The immunoelectronmicroscopic localization of human platelet factor 4 in tissue mast cells

Initial immunohistochemical localization of human platelet factor 4 (PF4) in tissue mast cells suggested that the protein was present in the mast cell granule. It was proposed that this could reflect binding of PF4 to heparin or heparan sulphate, known granule constituents. We report here the confirmation of granule localization by an immunoelectron microscopical method. The possible role of such binding is unknown, but the potential for cationic proteins of platelet origin interacting with vessel wall constituents is discussed.