The characterization of an interleukin-12 p35 homolog involved in the immune modulation of oyster Crassostrea gigas

Vertebrate interleukin-12 (IL-12) is a heterodimeric cytokine composing of two subunits (p35 and p40). In the present study, a p35-like subunit homolog of vertebrate IL-12 was identified from oyster Crassostrea gigas (designated as CgIL12p35L), with an open reading frame of 411 bp encoding a putative peptide of 136 amino acids. There was a long four-helix chain in CgIL12p35L, which was similar as that in vertebrate IL-12 p35. Comparative genomic analysis showed that there were conservative kinds of syntenic genes flanked CgIL12p35L. The mRNA transcripts of CgIL12p35L were constitutively expressed in various tissues and its mRNA expression level in haemocytes increased significantly after bacteria challenge. The activity of haemolymph to eliminate bacteria from the oysters treated with recombinant CgIL12p35L protein (rCgIL12p35L) in vivo increased significantly. The results collectively indicated that the homolog of vertebrate IL-12 p35 subunit existed in oysters, and it was involved in immune defense against bacteria challenge.