BOVINE ANTIBODY AGAINST CRYPTOSPORIDIUM-PARVUM ELICITS A CIRCUMSPOROZOITE PRECIPITATE-LIKE REACTION AND HAS IMMUNOTHERAPEUTIC EFFECT AGAINST PERSISTENT CRYPTOSPORIDIOSIS IN SCID MICE

Control of cryptosporidiosis is currently hampered by the absence of d rugs or vaccines proven consistently effective against Cryptosporidium parvum. On the basis of observations that anti-C. parvum antibody has therapeutic effect against cryptosporidiosis, cows were immunized wit h C. parvum to produce hyperimmune colostral antibody. An antibody-ric h fraction was prepared and differentiated from control (nonhyperimmun e) antibody by enzyme-linked immunosorbent assay, immunofluorescence a ssay, immunoelectron microscopy, and in vitro neutralizing titer again st DEAE-cellulose-isolated C. parvum sporozoites. Oocyst, purified spo rozoite, and merozoite antigens recognized by hyperimmune antibody wer e defined by Western blot (immunoblot). Hyperimmune antibody recognize d antigens common to oocysts, sporozoites, and merozoites, as well as stage-specific antigens. Upon incubation,vith hyperimmune antibody, sp orozoites underwent distinct morphologic changes characterized by prog ressive formation and eventual release of membranous sporozoite surfac e antigen-antibody complexes, similar to the malaria circumsporozoite precipitate reaction. The infectivity of sporozoites having undergone this reaction was neutralized. The reaction was minimal or absent on s porozoites incubated with control antibody. To determine therapeutic e ffect in vivo, persistent C. parvum infection was established in adult severe combined immune-deficient (SCID) mice by oral inoculation with 10(7) oocysts. At 5 weeks postinfection, infected mice were treated f or 10 days with hyperimmune or control antibody by inclusion in drinki ng water and daily gavage. Fecal oocyst shedding and infection scores in the gastrointestinal tract and gall bladder/common bile duct in hyp erimmune antibody-treated mice were significantly lower than those in the control antibody-treated mice. Hyperimmune bovine antibody prepare d against C. parvum may provide a first-generation therapy for control of cryptosporidiosis. Additionally, the defined antigens can be evalu ated as subunit immunogens to produce better-characterized polyclonal antibody for control of cryptosporidiosis or as targets for monoclonal antibody-based immunotherapy.