(A) Human platelets bind IgG in vivo. Gel-filtered human platelets were incubated with PE-labelled F(ab’)2 goat anti-human IgG-PE (grey line), PE-labelled F(ab’)2 goat anti-rabbit IgG (dashed line), or only saline (Solid black line). Binding of IgG complexes on the surface of platelets was detected by flow cytometry.
(B) Human platelets can bind heat aggregated (HA-IgG) in the presence of physiologic concentrations of monomeric IgG. Human platelets were incubated with monomeric IgG (10 mg/ml), mAb IV.3 (25 μg/ml) or saline before exposure to HA human IgG. IgG bound to the platelet surface was detected by flow cytometry using PE-tagged F(ab’)2 goat anti-human IgG.
(C). FcγRIIA binds aggregated HA-IgG but not monomeric IgG. COS cells transfected to stably express FcγRIIA were incubated with monomeric human IgG (dashed line), HA-IgG (grey line) or saline (solid black line). IgG bound to the platelet surface was detected by flow cytometry using PE-tagged F(ab’)2 goat anti-human IgG. Flow cytometry using PE-tagged F(ab’)2 goat anti-human IgG detected only aggregated IgG on the cell surface.