Abstract
Cleavage of C3, fibronectin, antithrombin III and α2-antiplasmin in human plasma following the addition of increasing amounts of human leucocyte elastase was studied using an in vitro model. The cleavage was correlated with the degree of saturation of the plasma protease inhibitors α2-macroglobulin and α1-protease inhibitor and also with varying amounts of secretory leucocyte protease inhibitor. When α1-protease inhibitor approached saturation, there was a prompt cleavage of all the four plasma proteins studied. The secretory leucocyte protease inhibitor was needed in a concentration of 6 μmol/l in the present model to block this consumption completely. This concentration also gave some protection of α1-protease inhibitor and α2-macroglobulin.