Molecular characterization of complement regulatory factor CD46 in Trachinotus ovatus and its role in the antimicrobial immune responses and complement regulation.

CD46, as a cofactor of complement I factor, not only regulates the complement system but also functions as a pathogen receptor and is involved in controlling early pathogen infection through autophagy. In this study, a new CD46 gene (ToCD46) was identified from golden pompano (Trachinotus ovatus), which showed higher sequence homology with other teleosts CD46. Homology comparison showed that ToCD46 had higher sequence homology (46.95-52.85%) with other teleosts CD46 and lower homology with mammal. Tissue expression profile analysis showed that ToCD46 was generally expressed in all tissues with the highest expression level in liver, followed by head kidney, and showed different patterns of up-regulation in immune-related tissues after stimulation by Streptococcus agalactiae and Vibrio alginolyticus. The hemolytic activity analysis and apoptosis assay showed that rToCD46 decreased the hemolytic activity of serum of golden pompano and effectively inhibited the damage of A549 cells, suggesting that ToCD46 might be involved in the regulation of complement activation of golden pompano. In vitro antibacterial experiments showed that rToCD46 had antibacterial activity against gram negative bacteria V. alginolyticus but no effect on positive bacteria S. agalactiae. These results suggest that ToCD46 may be involved in the immune response of golden pompano to pathogens, which will provide important basic information for elucidating the evolutionary history of the complement system of golden pompano.