ACPA (Anti-Citrullinated Protein Ab)
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ACPA ELISA is a test system for the quantitative measurement of IgG Anti-Citrullinated Protein Autoantibodies (ACPA) in human serum or plasma.This product is intended for professional in vitro diagnostic use only.Citrullinated Protein is bound to microwells. Antibodies against the coated antigen, if present in diluted patient sample, bind to the respective antigen. Washing of the microwells removes unbound unspecific serum and plasma components. Horseradish peroxidase (HRP) conjugated anti-human antibodies immunologically detect 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 toform a blue colour. The addition of an acid stops the reaction forming a yellow end-product. The intensity of this yellow colour is measured photometrically at 450 nm. The amount of colour is directly proportional to the concentration of antibodies present in the original sample. 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 support 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 infilament proteins occurs in RF negative patients. Citrullination is a peptidylarginine deiminase (PAD) catalyzed process in which the amino acid arginine (Arg) is modified to citrullin. During this conversion, the positively charged NH2-group is hydrolyzed to an oxygen group [4]. The ACPA (Anti-Citrullinated Protein Ab) ELISA shows both a high specificity and a high sensitivity for auto-antibodies against mutated citrullinated vimentin. Vimentin is an omnipresent citrullinated protein which was observed in the rheumatoid synovial tissue of RA patients. There are recent findings of secernation and modification of vimentin by macrophages depending on pro-inflammatory signals [1 2]. The titerof antibodies against vimentin in RA patients strongly correlates with the disease activity score (DAS).
