β-Conglycinin regulates distal intestinal immunity through the CIITA-mediated MHC II-PI3K/Akt/mTOR signaling pathway in hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂): The ameliorative effects of sodium butyrate (NaB)

Abstract Background β-Conglycinin (7S) is a strong immunogenic protein that modulates immune responses in the intestines of aquatic animals, whereas sodium butyrate (NaB) may promote growth by protecting the intestinal tract of fish. However, the mechanisms of action of 7S and NaB in these regards have yet to be determined. Results In this study, we investigated the effects of low and high doses of 7S and the ameliorative effects of NaB (based on high-dose 7S) on the growth performance, serum immunity, distal histopathology, and CIITA-mediated MHC II-PI3K/Akt/mTOR pathway in hybrid groupers (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). The results revealed that the specific growth rate of groupers significantly increased, decreased, and increased in the low-level 7S (bL), high-level 7S (bH) high-level 7S plus NaB (bH-NaB) groups, respectively. The feed coefficient ratio was significantly increased in the bH and bH-NaB groups, whereas serum levels of IgE, IFN-γ, IL-1β, and TNF-α were upregulated in the bH group, and IgE was upregulated in the bH-NaB group. With respect to distal intestine histopathology, the intestinal diameter/plica height ratio was significantly increased in the bH group. Furthermore, there were increases in nitric oxide, nitric oxide synthase (NOS), and peroxynitrite anion (ONOO) in the bH group, and decreases in NOS and ONOO in the bH-NaB group In the distal intestinal tract, the mRNA levels of TSC1, mTOR C2, CIITA, and CREB1 were significantly upregulated in all three treatment groups, whereas those of IKKα, Rheb, mTOR C1, mLST8, EIF4B, NFY, GILT, and AEP were upregulated and downregulated in the bH and bH-NaB groups, respectively. Conclusions Collectively, these results indicate that 7S has a regulatory effect on serum immunity and can also affect distal intestinal tract development in hybrid groupers by modulating hindgut injury-related parameters. Within the distal intestinal tract, 7S can induce intestinal inflammation by activating the CIITA-mediated MHC II-PI3K/Akt/mTOR pathway, which eventually manifests as a reduction in growth performance. Supplementing feed with NaB represents an effective approach for enhancing serum immunity, and also protects the intestines from damage caused by high doses of 7S.