RADIOIMMUNOASSAY OF HUMAN HIGH MOLECULAR-WEIGHT KININOGEN IN NORMAL AND DEFICIENT PLASMAS

Abstract

An RIA [radioimmunoassay] for human H[high]MW kininogen, capable of detecting 150 pg of antigen, was developed. Antibody to HMW kininogen was purified by immunoaffinity chromatography, and double-antibody precipitation was used to separate free and bound antigen. Of the L[low]MW kininogens only 1 of the forms tested (B3.2) showed significant cross-reaction (2%). Bradykinin and human plasma kallikrein both showed no cross-reaction, and monkey HMW kininogen showed identity to the human antigen. Intraassay and interassay coefficients of variation were 2% and 1.5%, respectively. Recovery of HMW kininogen added to 6 plasmas was 97.7% .+-. 1.8%. Assay of 17 normal plasmas gave a level of 90.8 .+-. 2.5 .mu.g/ml HMW kininogen. A bioassay of the samples, based on specific release of kinin by purified plasma kallikrein, yielded a level of 90.2 .+-. 2.8 .mu.g/ml HMW kininogen (r [correlation coefficient] = 0.83, P < 0.001). In neither assay was any significant sex difference observed. No evidence of any antigenic fragments was seen upon gel filtration of normal plasmas. RIA measurements were also performed on 7 plasmas reportedly deficient in HMW kininogen. Williams, Dayton, San Francisco and Flaujeac plasmas all showed no significant cross-reaction, whereas Fitzgerald, Reid and Detroit plasmas showed 1.0, 2.5 and 3.5% of normal antigenic levels, respectively. This sensitive, convenient method should facilitate studies on the role of the kallikrein-kinin system in health and disease.