Identification and the role of soluble antigens detected in bile from Eimeria stiedai-infected rabbits

Antibodies against Eimeria stiedai sporozoites and merozoites were detected in the sera of rabbits immunized with bile obtained from infected rabbits on the 15th day post-infection. The trails made by gliding sporozoites were also detected by the sera. After penetration into the host cell. an antibo dy-binding region was observed on the parasitophorous vacuole membranes of the parasites. Rabbits administered a combination of the bile and cholera t oxin shed fewer oocysts in the feces after infection than control rabbits. The immunized rabbits developed a high level of IgA antibody against solubl e antigens in the bile. By immunoblotting, antigens with molecular masses o f 32, 37. and 49 kDa were detected in the bile obtained from infected rabbi ts on the 15th day postinfection. Absorption treatment with sporozoites red uced or abolished the antibody reactivity to the 32-kDa antigen of merozoit es and the bile antigens. However, antibody reactivity to the 37- and 49-kD a antigens still remained. These results indicate that soluble antigens are present in the bile of rabbits in the acute phase of infection, and these may be produced and released by merozoites during the host cell invasion pr ocess.