Objective Autoantibodies against antigens carrying distinct post-translational modifications (PTMs), such as citrulline, homocitrulline or acetyllysine, are hallmarks of rheumatoid arthritis (RA). The relation between these anti-modified protein antibody (AMPA)-classes is poorly understood as is the ability of different PTM-antigens to activate B-cell receptors (BCRs) directed against citrullinated proteins (CP). Insights into the nature of PTMs able to activate such B cells are pivotal to understand the ‘evolution’ of the autoimmune response conceivable underlying the disease. Here, we investigated the cross-reactivity of monoclonal AMPA and the ability of different types of PTM-antigens to activate CP-reactive BCRs.
Methods BCR sequences from B cells isolated using citrullinated or acetylated antigens were used to produce monoclonal antibodies (mAb) followed by a detailed analysis of their cross-reactivity towards PTM-antigens. Ramos B-cell transfectants expressing CP-reactive IgG BCRs were generated and their activation on stimulation with PTM-antigens investigated.
Results Most mAbs were highly cross-reactive towards multiple PTMs, while no reactivity was observed to the unmodified controls. B cells carrying CP-reactive BCRs showed activation on stimulation with various types of PTM-antigens.
Conclusions Our study illustrates that AMPA exhibit a high cross-reactivity towards at least two PTMs indicating that their recognition pattern is not confined to one type of modification. Furthermore, our data show that CP-reactive B cells are not only activated by citrullinated, but also by carbamylated and/or acetylated antigens. These data are vital for the understanding of the breach of B-cell tolerance against PTM-antigens and the possible contribution of these antigens to RA-pathogenesis.
- rheumatoid arthritis
- B cells
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Handling editor Josef S Smolen
TK and SR contributed equally.
Contributors All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published.
Funding This work has been financially supported by ReumaNederland (17-1-402), the IMI funded project RTCure (777357), ZonMw TOP (91214031) and Target-to-B (LSHM18055-SGF). HUS is the recipient of a NWO-ZonMW clinical fellowship (90714509), a NWO-ZonMW VENI grant (91617107), a ZonMW Enabling Technology Hotels grant (435002030) and received support from the Dutch Arthritis Foundation (15-2-402 and 18-1-205). M.Reth is funded by the Excellence Initiative of the German Federal and State Governments (EXC 294) and by the DFG through TRR130-P02 and the RO1 grant (A031503). P.A. van Veelen is funded by an Investment Grant NWO Medium (91116004), which is (partially) financed by ZonMw.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.