IL-1β synthesis in DV-infected platelets and platelets from healthy volunteers. (A) The percentage of IL-1β–expressing platelets was assessed in platelets that were isolated from healthy subjects (control) or patients with dengue (dengue). The boxes indicate the median and interquartile ranges and the whiskers indicate 5 to 95 percentile. (B-C) Washed platelets from healthy volunteers were exposed to mock, infective DV-2 (DV) or heat-inactivated DV-2 (heat DV) as described in Patients and methods. Panel B shows the percentage of IL-1β–expressing platelets, and panel C shows the concentration of IL-1β in supernatants of platelets incubated in each condition. The bars represent mean ± standard error of the mean (SEM) of 8 experiments performed using samples from independent healthy donors. *P < .05 and **P < .01 compared with healthy volunteers or mock exposed platelets. (Insets) Representative density plots of (A) IL-1β–expressing platelets from 1 healthy volunteer and 1 dengue patient or (B) platelets from 1 healthy volunteer that were exposed to mock, DV, or heat DV. The values in each region of the quadrants indicate the cell frequencies in the respective quadrant.