Chitosan oligosaccharide improves the mucosal immunity of small intestine through activating SIgA production in mice: Proteomic analysis

Chitosan oligosaccharide (COS) plays a vital role in improving the host system and mucosal immune function. So far, the impact of COS on mucosal immune response in the early stage of oral administration is not well understood. Herein, the distribution of COS after oral gavage and the protein expression changes related to innate immune by tandem mass tag (TMT)-based proteomic analysis were investigated. The results revealed that COS was mainly distributed in the stomach, duodenum, and kidney and increased the number of monocytes and lymphocytes in peripheral blood. A total of 21,677 proteins and 7,483 protein groups were identified. Among them, 338 significant differentially expressed proteins were screened, including 205 upregulated and 133 downregulated. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the intestinal immune network for the IgA production pathway was activated, pIgR, MHCI, MHCII, Itgb2, Itgb7, and B2m were significantly increased (P < 0.05). Furthermore, the expression of the above molecular genes was detected by enzyme-linked immunosorbent assay (ELISA), western blotting, and quantitative real-time PCR. We found that the expressions of IgA, MHCII, TGF-β1, IL-6, and pIgR were significantly increased (P < 0.05) 1 h after exposure to COS. The protein and mRNA expression of pIgR and MHCI were significantly increased (P < 0.05) at 0.5 h, while the AID protein level was significantly increased (P < 0.05) 1.5 h after COS exposure. The expression of MHCII and H2-Q10 was significantly increased (P < 0.05) by 1 h and 2 h post-exposure to COS. In conclusion, oral administration of COS can significantly enhance intestinal mucosal immunity in mice by activating the SIgA secretion pathway. These results suggest that COS can be used as an oral vaccine or drug adjuvant for small intestinal mucosa.