Beyond Antagonism: IL-4 Exploits TNF signaling to Shape Its Gene Expression Signature in Monocytes and Macrophages.

Investigation of crosstalk between antagonistic pro- and anti-inflammatory cytokines has focused on mechanisms and functional consequences of cross-inhibition. We investigated cross-regulation between proinflammatory TNF and anti-inflammatory IL-4 in primary human monocytes and in a skin wound-healing model. Surprisingly, TNF functioned mainly as a costimulator of IL-4-induced gene expression, whereas IL-4 selectively inhibited the TNF-induced IFN response, leaving inflammatory gene expression mostly intact. TNF and IL-4 synergistically induced gene sets important for regulating inflammation and tissue repair, which were highly induced during the phase of wound healing when these cytokines are co-expressed. Crosstalk between TNF and IL-4 was mediated by epigenetic chromatin-mediated mechanisms associated with cooperation between NF-κB and STAT6 transcription factors, erasure of negative histone mark H3K27me3, and selective inhibition of IRF1. These results identify a long-sought mechanism for expansion of the IL-4 response, and highlight the complexity of crosstalk between antagonistic cytokines that includes cooperation for select gene responses important in immune response and tissue repair.