Abstract: This study was undertaken in order to understand the effect of Lactobacillus casei exopolysaccharide (EPS) on the maturation of mouse bone marrow-derived dendritic cells (BMDCs) in vitro, the effect of different doses of EPS on interleukin (IL)-6, transforming growth factor-β (TGF-β) and IL-23 secretion in BMDCs, and the effect of EPS on the antigen-presenting function of BMDCs. L. casei EPS was separated and purified from the fermentation broth, and its purity was determined. The bone marrow cells isolated from BALB/c mice were differentiated into BMDCs, and immature BMDCs were treated with phosphate buffer saline (PBS), EPS and lipopolysaccharide (LPS), respectively. The phenotypic maturation of BMDCs, MHC II and CD86 were analyzed using a flow cytometer, the production of cytokines was analyzed by enzyme-linked immunosorbent assay (ELISA), and the proliferation rate of splenic lymphocytes was analyzed by cell counting kit-8 (CCK-8) assay in a mixed culture system with BMDCs and mouse splenic lymphocytes. The results showed that the purity of EPS was 95%. The EPS up-regulated the expression of MHC II and CD86 on the surface of BMDCs. Meanwhile, the EPS significantly promoted the production of IL-6, TGF-β and IL-23 (P < 0.05) but not so effectively as LPS. The EPS also obviously promoted BMDCs-stimulated proliferation of allogenic lymphocytes. In conclusion, L. casei EPS can promote the maturation of BMDCs in vitro, induce BMDCs to secrete cytokines associated with the differentiation and proliferation of Th17 cells, and enhance the antigen-presenting function of BMDCs.

Key words: Lactobacillus casei, exopolysaccharide, dendritic cells, maturation, cytokines, secretion, antigen presentation