Vitamin A deficiency suppresses fish immune function with differences in different intestinal segments: the role of transcriptional factorNF-κBandp38 mitogen-activated protein kinasesignalling pathways

Abstract

AbstractThe present study investigated the effects of dietary vitamin A on immune function in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI) of young grass carp (Ctenopharyngodon idella). Fish were fed graded levels of dietary vitamin A for 10 weeks, and then a challenge test using an injection ofAeromonas hydrophilawas conducted for 14 d. The results showed that, compared with the optimum vitamin A level, vitamin A deficiency significantly decreased fish growth performance, increased enteritis morbidity, decreased intestinal innate humoral immune response and aggravated intestinal inflammation. However, liver-expressed antimicrobial peptide 2A/B mRNA in the DI andIL-6,IL-17D,IL-10, transforming growth factor (TGF)-β1andTGF-β2mRNA in the PI were not affected by vitamin A levels. Meanwhile, vitamin A deficiency disturbed inflammatory cytokines in the PI, MI and DI, which might be partly linked to p38 mitogen-activated protein kinase (p38MAPK) signalling andNF-κBcanonical signalling pathway (IκB kinaseβ(IKKβ),IKKγ, inhibitor ofκBα,NF-κB p65andc-Rel) rather thanNF-κBnon-canonical signalling pathway (NF-κB p52andIKKα). However, the signalling moleculesNF-κB p65andp38MAPKdid not participate in regulating cytokines in the PI. These results suggested that vitamin A deficiency decreased fish growth and impaired intestinal immune function, and that different immune responses in the PI, MI and DI were mediated partly byNF-κBcanonical signalling andp38MAPKsignalling pathways. On the basis of percentage of weight gain, to protect fish against enteritis morbidity and acid phosphatase activity, the optimum dietary vitamin A levels were estimated to be 0·664, 0·707 and 0·722 mg /kg, respectively.