DETECTION, IMMUNOFLUORESCENT LOCALIZATION, AND THROMBIN INDUCED RELEASE OF HUMAN PLATELET-ASSOCIATED FIBRONECTIN ANTIGEN

Platelets are cells which develop adhesive properties following stimulation. Since fibronectin (fn) mediates adhesive properties of several cells, we sought evidence for platelet associated fn. Lysates of suspensions of washed human platelets containing ≤ ng soluble fn/109 ng cells contained 2.58 μg fn antigen per 109 cells. The platelet fn antigen competition curve showed a similar slope to the curve for purified plasma fn suggesting antigenic identity. Immunofluorescent staining for fn was minimal in intact cells suggesting that the majority of fn antigen is intracellular. In permeable platelets, fluorescent staining for fn was seen in a punctate distribution suggesting a granule localization. Stimulation of platelet secretion by thrombin released platelet fn antigen. Suramin, a drug which inhibits platelet secretion, inhibited fn release. The apparent secretion of platlet fn, taken with the immunofluorescent data, support the localization of a portion of platelet fn antigen in a storage granule.