Glutamine protects against LPS-induced inflammation via adjusted NODs signaling and enhanced immunoglobulins secretion in rainbow trout leukocytes.

To evaluate effects of glutamine (GLN) on fish immune responses, leukocytes were isolated from head kidney of rainbow trout and cultured in GLN-free DMEM media supplemented with different combinations of lipopolysaccharide (LPS) and GLN. LPS significantly increased expression of pro-inflammatory cytokines, while GLN supplementation alleviated LPS-induced inflammation. Leukocytes in +GLN + LPS group showed more active GLN anabolism and catabolism, which signals could be sensed by O-GlcNAcylation, and then affected LPS binding to cell surface (LBP) and adjusted NODs signaling. The mRNA expression of immunoglobulins (Igs) and their receptor (pIgR) was also significantly increased after GLN supplementation. Further analysis showed that GLN increased the percentage of IgM⁺ B cells and IgT⁺ B cells, accompanied with the increased IgM and IgT secretion in culture media, which further increased complement C3 expression to perform effector functions. All these results illustrated the regulating mechanism of GLN against LPS-induced inflammation both via adjusted NODs signaling and increased Igs⁺ B cells to secrete Igs.