Acute phase proteins in salmonids: evolutionary analyses and acute phase response

Area of Science:

• Comparative immunology
• Molecular biology
• Evolutionary biology

Background:

• Inflammation alters liver protein synthesis, affecting positive and negative acute phase (AP) proteins.
• Serum amyloid A (SAA), C-reactive protein (CRP), and serum amyloid P component (SAP) are key AP proteins with significant serum level changes during inflammation.
• Understanding AP protein evolution and function provides insights into host defense mechanisms.

Purpose of the Study:

• To clone and characterize SAA and pentraxin genes from salmonid fish.
• To investigate the expression patterns of these genes in response to an AP stimulus.
• To explore the evolutionary conservation and functional divergence of AP proteins in vertebrates.

Main Methods:

• Cloning of SAA and pentraxin genes from salmonid species.
• Challenging salmonids with Aeromonas salmonicida to induce an AP response.
• Analyzing amino acid identity and evolutionary relationships of cloned proteins.
• Measuring hepatic mRNA concentrations of salmonid pentraxin.

Main Results:

• Salmonid SAA shares high amino acid identity with mammalian SAA and acts as a major AP reactant upon bacterial challenge.
• Salmonid pentraxin shows moderate identity to mammalian SAP and CRP, with evolutionary analysis suggesting a single ancestral protein in teleosts.
• Salmonid pentraxin functions as a negative AP reactant, with hepatic mRNA levels decreasing post-stimulus.

Conclusions:

• SAA induction is a conserved and universal feature of the vertebrate AP response, indicating its ancient role in host defense.
• Heterogeneity in pentraxin expression across species suggests that their primary ancestral function may not be directly related to the AP response.
• This study highlights the dual nature of AP protein evolution, with conserved roles for SAA and diverse functions for pentraxins.