IL-6 Negatively Regulates IL-22Rα Expression on Epidermal Keratinocytes: Implications for Irritant Contact Dermatitis

Irritant Contact Dermatitis (ICD) is characterized by epidermal hyperplasia and inflammatory cytokine release. IL-6 has been shown to be involved in the pathogenesis of ICD; however, the involvement of the IL-22/IL-22Rα axis and its relation to IL-6 in the inflammatory response following irritant exposure are unknown. Using a chemical model of ICD, it was observed that mice with a keratinocyte-specific knockout of IL-6Rα (IL-6Rα ^Δker) presented with increased inflammation and IL-22Rα and IL-22 protein expression relative to WT following irritant exposure, indicating that IL-6Rα deficiency in epidermal keratinocytes leads to the upregulation of IL-22Rα and its ligand during ICD. Furthermore, it was shown that IL-6 negatively regulates the expression of IL-22Rα on epidermal keratinocytes. This effect is functional as the effects of IL-22 on keratinocyte proliferation and differentiation were markedly reduced when keratinocytes were pretreated with IL-6 prior to IL-22 treatment. These results show that IL-6 modulates the IL-22/IL-22Rα axis in the skin and suggest that this occurrence may be associated with the increased epidermal hyperplasia and exacerbated inflammatory response observed in IL-6Rα ^Δker mice during ICD.