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 involved 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 intestinal epithelial cell lines were used to assay C. parvum attachment and invasion, Results: Exposure of C. parvum sporozoites to the sugar, galactose-N-acetylgalactosamine (GaI/GaINAc), and to bovine mucin reduced C. parvum attachment 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, decreased attachment up to 80%, Cytochalasin B and cytochalasin D, but not nocodazole, 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 epithelia directly adjacent to C. parvum. Conclusions: GaI/GaINAc epitopes of glycoproteins on the epithelial apical membrane and GaI/GaINAc-specific sporozoite surface lectins are involved in the mechanism(s) of C. parvum attachment to intestinal and biliary epithelial cells, and actin remodeling in host cells is required for C. parvum invasion.