Endo-chip assay. (A) Endothelial cells (HUVECs) are seeded into the microchannel of the chip and allowed to adhere for 4 to 12 hours. Inset on the left shows differential interference contrast image of cells coating the channel. Test sample (eg, patient serum) is injected into the channel and incubated with endothelial cells for 30 minutes and then washed off. Venous blood from a healthy donor is collected into a citrate tube. Fluorescent antibodies are added to the blood (to label platelets, neutrophils, and fibrin). Immediately before perfusion, the whole blood is recalcified. The blood is perfused over the HUVEC layer and fluorescent images are captured by confocal microscopy. Inset on the right shows a representative image of the channel after perfusion of blood showing platelet, fibrin, and neutrophil adhesion to the endothelial layer (thromboinflammation). Image created with BioRender.com. (B) Accumulation of platelets, neutrophils, and fibrin after 15-minute perfusion of blood on HUVECs treated with media, ChAdOx1 nCOV-19, or TNF-α (5 ng/mL, positive control). Representative images of platelet (green), neutrophil (red), and fibrin (magenta) merged images after perfusion of blood. (C) Surface area coverage per field of platelets, number of neutrophils per field, and surface area coverage per field of fibrin at the end of a 15-minute perfusion of blood on HUVECs treated with media, ChAdOx1 nCOV-19, or TNF-α (5 ng/mL). Mean ± standard deviation (SD) of n = 3 independent experiments. One-way analysis of variance (ANOVA) with Tukey post hoc test was used for comparisons. (D) Kinetics of the platelet, neutrophil, and fibrin accumulation on the endothelial surface over 15 minutes of perfusion.