SLPI is present in 2 distinct platelet compartments, including a β1 tubulin-dependent association with intact marginal band microtubules. (A) SLPI is found in 2 distinct compartments in normal resting platelets: a punctate distribution in the platelet body that suggests expression in granular stores, and a peripheral distribution wherein SLPI (red) colocalizes with β tubulin (green), as shown by the yellow color in the merged image. Only the latter distribution depends on β1 tubulin, as revealed by its loss in β1 tubulin (β1 tub)-null platelets. (B) The peripheral SLPI distribution depends on the presence of polymerized MTs: in cooled platelets (4°C) MTs depolymerize, losing both the marginal band together and peripheral SLPI staining (middle panels). Rewarmed platelets reconstitute the peripheral MT coil and restore native SLPI distribution (lower panels).