The endothelial thromboinflammatory response in VITT is antibody dependent. (A) Platelet fluorescence area per field, neutrophil count per field, and fibrin fluorescence area per field following a 15-minute blood perfusion in the Endo-chip after treatment with VITT ELISA positive serum or IgG depleted serum (upper panel) or with VITT ELISA negative serum or IgG depleted serum (lower panel) in the presence or absence of 25 μg/mL PF4. VITT ELISA positive n = 5 (patients 2, 3, 4, 6, 12), VITT ELISA negative n = 5 (patients 1, 3, 4, 5, 6). One-way ANOVA with Dunn post hoc test was used for comparisons. (B) Platelet fluorescence area per field, neutrophil count per field, and fibrin fluorescence area per field following a 15-minute blood perfusion in the Endo-chip after treatment with IgG isolated from the same VITT ELISA positive serum or VITT ELISA negative serum as in (A), in the presence or absence of 25 μg/mL PF4, in comparison with IgG isolated from vax control serum. VITT ELISA positive n = 5 (patients 2, 3, 4, 6, 12), VITT ELISA negative n = 5 (patients 1, 3, 4, 5, 6), vax controls n = 5. One-way ANOVA with Dunn post hoc test was used for comparison.