The cytokine CSBF inhibits the IL-17A and TNF-α inflammatory pathways via SUSD2-ACT1 in keratinocytes and alleviates IMQ-induced psoriasis.

Overactivation of inflammatory signaling in keratinocytes is critical for psoriatic skin inflammation, but its regulatory mechanisms remain incompletely understood. Here, we demonstrate that the cytokine CSBF inhibits both individual and synergistic proinflammatory signaling induced by IL-17A and TNF-α (IL-17A/TNF-α) in keratinocytes, playing a protective role in psoriatic inflammation. The expression of CSBF was increased in the skin lesions and serum of psoriatic patients, and IL-17A/TNF-α enhanced its production. Csbf deletion exacerbated IMQ-induced psoriasis-like skin inflammation and led to hyperactivation of IL-17A/TNF-α signaling in keratinocytes. The CSBF protein significantly ameliorated psoriatic manifestations and suppressed IL-17A/TNF-α signaling through the receptor SUSD2. Mechanistically, CSBF-SUSD2 competed with TRAF6 and TNFR1 for interaction with ACT1, inhibiting the IL-17A/TNF-α signaling pathway. Overall, the anti-inflammatory cytokine CSBF has the potential to be a therapeutic option for psoriasis by targeting keratinocytes.