SELP and COVID-19: Consistent with previous studies, COVID-19 platelets exhibited higher reactivity, as characterized by increased aggregation capacity under ADP stimulation (Supplementary Fig. 6a, b), elevated P-selectin exposure (Supplementary Fig. 6c), increased spreading area on immobilized Fg (Supplementary Fig. 6d, e), and enhanced clot contraction (Supplementary Fig. 6f, g).