Expression of allograft inflammatory factor-1 (AIF-1) in response to bacterial challenge and tissue injury in the pearl oyster, Pinctada martensii.

Allograft inflammatory factor-1 (AIF-1), an interferon (IFN)-γ-inducible calcium-binding cytokine, is associated with the inflammatory response and defense. We cloned and analyzed the expression pattern of the AIF-1 gene of the pearl oyster Pinctada martensii, hereafter designated PmAIF-1. The full-length PmAIF-1 cDNA is 946 bp in length and consists of a 5'-untranslated region (UTR) of 120 bp, a 3'-UTR of 376 bp, and an open reading frame (ORF) of 450 bp encoding a polypeptide of 149 amino acids with an estimated molecular mass of 17 kDa. Sequence analysis reveals that PmAIF-1 contains two EF hand Ca(+2)-binding motifs like those in previously characterized AIF-1s while alignment with known AIF-1 protein sequences reveals higher similarity to invertebrate orthologs than to those of vertebrates. Quantitative PCR analysis reveals that PmAIF-1 is constitutively expressed, with the highest expression detected in hemocytes, and the expression level of PmAIF-1 mRNA was significantly up-regulated in hemocytes, gill, digestive gland under bacterial challenge and tissue injury. After challenged by gram-negative bacteria Vibrio alginolyticus and Vibrio parahaemolyticus, gram-positive bacteria Bacillus subtilis, the expression level of this gene in hemocytes were all up-regulated and reached the maximum point at 12h (5.80 folds, P<0.01), 6h (5.02 folds, P<0.01) and 12h (5.49 folds, P<0.01), respectively. Under shell damage and mantle injury, PmAIF-1 mRNA increased gradually in the first 3h and reached a peak of expression at 6h post-injury. These findings suggest that PmAIF-1 is an acute-response protein involved in the innate immune responses of pearl oysters, and provide general information about the mechanisms of innate immune defense against bacterial infection in pearl oysters.