Mechanisms of Protection in Ayu Orally Vaccinated for Vibriosis

抄録

Both orally immunized ayu, Plecoglossus altivelis, and control fish were challenged with organism, Vibrio anguillarum, by three ways. First, fish were exposed to organism discharged from naturally infected fish for 24 hr. Organism was isolated at high percentage from almost all part of body in the control fish, while the isolation rate was low particularly on the body surface in the immunized fish.
Secondary, fish were bathed in bacterial suspension of a concentration of 10⁷ cells per milliliter for 15 min. Twenty four hours after challenge organism was isolated from the skin of the control fish, then the number of organism increased gradually for the next 72 hr. No organism was detected in the intestine or its contents in both groups neither in the skin of the immunized fish.
Finally, fish were injected intramuscularly resulting almost equal mortality in both groups. Agglutinin titer in the body surface mucus rose to 1: 64 in the immunized fish, but did not occur in the control fish. Agglutinin titer rose in neither serum nor intestinal mucus in both groups. The body surface mucus of the immunized fish prevented organism from adhering to the skin more effectively than that of the control fish did.
From these results it is assumed that the defence effect by the oral immunization is attributed mainly to the agglutinin secreted in the body surface mucus.