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 Ptpn6(spin) mice) spontaneously develop a severe inflammatory disease resembling neutrophilic dermatosis in humans. Disease in Ptpn6(spin) mice is characterized by persistent footpad swelling and suppurative inflammation. Recently, in addition to IL-1 alpha and IL-1R signaling, we demonstrated a pivotal role for RIPK1, TAK1, and ASK1 in promoting inflammatory disease in Ptpn6(spin) mice. In the current study we have identified a previously unknown role for CARD9 signaling as a critical regulator for Ptpn6(spin) -mediated footpad inflammation. Genetic deletion of CARD9 significantly rescued the Ptpn6(spin)-mediated footpad inflammation. Mechanistically, enhanced IL-1 alpha-mediated signaling in Ptpn6(spin) mice neutrophils was dampened in Ptpn6(spin) Card9(-/-) mice. Collectively, this study identifies SHP-1 and CARD9 cross-talk as a novel regulator of IL-1 alpha-driven inflammation and opens future avenues for finding novel drug targets to treat neutrophilic dermatosis in humans.