Characterization of an intestinal epithelial cell receptor recognized by the Cryptosporidium parvum sporozoite ligand CSL

The protozoan parasite Cryptosporidium parvum is a leading cause of diarrhe a in humans and neonatal calves. The absence of approved parasite-specific drugs, vaccines, and immunotherapies for cryptosporidiosis relates in part to limited knowledge on the pathogenesis of zoite attachment and invasion. We recently reported that the C. parvum apical complex glycoprotein CSL con tains a zoite ligand for intestinal epithelial cells which is defined by mo noclonal antibody (MAb) 3E2. In the present study, the host cell receptor f or CSL was characterized. For these studies, a panel of epithelial and mese nchymal cell lines was examined for permissiveness to C. parvum and the abi lity to bind CSL. Cells of epithelial origin were significantly more permis sive and bound significantly greater quantities of CSL than cells of mesenc hymal origin. Caco-2 intestinal cells were selected from the epithelial pan el for further characterization of the CSL receptor. Immunoelectron microsc opy demonstrated that CSL bound initially to the surface of Caco-2 cells an d was rapidly internalized. The molecule bound by CSL was identified as an 85-kDa Caco-2 cell surface protein by radioimmunoprecipitation and CSL affi nity chromatography. Sporozoite incubation with the isolated 85-kDa protein reduced binding of MAb 3E2. Further, attachment and invasion were signific antly inhibited when sporozoites were incubated with the 85-kDa protein pri or to inoculation onto Caco-2 cells. These observations indicate that the 8 5-kDa protein functions as a Caco-2 cell receptor for CSL. CSL also bound s pecifically to intestinal epithelium from calves, indicating receptor expre ssion in a second important host species. Molecular characterization of the CSL receptor may lead to novel avenues for disrupting ligand-receptor inte ractions in the pathogenesis of C. parvum infection.