Cutting Edge: Dysregulated CARD9 Signaling in Neutrophils Drives Inflammation in a Mouse Model of Neutrophilic Dermatoses.

Mice homozygous for the Y208N amino acid substitution in the carboxy terminus of SHP-1 (referred to as Ptpn6spin mice) spontaneously develop a severe inflammatory disease resembling neutrophilic dermatosis in humans. Disease in Ptpn6spin mice is characterized by persistent footpad swelling and suppurative inflammation. Recently, in addition to IL-1α and IL-1R signaling, we demonstrated a pivotal role for RIPK1, TAK1, and ASK1 in promoting inflammatory disease in Ptpn6spin mice. In the current study we have identified a previously unknown role for CARD9 signaling as a critical regulator for Ptpn6spin-mediated footpad inflammation. Genetic deletion of CARD9 significantly rescued the Ptpn6spin-mediated footpad inflammation. Mechanistically, enhanced IL-1α-mediated signaling in Ptpn6spin mice neutrophils was dampened in Ptpn6spinCard9-/- mice. Collectively, this study identifies SHP-1 and CARD9 cross-talk as a novel regulator of IL-1α-driven inflammation and opens future avenues for finding novel drug targets to treat neutrophilic dermatosis in humans.