Introduction Individual patients with rheumatoid arthritis (RA) show divergent specific anti-citrullinated protein/peptide antibodies (ACPA) patterns, but hitherto no individual ACPA specificity has consistently been linked to RA pathogenesis. ACPA are also implicated in immune complexes (IC)-associated joint pathology, but until now, there has been no method to investigate the role of individual ACPA in RA IC formation and IC-associated pathogenesis.
Methods We have developed a new technique based on IC binding to C1q-coated magnetic beads to purify and solubilise circulating IC in sera and synovial fluids (SF) from 77 patients with RA. This was combined with measurement of 19 individual ACPA in serum, SF and in the IC fractions from serum and SF. We investigated whether occurrence of individual ACPA as well as number of ACPA in these compartments was related to clinical and laboratory measures of disease activity and inflammation.
Results The majority of individual ACPA reactivities were enriched in SF as compared with in serum, and levels of ACPA in IC were regulated independently of levels in serum and SF. No individual ACPA reactivity in any compartment showed a dominating association to clinical and laboratory measures of disease activity and severity. Instead, the number of individual ACPA reactivities in the IC fraction from SF associated with a number of markers of joint destruction and inflammation.
Conclusions Our data highlight the polyclonality of ACPA in joint IC and the possibility that a broad ACPA repertoire in synovial fluid IC might drive the local inflammatory and matrix-degrading processes in joints, in analogy with antibody-induced rodent arthritis models.
- rheumatoid arthritis
- synovial fluid
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TW and JR contributed equally.
Handling editor Josef S Smolen
Contributors AS and JR conceived the study. AS developed the IC purification technique described in this paper and performed most of the laboratory work. MH and LM-A developed the multiplex microarray. MC, KS and GS provided peptides for the analyses, including validation of their performance. AK, JL and TW included and performed clinical characterisation of the investigated patients. AL investigated inflammatory markers. AS and JR drafted the manuscript. All authors read, commented on and approved the final manuscript.
Funding This study was funded by grants from the Swedish Research Council, the Swedish Rheumatism Association, King Gustav V 80-year foundation, ALF grants provided by the Uppsala County Council, the Rudberg Foundation and the Brunnberg Foundation.
Competing interests LM-A is employed by Thermo Fisher Scientific. KS is co-inventor of the patents US 13/141,960, EP 09799354.7 describing the diagnostic use of the hnRNP-A3 peptide epitopes. GS is co-inventor of several international patents about ACPA antigens held by BioMérieux Cy and licensed to Eurodiagnostica Cy, and Axis-Shield Cy for commercialisation of the CCP2 assays; according to French laws, he receives a part of the royalties paid to the Toulouse III University and the University Hospital of Toulouse.
Patient consent Not required.
Ethics approval The ethics board in Uppsala.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Most data are shown in the manuscript and supplementary files. However, calculations using the alternative cut-offs (see Results section) are not included but can be obtained from JR.
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