NLRC4 suppresses IL-17A-mediated neutrophil-dependent host defense through upregulation of IL-18 and induction of necroptosis during Gram-positive pneumonia.

Gram-positive pathogens, including Staphylococcus aureus, cause necrotizing pneumonia. The central feature of S. aureus pneumonia is toxin-induced necroptosis of immune and resident cells, which impedes host defense. However, the role of the NLRC4 in the lung following S. aureus infection remains elusive. Here, we demonstrate that S. aureus activates the NLRC4 to drive necroptosis and IL-18 production, which impaired IL-17A-dependent neutrophil-mediated host susceptibility. In particular, Nlrc4-/- mice exhibit reduced necroptosis, enhanced neutrophil influx into the lungs, decreased bacterial burden, and improved host survival. Loss of NLRC4 signaling in both hematopoietic and non-hematopoietic cells contributes to the host protection against S. aureus pneumonia. Secretion of IL-17A by γδ T cells is essential for neutrophil recruitment into the lungs of Nlrc4-/- mice following infection. Moreover, treatment of wild-type mice with necroptosis inhibitors or genetic ablation of MLKL and IL-18 improves host defense against S. aureus infection, which is associated with increased IL-17A+γδ T cells and neutrophils. Taken together, these novel findings reveal that S. aureus activates the NLRC4 to dampen IL-17A-dependent neutrophil accumulation through induction of necroptosis and IL-18. Thus, modulating the function of the NLRC4 may be an attractive therapeutic approach for treating S. aureus infections.