β-2 Glycoprotein-I IgA
Enzyme-linked immunosorbent assay method for the semi-quantitative determination of specific IgA autoantibodies to β -2 GPI in human serum.
Anti-phospholipid antibodies (aPL) are a group of immunoglobulins associated with binding of negatively charged phospholipids including cardiolipin and phosphatidyl serine. High serum levels of anti-phospholipid antibodies are frequently found in patients with recurrent arterial and venous thromboembolism , recurrent foetal loss and thrombocytopenia, the main features of anti-phospholipid syndrome (APS). These symptoms are also often present in cases of Systemic Lupus Erythematosis (SLE), when elevated levels of aPL are detected.
It has been reported that β-2-Glycoprotein I (β2-GPI), a 50 kD plasma protein, is required for binding of anti-cardiolipin and anti-phospholipid antibodies and was more recently found to be the target for a specific group of aPL. The conformational epitope for anti-β-2GPI antibodies is thought to develop when β2-GPI interacts with a lipid membrane composed of negatively charged phospholipids or, more recently reported, when it is adsorbed to the surface of a polystyrene microtitre plate.
Antibodies targeting β-2-GPI specifically have been found to be the dominant autoanitbody type in anti-phospholipid positive sera and is widely accepted as a clear diagnostic indicator of APS and of SLE associated with APS.
To increase the efficiency of clinical laboratory testing for APS, anti-cardiolipin IgM and IgG, β-2-GPI IgM and IgG ELISAs are also available from Hycor Biomedical.
The AutostatTM II assay for detection of autoantibodies is a solid phase immunosorbent assay (ELISA) in which the analyte is indicated by a colour reaction of an enzyme and substrate. The AutostatTM II wells are coated with purified antigen.
On adding diluted serum to the wells the antibodies present bind to the antigen. After incubating at room temperature and washing away unbound material, horseradish peroxidase conjugated anti-IgA antibody is added, which binds to the immobilised antibodies.
Following further incubation and washing, tetra-methyl benzidine substrate (TMB) is added to each well. The presence of the antigen-antibody-conjugate complex turns the substrate to a dark blue colour. Addition of the stop solution turns the colour to yellow.
The colour intensity is proportional to the amount of autoantibodies present in the original serum sample.