title: Factor XI and platelets: Evidence that platelets contain only minimal factor XI activity and antigen.
abstract: Factor-XI activity of platelets has been studied in platelet-rich plasmas and isolated platelet suspensions. Fresh platelets in both environments had little or no measurable factor-XI activity. Frozen and thawed platelet-rich normal plasma had markedly elevated apparent factor-XI activity and factor-XI activity as compared to platelet-poor plasma. Frozen and thawed platelet-rich and platelet-poor normal plasmas had equivalent factor-XI antigen. Platelets isolated from normal blood and from factor-XI deficient blood had the same small amounts of apparent factor-XI activity, which increased slightly on freezing and thawing. The data indicates that minimal factor XI is associated with the platelet. The markedly elevated apparent factor-XI activity of frozen and thawed platelet-rich plasma is shown to reflect the interaction of a platelet activator with plasma clotting factors to produce a later activated-clotting-intermediate.
mesh_terms: D000941:Antigens; D001777:Blood Coagulation; D001792:Blood Platelets / Q000276:immunology*; D005164:Factor IX; D005172:Factor XI; D005173:Factor XI Deficiency / Q000097:blood; D005615:Freezing; D006801:Humans
chemical_list: D000941:Antigens; D005164:Factor IX; D005172:Factor XI