The role of alpha1-antitrypsin and alpha-macroglobulins in the uptake of proteinase by rabbit alveolar macrophages.

Proteinases in plasma bind largely to alpha1-antitrypsin and alpha-macroglobin. The latter is represented in humans by alpha2-macroglobulin and in the rabbit by alpha2-macroglobulin and alpha1-macroglobulin. There is a selective and rapid uptake of proteinase-macroglobulin complexes by rabbit alveolar macrophages. It was found that complexes of labelled trypsin or subtilopeptidase A with rabbit alpha1-antitrypsin do not become similarly associated with rabbit alveolar macrophages. Moreover, proteinase-alpha1-antitrypsin complexes failed to inhibit the uptake of labelled proteinase-macroglobulin complexes. Thus, the interaction with macrophages of proteinase-macroglobulin complexes represents a pathway of proteinase metabolism distinct from that involving proteinase bound to alpha1-antitrypsin.