Platelet activation by immune complexes. Washed human platelets (100 × 106/mL) were incubated in the presence of monomeric IgG or HA-IgG in the absence or in the presence of IV.3 monoclonal antibody (mAb). After 20 minutes, MP production (A) and expression of the active form of integrin α2β3 (PAC-1 binding) and CD62P (B) were determined. N = 3; data are mean ± SEM. (C) IAV H1N1 was incubated in presence of purified human IgG, and the formation of virus-containing immune complexes (right panel) was determined by hs-FCM using a fluorescent antibody, the antigen-binding fragment Fab2, conjugated to anti-human IgG. The relative dimensions (in nanometers) of the immune complexes are presented according to size-defined microsphere calibrations. (D-F) Washed human platelets (100 × 106/mL) were incubated with purified human IgG without or with IAV H1N1 in the absence or in the presence of IV.3 mAb. After 20 minutes, the production of 12-HETE (D), formation of MPs (E), and induction of PAC-1 binding/CD62P (F) were evaluated. (D-F) N = 5; data are mean + SEM. Human platelets (100 × 106/mL) bathed in 2% HS were preincubated or not with IV.3 mAb and stimulated with HBSS (as control) or stimulated with IAV H1N1 for 20 minutes. The production of 12-HETE (G), formation of MPs (95% confidence interval, 9813-472 494) (H), and induction of the active form of integrin α2β3 (PAC-1 binding) and CD62P (I) were determined. (G-I) N = 35; data are mean + SEM. **P < .001; ***P < .0001; NS, nonsignificant.
