[Propionibacterium acnes induces the formation of granulomas via promoting Th1 and Th17 cell differentiation]

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.

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.

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.

P. acnes could activate BMDCs, promote the differentiation of Th1 and Th17 cells, and further induce the formation of granulomas.