TLR7-activated platelets adhere to collagen but do not aggregate or form significant thrombi. Fluorescently labeled and stimulated, washed platelets were run over collagen-coated slides. (A) Human platelets treated with TLR7 ligand (TLR7-L) (R837, 2 μg/mL or 8.3 μM) or with thrombin (0.5 U/mL). (B) Quantitation of (A) for n = 6 individuals (3 females and 3 males). (C) Murine platelets treated with thrombin (0.5 U/mL) or TLR7-L: Loxo (100 μM) or R837 (2 μg/mL). (D) Quantitation of (C) using n = 3 (Loxo), n = 5 (R837), and n = 5 (thrombin). (E) SEM images of platelets treated with different agonists. (F) Aggregation of isolated human or (G) murine platelets treated with various concentrations of agonists depicted in the graph. Data are average ± SD and were analyzed by Student t test using n = 5 for human platelets (except Loxo, n = 3) and n = 3 for each condition in mice, as each n is pooled platelets from 4 to 5 mice. (H) PAC-1 binding to isolated human platelets post isotype control, control, Loxo (1 mM), and thrombin (0.005 U/mL) tested by flow cytometry. Histogram is representative of n = 4 individuals. PAC-1 tests for epitope on αII_bβ₃ integrin of human platelets, necessary for fibrinogen binding and aggregation. Bars in A and D represent 100 μm and in E represent 4 μm.