Functional expression and characterization of grass carp IL-10: An essential mediator of TGF-β1 immune regulation in peripheral blood lymphocytes

In mammals, interleukin-10 (IL-10) is known as a potent regulatory cytokine with pleiotropic effects on various leukocytes. Although teleost IL-10 has been identified in several fish species, its immunoregulatory role is still poorly understood. In the present study, grass carp IL-10 (gcIL-10) has been identified and recombinant gcIL-10 (rgcIL-10) was prepared by using a prokaryotic expression system. Using grass carp peripheral blood lymphocytes (PBLs) as a cell model, rgcIL-10 was shown to up-regulate the cell activity, which was consistent with the regulatory tone of transforming growth factor β1 (TGF-β1). An interesting question that follows would be whether IL-10 and TGF-β1 redundantly regulate PBL activity. To address this question, we investigated the effect of IL-10 on the cell activity of grass carp PBLs challenged by TGF-β1 using immunoneutralization, showing that removal of endogenous IL-10 could abolish TGF-β1-induced cell activity, indicating an essential role of IL-10 in TGF-β1 immune regulation. Furthermore, to examine the connection between TGF-β1 and IL-10 during immunoregulatory process, effect of TGF-β1 on IL-10 expression was investigated. Results showed that TGF-β1 displayed stimulatory effects on gcIL-10 mRNA expression and protein secretion in the same cell model, suggesting that TGF-β1 may function through its effect on IL-10 production in fish immunity. These results provide clues to the potential immunoregulatory role and production of IL-10 in teleost.