Abstract
To know the host defense mechanism against infection with Vibrio anguillarum in rainbow trout, phagocytic activities of macrophages were examined with those collected from normal fish and fish immunized with formalin-killed V. anguillarum. Opsonic activity with specific antibody and complement was also investigated. Forty to 50% of the macrophages of peritoneum, pronephron and peripheral blood phagocytosed latex particles. The phagocytosis of V. anguillarum by normal peritoneal macrophages was enhanced in the presence of antibody and complement. Enhanced opsonization was also observed after treatment of either macrophages or bacteria with antibody. In rainbow trout immunized with V. anguillarum, phagocytic activity of macrophages increased significantly 5 weeks after immunization as compared to the activity of macrophages from normal fish. The agglutinin titers increased 3 weeks after immunization. However, bactericidal activity of antibody and complement was not detected in the present experiment. All 8 rainbow trout were protected from infection with the bacteria 5 weeks after immunization and 7 out of 10 fish challenged 1 week after immunization survived. These results indicate that immunized fish were able to develop protective immunity against Vibrio infection before significant levels of antibody or phagocytic activity become detectable.
