Activation of trout macrophages and production of CRP after immunization with Vibrio anguillarum

To examine the mechanism of the protection of rainbow trout (Salmo gairdneri) against Vibrio anguillarum in the early stage of immunization, the activation of macrophages and production of C-reactive protein (CRP) were investigated. Fish immunized with formalin-killed bacteria emulsified in Freund's complete adjuvant (FCA) resisted intraperitoneal challenge with living bacteria seven and ten days after immunization. The activation of macrophages was demonstrated by a significant increase of the chemiluminescent (CL) response and phagocytic activity. These fish also showed a significant increase of the CRP level in sera. Fish immunized with V. anguillarum alone or injected with FCA, however, did not resist the challenge. Though FCA itself increased CRP level and the sera enhanced phagocytic activity, increase of CL activity was weak. These results indicated that the increase of CL activity and opsonising effect of CRP on the phagocytosis of specifically activated macrophages concern to host defense in the early stage of infection.