Acpa $$$

Acronym for anti-citrulline peptide antibody.

ACPAs or autoantibodies against citrullinated proteins/peptides occur in patients with rheumatoid arthritis (RA). They have a higher sensitivity in the diagnosis of rheumatoid arthritis than rheumatoid factor (RF). In the meantime, autoantibodies against citrullinated peptides have been included in the ACR criteria. APCAs as well as RF prove to be negative in psoriatic arthritis (Chimenti MS et al. 2015).

Citrulline is a modified amino acid that is produced from arginine by enzymatic deamination (by peptidylarginine deaminases).

The most common ACPAs are anti-CCP (cyclic citrullinated peptides) and anti-MVC mutated citrullinated vimentin (Böhm BO 2018). Detection methods are the anti-MCV ELISA and the CCP assay. Both achieve sensitivities of almost 80% and specificities of almost 98% in RA.

The citrullination of proteins is a physiological process; it takes place enzymatically by deamination of the amino acid arginine to the amino acid citrulline. Citrullination changes the charge of the molecule. This leads to a change in the three-dimensional structure of the molecule. This changes the antigenic property of the protein. The citrullinated, altered endogenous protein is regarded as an antigen by the immune system and responds by the formation of autoreactive antibodies (Schellekens GA et al. 1998).

For certain ACPAs (anti-CCP autoantibodies) a correlation between antibody titer and disease activity has been proven (Böhm BO). This results in a reliable, good parameter for disease progression and prognosis and a good basis for individual therapy decisions.

1. Böhm BO (2018) Autoantibody diagnostics. In: Neumeier B et al. (Eds) Clinical guide to laboratory diagnostics. Elsevier GmbH S. 413-414
2. Chimenti MS et al (2015) Auto-reactions, autoimmunity and psoriatic arthritis. Autoimmune Rev 14:1142-1146.https://www.ncbi.nlm.nih.gov/pubmed/26254734
3. Schellekens GA et al (1998) Citrulline is an essential constituent of antigenic determinants recognized by rheumatoid arthritis-specific autoantibodies. Journal of Clinical Investigation 101: 273-281.
4. Innala L et al (2008) Antibodies against mutated citrullinated vimentin are a better predictor of disease activity at 24 months in early rheumatoid arthritis than antibodies against cyclic citrullinated peptides. J Rheumatol35: 1002-1008.