Complement activation in human autoimmune diseases and mouse models; employing a sandwich immunoassay specific for C3dg

Anne Troldborg, Lene Halkjær, Henrik Pedersen, Annette Hansen, Anne Gitte Loft, Hanne Lindegaard, Kristian Stengaard-Pedersen, Jonas Heilskov Graversen, Yaseelan Palarasah, Steffen Thiel

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

In human autoimmune diseases, low plasma levels of complement factors C3 and C4 are commonly used as a proxy for complement activation. The measurements of C3 and C4 concentrations (the result of synthesis and consumption) however, show low sensitivity in patient follow-up. We find that the estimation of the C3dg fragment released during complement activation is a better parameter for complement activation. Available techniques for measuring the activation fragment C3dg, e.g. immune-electrophoresis or involving PEG-precipitation, are time-consuming and difficult to standardize. Here we examine the specificity and use of an antibody with mono-specificity for a neoepitope at the N-terminus of C3dg, which is only exposed after cleavage of C3. We present a stable, reproducible, and easy-to-use, time-resolved immunoassay with specificity for C3dg that can be used to directly evaluate ongoing complement activation. We demonstrate that the assay can be applied to clinical samples with a high specificity (95%) and a positive likelihood ratio of 10. It can also differentiate the complement related disease Systemic Lupus Erythematosus from controls and other immune-mediatedimmune mediated diseases like Rheumatoid Arthritis (86% specificity) and Spondyloarthritis (91% specificity). Further, we establish how the assay may also be used for experimental research in in vivo mouse models.

Original languageEnglish
Article number112866
JournalJournal of Immunological Methods
Volume486
ISSN0022-1759
DOIs
Publication statusPublished - Nov 2020

Keywords

  • C3dg
  • Complement activation
  • Complement measurement
  • Complement proteins

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