Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 28, 1995
Publication Date: N/A
Interpretive Summary: Cryptosporidiosis is an intestinal disease of humans and animals caused by the protozoan parasite Cryptosporidium parvum. The disease is most prevalent in the young whose immune system may be incompletely developed and in AIDS patients who have impaired immune cell function. At present there are no drugs to treat cryptosporidiosis in humans or animals. Previous research has shown that colostrum from cows immunized with cryptosporidial antigens can ameliorate infection by binding the surface of the parasite and thereby preventing invasion of and development in host cells. The purpose of this study was to test a novel means of immunizing ruminants with a recombinant Cryptosporidium protein using direct injection of DNA. Lactating sheep that were immunized with plasmid DNA that codes for a parasite antigen produced high titer antibodies in their serum and colostrum specific for the parasite antigen. The study showed that route of injection and the DNA dose influenced the titer of antigen-specific immunoglobulin produced in these animals. The colostrum and serum antibodies were shown to bind the surface of the parasite and thus may be useful in preventing infection when administered to Cryptosporidium-infected individuals.
In an effort to generate high titer colostrum for immunotherapy of cryptosporidiosis, a study was conducted to test the efficacy of immunizing sheep with recombinant plasmid DNA (pCMV-CP15/60) encoding epitopes of 15 kDa and 60 kDa surface antigens of Cryptosporidium parvum sporozoites. The plasmid DNA was used to immunize preparturient ewes at three dose levels by jet-injection into either hind limb muscle (IM) or mammary tissue (IMAM). Regardless of route of injection, a dose-dependent anti-CP15/60 immunoglobulin response was observed in sera and colostrum from sheep immunized with pCMV-CP15/60 plasmid DNA. High titer antibody responses were observed in one of three animals per group receiving an IM injection of 100 ug or 1000 ug pCMV-CP15/60. IMAM immunization with 100 ug or 1000 ug pCMV-CP15/60 plasmid DNA elicited higher titer colostrum responses and more consistent serum responses compared to IM injections. A negligible serum and colostrum anti-CP15/60 response was observed in ewes injected IM with 10 ug pCMV-CP15/60 or 1000 ug control plasmid DNA. Immunoblotting of native C. parvum sporozoite/oocyst protein with hyperimmune serum and colostrum corroborated the increased titers against CP15/60 antigen. Serum and colostrum antibodies from pCMV-CP15/60-immunized sheep were eluted from native CP15 protein and bound a surface antigen of C. parvum sporozoites as indicated by indirect immunofluorescence staining.