Grass carp transforming growth factor-β1 (TGF-β1): Molecular cloning, tissue distribution and immunobiological activity in teleost peripheral blood lymphocytes

Transforming growth factor-β1 (TGF-β1) is a potent regulatory cytokine with pleiotropic effects on the immune system. To examine the role of TGF-β1 in fish immunity, the full-length cDNA of grass carp TGF-β1 was isolated from grass carp spleen. The open reading frame of grass carp TGF-β1, 1134 bp in length, encodes a 377 amino acid protein. Tissue distribution study by RT-PCR showed TGF-β1 mRNA was predominantly expressed in the thymus, head kidney and spleen in grass carp tissues. Moreover, the time-course effect of TGF-β1 on peripheral blood lymphocyte proliferation in response to mitogens was evaluated in grass carp. Interestingly, TGF-β1 induced PBL proliferation while it significantly blocked phytohemagglutinin- or lipopolysaccharide-stimulated PBL proliferation, and TGF-β1 mimicked the stimulatory effects of lipopolysaccharide on grass carp MHC I mRNA expression. These results, for the first time, strongly suggest that TGF-β1 plays a functional role in lymphocyte proliferation in fish.