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  • Title: Release of IL-12 by dendritic cells activated by TLR ligation is dependent on MyD88 signaling, whereas TRIF signaling is indispensable for TLR synergy.
    Author: Krummen M, Balkow S, Shen L, Heinz S, Loquai C, Probst HC, Grabbe S.
    Journal: J Leukoc Biol; 2010 Jul; 88(1):189-99. PubMed ID: 20360404.
    Abstract:
    Recently, it has been shown that certain combinations of TLR ligands act in synergy to induce the release of IL-12 by DCs. In this study, we sought to define the critical parameters underlying TLR synergy. Our data show that TLR ligands act synergistically if MyD88- and TRIF-dependent ligands are combined. TLR4 uses both of these adaptor molecules, thus activation via TLR4 proved to be a synergistic event on its own. TLR synergy did not affect all aspects of DC activation but enhanced primarily the release of certain cytokines, particularly IL-12, whereas the expression of costimulatory molecules remained unchanged. Consequently, synergistic activation of DC did not affect their ability to induce T cell proliferation but resulted in T(H)1-biased responses in vitro and in vivo. Furthermore, we examined the impact of TLR ligand combinations on primary DC in vitro but observed only modest effects with a combination of CpG + Poly (I:C). However, noticeable synergy in terms of IL-12 production by DCs was detectable in vivo after systemic administration of CpG + Poly (I:C). Finally, we show that synergy is partially dependent on IFNAR signaling but does not require the release of IFNs to the enviroment, suggesting an autocrine action of type I IFNs.
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