Characterization of a > 900,000-M(r) Cryptosporidium parvum sporozoite glycoprotein recognized by protective hyperimmune bovine colostral immunoglobulin

Abstract

Cryptosporidium parvum, a zoonotic Apicomplexan pathogen, causes profound diarrhea, malnutrition, and dehydration in patients with AIDS. A less severe, self-limited disease occurs in immunocompetent individuals, particularly children, animal handlers, and residents of the developing world. Very little is known about the biology of the organism, the pathophysiology of the disease process, or the mechanism of protective immunity. There is no effective therapy for cryptosporidiosis, but hyperimmune bovine colostrum raised against Cryptosporidium oocysts and sporozoites has ameliorated infection and disease in some patients with AIDS, and a variety of monoclonal antibodies, as well as hyperimmune bovine colostrum, have significantly reduced cryptosporidial infection of mice and calves. We report here the identification and initial characterization of a > 900,000-M(r) Cryptosporodium sporozoite glycoprotein (GP900) that is a prominent antigen recognized by protective hyperimmune bovine colostral immunoglobulin. Three of six murine anticryptosporidial monoclonal antibodies reacted with GP900, indicating that the molecule is highly immunogenic in mice as well as in cows. GP900 is Triton X-100 soluble and N glycosylated. Western blotting of the N-deglycosylated protein, detected with antibodies eluted from recombinant clones expressing a partial GP900 fusion protein, suggested that the polypeptide backbone of the glycoprotein has an M(r) of < 190,000. GP900 is encoded by a single-copy gene that resides on the largest Cryptosporidium chromosome.