Complement receptor analogous factors in human serum: I. Isolation of a molecule inhibitory for complement dependent rosette formation, its identification as alpha 1-antitrypsin and its functional characterization.
A glycoprotein was isolated from human plasma which partially inhibited C3 carrying erythrocytes from binding to complement receptor cells (CR+C). Based on its physicochemical characteristics and its antigenicity this glycoprotein was identified as alpha 1-antitrypsin (alpha 1-AT). The activity of alpha 1-AT towards C3 and its fragments was unaffected by heating but it was destroyed by periodic acid. The isolated carbohydrate moiety of alpha 1-AT showed the same effect as the intact molecule. Using F(ab)2 of IgG-anti-alpha 1-AT could be demonstrated on Raji cells and human erythrocytes. Treatment of these CR+C with IgG-anti-alpha 1-AT resulted in a blockade of their C3 receptor activity. The results suggest, that alpha 1-AT interacts through its carbohydrate portion with C3 and its fragments and functions as a complement receptor molecule.
D001402:B-Lymphocytes / Q000502:physiology; D001667:Binding, Competitive; D003176:Complement C3 / Q000378:metabolism*; D006801:Humans; D011951:Receptors, Complement / Q000502:physiology*; D012397:Rosette Formation; D013601:T-Lymphocytes / Q000502:physiology; D000515:alpha 1-Antitrypsin / Q000276:immunology*
D003176:Complement C3; D011951:Receptors, Complement; D000515:alpha 1-Antitrypsin