title: Analysis of C3 deposition and degradation on bacterial surfaces after opsonization.
abstract: C3b and iC3b, opsonic fragments of C3, interact with specific receptors on phagocytic cells. After bacterial opsonization, C3 fragments were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, western blotting, and immunodetection. For bacteria opsonized in 50% pooled human serum (PHS), C3 deposition and cleavage to iC3b occurred rapidly. C3b, iC3b, and C3d made up 17%, 64%, and 19%, respectively, of the C3 on Staphylococcus aureus and 53%, 44%, and 2% respectively, on Escherichia coli. Residual C3b was refractory to factor I cleavage, an occurrence enabling alternative pathway activation to continue. C3 deposited was quantitated by enzyme-linked immunosorbent assay; with 50% PHS, greater than 50% and 90% of total C3 deposition occurred within 5 and 10 min, respectively. With a lower percentage of PHS, maximal deposition required up to 60 min and was not achieved in less than 10% PHS. Ester-bound fragments represented 34% and 82% of covalently bound C3 on S. aureus and E. coli, respectively.
authors.affiliation: Department of Clinical Microbiology, Flinders Medical Center, Bedford Park, South Australia.
authors.forename: D L
authors.initials: DL
authors.lastname: Gordon
authors.forename: J
authors.initials: J
authors.lastname: Rice
authors.forename: J J
authors.initials: JJ
authors.lastname: Finlay-Jones
authors.forename: P J
authors.initials: PJ
authors.lastname: McDonald
authors.forename: M K
authors.initials: MK
authors.lastname: Hostetter
mesh_terms: D000577:Amides; D003176:Complement C3 / Q000378:metabolism*; D003179:Complement C3b / Q000378:metabolism; D015933:Complement C3d; D003170:Complement Pathway, Alternative; D004926:Escherichia coli / Q000276:immunology*; D004952:Esters; D006801:Humans; D066298:In Vitro Techniques; D010587:Phagocytosis; D013211:Staphylococcus aureus / Q000276:immunology*
chemical_list: D000577:Amides; D003176:Complement C3; D004952:Esters; D003179:Complement C3b; D015933:Complement C3d