Mediation of Cryptosporidium parvum infection in vitro by mucin-like glycoproteins defined by a neutralizing monoclonal antibody

The protozoan parasite Cryptosporidium parvum is a significant cause of dia rrheal disease worldwide. Attachment to and invasion of host intestinal epi thelial cells by C. parvum sporozoites are crucial steps in the pathogenesi s of cryptosporidiosis. The molecular basis of these initial interactions i s unknown. In order to identify putative C. parvum adhesion- and invasion-s pecific proteins, we raised monoclonal antibodies (MAbs) to sporozoites and evaluated them for inhibition of attachment and invasion in vitro. Using t his approach, we identified two glycoproteins recognized by 4E9, a MAb whic h neutralized C. parvum infection and inhibited sporozoite attachment to in testinal epithelial cells in vitro. 4E9 recognized a 40-kDa glycoprotein na med gp40 and a second, >220-kDa protein which was identified as GP900, a pr eviously described mucin-like glycoprotein, Glycoproteins recognized by 4E9 are localized to the surface and apical region of invasive stages and are shed in trails from the parasite during gliding motility, The epitope recog nized by 4E9 contains alpha-N-acetylgalactosamine residues, which are prese nt in a mucin-type O-glycosidic linkage. Lectins specific for these glycans bind to the surface and apical region of sporozoites and block attachment to host cells. The surface and apical localization of these glycoproteins a nd the neutralizing effect of the MAb and alpha-N-acetylgalactosamine-speci fic lectins strongly implicate these proteins and their glycotopes as playi ng a role in C. parvum-host cell interactions.