Two phases of inflammatory mediator production defined by the study of IRAK2 and IRAK1 knock-in mice

E Pauls, SK Nanda, H Smith, R Toth… - The Journal of …, 2013 - journals.aai.org
E Pauls, SK Nanda, H Smith, R Toth, JSC Arthur, P Cohen
The Journal of Immunology, 2013journals.aai.org
The roles of IL-1R–associated kinase (IRAK) 2 and IRAK1 in cytokine production were
investigated using immune cells from knock-in mice expressing the TNFR-associated factor
6 (TRAF6) binding-defective mutant IRAK2 [E525A] or the catalytically inactive IRAK1
[D359A] mutant. In bone marrow–derived macrophages (BMDMs), the IRAK2–TRAF6
interaction was required for the late (2–8 h) but not the early phase (0–2 h) of il6 and tnfa
mRNA production, and hence for IL-6 and TNF-α secretion by TLR agonists that signal via …
Abstract
The roles of IL-1R–associated kinase (IRAK) 2 and IRAK1 in cytokine production were investigated using immune cells from knock-in mice expressing the TNFR-associated factor 6 (TRAF6) binding-defective mutant IRAK2 [E525A] or the catalytically inactive IRAK1 [D359A] mutant. In bone marrow–derived macrophages (BMDMs), the IRAK2–TRAF6 interaction was required for the late (2–8 h) but not the early phase (0–2 h) of il6 and tnfa mRNA production, and hence for IL-6 and TNF-α secretion by TLR agonists that signal via MyD88. Loss of the IRAK2–TRAF6 interaction had little effect on the MyD88-dependent production of anti-inflammatory molecules produced during the early phase, such as Dual Specificity Phosphatase 1, and a modest effect on IL-10 secretion. The LPS/TLR4-stimulated production of il6 and tnfa mRNA and IL-6 and TNF-α secretion was hardly affected, because the Toll/IL-1R domain–containing adapter-inducing IFN-β (TRIF) signaling pathway was used instead of the IRAK2–TRAF6 interaction to sustain late-phase mRNA production. IRAK1 catalytic activity was not rate limiting for il6, tnfa, or il10 mRNA production or the secretion of these cytokines by BMDMs, but IFN-β mRNA induction by TLR7 and TLR9 agonists was greatly delayed in plasmacytoid dendritic cells (pDCs) from IRAK1 [D359A] mice. In contrast, IFN-β mRNA production was little affected in pDCs from IRAK2 [E525A] mice, but subsequent IFN-α mRNA production and IFN-α secretion were reduced. IFN-β and IFN-α production were abolished in pDCs from IRAK1 [D359A]× IRAK2 [E525A] double knock-in mice. Our results establish that the IRAK2–TRAF6 interaction is rate limiting for the late, but not the early phase of cytokine production in BMDM and pDCs, and that the IRAK2–TRAF6 interaction is needed to sustain IκB-inducing kinase β activity during prolonged activation of the MyD88 signaling.
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