The pathogenesis of the enteric protozoan parasite Entamoeba histolytica remains poorly understood. Moreover, the host responses during the early periods of interaction in the gut remain to be clarified. In this study I investigated the cell specific responses to the parasite and the importance of cross talk between epithelial-immune cells that could potentially influence the outcome of infection, with a central focus on Nuclear factor (NF)-kappaB. NF-kappaB is a ubiquitous transcription factor that plays a critical role in mucosal inflammation and its regulation by E. histolytica has not been studied so far. Gal-lectin is a well characterized parasite virulence factor and vaccine candidate. I first characterized the interactions between Gal-lectin and macrophages and found that several proinflammatory genes are upregulated as early as 2h. The Gal-lectin activated NF-kappaB and up-regulated Toll like receptor-2 expression in an NF-kappaB- and p38 Mitogen Activated Protein (MAP) kinase-dependent manner. As intestinal epithelial cells (IEC) form the first line of active host defense against mucosal pathogens, I determined the interaction between ameba soluble proteins and naive IEC. I observed that the parasite could elicit a chemokine response via activation of PI3 kinase and phosphorylation of p65 subunit to induce monocyte chemoattractant protein-1. The consequent recruitment of immune cells could be responsible for colonic inflammation. Finally, I made the novel observation that in macrophage-primed IEC, ameba proteins elicited a cytoprotective stress response. Using a combination of siRNA and over expression studies, I demonstrated that amebic proteins increased the expression and phosphorylation of Heat shock protein (Hsp) 27 thereby enhancing its association with and subsequent inhibition of Inhibitory kappaB kinase (IKK). The resulting inhibition of NF-kappaB could be a potential mechanism that explains the absence of inflammation in the majority of infected individuals. Taken together, the findings of this study open up a new facet in the pathogenesis of amebiasis and unravel a novel paradigm to study host-parasite interactions in the gut.

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