Microparticles released from platelet balloons interact with circulating leukocytes in trauma patients. (A) Representative images from imaging flow cytometry showing interactions between platelet-derived microparticles (CD61, green) expressing the platelet activation marker P-selectin (CD62P, blue) with monocytes (CD14, red) and neutrophils (CD66b, purple). (B) Correlation between proportion of ballooning platelets and frequency of interactions between PMPs and leukocytes. Dashed lines indicate 95% confidence intervals. (C) Impact of injury severity on frequency of interactions between leukocytes and whole platelets or PMPs in trauma patients (n = 45). **P < 0.01, 1-way ANOVA. (D) Expression of platelet activation markers CD62P (i) and CD63 (ii) on platelets and CD42b+ve leukocytes from trauma patients (n = 30). ****P < 0.0001, student’s t test. MFI, mean fluorescence intensity. (E) Frequency of PMP-leukocyte aggregates in healthy volunteers (n = 10), trauma patients who developed MODS (n = 18), and those who did not develop MODS (n = 14). **P < 0.01, 1-way ANOVA.