Antibodies and B cells recognising citrullinated proteins display a broad cross-reactivity towards other post-translational modifications

Abstract

ObjectiveAutoantibodies 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.MethodsBCR 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.ResultsMost 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.ConclusionsOur 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.

Improved classification of rheumatoid arthritis with a score including anti-acetylated ornithine antibodies

“…This extreme was evidenced in the logistic regression analysis including RF, anti-CCP and anti-CarP antibodies in addition to the anti-AcOrn antibodies. These same arguments show that the improvements we have found are not undermined by the recent studies demonstrating various levels of cross-reactivity between RA autoantibodies 46,47 .…”

RB139, RB140, RB141 and RB142 antibodies recognize human citrullinated LL37 by ELISA

“…Thus, these antibodies can represent important tools for studying citrullination of LL37, avoiding confusion with carbamylation of the same protein. Of note, naturally occurring antibodies to citrullinated proteins are in general very likely to be cross-reactive between the citrullinated and carbamylated forms (Kissel et al, 2020). RB142 has since been shown to recognize citrullinated LL37 in human tissue by immunofluorescence and immunohistochemistry (Lande et al, 2020).…”

Autoantikörper und die autoreaktive Immunantwort

“…Da es sich bei Lysin um eine andere Aminosäure handelt als Arginin, sind carbamylierte und acetylierte Antigene per Definition nicht identisch mit citrullinierten Antigenen und befinden sich an anderer Stelle im jeweiligen Protein. Dennoch konnten Studien mit monoklonalen ACPA zeigen, dass diese vermeintlich citrullinspezifischen Antikörper in hohem Maß kreuzreagieren mit carbamylierten und acetylierten Antigenen [ 5 ]. Kristallstrukturen von monoklonalen ACPA mit acetylierten oder carbamylierten Antigenen liegen noch nicht vor.…”