| Summary: | Leishmaniasis represents a spectrum of infectious diseases caused by Leishmania kinetoplastids, which disproportionately affects low-income populations within tropical and subtropical regions. The Leishmania amastigote perpetuates infection in the vertebrate host by replicating within phagocytic cells. The aim of this study was to investigate the molecular mechanisms through which L. mexicana amastigotes interact and establish themselves within macrophages. For this purpose, I initially established an in vitro model system based on axenic L. mexicana amastigotes and cultured macrophages, and developed a phagocytosis assay that relies on the use of Propidium iodide to stain parasite-containing vacuoles. I used this in vitro system to investigate the effect of L. mexicana amastigotes on macrophage intracellular signalling [ie. nuclear factor-K B (NFKB) activation] and to characterise which macrophage receptors mediate amastigote recognition and internalisation. I found that macrophages but not non-professional phagocytes exhibited a high capacity to bind and ingest unopsonized and opsonized amastigotes. Pharmacological studies suggested a role for EDTA- and RGD peptide- sensitive receptors, most likely integrins, in the direct binding of unopsonized amastigotes. Interestingly, a phagocyte-specific integrin, Complement Receptor 3 (CR3) integrin was implicated in amastigote phagocytosis but had no significant role in parasite binding. Amastigote recognition and uptake thus involve distinct steps, controlled by distinct surface receptors. In addition, I have demonstrated that L. mexicana amastigotes interfere with FcyR-induced activation of the pro-inflammatory coupled transcription factor NFKB. The main results obtained with axenic parasites were confirmed using lesion-derived amastigotes, supporting the idea that in vitro studies will help better define the key mechanisms ofthe interaction between macrophages and amastigotes.
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