CCP domain containing protein from complement factor H of Paralichthys olivaceus has potential effects against Edwardsiella piscicida infection

Edwardsiella piscicida is a pathogenic bacterium that causes edwardsiellosis, and resist serum killing via recruitment of complement factors H (CFH). CFH is a key complement regulator, which prevents self-tissue damage and modulates immune responses. PoCFH, a CFH homologue from Paralichthys olivaceus, was characterized in this study. It consists of 1259 amino acids and 18 complement control protein (CCP) domains. In addition, PoCFH was further divided into three CCP domain containing proteins (PoCFH-CCP1, PoCFH-CCP2, and PoCFH-CCP3). Sequence homology and phylogenetic analysis indicated that PoCFH was clustered with teleost CFHs. Following infection with E. piscicida or Vibrio harveyi, PoCFH expression was significantly up-regulated in the spleen, kidney, and blood. Recombinant PoCFH-CCP2 (rPoCFH-CCP2), but not PoCCP1 or PoCCP3, exhibited highly binding capability to E. piscicida via interaction with bacterial wall components. Surface charge analysis revealed that PoCFH-CCP2 had more positively charged amino acids, implying interaction via electrostatic attraction. rPoCFH-CCP2 treatment significantly reduced the survival rate of E. piscicida in serum by preventing the recruitment of CFH and CFI to the bacterial surface. When P. olivaceus was infected with E. piscicida, rPoCFH-CCP2 treatment significantly reduced tissue bacterial loads, pathological feature, and mortality of fish. This study provided new insights into the functional mechanisms of teleost CFHs, suggesting that rPoCFH-CCP2 had potential effects against E. piscicida infection in P. olivaceus.