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Entamoeba histolytica Gal/GalNAc lectin depletes antioxidant defences of target epithelial cells

Among the variety of virulence factors of Entamoeba histolytica, an adherence lectin (Gal/GalNAc, 260 kDa) is known to mediate colonization and subsequent host responses. Gal/GalNAc lectin is universally recognized by the immune sera of patients with amoebic liver abscess. It plays a crucial role in cytolysis and phagocytosis of human and rat colonic mucin glycoproteins. The objective of the present study was to elucidate the role of antioxidants in E. histolytica Gal/GalNAc lectin-induced signals in the target epithelial cells. We have attempted to define a pathway in target cells, Henle-407 cells (human intestinal epithelial cell line), that could link this immunodominant antigen to a known biological pathway for target cell activation and triggering of subsequent disease pathology/parasite survival. Since several workers have demonstrated that cAMP and cGMP may act as important cellular signals for altering ion transport, so in the present study, cAMP and cGMP levels were measured in Henle-407 cells which showed significant increase at 15 min after stimulation. Elevated cAMP and cGMP levels are implicated in altered electrolyte transport and conductance. Results showed that there were increased levels of ROS and RNI which led to reduced activities of antioxidant enzymes – catalase, superoxide dismutase and glutathione peroxidase. Despite the increased glutathione (reduced) levels, the enzymes were not able to combat the damage caused by ROS and RNI. Thus, there was an increased local concentration of the free radicals and reduced activities of all the three enzymes which could damage the target cell in terms of cytoskeleton and permeability changes.