Brucella abortus is a Gram-negative intracellular bacterium that induces MyD88-dependent IL-12 production in dentritic cells （DCs） and a subsequent protective Thl immune response. Previous studies have shown that th...Brucella abortus is a Gram-negative intracellular bacterium that induces MyD88-dependent IL-12 production in dentritic cells （DCs） and a subsequent protective Thl immune response. Previous studies have shown that the Toll-like receptor 2 （TLR2） is required for tumor-necrosis factor （TNF） production, whereas TLR9 is responsible for IL-12 induction in DCs after exposure to heat-killed Brucella abortus（HKBA）. TLR2 is located on the cell surface and is required for optimal microorganism-induced phagocytosis by innate immune cells; thus, phagocytosis is an indispensable preliminary step for bacterial genomic DNA recognition by TLR9 in late-endosomal compartments. Here, we hypothesized that TLR2-triggered signals after HKBA stimulation might cross-regulate TLR9 signaling through the indirect modulation of the phagocytic function of DCs or the direct modulation of cytokine gene expression. Our results indicate that HKBA phagocytosis was TLR2-dependent and an essential step for IL-12p40 induction. In addition, HKBA exposure triggered the TLR2-mediated activation of both p38 and extracellular signal-regulated kinase 1/2 （ERKI/2）. Interestingly, although p38 was required for HKBA phagocytosis and phagosome maturation, ERK1/2 did not affect these processes but negatively regulated IL-12 production, Although p38 inhibitors tempered both TNF and IL.12 responses to HKBA, pre-treatment with an ERKI/2 inhibitor significantly increased IL-12p40 and abrogated TNF production in HKBA-stimulated DCs. Further experiments showed that the signaling events that mediated ERK1/2 activation after TLR2 triggering also required HKBA-induced Ras activation. Furthermore, Ras-guanine nucleotide-releasing protein 1 （RasGRP1） mediated the TLR2-induced ERKI/2 activation and inhibition of IL-12p40 production. Taken together, our results demonstrated that HKBA-mediated TLR2-triggering activates both the p38 and ERK1/2 signaling subpathways, which divergently regulate TLR9 activation at several levels to induce an appropriate protective IL- 12 response.展开更多
文摘Brucella abortus is a Gram-negative intracellular bacterium that induces MyD88-dependent IL-12 production in dentritic cells （DCs） and a subsequent protective Thl immune response. Previous studies have shown that the Toll-like receptor 2 （TLR2） is required for tumor-necrosis factor （TNF） production, whereas TLR9 is responsible for IL-12 induction in DCs after exposure to heat-killed Brucella abortus（HKBA）. TLR2 is located on the cell surface and is required for optimal microorganism-induced phagocytosis by innate immune cells; thus, phagocytosis is an indispensable preliminary step for bacterial genomic DNA recognition by TLR9 in late-endosomal compartments. Here, we hypothesized that TLR2-triggered signals after HKBA stimulation might cross-regulate TLR9 signaling through the indirect modulation of the phagocytic function of DCs or the direct modulation of cytokine gene expression. Our results indicate that HKBA phagocytosis was TLR2-dependent and an essential step for IL-12p40 induction. In addition, HKBA exposure triggered the TLR2-mediated activation of both p38 and extracellular signal-regulated kinase 1/2 （ERKI/2）. Interestingly, although p38 was required for HKBA phagocytosis and phagosome maturation, ERK1/2 did not affect these processes but negatively regulated IL-12 production, Although p38 inhibitors tempered both TNF and IL.12 responses to HKBA, pre-treatment with an ERKI/2 inhibitor significantly increased IL-12p40 and abrogated TNF production in HKBA-stimulated DCs. Further experiments showed that the signaling events that mediated ERK1/2 activation after TLR2 triggering also required HKBA-induced Ras activation. Furthermore, Ras-guanine nucleotide-releasing protein 1 （RasGRP1） mediated the TLR2-induced ERKI/2 activation and inhibition of IL-12p40 production. Taken together, our results demonstrated that HKBA-mediated TLR2-triggering activates both the p38 and ERK1/2 signaling subpathways, which divergently regulate TLR9 activation at several levels to induce an appropriate protective IL- 12 response.
