Activation of rainbow trout complement by C-reactive protein

Area of Science:

• Immunology
• Aquatic Animal Health
• Biochemistry

Background:

• The complement system is crucial for innate immunity in fish.
• C-reactive protein (CRP) is an acute-phase protein with known immune functions.
• Rainbow trout (Oncorhynchus mykiss) are important aquaculture species susceptible to bacterial diseases.

Purpose of the Study:

• To investigate the role of rainbow trout CRP in activating the complement system.
• To determine CRP's contribution to host defense mechanisms against bacterial pathogens.
• To elucidate CRP's function during the acute-phase response in trout.

Main Methods:

• Complement fixation tests using sensitized erythrocytes and rainbow trout complement.
• Purification of CRP and its interaction with Streptococcus pneumoniae C-polysaccharide (CPS).
• Affinity chromatography to remove CRP from acute-phase serum.
• In vitro assays assessing bacterial growth suppression and phagocytosis enhancement.

Main Results:

• Purified CRP activated complement in the presence of CPS, indicating direct activation.
• Acute-phase serum activated complement independently of CPS, but CRP removal reduced this activity.
• CRP-mediated complement activation enhanced phagocytosis of Vibrio anguillarum by immune cells.
• CRP, with or without CPS, suppressed in vitro growth of V. anguillarum in a complement-dependent manner.

Conclusions:

• Rainbow trout CRP plays a significant role in host defense by activating the complement system.
• CRP contributes to the acute-phase response by enhancing bacterial clearance through phagocytosis and growth inhibition.
• These findings highlight CRP as a key mediator of innate immunity in rainbow trout, crucial for combating bacterial infections.