No abstract

As the rheumatology field is moving toward very early identification of RA and possible screening for individuals at maximum risk of RA in populations with a low pretest probability, an autoantibody profile of triple positivity for ACPAs, RF, and anti-CarP provides interesting information that might help identify individuals at risk of developing RA.

ACPA conferred the highest risk for arthritis development and had an additive value to RF. However, >30% of ACPA-positive/RF-positive CSA patients did not develop arthritis during the 2-year follow-up. Thus, CSA and information on autoantibodies is insufficient for accurately identifying imminent autoantibody-positive RA.

Carbamylation and citrullination are both post-translational modifications against which (auto)antibodies can be detected in sera of rheumatoid arthritis (RA) patients. Carbamylation is the chemical modification of a lysine into a homocitrulline, whereas citrullination is an enzymatic conversion of an arginine into a citrulline. It is difficult to distinguish between the two resulting amino acids due to similarities in structure. However, differentiation between citrulline and homocitrulline is important to understand the antigens that induce antibody production and to determine which modified antigens are present in target tissues. We have observed in literature that conclusions are frequently drawn regarding the citrullination or carbamylation of proteins based on reagents that are not able to distinguish between these two modifications. Therefore, we have analyzed a wide spectrum of methods and describe here which method we consider most optimal to distinguish between citrulline and homocitrulline. We have produced several carbamylated and citrullinated proteins and investigated the specificity of (commercial) antibodies by both ELISA and western blot. Furthermore, detection methods based on chemical modifications, such as the anti-modified citrulline-"Senshu" method and also mass spectrometry were investigated for their capacity to distinguish between carbamylation and citrullination. We observed that some antibodies are able to distinguish between carbamylation and citrullination, but an overlap in reactivity is often present in the commercially available anti-citrulline antibodies. Finally, we conclude that the use of mass spectrometry is currently essential to differentiate between citrullinated and carbamylated proteins present in complex biological samples.

Background Immune regulation is necessary to control inflammatory responses and to prevent autoimmune diseases. Therefore, mechanisms of central and peripheral tolerance have evolved to ensure that T cells recognize antigens as self-or non-self-antigens. The thymus is crucially important for central tolerance induction to self-antigens via negative selection of T cells. However, if T cells escape negative selection in the thymus and enter the periphery, peripheral mechanisms are active to warrant immune tolerance. Secondary lymphoid organs, as well as tolerogenic dendritic cells and regulatory T cells, play an important role in peripheral tolerance. In chronic inflammatory diseases, tertiary lymphoid organs are sometimes formed that may also be involved in the induction of peripheral tolerance. This review discusses the main processes that are involved in immune regulation and tolerance, and focuses on the contribution of NF-jB signalling to these processes.