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-beta 2 glycoprotein I antibodies (a beta 2GPI) 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 a beta 2GPI of isotype IgG, IgA and IgM were detected by ELISA. Result The frequency of antiphopholipid antibodies (aPL) (aCL and/or a beta 2GPI) was significantly higher in patients with RA than in HBD (35.5% vs 11.1%,P = .0001). The frequencies of aCL and a beta 2GPI were significantly higher in patients than in healthy subjects (15.5% vs 5.5%,P = .04 and 32.2% vs 11.1%,P = .0005 respectively). a beta 2GPI-IgA were significantly more frequent in patients than in the control group (26.7% vs 7.8%,P = .0007). In patients, a beta 2GPI-IgA were significantly more frequent than a beta 2GPI-IgG (26.7% vs. 6.7%,P = .0003) and a beta 2GPI-IgM (26.7% vs 5.6%,P = .0001). In RA patients, the frequency of a beta 2GPI was significantly higher than that of aCL (32.2% vs 15.5%,P = .008). a beta 2GPI-IgA was significantly more frequent than aCL-IgA (26.7% vs 4.4%,P = .00005). The average titer of anti-CCP in aPL positive patients was significantly higher than in aPL negative patients (170.6 +/- 50 RU/mL vs 147.7 +/- 51 RU/mL,P = .04). Significant correlation was found between a beta 2GPI-IgA and anti-CCP (r = .235,P = .026). Conclusions aPL and particularly a beta 2GPI-IgA are frequent in RA and are correlated with anti-CCP.