Autoantibodies quiz: series 1

The passage describes RF as typically pentameric IgM autoantibodies that bind the Fc portion of IgG. This implies that RF is primarily of the IgM class and binds to the Fc region of IgG.

Citrullination is a post-translational modification that involves the conversion of arginine amino acids to citrulline. Therefore, the correct answer is B, as citrullination specifically modifies arginine residues.

Apart from ACPAs, autoantibodies to carbamylated and acetylated protein antibodies (AMPAs) are well-described but are unlikely to add diagnostic value and are not routinely tested for.

The first citrullinated autoantigen used in rheumatoid arthritis studies was filaggrin, and it was modified for diagnostic assays by making the public peptide sequence cyclic, resulting in cyclic citrullinated peptide (CCP).

Anti-CarP are part of the group of anti-modified peptide antibodies (AMPAs), belonging to antibodies against post-translationally modified (PTM) proteins/peptides.

Antibodies against peptidyl arginine deiminase-4 PAD-4, an enzyme responsible for citrullination, have been detected in 36-42% of RA patients.

Anti-CII is a marker for an acute onset RA subgroup with a good prognosis, where the levels drop during the first year along with the anti-CII induced inflammation.

The presence of anti-citrullinated peptide antibodies (ACPA) is highly associated with the human leukocyte antigen (HLA)-shared epitope (SE), which includes HLA-DR4, HLA-DR1, or HLA-DR10.

For more information regarding the clinical use of autoantibodies in rheumatology, please refer to the expert talks:

https://rheumatv.com/use-of-autoantibodies-in-diagnosis-of-rheumatic-diseases-by-dr-chandrashekara-s/#more-4150

https://rheumatv.com/investigation-in-rheumatology-session-2/