Defined chemically cross-linked oligomers of human C-reactive protein: characterization and reactivity with the complement system.
Chemically cross-linked C-reactive protein (CRP) oligomers were prepared and characterized, and C1q binding and C activation were investigated. Purified human CRP was polymerized in the presence of both non-cleavable and cleavable cross-linking agents and further separated by Superose 12 analytical FPLC column chromatography into fractions of 110 KDa (pentameric monomers), 220 KDa (dimers) and 330 KDa (trimers); virtually no larger oligomers were formed under a variety of experimental conditions. CRP subunits were cross-linked both within and between CRP pentamers. CRP trimers retained native CRP antigenicity without expression of neo-CRP epitopes. CRP trimers showed maximal binding and CRP dimers showed partial binding of solid phase C1q while CRP monomers bound virtually no C1q at all; CRP trimers also bound to fluid phase C1q. Binding was Ca++ independent and increased as the ionic strength or pH were lowered, characteristics comparable to binding of aggregated IgG to C1q; it was not inhibited by phosphorylcholine. CRP trimers consumed total C, C1 and C2 haemolytic activities upon incubation in fresh human serum, but much less efficiently than did CRP-protamine complexes or Agg-IgG. CRP trimers failed to deplete alternative C pathway haemolytic activity at all. The stable, chemically defined CRP oligomers described in this report, which bind C1q efficiently but display poor ability to activate the classical C pathway in the absence of an appropriate ligand, should be valuable in further studies of the interactions between CRP and the C system.
Jiang
H
H
Department of Immunology/Microbiology, Rush Medical College, Chicago, Illinois 60612.
Lint
T F
TF
Gewurz
H
H
D002097:C-Reactive Protein / Q000276:immunology* / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D002853:Chromatography, Liquid; D003167:Complement Activation / Q000276:immunology*; D015922:Complement C1q / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006461:Hemolysis / Q000276:immunology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration
D015922:Complement C1q; D002097:C-Reactive Protein; D002118:Calcium