Clinical significance of IgA anti-cardiolipin and IgA anti-β2glycoprotein I antibodies.

IgA antiphospholipid antibodies (aPL) are not currently recognized as formal laboratory criteria for the Antiphospholipid Syndrome (APS). This is mainly due to methodological issues (different study designs, use of various non-standardized IgA assays). However, there are experimental data showing the pathogenic role of IgA anti-cardiolipin antibodies (aCL) and IgA anti-β2glycoprotein I antibodies (anti-β2GPI). Isolated IgA aCL are not very common, therefore their testing could be useful in the case of strong suspicion of APS but negative results for other aPL tests. IgA anti-β2GPI seem to be the most prevalent isotype in patients with Systemic Lupus Erythematosus (SLE), with a significant association with thrombotic events. Such a clinical relevance has been recently recognized by the inclusion of these autoantibodies among the aPL tests in the novel SLICC classification criteria for SLE. Emerging interest has been raised by IgA anti-β2GPI against domain 4/5 as a novel subgroup of clinically relevant aPL.