Impaired thrombus formation and α granule secretion after laser injury in HPS model mice. WT, pallid, pearl, or light ear mice were injected with fluorophore-conjugated antibodies to CD41 (to detect total platelets) and to P-selectin (to detect α granule secretion) and then subjected to laser-induced injury in the cremaster muscle microvasculature. Accumulation of signal for CD41 and P-selectin at injury sites was imaged by live intravital video microscopy. The total area of CD41⁺ (A-D) and P-selectin⁺ (I-L) platelet accumulation at injury sites was quantified over time. The time course in separate sets of experiments is shown for WT vs pallid and pearl mice for 4 minutes (A and I) or WT vs light ear mice for 3 minutes (C and K). Panels B,D,J,L show the peak area of accumulation at the end of the time course (mean ± standard deviation from at least 3 independent experiments). (E-H) Frames from movies at the 3-minute time point of representative thrombi labeled for P-selectin (green) and CD41 (red) in WT, pallid, pearl, and light ear mice (red and green overlay is yellow). *P < .05.