SLPI is dispensable for platelet discoid shape and resting integrity or activation-induced reorganization of the marginal MT band. (A) Differential interference contrast (DIC) and scanning electron (SEM, insets) microscopy reveal the elliptical shape of resting wild-type and SLPI^-/- platelets, whereas β1 tubulin^-/- platelets are spherical. (B) IF microscopy after staining with β-tubulin antibody reveals a normal marginal MT band in SLPI^-/- platelets, in contrast to β1 tubulin^-/- platelets, which have an indistinct marginal band. (C) Washed platelets were deposited on coverslips and stimulated with thrombin for 5 minutes prior to fixation. SLPI^-/- platelets show normal contraction of the marginal band and short MT protrusions, similar to wild-type platelets, whereas β1 tubulin^-/- platelets have a diminished resting marginal band that is defective in reorganization. (D-E) Platelets from compound SLPI^+/- β1 tubulin^+/- mice and control SLPI^+/+ β1 tubulin^+/- mice show normal discoid cell shape by DIC microscopy (D), intact marginal MT bands in β-tubulin IF (insets), and the normal MT morphology after thrombin stimulation. Scale bars: B-C, 10 μm; D-E, 2 μm.