Nucleic acid sensing promotes inflammatory monocyte migration through biased coagulation factor VIIa signaling.

Protease activated receptors (PARs) are cleaved by coagulation proteases and thereby connect hemostasis with innate immune responses. Signaling of the tissue factor (TF) complex with FVIIa via PAR2 stimulates extracellular signal-regulated kinase (ERK) activation and cancer cell migration, but functions of cell autonomous TF-FVIIa signaling in immune cells are unknown. Here we show that myeloid cell expression of FVII but not of FX is crucial for inflammatory cell recruitment to the alveolar space after challenge with the double stranded viral RNA mimic Poly(I:C). In line with these data, genetically modified mice completely resistant to PAR2 cleavage but not FXa-resistant PAR2 mutant mice are protected from lung inflammation. Poly(I:C) stimulated migration of monocytes/macrophages is dependent on ERK activation and mitochondrial antiviral signaling (MAVS), but independent of toll-like receptor (TLR) 3. Monocyte/ macrophage synthesized FVIIa cleaving PAR2 is required for integrin αMβ2-dependent migration on fibrinogen, but not for integrin β1-dependent migration on fibronectin. To further dissect the downstream signaling pathway, we generated PAR2S365/T368A mutant mice deficient in β-arrestin recruitment and ERK scaffolding. This mutation reduces cytosolic, but not nuclear ERK phosphorylation by Poly(I:C) stimulation and prevents macrophage migration on fibrinogen, but not fibronectin following stimulation with Poly(I:C) or CpG-B, a single stranded DNA TLR9 agonist. In addition, PAR2S365/T368A mutant mice display markedly reduced immune cell recruitment to the alveolar space after Poly(I:C) challenge. These results identify TF-FVIIa-PAR2-β-arrestin biased signaling as a driver for lung infiltration in response to viral nucleic acids and suggest potential therapeutic interventions specifically targeting TF-VIIa signaling in thrombo-inflammation.