Dual oxidase 2 is essential for house dust mite‐induced pro‐inflammatory cytokine production in human keratinocytes

House dust mites (HDMs) are known to trigger chronic inflammation through Toll‐like receptors (TLRs) and their signalling cascades. In this study, we found that TLR2 ligation by HDMs induced the activation of dual oxidase 2 (Duox2) and nuclear factor‐κB (NF‐κB), leading to the production of pro‐inflammatory cytokines in human keratinocytes. Stimulation of human keratinocytes with HDMs resulted in increases in interleukin‐8 (IL‐8) and chemokine (C–C motif) ligand 20 (CCL20) levels. However, pro‐inflammatory cytokine production was abolished in keratinocytes transfected with TLR2 siRNA, indicating that HDM‐induced cytokine production was mediated via TLR2 signalling. We also examined the function of Duox1/2 isozymes, which are primarily expressed in keratinocytes, in HDM‐mediated pro‐inflammatory cytokine production. Human keratinocytes transfected with control siRNA or Duox1 siRNA showed no inhibition of IL‐8 or CCL20 production in response to HDMs, whereas the silencing of Duox2 expression resulted in a failure to induce cytokine production. Moreover, the phosphorylation and nuclear localization of RelA/p65, a component of NF‐κB, were induced by HDMs in human keratinocytes. Transfection of human keratinocytes with TLR2 siRNA or Duox2 siRNA resulted in the complete abolishment of RelA/p65 nuclear localization in response to HDMs. Taken together, these results indicate that the HDM‐dependent TLR2‐Duox2 signalling axis indeed promotes NF‐κB activation, which induces IL‐8 and CCL20 production and mediates epidermal keratinocyte inflammation.