CR3 and MR, is integral for pathogen entry through recognition of the Fc portion of antibodies. This dissertation focuses on identification of host cell signaling and characterizing phagosome maturation during Leishmania infection. Use of MR has not been well characterized such as CR3 or FcR during Leishmania infection. Our studies indicate that MR is not essential for in vivo Leishmania infection, WT or MR knock out mice infected with L. major or L. donovani do not display differences during infection. Analysis of cytokine production and MAPK signaling also are not different between WT and MR knock out mice. Leishmania survive inside macrophages by delaying phagosome maturation through preventing fusion with lysosomes. This delay allows parasites time to differentiate into more microbiocidal resistant life stage. Our data is the first step toward characterizing a role for macrophage receptors and their influence on phagosome maturation. The major receptors implicated in Leishmania entry, MR, CR3, FcγR, and TLRs, are all necessary for delaying phagosome maturation and none of these receptor deficient macrophages exhibit actin retention around Leishmania phagosomes. Using different serum components such as complement and anti- Leishmania antibodies allowed us to force parasites through certain receptors. Thus, receptor engagement and opsonization both influence Leishmania phagosome maturation and potentially parasite survival.