Carbamylation of immunoglobulin abrogates activation of the classical complement pathway.
Bottom Line: We found that the lysine residues of IgG1 are rapidly modified after brief exposure to CNO- .The reaction can apparently occur in vivo, as we found carbamylated antibodies in synovial fluid from rheumatoid arthritis patients.Taken together, our data suggest that carbamylation has a profound impact on the complement-activating ability of IgG1 and reveals a pivotal role for previously uncharacterized lysine residues in this process.
Affiliation: Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway.Show MeSH
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Mentions: Efficient binding of C1q to the Fc portion of IgG1 is a pivotal step in complement activation. This prompted us to investigate the capacity of carbamylated IgG1 to trigger this event. Our results revealed that carbamylation has a profound impact on the ability of C1q to bind IgG1 (Fig.3A–C). After 3 h incubation, we detected a nearly 60% decrease in the deposition of C1q on modified immunoglobulins (Fig.3A, p < 0.05). Longer carbamylation times (6, 9 or 12 h) resulted in complete abrogation of the ability of IgG1 to bind C1q. For these time points, C1q deposition was approximately equal to that of the negative control (Fig.3A). In addition, we observed decreased deposition of the C4b fragment, a component of C3 convertase in the classical pathway of complement activation (Fig.3B). Carbamylated IgG1 (6 h) triggered significantly less formation of C4b in response to 1% normal human serum (NHS) than intact IgG1. Subsequently, deposition of opsonin C3b was also significantly abrogated (9 h and 12 h p < 0.05 and p < 0.01, respectively, Fig.3C). This significant difference was clearly not a result of impaired plate-binding capacity of IgG1 after carbamylation since there was no difference in coating with carbamylated IgG and control IgG (Fig.3D).
Affiliation: Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway.