Transforming growth factor-β1b: A second TGF-β1 paralogue in the rainbow trout (Oncorhynchus mykiss) that has a lower constitutive expression but is more responsive to immune stimulation

► A second TGF-β1 paralogue, TGF-β1b, was identified in Oncorhynchus mykiss. ► The TGF-β1b mature peptide is 83% identical with the first described copy, TGF-β1a. ► Highest in vivo expression of both isoforms was found in immune tissues. ► TGF-β1b is highly inducible during immune responses of HK macrophages and cell lines. ► TGF-β1b but not TGF-β1a expression was up-regulated in VHSV infected trout.