ACPA (Anti-Citrullinated Protein Ab)
ACPA is an indirect solid-phase enzyme immunoassay (ELISA) for the quantitative measurement of IgG class autoantibodies against citrullinated Proteins (ACP) in human serum or plasma.
Rheumatoid arthritis (RA) is one of the most common autoimmune diseases. The main characteristic of RA is joint inflammation that results in joint damage and loss of function. An early diagnosis of RA and an immediate beginning of an appropriate treatment is important to prevent a complete joint damage. RA is diagnosed primarily on clinical manifestations and serological suppport has, up to now, been mainly restricted to the determination of autoantibodies against rheumatoid factor (RF). RF is a sensitive serological marker for RA with a moderate specificity of about 70%. In several studies it has been demonstrated that the determination of antibodies against citrullinated arginine residues in filament proteins occurs in RF negative patients. Citrullination is a peptidylarginine deiminase (PAD) catalysed process in which the amino acid arginine (Arg) is modified to citrulline. During this conversion, the positively charged NH2-group is hydrolyzed to an oxygen group.
The ACPA ELISA shows both a high specificity and a high sensitivity for autoantibodies against citrullinated proteins.
ACPA is bound to microwells. Antibodies against this antigen, if present in diluted serum or plasma, bind to the respective antigen. Washing of the microwells removes unspecific serum and plasma components. Horseradish peroxidase (HRP) conjugated anti-human IgG immunologically detects the bound patient antibodies forming a conjugate/antibody/antigen complex. Washing of the microwells removes unbound conjugate. An enzyme substrate in the presence of bound conjugate hydrolyzes to form a blue color. The addition of an acid stops the reaction forming a yellow end-product. The intensity of this yellow color is measured photometrically at 450 nm. The amount of colour is directly proportional to the concentration of IgG antibodies present in the original sample.
- F.Bobbio-Pallavicini, C.Alpini, R.Caporali, S.Avalle, S.Bugatti, C.Montecuccio. Autoantibody profile in rheumatoid arthritis during long-term infliximab treatment. Arthritis Res Ther 2004, 6:R264-R272 (DOI 10.1186/ar1173)
- E.R.Vossenaar, N.Deprés, E.Lapointe, A.van der Heijden, M.Lora, T.Senshu, W.J. van Venfooij, H.A. Ménard. Rheumatoid arthritis specific anti Sa antibodies target citrullinated vimentin. Arthritis Research & Therapie Vol. 6 No. 2
- M.Escalon, F.J.Lópees-Longo, C.M. González, I.Monteagudo, M.Rodriguez-Mahou, R.Grau, L.Carreno. Anti-Sa Sera from patients with Rheumatoid Arthritis contain at least 2 different subpopulations of Anti-Sa antibodies. The Journal of Rheumatology 2002; 29:10 2053-60
- Ch.Vincent, L.Nogueira, M.Sebba, S.Chapuy-Regaud, M.Arnaud, O.Letourneur, D.Rolland, B.Rounie, A.Cantagrel, M.Jolivet, G.Serre. Detecion of antibodies to dertermined recombinant tat filaggrin by Enzyme-Linked Immunosorbent Assay. Arthritis & Rheumatism Vo. 46, No. 8, August 2002, pp. 2051-58
- G.Steiner, J.Smolen. Antibodies in rheumatoid arthritis and their clinical significance. Arthritis Res 2002, 4 (suppl 2):S1-S5
- R.Goldbach-Mansky, J.Lee, A.McCoy, J.Hoxworth, C.Yarboro, J.S.Smolen, G.Steiner, A.Rosen, C.Zhang, H.A.Ménard, Z.J.Zhou, T.Palosuo, W.J.Van Venrooij, R.L.Wilder, J.H.Klippel, H.R.Schumacher Jr., H.S.El- Gabalawy. Rheumatoid arthritis associated antibodies in patients with synovitis of recent onset. Arthritis Res 2000, 2:236–243