Structural analysis of an expolysaccharide from Lactiplantibacillus plantarum PA01 and its immunoenhancing properties

The aim of this study was to structurally characterize exopolysaccharide EPS2 extracted from Lactiplantibacillus plantarum PA01, and to investigate its immunological activity in vitro and in vivo. Structural characterization revealed that EPS2 was mainly comprised of mannose, glucose and a trace of galactose, arabinose, and glucosamine, with a molecular weight of 73.34 kDa. By methylation and NMR analysis, the backbone of EPS2 was composed of 2,6)-α-D-Manp→ and 6)-α-D-Manp (1→, with three different branch at O-2 of →2,6)-α-D-Manp. The in vitro results indicated that EPS2 promoted proliferation, phagocytosis and the secretion of NO and cytokines in RAW264.7 cells by activating MAPK pathway via pattern recognition receptors TLR2, TLR4, and MR. Meanwhile, in vivo results showed that EPS2 treatment alleviated spleen damage, enhanced lymphocyte proliferation, and mitigated myelosuppression in cyclophosphamide induced mice. These results suggested that EPS2 efficiently enhance the immunomodulatory activity of macrophages and immunosuppressed mice. In summary, the current work provided a solid foundation for the potential utilization of EPS2 as an immunomodulator.