Effects and mechanisms of Portulaca oleracea L. polysaccharides on the activation of dendritic cells derived from mice immunized with FMD vaccine

Background Our previous study has showed that Portulaca oleracea L. (POL-P), as an immunoenhancer, could increase the IgG and isotypes antibody titers in mice immunized with foot and mouth disease (FMD) vaccines. However, the structural features and the mechanism of action are still unclear. Enhancing antigen presentation is one of the main ways that immunoenhancer boost immune response. Dendritic cells (DCs) are the most potent antigen presenting cell (APC), which stimulate the initial T cells directly and initiate the specific immune responses. In addition to extracellular factors and intracellular genetic factors, epigenetics plays a major role in the regulation of DCs. In this study, we obtained POL-P, and structural features and monosaccharide composition were analyzed. We evaluated the effect of POL-P on functional maturation of DCs derived from mice immunized with foot and mouth disease (FMD) vaccine and explored the related mechanism responsible for immunoenhancer. The levels of protein and gene related to IL-12p35 and IL-12p40 were determined by western blot and chromatin immunoprecipitation (ChIP) assays. The expressions of TLR2, TLR4 receptors and the downstream molecules of MyD88 and NF-κB were examined using immunohistochemistry. Results The average molecular weight (Mw) of the POL-P was 4×104 Da. The monosaccharide composition of the POL-P was mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose and arabinose with a relative mass of 1.2%, 13.2%, 33.5%, 1.2%, 3.3%, 32.2% and 15.4%, respectively. We concluded that co-administration of POL-P with the FMD vaccine could significantly promote DCs maturation of phenotype and the immune function. In addition, the acetylation level of histone H3 of IL-12 was closely connected with the immune activity of DCs. Moreover, POL-P induced immune response was related to up-regulating protein expression of TLR2, TLR4, MyD88 and NF-κB in DCs. Conclusions Our evidence suggested that POL-P could be a potential immunostimulant in the regulation of DCs maturation for FMD vaccine.