The Biological Functions and Intestinal Inflammation Regulation of IL-21 in Grass Carp () during Infection with .

Interleukin (IL) 21 is a pleiotropic cytokine that plays an important role in regulating innate and adaptive immune responses. In fish, the biological functions and cell source of IL-21 remain largely unknown. In this study, we performed qRT-PCR, Western blotting and immunofluorescent microscopy to examine the expression of IL-21 at the mRNA and protein levels. We found that expression was induced in the primary head kidney leukocytes of grass carp () by heat-inactivated () and LPS and in tissues after infection with . Recombinant IL-21 protein produced in the CHO-S cells was effective in elevating the expression of antibacterial genes, including and , and, interestingly, inhibited the NF-κB signaling pathway. Furthermore, we investigated the response of the IL-21 expressing cells to infection. Immunofluorescent assay showed that IL-21 protein was detected in the CD3γ/δ T cells and was markedly accumulated in the anterior, middle and posterior intestine. Collectively, the results indicate that IL-21 plays an important role in regulating the intestinal inflammation induced by bacterial infection in grass carp.