ABSTRACT
Normal platelets were examined by conventional coagulation methods and specific immunological techniques for the presence of platelet-associated coagulation factors. Platelets washed in buffer containing calcium chloride gave different results form those washed in the absence of calcium. Factor XI was not detected in washed platelets by any technique. Factor II and factor X were removed from platelets by washing in calcium-free buffer but not by calcium-containing buffer. Procoagulant factor VIII was readily removed or inactivated by washing in the presence or absence of calcium, but factor VIII related antigen was consistently demonstrated after multiple washes in either buffer. Factor V activity and antigen was detected in platelet suspensions after multiple washes although the presence of calcium in the washing buffer gave higher factor V assays and stronger immunological reactions than when calcium-free buffer was used. The results are consistent with the presence of calcium dependent binding sites in platelets which may have a role in the enhancement of factor V and phospholipid reactions.
Subject(s)
Blood Coagulation Factors/analysis , Blood Platelets/analysis , Blood Coagulation/drug effects , Blood Platelets/immunology , Calcium/pharmacology , Cell Separation , Fluorescent Antibody Technique , HumansABSTRACT
Antibody to factor V was produced by immunizing rabbits with purified factor V from human plasma. Various tissues were examined for the presence of factor-V antigen using this antiserum. It was consistently demonstrated in homogenates of liver and spleen by means of an antibody (coagulation inhibitor) neutralization technique. The antigen was further localized histologically by the indirect fluorescent antiglobulin technique. It was present on the endothelium of normal blood vessels in all organs examined. In the liver it was detected in hepatic parenchymal cells and a distinctive pattern of fluorescence in the spleen suggested that it was being detected on platelets. Results were negative in all other tissues examined. The findings confirm the presence of factor V in hepatic parenchymal cells and support the suggestion that endothelial coagulation factors may play a role in haemostasis and thrombosis.
