Immunoprecipitation of FVa from plasma and platelets. FVa was immunoprecipitated from 200 μL of plasma (A) or 200 μL of 1.5 × 108 activated platelets/mL (B), concentrated 6 times (FV-deficient patients PD I, PD II, PD III, PD VII) or not concentrated (control), and subjected to SDS–polyacrylamide gel electrophoresis and Western blotting. Control plasma and platelet FVa preparations were run at different dilutions (100%, 50%, 25%, or 5%). FVa was detected with a monoclonal anti-FV heavy chain antibody and chemiluminescence. The FVa heavy chain has a molecular weight of 105 kDa; smaller fragments (only visible in platelet FVa) are degradation products of the FVa heavy chain.