We have demonstrated Factor IX activation by sonicated polymorphonuclear leukocytes (PMNs). This activation reaction required the disrupted leukocytes, calcium chloride, and a small amount of normal human plasma. The requirement for normal plasma was met by plasma deficient in all of the known coagulation factors, and thus the substance present in normal plasma which facilitates this reaction was not identified. The fact that factor XI deficient plasma supported the reaction as well as normal plasma implied that factor XIa was not involved in this activation. Strontium ions could not substitute for calcium ions in the activation reaction, also implying that factor XIa was not involved. This factor IX activating principle in leukocytes could provide a mechanism for by-passing the contact factors of blood coagulation, thus providing an explanation for the discrepancy in clinical severity between deficiencies of the contact factors on the one hand and hemophilias A and B on the other.
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