Cryoprecipitation of fibrin-fibrinogen complexes induced by the cold-insoluble globulin of plasma

Abstract

A cold-insoluble precipitate that formed from normal plasma treated with small amounts of thrombin was comprised of three main components: cold-insoluble globulin (Clg), fibrin, and fibrinogen. Its composition appeared to be the same as that of a pathologic plasma precipitate termed 'cryofibrinogen'. We examined the roles played by each of these components in generating such a precipitate. Fibrinogen from a preparation containing a high proportion of molecules with intact Aα chains (fraction 1-4) was coupled to Sepharose 4B; columns of this material were compared before and after conversion to fibrin with respect to their Clg binding capacity. Fibrinogen columns displayed significant Clg binding at 4°C but very little at 22°C; fibrin columns bound significant quantities of Clg at both temperatures. Under standardized conditions of pH (7.3 ± 0.1), ionic strength (0.2-0.25), and temperature (2°C), Clg or fibrinogen (fraction 1-2 or 1-4) alone or mixtures of Clg and fibrinogen did not form cold-insoluble precipitates. This was true as well of soluble complexes of fibrin and fibrinogen, even when saturated with fibrin, except when Clg was included in the mixture. In contrast, fibrin-fibrinogen complexes produced from molecules lacking the COOH-terminal region of the Aα chain (fraction 1-8 or 1-9) failed to precipitate in the cold in the presence of Clg, thus indicating that this region must be present for Clg-induced precipitation to occur. We conclude that each component of 'cryofibrinogen' plays an important role in its formation. Fibrinogen, which is well known to form soluble complexes with fibrin, is necessary for maintaining fibrin in a soluble state prior to complexing and precipitation with Clg. There is an absolute requirement for both Clg and fibrin in this reaction, since precipitation does not take place in their absence. Considerations of the Clg:fibrin-fibrinogen ratios in precipitating mixtures suggest that Clg acts as a nucleus with multiple binding sites for participating fibrin-fibrinogen complexes.