摘要
The cytoplasmic nucleotide oligomerization domain 2 （NOD2） receptor recognizes the bacterial cell wall component muramyl dipeptide （MDP）. NOD2 ligation initiates the nuclear factor kappa B and the mitogen-activated protein kinase cascades. However, administering MDP alone is insufficient to elicit strong cytokine responses in various immune cells, including dendritic cells （DCs）. Because the simultaneous presence of various microbial products and cytokines in inflamed tissues modulates DC function, we initiated this study to examine how interferon gamma （IFNy）, a central modulator of inflammation, affects the NOD2-mediated signaling pathway in human conventional DCs （cDCs）. Synergistic stimulation of DCs with MDP and IFNy increased the expression of CD40, CD80, CD83, CD86, and human leukocyte antigen DQ proteins and significantly elevated the production of pro-inflammatory cytokines IL- 1β, IL-6, IL-12, and tumour necrosis factor （TNF）, as well as anti-inflammatory cytokine IL-10. Furthermore, the simultaneous presence of MDP and I FNy was necessary to decrease IkBe protein levels. By investigating various mechanisms implicated in MDP- and IFNγ-mediated signaling pathways, we revealed that the increased production of pro-inflammatory cytokines is highly dependent on the X-linked inhibitor of apoptosis protein （XIAP） but not on cellular lAP1 and lAP2. We also found that the NOD2 signaling pathway is regulated by the mammalian target of rapamycin （mTOR） but is not affected by phosphatidylinositol-3 kinase or signal transducer and activator of transcription 1 inhibition. Our results demonstrate, for the first time, that IFNy positively affects NOD2-mediated signaling in human cDCs, in a manner considerably dependent on XIAP and partially dependent on mTOR.
The cytoplasmic nucleotide oligomerization domain 2 （NOD2） receptor recognizes the bacterial cell wall component muramyl dipeptide （MDP）. NOD2 ligation initiates the nuclear factor kappa B and the mitogen-activated protein kinase cascades. However, administering MDP alone is insufficient to elicit strong cytokine responses in various immune cells, including dendritic cells （DCs）. Because the simultaneous presence of various microbial products and cytokines in inflamed tissues modulates DC function, we initiated this study to examine how interferon gamma （IFNy）, a central modulator of inflammation, affects the NOD2-mediated signaling pathway in human conventional DCs （cDCs）. Synergistic stimulation of DCs with MDP and IFNy increased the expression of CD40, CD80, CD83, CD86, and human leukocyte antigen DQ proteins and significantly elevated the production of pro-inflammatory cytokines IL- 1β, IL-6, IL-12, and tumour necrosis factor （TNF）, as well as anti-inflammatory cytokine IL-10. Furthermore, the simultaneous presence of MDP and I FNy was necessary to decrease IkBe protein levels. By investigating various mechanisms implicated in MDP- and IFNγ-mediated signaling pathways, we revealed that the increased production of pro-inflammatory cytokines is highly dependent on the X-linked inhibitor of apoptosis protein （XIAP） but not on cellular lAP1 and lAP2. We also found that the NOD2 signaling pathway is regulated by the mammalian target of rapamycin （mTOR） but is not affected by phosphatidylinositol-3 kinase or signal transducer and activator of transcription 1 inhibition. Our results demonstrate, for the first time, that IFNy positively affects NOD2-mediated signaling in human cDCs, in a manner considerably dependent on XIAP and partially dependent on mTOR.
