Activation of rainbow trout complement by C-reactive protein.

The activation of the complement system of rainbow trout by trout C-reactive protein (CRP) was investigated. Complement fixation tests were performed by using rabbit hemolysin-sensitized sheep erythrocytes and rainbow trout complement. Purified CRP increased the consumption of complement in the presence of Streptococcus pneumoniae C-polysaccharide (CPS), indicating the activation of the complement system. In contrast to this, acute phase serum activated the complement in the absence of CPS. Consumption of the complement by acute-phase serum was depressed when CRP was removed from acute-phase serum by CPS-sepharose 4B affinity chromatography. The acute-phase serum, as well as CRP plus CPS, suppressed in vitro growth of Vibrio anguillarum in the presence of complement, and enhanced the phagocytosis of the bacteria by glass-adherent peritoneal exudate cells. These results indicated that CRP has a role in host defense during acute-phase response through the activation of the complement system, enhancement of phagocytosis, and suppression of bacterial growth.