IgA anticardiolipin and IgA anti-β2 glycoprotein I antibody positivity determined by fluorescence enzyme immunoassay in primary antiphospholipid syndrome.

BACKGROUND: Primary antiphospholipid syndrome (PAPS) is an autoimmune disease characterized by thrombosis and/or pregnancy morbidity as well as blood antiphospholipid (aPL) antibodies such as anticardiolipin (aCL), anti-β2 glycoprotein I (anti-β2GPI) antibodies of the IgG/IgM isotype and lupus anticoagulant (LA). The clinical significance of aCL and anti-β2GPI antibodies of the IgA isotype in PAPS is still a controversial issue. METHODS: Sera and plasma were collected from 84 PAPS patients (54 with thrombosis and/or pregnancy morbidity and 30 with pregnancy morbidity alone), 66 seronegative patients (subjects with clinical manifestations of PAPS although with negative results on conventional antiphospholipid antibody testing), and 78 healthy blood donors. IgA aCL and IgA anti-β2GPI were determined using fluorescence enzyme immunoassay (FEIA), (EliATM, Phadia AB, Uppsala, Sweden). For comparison purposes, the sera were also tested for IgG/IgM aCL/anti-β2GPI antibodies using the same immunoassay method. LA was assayed following internationally accepted guidelines. RESULTS: Present respectively in 19% and 50% of the PAPS patients studied, IgA aCL and IgA anti-β2GPI antibody frequencies were both statistically significant (p=0.001 and p<0.001, respectively). The mean titers of both IgA aCL and IgA anti-β2GPI antibodies were higher in the thrombotic patients, but only the latter were significantly associated with thrombosis. Isolated IgA anti-β2GPI antibody positivity was significantly prevalent (p=0.04) in seven (10.6%) of the seronegative patients. CONCLUSIONS: Positivity to IgA anti-β2GPI antibody detected using FEIA was found to be clinically relevant in PAPS patients. Moreover the prevalence of isolated IgA anti-β2GPI antibody positivity was significant in the seronegative patients.