Avian thrombocytes adhere to collagen but fail to form 3-dimensional aggregates under flow. PPACK-anticoagulated human or chicken whole blood was perfused through a tapered-wall parallel plate flow chamber for 5 minutes over a collagen-coated glass slide. (A) Representative fluorescent images captured at areas corresponding to shear rates of 1300, 1100, 700, and 400 seconds⁻¹ after 5 minutes perfusion of whole blood labeled with AP-2 mAb. (B) Representative images of thrombocyte or platelet adhesion to collagen after whole blood flow for 5 or 15 minutes at 1300 seconds⁻¹. Slides were fixed, permeabilized, and stained with Alex-Fluor 594–conjugated phalloidin to detect actin filaments. Nuclear staining of thrombocytes with DAPI is also shown. (C) Time traces of percent surface coverage of collagen surface by platelets or thrombocytes. Shown is mean ± SD (gray zone); n = 7-10 experiments for each condition. Percent collagen surface area coverage (D) and mean aggregate area (E) of human platelets and chicken thrombocytes after perfusion of whole blood for 5 minutes was determined by analysis of fluorescent images. Shown are the mean ± SEM, n = 7-10 experiments for each condition. (F) Scanning electron microscopy is shown after perfusion of human and chicken blood over collagen at a shear rate of approximately 1300 seconds⁻¹. Scale bars indicate 50 μm (500×), 20 μm (1000×), and 5 μm (5000×). Shown are representative images from 3 and 5 human and chicken flow experiments, respectively.