Structure elucidation, proliferation effect on macrophage and its mechanism of a new heteropolysaccharide from Lactarius deliciosus Gray

• A new heteropolysaccharide was isolated from Lactarius deliciosus Gray.
• The structural characteristics of LDG-B was investigated.
• LDG-B can proliferate growth of both B cells and macrophages cells.
• The transcriptomes of macrophages was sequenced.
• The candidate signaling pathways were selected.

A new heteropolysaccharide was isolated from the fruiting bodies of Lactarius deliciosus Gray which had a molecular weight of 16 kDa and was mainly composed of the galactose and glucose. Structural elucidation results indicated that Lactarius deliciosus Gray polysaccharide (LDG-B) had a backbone of (1,6)-linked d-galactose and (1, 2, 6)-linked d-galactose which branches were mainly composed of 4-linked d-glucose and 6-linked d-galactose residue. Cell cycle test results showed that LDG-B could promote the proliferation of B cells and macrophage cells by affecting G0/G1 phase, S phases and G2/M phases. The analysis of transcriptomes sequence of macrophages showed a total of 1839 genes were identified as DEGs, and approximately 708 genes were up-regulated, whereas 1131 genes were down-regulated in LDG-B group. KEGG pathway enrichment analysis showed that the MAPK, JAK-STAT and NF-κB signaling pathways are significantly enriched for DEGs in LDG-B group. Analysis of transcriptome resources enabled us to examine gene expression profiles, verify differential gene expression, and select candidate signaling pathways as the mechanisms of the immunomodulatory activity of LDG-B.