Mechanisms of attachment and internalization of Cryptosporidium parvum to biliary and intestinal epithelial cells

Background & Aims: Although infection of the intestinal and biliary tracts by Cryptosporidium parvum is a major problem in patients with the acquired immunodeficiency syndrome, the specific microbial and host molecules involv ed in C. parvum infection are unknown. We tested the hypothesis that lectin -carbohydrate interactions and cytoskeleton reorganization are involved in the infection of biliary and intestinal epithelia by C, parvum. Methods: In vitro models of cryptosporidial infection using human biliary and intestin al epithelial cell lines were used to assay C. parvum attachment and invasi on, Results: Exposure of C. parvum sporozoites to the sugar, galactose-N-ac etylgalactosamine (GaI/GaINAc), and to bovine mucin reduced C. parvum attac hment to biliary and intestinal epithelia up to 70%, Preincubation of cell monolayers with either lectins specific to GaI/GaINAc, or glycosidases that specifically release GaI/GaINAc oligosaccharides from glycoproteins, decre ased attachment up to 80%, Cytochalasin B and cytochalasin D, but not nocod azole, decreased invasion of cells by C. parvum up to 70% without affecting attachment. During cell invasion (but not attachment), confocal microscopy showed recruitment of actin (but not tubulin) in biliary and intestinal ep ithelia directly adjacent to C. parvum. Conclusions: GaI/GaINAc epitopes of glycoproteins on the epithelial apical membrane and GaI/GaINAc-specific sp orozoite surface lectins are involved in the mechanism(s) of C. parvum atta chment to intestinal and biliary epithelial cells, and actin remodeling in host cells is required for C. parvum invasion.