Serum and colostrum antibody responses induced by jet-injection of sheep with DNA encoding a Cryptosporidium parvum antigen

Abstract

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 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 or 1000 μg pCMV-CP15/60. IMAM immunization with 100 or 1000 μg 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 μg pCMV-CP15/60 or 1000 μg control plasmid DNA. Immunoblotting of native C. parvum sporozoiteloocyst 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.