FX binding to human monocytes and macrophages. (A-B) Undifferentiated THP1 (A) or THP1-derived macrophages (B) were incubated with Alexa 488–labeled FX or Alexa 488–labeled Fab′2 as a control (10 µg/mL, 1 hour at 37°C) and subsequently analyzed by flow cytometry for FX binding. Black curves represent Fab′2-incubated cells (control) whereas red curves represent Alexa 488-FX–incubated cells. Representative plots of 3 different experiments are shown. (C) The mean FX fluorescence was quantified and is expressed in arbitrary units. Each dot represents 1 experiment (N = 5-6 in total) and bars represent the mean ± SD. ***P < .001 in a 2-way ANOVA followed by the Sidak posttest for multiple comparison. (D-E) Widefield microscopy images of immunofluorescent staining for FX (green) in undifferentiated THP1 (D) or THP1-derived macrophages (E) incubated with 10 µg/mL FX (1 hour at 37°C). Nuclei and polymerized actin were counterstained using DAPI (blue) and Alexa 647–labeled phalloidin (magenta), respectively. Arrows indicate spots of FX staining. Bars represent 10 µm; objective, ×63. DAPI, 4,6 diamidino-2-phenylindole; N.S., not significant.