Abstract

IL-20 is a pleiotropic cytokine that belongs to the IL-10 family and plays an important biological role in tissue homeostasis and regulation of host immune defenses. IL-20 homologues have recently been discovered in fish, but their functions have not been studied. In this study, an IL-20 like (IL-20L) cytokine was cloned in grass carp ( Ctenopharyngodon idella ) and its bioactivities were investigated. Expression analysis showed that the Ci IL-20L gene was constitutively expressed in tissues with the highest expression detected in the head kidney . It was upregulated in the head kidney after infection with Flavobactrium columnare ( F. cloumnare ) and grass carp reovirus II (GCRV II). The recombinant Ci IL-20L produced in E. coli cells was shown to be effective in inducing the expression of Th cytokine genes (IFN-γ, IL-4/13A, IL-4/13B and IL-10), macrophage marker genes (arginase 2, IRF4 , KLF4 and SOCS3) and inflammatory genes (IL-1β, IL-6, IL-8 and TNFα) in the head kidney leukocytes when stimulated at 12 h. Long term culture (6 days) of head kidney macrophages in the presence of Ci IL-20L leads to high expression of IRF4, TGFβ1 and arginase 2. Our data suggest that IL-20 may play regulatory roles in promoting Th responses, macrophage differentiation and inflammation.