The RIPK3 Scaffold Regulates Lung Inflammation During Pneumonia.

RIPK3 (receptor-interacting protein kinase 3) activity triggers cell death via necroptosis, whereas scaffold function supports protein binding and cytokine production. To determine if RIPK3 kinase or scaffold domains mediate pathology during infection, control mice and those with deletion or mutation of RIPK3 and associated signaling partners were subjected to pneumonia and followed for survival or killed for biologic assays. Murine immune cells were studied for -induced cytokine production and cell death, and RIPK3 binding interactions were blocked with the viral inhibitor M45. Human tissue effects were assayed by infecting airway epithelial cells with and measuring cytokine production after siRNA inhibition of RIPK3. Deletion of RIPK3 reduced inflammation and decreased animal mortality after pneumonia. RIPK3 kinase inactivation did neither. In cell culture, RIPK3 was dispensable for cell killing by and instead drove cytokine production that required the RIPK3 scaffold domain but not kinase activity. Blocking the RIP homotypic interaction motif (RHIM) with M45 reduced the inflammatory response to infection . Similarly, siRNA knockdown of RIPK3 decreased infection-triggered inflammation in human airway epithelial cells. Thus, the RIPK3 scaffold drives deleterious pulmonary inflammation and mortality in a relevant clinical model of pneumonia. This process is distinct from kinase-mediated necroptosis, requiring only the RIPK3 RHIM. Inhibition of RHIM signaling is a potential strategy to reduce lung inflammation during infection.