Objective: To investigate the immunostimulatory role of Propionibacterium acnes (P. acnes) in the differentiation of dendritic cell maturation and T helper (Th) subsets, and further explore the potential mechanism of its granuloma-inducing effect.
Methods: After the mouse bone marrow-derived dendritic cells (BMDCs) were stimulated by P. acnes, the expressions of co-stimulatory molecules CD40, CD80, CD86 and major histocompatibility complex II (MHCII) on BMDCs were detected by flow cytometry, the mRNA levels of inflammatory cytokines IL-12, IL-6 and IL-23 were measured by real-time quantitative PCR (qRT-PCR), and the protein concentrations of corresponding cytokines were analyzed by ELISA. Thereafter, BMDCs were cultured in the presence of P. acnes and CD4(+) T cells, and the percentages of Th1 and Th17 cells were detected by flow cytometry. In addition, murine model of liver granuloma was constructed by injecting heat-killed P. acnes through tail vein, and the mRNA levels of IL-17 and IFN-γ were measured by qRT-PCR.
Results: P. acnes up-regulated the expressions of CD40, CD80, CD86 and MHCII on BMDCs, and the mRNA and protein levels of the IL-12, IL-6 and IL-23 cytokines were also higher on P. acnes-treated BMDCs compared with non-stimulated BMDCs. Furthermore, the percentages of Th1 and Th17 cells in the co-culture system increased. In addition, the mRNA levels of IL-17 and IFN-γ were elevated obviously in the liver with abundant granulomas after P. acnes treatment.
Conclusion: P. acnes could activate BMDCs, promote the differentiation of Th1 and Th17 cells, and further induce the formation of granulomas.