Objectives Over 50% of patients with rheumatoid arthritis (RA) harbour a variety of anti-modified protein antibodies (AMPA) against different post-translationally modified (PTM) proteins, including anti-carbamylated protein (anti-CarP) antibodies. At present, it is unknown how AMPA are generated and how autoreactive B cell responses against PTM proteins are induced. Here we studied whether PTM foreign antigens can breach B cell tolerance towards PTM self-proteins.
Methods Serum reactivity towards five carbamylated proteins was determined for 160 patients with RA and 40 healthy individuals. Antibody cross-reactivity was studied by inhibition experiments. Mass spectrometry was performed to identify carbamylated self-proteins in human rheumatic joint tissue. Mice were immunised with carbamylated or non-modified (auto)antigens and analysed for autoantibody responses.
Results We show that anti-CarP antibodies in RA are highly cross-reactive towards multiple carbamylated proteins, including modified self-proteins and modified non-self-proteins. Studies in mice show that anti-CarP antibody responses recognising carbamylated self-proteins are induced by immunisation with carbamylated self-proteins and by immunisation with carbamylated proteins of non-self-origin. Similar to the data observed with sera from patients with RA, the murine anti-CarP antibody response was, both at the monoclonal level and the polyclonal level, highly cross-reactive towards multiple carbamylated proteins, including carbamylated self-proteins.
Conclusions Self-reactive AMPA responses can be induced by exposure to foreign proteins containing PTM. These data show how autoreactive B cell responses against PTM self-proteins can be induced by exposure to PTM foreign proteins and provide new insights on the breach of autoreactive B cell tolerance.
- Rheumatoid arthritis
- B cell tolerance
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Acknowledgements We thank Nivine Levarht for technical assistance. We thank Professor A M Blom for the gift of prothrombin.
Contributors REMT, LAT, TWJH, JNS, JSD and MKV designed the study and experiments. JSD, MKV, JNS, BL, PAvV, AHdR, GMCJ, SR, AIF and MH conducted the experiments and acquired and analyzed the data. JSD, MKV, LAT and REMT wrote the manuscript. All authors read and commented on the manuscript.
Funding The authors wish to acknowledge the support of the IMI JU-funded project BeTheCure (contract no. 115142-2) and Pfizer (code: RA-IMI-037). LAT was financially supported by a VIDI grant from NWO-Zon-MW. RT was financially supported by a VICI grant from NWO-Zon-MW. JSD was financially supported by the Dutch Arthritis Foundation (project no. 13-3-401). MH (who is an employee of Pfizer) has been involved in technical discussions and scientific collaboration. The funders had no final role in study design, data collection and analysis, decision to publish or preparation of the manuscript.
Competing interests None declared.
Ethics approval Ethics Committee/Institutional Review Board of the Leiden University Medical Center.
Provenance and peer review Not commissioned; externally peer reviewed.
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