Differential roles of Porphyromonas gingivalis lipopolysaccharide and Escherichia coli lipopolysaccharide in maturation and antigen-presenting functions of dentritic cells.

OBJECTIVE: The aim of this research is to study the roles of Porphyromonas gingivalis-lipopolysaccharide (P. gingivalis-LPS) and Escherichia coli-lipopolysaccharide (E. coli-LPS) on maturation and antigen-presenting functions of dendritic cells (DCs), and to provide experimental evidences to explore the possible mechanism of DCs in periodontitis.

MATERIALS AND METHODS: Flow cytometry was used to detect CD11c, MHC-II, CD80, CD86 and CD40 expression on DCs which were stimulated by P. gingivalis-LPS or E. coli-LPS and ELISA was used to detect IL-12, IFN-γ, IL-10 and IL-13 secreted by DCs. CCK8 was used to assay CD4+T cells proliferation after co-cultured with DCs stimulated by P. gingivalis-LPS or E. coli-LPS and ELISA was used to detect IL-2, IFN-γ, IL-10 and IL-13 secreted by T cells. TLR4 inhibitor (polymyxin B) or TLR2 and TLR4 inhibitor (OxPAPC) was added to P. gingivalis-LPS group and E. coli-LPS group to observe the effects of these two TLR inhibitors on the maturation and antigen-presenting functions of DCs.

RESULTS: The capacity of P. gingivalis-LPS to stimulate DCs maturation was similar to that of E. coli-LPS. The amount of IL-12 and IFN-γ secreted by DCs in P. gingivalis-LPS group was significantly lower than that of E. coli-LPS group (p < 0.05), meanwhile, IL-10 and IL-13 secreted by DCs in P. gingivalis-LPS group was significantly higher than that of E. coli-LPS group (p < 0.05). DCs stimulated by both P. gingivalis-LPS and E. coli-LPS could promote the proliferation of CD4+T cells. The amount of IL-2 and IFN-γ secreted by T cells stimulated by DCs in P. gingivalis-LPS group was significantly lower than that of E. coli-LPS group (p < 0.05), meanwhile, IL-10 secreted by T cells stimulated by DCs in P. gingivalis-LPS group was significantly higher than that of E. coli-LPS group (p < 0.05). When TLR4 inhibitor was added to E. coli-LPS group, maturation and antigen-presenting functions of DCs were significantly inhibited. When TLR4 inhibitor was added to P. gingivalis-LPS group, maturation and antigen-presenting functions of DCs were not significantly inhibited. When TLR2 and TLR4 inhibitor was added to P. gingivalis-LPS group, maturation and antigen-presenting functions of DCs were significantly inhibited.

CONCLUSIONS: P. gingivalis-LPS could prime DCs maturation and antigen-presenting functions. DCs stimulated by P. gingivalis-LPS are prone to induce a stronger Th2 cell responses while DCs stimulated by E. coli-LPS are prone to induce a stronger Th1 cell responses. P. gingivalis-LPS triggers DCs through TLR2 pathway while E. coli-LPS triggers DCs through TLR4 pathway.