P2X1 receptor expressed on PMNs and platelets is required for fibrin generation and thrombus formation. (A) PMNs isolated from WT mice were loaded with red-orange calcein. Exogenous PMNs (3 × 10⁶ cells) were infused into the circulation of a recipient P2X1^−/− mouse. Following a laser-induced vessel wall injury on the cremaster, the PMN accumulation was observed and images recorded over time. (A) Representative composite images of fluorescence and brightfield data depicting calcein-loaded WT PMNs (blue) in a P2X1^−/− mouse (representative of 31 thrombi performed in 3 mice). (B) Fibrin generation and thrombus formation at the site of the laser-injury in P2X1^−/− mice before and after infusion of isolated WT PMNs, WT platelets, or WT PMNs plus WT platelets. Fibrin is depicted in green, platelets in red (representative of 30 thrombi performed in 3 mice). Graphs represent median of fibrin-integrated fluorescence intensity (left) and platelet-integrated fluorescence intensity (right) in all the conditions tested. (C-D) Fibrin generation (C) and thrombus formation (D) at the site of the laser-injury in WT mice, before and after infusion of isolated P2X1^−/−, PMN, or P2X1 ^−/− platelets after depletion of WT PMNs and WT platelets, respectively (representative of 31 thrombi performed in 3 mice for panel C and 15 thrombi in 3 mice for panel D).