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Chlorella contains a variety of polysaccharides with complex composition and structure, which are composed of various monosaccharides such as galactose, rhamnose, glucose, arabinose, mannose, xylose and glucuronic acid. The glycosidic linkages of polysaccharides are diverse, including α-1,6-glucose, β-1,3-galactose, α-1,6-galactose, α-1,3-rhamnose, α-1,2-rhamnose, α-1,5-arabinose, α-1,6-mannose and β-1,4-xylose. Some polysaccharides are modified by methylation, sulfation and acetylation. Meanwhile, many studies have shown that polysaccharides have multiple functions such as immunoregulatory, anti-inflammatory, antioxidant, anti-tumor, antibacterial and intestinal flora-regulatory effects. At present, monosaccharide composition analysis, methylation combined with gas chromatography-mass spectrometry (GC-MS) and two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy are mainly used for research on the structure of chlorella polysaccharides such as analysis of monosaccharide composition, glycosidic bond types, branch chain substitution positions and branch chain types. This review hopes to provide valuable information for the fine structural analysis and structure-activity relationship study of polysaccharides from Chlorella.

Objective: This study aimed to compare the compositions of peptides from Engraulis japonicus and Glycine max and their immunomodulatory effects on the intestinal mucosa in mice. Methods: The sequences of peptides from E. japonicus and G. max were analyzed by ultra-performance liquid chromatography-high resolution mass spectrometry (UPLC-MS/MS) combined with Peaks Online 1.7 software, and the differences in peptide composition were compared. The effects of the two peptides on the mucosal structure, immune factors, immunoglobulin (Ig) levels, and gene expression of factors associated with the Toll-like receptors (TLRs)/nuclear factor kappa B (NF-κB) signaling pathway in the small intestine of mice with cyclophosphamide-induced immunosuppression were investigated. Results: The peptide compositions from E. japonicus and G. max were quite different. Only 11% of the peptide sequences were identical between them. Administration of the peptides from E. japonicus and G. max at 300 mg/kg mb for 30 d could significantly increase the spleen index and thymus index, alleviate intestinal mucosal damage, increase the length of intestinal villi and decrease the depth of crypts in cyclophosphamide-induced immunosuppressed mice. Moreover, the inhibitory effect of cyclophosphamide on the expression of tumor necrosis factor-α (TNF-α), interferon-gamma (IFN-γ), interleukin-4 (IL-4), and IL-13 was ameliorated, and the secretion of IgA and secretory IgA and the gene expression of TLR-4, TLR-6, TLR-9 and NF-κB were upregulated in the small intestine mucosa. Conclusion: The peptides from E. japonicus and G. max can promote the secretion of immune factors and immunoglobulins in the small intestinal mucosa and alleviate cyclophosphamide-induced intestinal mucosal damage and immunosuppression in mice by protecting the TLRs/NF-κB signaling pathway. Although the average molecular masses, amino acid compositions and polypeptide compositions of the two peptides are different and the protective effect of the peptides from E. japonicu on secretory IgA in the intestinal mucosa is more pronounced than that of the peptides from G. max, there is no significant difference between their efficacy in protecting intestinal mucosal structure and regulating mucosal immunity in mice.