Hyperimmune bovine colostrum specific for recombinant Cryptosporidium parvum antigen confers partial protection against cryptosporidiosis in immunosuppressed adult mice.

Preparturient cows were immunized three times over a six-week period with recombinant plasmid DNA encoding the Cryptosporidium parvum CP15/60 antigen by injecting the DNA in the mammary gland. Serum was collected at each immunization and first colostrum was collected after parturition; all were assayed for Cryptosporidium-specific antibodies (Ab). A serological response to C. parvum sporozoite and oocyst antigen was detected in cows immunized with pCP15/60 plasmid DNA. Colostrum from these cows, unlike colostrum from normal controls, contained Ab specific for C. parvum sporozoites and oocysts as indicated by immunofluorescence Ab (IFA) staining. Colostrum was also tested for conferring passive immunity against C. parvum infection by oral administration to immunosuppressed adult inbred mice. Immune colostrum and control colostrum were administered to separate groups of dexamethasone (DEX)-treated adult C57BL/6NCr mice beginning 12 h before and at 12 h intervals for 3 days after oral C. parvum oocyst infection. Cryptosporidium development was assayed in ilea of immune- and control-colostrum-treated mice 96 h postinfection by semiquantitative PCR. Mice receiving immune colostrum showed partial protection (about 50% reduction) against intestinal C. parvum development compared to mice receiving control colostrum. This protection was evident at a challenge dose of 10(3) C. parvum oocysts per mouse; no differences were noted in parasite development between groups receiving immune or control colostrum and infected with 10(4) oocysts. This study showed that serum and colostrum Ab response to C. parvum can be elicited in preparturient cows by direct injection of recombinant pCP15/60 plasmid DNA and that passive protection against cryptosporidiosis can be obtained by treating immunosuppressed mice with immune colostrum before and after C. parvum infection.