Chemotactic activity of platelet alpha granule proteins for fibroblasts.

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Abstract
At sites of blood vessel injury, [human] platelets release numerous substances that may have biological activities influencing cellular responses. The chemotactic activity was studied in fibroblasts of 3 highly purified proteins obtained from platelet .alpha. granules: platelet factor 4 (PF4), platelet-derived growth factor (PDGF) and .beta.-thromboglobulin (BTG). Each of these proteins was strongly chemotactic for fibroblasts, with maximum chemotactic activity in each instance comparable to that observed with an optimal concentration of the control chemotactic protein, plasma fibronectin. Each protein was active at very low concentrations. The peak chemotactic activities of PF4, PDGF and BTG occurred at 200, 30 and 6 ng/ml, respectively. Specificity of fibroblast chemotaxis to individual platelet proteins was provided by finding that anti-PF4 Ig blocked the chemotactic activity of PF4 without affecting the chemotactic activity of PDGF, while anti-PDGF Ig blocked the activity of PDGF but did not alter the capacity of PF4 to promote fibroblast chemotaxis. In vivo, several .alpha. granule proteins released from platelets may affect wound healing by causing directed fibroblast migration.