Histones increase thrombin generation in human PRP. Thrombin generation was monitored in real time by CAT in the absence of any trigger. (A) Typical thrombograms in the presence of increasing concentrations of calf thymus histones (0-160 μg/mL) in recalcified citrated PRP. (B) Thrombograms in the presence of histones in recalcified CTI-inhibited PRP. Note that the control curve is flat. In both cases, a representative experiment of 4 performed with PRP from different donors is shown. The tails of the thrombograms have been cut for clarity in these and next graphs. (C) Changes in CAT parameters as a function of histone concentration in CTI-inhibited PRP. Lag time and time-to-peak (ttPeak) are shown on the left; thrombin peak and ETP on the right. Data are the means ± SD of 4 independent experiments. (D) Recalcified CTI-inhibited PRP was treated with single recombinant histones (20 μg/mL) and then thrombin generation was evaluated. A representative experiment of 3 performed with PRP from different donors is shown.