Anti-cardiolipin antibodies (ACA) are antibodies often directed against cardiolipin and found in several diseases, including syphilis,^[1] antiphospholipid syndrome, livedoid vasculitis, vertebrobasilar insufficiency, Behçet's syndrome,^[2] idiopathic spontaneous abortion,^[3] and systemic lupus erythematosus (SLE).^[4] They are a form of anti-mitochondrial antibody. In SLE, anti-DNA antibodies and anti-cardiolipin antibodies may be present individually or together; the two types of antibodies act independently.^[5] This is in contrast to rheumatoid arthritis^[6] with systemic sclerosis (scleroderma)^[7] because anti-cardiolipin antibodies are present in both conditions, and therefore may tie the two conditions together.

Anti-cardiolipin antibodies can be classified in two ways:

• As IgM, IgG or IgA
• As β₂-glycoprotein dependent or independent
  • In autoimmune disease, ACA are beta-2 glycoprotein dependent
  • In syphilis, ACA^[1] are beta-2 glycoprotein independent and can be assayed using the Venereal Disease Research Laboratory test

Apolipoprotein H involvement

β₂-glycoprotein I has been identified as apolipoprotein H and is required for the recognition of ACA in autoimmune disease.^[8] Only a subset of autoimmune anti-cardiolipin antibodies bind Apo-H, these anti-apolipoprotein antibodies are associated with increased thrombosis.

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