Quantification of human high molecular weight kininogen by immunoblotting with a monoclonal anti-light chain antibody

Activation of the Hageman factor-dependent pathways in human plasma leads to the cleavage of high molecular weight kininogen (HMWK) into a disulfide-linked two-chain (heavy and light chain) molecule and release of bradykinin, a vasoactive peptide. We have utilized murine monoclonal antibodies to the light chain of HMWK (Blood (1988) 71, 1344) and developed a very sensitive immunoblotting assay to detect and quantify the amount of cleaved or uncleaved HMWK in whole plasma. The total HMWK content of plasma from apparently healthy donors was 55 micrograms/ml by this method. Cleaved HMWK was detected when only 2% of the plasma had been activated and the method was sensitive down to 2 ng of HMWK. Because of the extreme lability of bradykinin in body fluids, quantification of cleaved HMWK provides an important adjunct which reflects contact activation and permits calculation of a theoretical upper limit of the potential kinin formed.