VEGF localization in resting and activated platelets. Double-label immunofluorescence microscopy on fixed and permeabilized platelets was used to determine the intracellular localization of VEGF in the resting and activated states. In resting platelets, tubulin is concentrated, as expected, in the marginal microtubule band (A). In thrombin-activated platelets, phalloidin stain confirms the morphologic changes expected with activation (ie, the development of filopodia, lamellipodia, and pseudopodia) (D). The VEGF stain labels punctate, vesicle-like structures distributed throughout the platelet cytoplasm in both resting (arrowheads in panel B) and activated platelets (E), consistent with the lack of release of VEGF on activation, as noted in Figure 2. In the activated state, VEGF is redistributed to filopodia and lamellipodia (arrows in panel E and arrowheads in panel F) in contrast to its granular pattern of distribution in resting state (C).