Longan Pulp Polysaccharide Protects Systemic Immunity and Intestinal Immunity in Mice Induced by Cyclophosphamide

This study aimed to explore the effect of longan pulp polysaccharide (LP) on the systemic immunity and intestinal mucosal immunity with immunosuppressive mice. The synthesis processing and secretion of intestinal secretory IgA (SIgA) were investigated. Serum IgA, IgG, IgM and intestinal SIgA were detected by ELISA. Genes involved in the synthesis and secretion of SIgA were detected by Q-PCR and western blot. LP increased the thymus index, spleen index, and serum IgA level in cyclophosphamide (CTX)-treated mice. SIgA secretion in intestinal lumen was increased by LP as well. The underlying mechanism comes down to the facts as follows: LP increased intestinal cytokines expression and TGFβRII that is associated with pathways of IgA class switch recombination (CSR). By improving protein expression of mucosal address in cell-adhesion molecule-1 (MAdCAM-1) and integrin α4β7, LP was beneficial to gut homing of IgA + plasma cells. LP increased IgA, polymeric immunoglobulin receptor (pIgR), and secretory component (SC) to fortify the SIgA secretion. This study suggested that moderate consumption of LP is helpful for improving systemic immunity and intestinal mucosal immunity via promotion of intestinal SIgA to strengthen the mucosal barrier. This work was supported by the National Key Research Project of China (2018YFC1602105, 2019YFD1002304), Guangdong Provincial Science and Technology Project (2018A050506050), President Foundation of Guangdong Academy of Agricultural Sciences (201812B).