期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1978
卷号：75
期号：4
页码：1971-1975
DOI：10.1073/pnas.75.4.1971
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Sheep erythrocytes in their native state did not activate the alternative complement pathway, as measured by lysis in dilutions of normal human serum containing [ethylenebis(oxyethylenenitrilo)] tetraacetic acid but acquired this capacity after membrane sialic acid residues had been removed (by sialidase) or modified (by NaIO4). Activation of the alternative pathway by sheep erythrocytes required removal or modification of at least 40% of the membrane sialic acid to reach threshold, and it increased proportionately when larger amounts of sialic acid had been affected. Studies with isolated proteins of the alternative pathway demonstrated that the altered erythrocyte membranes resembled natural activators in protecting bound C3b from inactivation by C3b inactivator and {beta}1H and protecting bound amplification C3 convertase (C3b,Bb) from decay-dissociation by {beta}1H. A 1% decrease in intact sialic acid was associated with a 1% decrease in {beta}1H activity in decay-dissociation of membrane bound C3b,Bb. Because removal of the C8 and C9 carbon atoms from the polyhydroxylated side chain of sialic acid by oxidation with NaIO4 was functionally equivalent to removal of the entire sialic acid moiety, secondary effects of the latter reaction, such as diminution of the negative charge of the membrane or exposure of penultimate galactose residues, were not considered to be responsible for the altered activity of {beta}1H. These studies suggest that facilitation, by membrane sialic acid residues, of the interaction between bound C3b and {beta}1H is essential to prevent the particle from effectively activating the alternative pathway.
