Immunization of carp (Cyprinus carpio) with a Vibrio anguillarum bacterin: indications for a common mucosal immune system.

Uptake and transport of formalin-killed Vibrio anguillarum bacteria were studied in the second gut segment of carp and the resulting reaction of the immune system was investigated. Within a few hours after anal administration antigenic determinants of bacteria were present in intraepithelial macrophages of the second gut segment. In gut and skin mucus and bile, immunoglobulins (Ig's) were detected, but the amount was much lower than found in serum. In mucus of the second gut segment, 4 times more Ig (per mg protein) was found than in the first segment. Upon oral or anal immunization, slightly enhanced antigen-specific Ig titers could be detected in skin mucus and bile, but only after a booster along the same route. The existence of a common mucosal immune system is discussed, with special reference to the significance of the second gut segment. After anal intubation an increase of antigen-specific Ig could also be observed in serum. Following a booster, an enhanced cal memory. After anal boosting equal levels of serum antibody were reached compared with two consecutive intramuscular injections. However, no significant antibody increase occurred in serum after oral immunization, not even when bacteria were administered daily with the food.