Cryptosporidium parvum apical complex glycoprotein CSL contains a sporozoite ligand for intestinal epithelial cells

• Published in: Infection and Immunity 1999-10, Vol.67 (10), p.5282-5291
• Main Authors: Langer, R.C, Riggs, M.W
• Format: Article
• Language: English
• Subjects: animal health; animal parasites and pests; Animals; Antibodies, Monoclonal - immunology; Biological and medical sciences; Caco-2 Cells; Cryptosporidium parvum; Cryptosporidium parvum - physiology; Electrophoresis, Gel, Two-Dimensional; Fundamental and applied biological sciences. Psychology; Glycoproteins - isolation & purification; Glycoproteins - physiology; Humans; Intestines - parasitology; Life cycle. Host-agent relationship. Pathogenesis; Ligands; Molecular and Cellular Pathogenesis; Protozoa; Protozoan Proteins - isolation & purification; Protozoan Proteins - physiology
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.67.10.5282-5291.1999

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 ia 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.