We have reported that the adhesion of human formalin-fixed washed platelets (FWP) to collagen was enhanced by von Willebrand factor but inhibited by plasma fibronectin (Thromb. Res. 44, 1986). Recently, platelet factor XIII is reported to be a receptor for collagen (Saito, JBC, 261, 1986). To investigate the role of factor XIII in the interaction between platelets and collagen, effect of purified XIII or rabbit anti-XIIIa on the adhesion of FWP to collagen or on the in vitro bleeding time was studies. FWP adhesion was measured by either collagen-coated glass beads column or aggregometric method using bovine type I collagen (Ethicon Inc., Dr. Kronenthal). In vitro bleeding time was measured with Thrombostat-4000 (VDG-VONDERGOLTZ), in which citrated whole blood as a sample and ADP, CaCl2 and rat type I collagen as the reagents were used. Platelet adhesion to the collagen immobilized column (1,300 ug collagen, flow rate 5 ml/min) was not changed by the addition of purified XIII (Fibrogammin, Hoechst); the adhesion were 42.7 ± 1.7% in the presence of 1% human serum albumin, 42,0 ± 0.3%, 43,0 ± 1.4% in the presence of 1 or 2 u/ml factor XIII. Furthermore, the adhesion of FWP which was added by 1:100 rabbit anti-XIIIa was 42.3 ± 1.4% and not different from that of control rabbit serum (46.1 ± 1.3%). Similar results were also obtained with different technique using aggregometer. No significant change on in vitro bleeding time was observed after the addition of 1:100 rabbit anti-XIIIa to citrated normal blood. When the binding of factor XIII to the collagen was investigated by batch method, 17%, 23% and 54% of factor XHIa in normal plasma bound to 250, 500 and 1000 ug/ml collagen, respectively. These data suggest that factor XIII is not involved in the platelet adhesion to the type I fibrillar collagen, while factor XHIa in normal plasma binds to the collaeen.
Platelet Adhesion to Native Type I Collagen Fibrils