ACA Isotype
Enzyme-linked immunosorbent assay method for the semi-quantitative determination of IgG, IgM and IgA autoantibodies to cardiolipin in human serum.
Anti-cardiolipin and anti-phosphatidyl serine antibodies along with others, such as the Lupus Anticoagulant (LAC), belong to the family of anti-phospholipid antibodies. Anti-cardiolipin antibodies are circulating serum antibodies often associated with recurrent arterial and venous thromboembolism, recurrent foetal loss and thrombocytopenia.
These symptoms are often present in cases of Systemic Lupus Erythematosus (SLE) and in many other conditions, both of an autoimmune and of a non-autoimmune nature. Some studies show that over 50% of SLE patients have one or more classes of anti-cardiolipin antibodies. The presence of this antibody serves as a marker for the risk of a thromboembolitic event. Those SLE patients exhibiting high levels of these autoantibodies are 4 times more likely to have such an event than those not expressing the autoantibodies.
Anti-cardiolipin autoantibodies can be of any combination of the IgM, IgA and IgG classes. IgG antibodies are the most prevalent class of autoantibody and the class with the greatest clinical correlation. Samples found to have IgG levels in the ‘high’ anti-cardiolipin band are the most likely to display overt clinical symptoms. However, IgA and IgM autoantibodies are often found either alone or in association with the IgG class. Measurement of all three classes is therefore recommended.
Anti-cardiolipin are the most commonly measured anti-phospholipid antibodies. However, it is known that some patients with infectious diseases and other autoimmune disorders show some antibody activity against cardiolipin.
The AutostatII 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 AutostatII wells are coated with purified antigen (1).
On adding diluted serum to the wells the antibodies (2) present bind to the antigen. After incubating at room temperature and washing away unbound material, horseradish peroxidase conjugated anti-IgG, anti-IgM or anti-IgA (3) is added, which binds to the immobilised antibodies.
Following further incubation and washing, tetra-methyl benzidine substrate (TMB) (4) 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.