UV-C irradiation of platelets activates αIIbβ3. (A) An increasing dose of UV-C was delivered to platelets by decreasing the distance between lamp and incubation plate and thereby increasing the light intensity, while irradiation time was kept constant. Higher doses of UV-C caused increased PAC-1 binding to the platelets, resulting in higher fluorescence. Data were corrected for PAC-1 binding to unstimulated platelets and are represented as the mean plus or minus SEM (n = 6). (B) Histograms depicting higher PAC-1 binding after UV-C irradiation (shaded histogram) or thrombin stimulation (open histogram) as compared with the untreated control (filled histogram). This experiment is representative of 3 similar experiments. (C) Histograms depicting higher binding of antifibrinogen antibody (as detected by goat anti–mouse IgG-FITC) after UV-C irradiation (open histogram) as compared with the untreated control (filled histogram). The increase in binding induced by UV-C was prevented by inclusion of tirofiban (1 μg/mL, shaded histogram). This experiment is representative of 3 similar experiments.