Influence of plasma protease inhibitors and the secretory leucocyte protease inhibitor on leucocyte elastase-induced consumption of selected plasma proteins in vitro in man.

Cleavage of C3, fibronectin, antithrombin III and alpha 2-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 alpha 2-macroglobulin and alpha 1-protease inhibitor and also with varying amounts of secretory leucocyte protease inhibitor. When alpha 1-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 mumol/l in the present model to block this consumption completely. This concentration also gave some protection of alpha 1-protease inhibitor and alpha 2-macroglobulin.