title: Cryptosporidium parvum apical complex glycoprotein CSL contains a sporozoite ligand for intestinal epithelial cells.
abstract: Cryptosporidiosis, caused by the apicomplexan parasite Cryptosporidium parvum, has become a well-recognized diarrheal disease of humans and other mammals throughout the world. No approved parasite-specific drugs, vaccines, or immunotherapies for control of the disease are currently available, although passive immunization with C. parvum-specific antibodies has some efficacy in immunocompromised and neonatal hosts. We previously reported that CSL, an approximately 1,300-kDa conserved apical glycoprotein of C. parvum sporozoites and merozoites, is the antigenic species mechanistically bound by neutralizing monoclonal antibody 3E2 which elicits the circumsporozoite precipitate (CSP)-like reaction and passively protects against C. parvum infection in vivo. These findings indicated that CSL has a functional role in sporozoite infectivity. Here we report that CSL has properties consistent with being a sporozoite ligand for intestinal epithelial cells. For these studies, native CSL was isolated from whole sporozoites by isoelectric focusing (IEF) following observations that the approximately 1,300-kDa region containing CSL as seen by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was comprised of approximately 15 molecular species (pI 3 to 10) when examined by two-dimensional (2-D) electrophoresis and silver staining. A subset of six approximately 1,300-kDa species (pI 4.0 to 6.5) was specifically recognized by 3E2 in 2-D Western immunoblots of IEF-isolated CSL. Isolated native CSL bound specifically and with high affinity to permissive human intestinal epithelial Caco-2 cells in a dose-dependent, saturable, and self-displaceable manner. Further, CSL specifically bound to the surface of live Caco-2 cells inhibited sporozoite attachment and invasion. In addition, sporozoites having released CSL after incubation with 3E2 and occurrence of the CSP-like reaction did not attach to and invade Caco-2 cells. These findings indicate that CSL contains a sporozoite ligand which facilitates attachment to and invasion of Caco-2 cells and, further, that ligand function may be disrupted by CSL-reactive monoclonal antibody. We conclude that CSL is a rational target for passive or active immunization against cryptosporidiosis.
authors.affiliation: Department of Veterinary Science and Microbiology, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: R C
authors.initials: RC
authors.lastname: Langer
authors.forename: M W
authors.initials: MW
authors.lastname: Riggs
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D018938:Caco-2 Cells; D016785:Cryptosporidium parvum / Q000502:physiology*; D015180:Electrophoresis, Gel, Two-Dimensional; D006023:Glycoproteins / Q000302:isolation & purification / Q000502:physiology*; D006801:Humans; D007422:Intestines / Q000469:parasitology*; D008024:Ligands; D015800:Protozoan Proteins / Q000302:isolation & purification / Q000502:physiology*
chemical_list: D000911:Antibodies, Monoclonal; D006023:Glycoproteins; D008024:Ligands; D015800:Protozoan Proteins