IL‐18 enhances IFN‐γ‐induced production of CXCL9, CXCL10, and CXCL11 in human keratinocytes

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Abstract
IL-18 is involved in the pathogenesis of atopic dermatitis, psoriasis, and allergic contact dermatitis. CXCL9, CXCL10, and CXCL11 recruit type 1 T cells, and the production of these chemokines by keratinocytes is enhanced in these dermatoses. We examined the in vitro effects of IL-18 on IFN-γ-induced CXCL9, CXCL10, and CXCL11 production in human keratinocytes. IL-18 enhanced the IFN-γ-induced secretion and mRNA expression of CXCL9, CXCL10, and CXCL11 in parallel to the activation of NF-κB, STAT1, and IFN-regulatory factor (IRF)-1. Antisense oligonucleotides against NF-κB p50, p65, or STAT1 suppressed CXCL9, CXCL10, and CXCL11 production, and antisense IRF-1 suppressed CXCL11 production. Inhibitors of PI3 K, p38 MAPK, and MEK suppressed IL-18 plus IFN-γ-induced CXCL9, CXCL10, and CXCL11 production and NF-κB, STAT1, and IRF-1 activities. IL-18 induced phosphorylation of ERK and Akt, while IFN-γ induced phosphorylation of p38 MAPK. These results suggest that IL-18 may potentiate IFN-γ-induced CXCL9, CXCL10, and CXCL11 production in keratinocytes by activating NF-κB, STAT1, or IRF-1 through PI3 K/Akt and MEK/ERK pathways. These effects of IL-18 may promote the infiltration of type 1 T cells into lesions with inflammatory dermatoses and amplify the skin inflammation. IL-18 may act as a pro-inflammatory cytokine in these dermatoses and thus is a candidate therapeutic target.

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