Fig. 5: Immuno-mechanical modulation by autoantibodies directed to specific α_IIbβ₃ integrin epitopes is associated with increases and decreases in platelet contractile force.

a To investigate the relationship between conformation- and epitope-dependent platelet contractile force modulation, we used a panel of well-characterized monoclonal antibodies (2.5 μg/mL) directed toward different epitopes of α_IIbβ₃. b Our data show that exposure to monoclonal antibodies alone can modulate average platelet force by ~ ±15 nN (55%). Moreover, a pattern became evident in which antibodies that bind closer to the tail region increase platelet contractile force, whereas those that bind toward the head region decrease force (n = 3,3,3,4,2,3,3,3,2,3 donors/condition with 434, 514, 450, 421, 213, 331, 176, 144, 123, 192 antibody treated platelets, respectively and 1139 untreated control platelets analyzed as shown in Supplementary Fig. 10). c Consistent with our electron microscopy data from patient polyclonal autoantibodies, negative stain electron microscopy showed that antibodies that cause a decrease in contractile force bound mostly to the bent conformation and extended closed formation of the integrin, although this data show that there is only a minor decrease in force when all integrins are stabilized in the extended closed conformation. Antibodies that stabilized integrins in an extended open conformation were associated with increased forces. For (b), all antibody-treated platelets were compared to the untreated condition, and statistical significance was determined by mixed effects model, to account for within-subject variation, followed by the Benjamini-Hochberg’s posthoc test to account for multiple comparisons. Antibody treated platelet contraction force difference for (b) is shown as mean ± the minimum and maximum differences from the untreated control mean. *P ≤ 0.05, **P ≤ 0.01, ****P ≤ 0 .0001 and specific p-values are shown in Supplementary Table 5. Source data are provided as a Source Data file.