IgA is the predominant isotype of anti-β2 glycoprotein I antibodies in rheumatoid arthritis.

Background: The aim of this study was to determine the frequency of anti-cardiolipin antibodies (aCL) and anti-β2 glycoprotein I antibodies (aβ2GPI) among Tunisian patients with rheumatoid arthritis (RA).

Methods: Ninety RA patients with positive anti-cyclic citrullinated antibodies (anti-CCP) and 90 healthy blood donors (HBD) were studied. aCL and aβ2GPI of isotype IgG, IgA and IgM were detected by ELISA.