Identification and functional analysis of a novel IFN-like protein (CgIFNLP) in Crassostrea gigas

Interferons (IFNs) belong to class II helical cytokines family with pleiotropic biological activities, which have been demonstrated to play crucial roles in innate and adaptive immunity in vertebrates. In the present study, a novel IFN-like protein (designed CgIFNLP) was identified from oyster Crassostrea gigas, which contained an interferon domain from 14 to 97 amino acids showing low sequence similarities with vertebrates IFNs, but shared a similar three-dimensional structure with class II helical cytokines. The mRNA transcripts of CgIFNLP was detected in all the tested tissues including gonad, adductor muscle, hemocytes, mantle, gills, and hepatopancreas, with the highest expression level in gills (39-fold, P < 0.05). Moreover, the expression level of CgIFNLP mRNA in hemocytes increased significantly at 12 h (8.35-fold, P < 0.01) and 24 h (4.95-fold, P < 0.01) after poly (I: C) stimulation. After the treatments by recombinant CgIFNLP protein (rCgIFNLP) at different concentrations, the apoptosis and phagocytosis rates of oyster hemocytes increased obviously. The proliferation rate of L929 did not change obviously after incubation with rCgIFNLP for 72 h, but the proliferation rate of A549 abated significantly at 36 h and 48 h after incubation with rCgIFNLP. The results collectively suggested that the IFN-like molecule existed in oyster and it tended to present conserved functions rather than conserved amino acid sequence in comparison with vertebrate IFNs.