Assay of complexed alpha 1-antichymotrypsin in plasma

We introduce an assay to measure complexed alpha 1-antichymotrypsin in human plasma. The assay works on the principle that the target proteinase cathepsin G has a very high affinity to the surface of microtiter plates, even if these surfaces are blocked with albumin and Tween 20. alpha 1-Antichymotrypsin, when complexed to cathepsin G, is thus immobilized and can be detected with specific antibodies. The mean (SD) concentration of alpha 1-antichymotrypsin in 50 healthy individuals was 1.73 (0.58) nmol/L. The detection limit was 0.84 nmol/L. The results of the assay are linear to at least 14 nmol/L. We propose to use this assay for diseases in which increased turnover of alpha 1-antichymotrypsin or cathepsin G can be expected to clarify further the function of this enzyme-inhibitor system.