Fig. 3.

hIgA binds and activates human platelets. (A) Binding of hIgA to platelets, which were preincubated with anti-FcαRI-blocking mAb MIP8a (final concentration: 50 μg/ml; thin line, MIP8a+hIgA), mIgG1 isotype control (final concentration: 50 μg/ml; dashed line), or without any treatment (bold line, hIgA). After washing, human platelets were incubated with hIgA (final concentration: 100 μg/ml) and followed by FITC-conjugated goat anti-hIgA antibody. Platelets stained with FITC-conjugated goat anti-hIgA antibody alone were used as autofluorescence control (shaded histogram). (B) Induction of platelet activation by hIgA. Human platelets were stimulated as described in Materials and Methods. Platelet activation was defined as an increase of CD62P expression. The results were representative of four independent experiments.