Purification of F.VIII:C devoid of F.VIII:Ag was achieved by antigen-antibody chromatography. The antibody used neutralized VIIIR:Ag but not VIII:C in liquid phase but extracted both VIII:Ag and VIII:C from plasma when bound to Sepharose. VIII:C was eluted with calcium-containing buffer. When plasma was used as starting material VIII:C was obtained free from VIIIR:Ag but contaminated with some other proteins. When a well-defined pure F.VIII preparation was used as starting material the VIII:C active fractions contained no immunoradiometrically detectable VIIIR:Ag, no VIIIR:RCF and no detectable protein. When stabilized with albumin VIII:C could be frozen and thawed with retained activity and could be activated with thrombin.
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