QITP antibodies bind mature Mks. Human platelets (A) and Mks (B) were incubated with QITP sera or NS without (left panels) and with Qn (right panels) and the anti-GPIX monoclonal antibody FMC25, followed by anti-human IgG–Alexa Fluor 488 (green) and anti-mouse IgG (H+L)–Alexa Fluor 594 (red). Binding of human IgG (green) was considerably enhanced only in the presence of the drug (right panels, middle image). The microphotographs were acquired by confocal laser scanning microscopy (Olympus FV300, 60× oil objective, Fluoview Version 4.3 software). Scale bars indicate 20 μm. Images were cropped and revised using Adobe Photoshop CS5.