Allograft inflammatory factor-1 stimulates hemocyte immune activation by enhancing phagocytosis and expression of inflammatory cytokines in Crassostrea gigas

Allograft inflammatory factor-1 (AIF-1) is a calcium-binding cytokine associated with immune cell activation and inflammatory response. Presently, we have identified and characterized an AIF-1 in a marine bivalve mollusk, Crassostrea gigas, and designated it as CgAIF-1. The full-length CgAIF-1 cDNA is 794 bp, encoding a protein of 149 amino acids with two conserved EF hand Ca2+-binding motifs. CgAIF-1 is constitutively expressed in various tissues with enriched expression in hemocytes. Moreover, CgAIF-1 transcription is induced by multiple Pathogen-Associated Molecular Patterns (PAMPs), including poly (I: C), LPS, PGN, HKLM and HKVA, but is limited by 1,3-β-glucan. Furthermore, recombinant CgAIF-1 can specifically stimulate phagocytic ability of granulocytes, but not of intermediate cells and hyalinocytes. CgAIF-1 also enhances mRNA levels of MIF, TNF and IL-17. These results provide the first functional evidence that CgAIF-1 is involved in hemocyte activation in C. gigas, revealing conserved functions of AIF-1 in host defense from mollusks to mammals.