Immune response of rainbow trout (Oncorhynchus mykiss) to antigenic preparations fromVibrio anguillarumserogroup O1

The humoral and cellular immune responses of rainbow trout were investigated following injection with formalin-killedVibrio anguillarumin Freund's incomplete adjuvant (FIA) in terms of reactivity towards different antigen preparations of the bacterium. Vaccinated fish were compared with control fish that had been injected only with FIA. The antigen preparations used for the comparative studies were formalin-killed bacteria, extracellular products (ECP), outer membrane proteins (OMP) and cytoplasmic membrane proteins (CMP). Humoral antibody as measured by ELISA was detected with all antigen preparations. As evaluated by ELISPOT and by proliferation assays, leucocytes isolated from vaccinated fish reacted most strongly with the OMP preparation. This observation suggests the existence of undefined potent antigenic components among these proteins. In proliferation assays, the tested antigen preparations contained components that were mitogenic to cell cultures from unvaccinated fish. However, in terms of antibodies measured by ELISA and ELISPOT techniques, only vaccinated fish reacted with theV. anguillarumpreparations.