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Recently, a novel family of autoantibodies in rheumatoid arthritis (RA) patients was described: anti-carbamylated protein (Anti-CarP) antibodies, which target carbamylated (homocitrulline-containing) epitopes.1 ,2 Since citrulline and homocitrulline have a similar structure, we wished to determine to what extent human autoantibodies can differentiate between them. Unlike human antibodies, the anti-modified citrulline (AMC) antibody developed by Dr Senshu3–8 is able to recognise citrullinated epitopes irrespective of the neighbouring amino acids. Thus, we also aimed to verify whether the AMC assay could distinguish between these two amino acids.
To address this, we loaded gels with citrullinated, carbamylated and non-modified forms of foetal calf's serum (FCS) and human fibrinogen (Fib). Gels loaded with equal amounts of these protein preparations (figure 1A) were used for western blotting and staining with the ‘AMC-Senshu’ method. Both the citrullinated and the carbamylated forms of the proteins tested were strongly recognised, whereas, the non-modified form did not reveal any staining (figure 1B). Staining similar western blots with selected human sera1 revealed that sera-positive …
Funding These studies were supported by the Netherlands Proteomics Center and the Center for Medical Systems Biology as part of the Netherlands Genomics Initiative, the Dutch Arthritis Foundation, a NWO Zon-MW Vidi grant to LAT, FP7 project Masterswitch, as well as the IMI JU funded project BeTheCure, contract no 115142-2.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.