Platelet-monocyte aggregates formation, TF expression, and CD16 expression follows differential kinetics in COVID-19. (A) Monocytes from healthy volunteers (control monocyte) were incubated in the absence of platelets (open circles) or with platelets from severe COVID-19 patients (COVID-19 platelets, red circles) or from a different healthy volunteer (control platelets, gray circles) for the indicated time points. Monocytes from COVID-19 patients (COVID-19 monocyte) were also incubated in the absence of platelets (open squares) or with platelets from healthy volunteers (control platelets, black squares). The percentage of platelet-monocyte aggregates formation (B), TF-expressing monocytes (C), and CD16-positive monocytes (D) are shown. Dots represent mean ± standard error of 4 to 6 platelet and monocyte combinations from patients with COVID-19 or control participants. All experiments were repeated with cells from at least 2 independent control participants exposed to platelets or monocytes from the same patients with COVID-19 with similar results, and a representative data from 1 of the donors is shown. #P < .05 compared with baseline; *P < .05 compared with control monocytes exposed to control platelets.