C-1 inactivator and cold-promoted activation of factor VII.

When exposed to temperatures between -5 degree and +5 degree C, plasma from pregnant women and from certain blood donors show shortening of the Thrombotest clotting time, kallikrein formation, and activation of blood-clotting factor VII. This phenomenon has been called cold-promoted activation of factor VII (CPA). In this study, it was found that CPA-positive plasma or serum samples which had been exposed to low temepratures showed spontaneous disappearance of C-1-inactivator activity in parallel to the shortening of the Thrombotest clotting time. C-1-inactivator antigen was not affected by storage at 4 degree C. In these CPA-possitive samples the loss of C-1-inactivator activity is caused partially by the formation of kallikrein at this temperature because when kallikrelin was added to C-1 inactivator, the latter was inactive when tested in the esterolytic assay. The formation of Hageman factor fragments may add to further loss. Purified C-1 inactivator effectively inhibited the CPA phenomenon, whereas alpha2-macroglobulin did so only weakly. This finding indicates that during exposure of CPA-positive plasma samples to low temperatures, Hageman factor fragments, which are inhibited only by C-1 inactivator, induce the activation of the kallikrein system and blood clotting factor VII. The reported lowered activity of C-1 inactivator in pregnancy is probably an artifact caused by generation of CPA during storage, since in fresh samples the levels were compeletely normal. Similarly, various subjects classified as belonging to the variant type of HANE (low C-1-inactivator activity with a normal antigen content) were found to have normal C-1-inactivator activity when determinations were made on fresh instead of frozen samples. It is recommended that plasma or serum samples should not be exposed to temperatures between -5degree and +5degree C prior to the determination of C-1-inactivator activity. Moreover, during purification procedures of kallikrein-binding antiproteases such as C-1 inactivator and also alpha2-macroglobulin, the occurrence of CPA should be avoided by the use of CPA-negative plasma as starting material.