Isotype distribution and clinical relevance of anti-beta(2)-glycoprotein I(beta(2)-GPI) antibodies: importance of IgA isotype

The aim of this study was to evaluate the prevalence of IgG, IgA and IgM an ti-beta(2)-GPI antibodies in antiphospholipid syndrome (APS), and to establ ish the clinical significance of IgA type antibodies compared with the othe r isotypes. Anti-beta(2)-GPI antibodies were measured in the sera of 70 pat ients by solid-phase enzyme immunoassay in gamma-irradiated polystyrene pla tes coated with human purified beta(2)-GPI. Thirty-three out of the 70 pati ents were classified as having APS: three of them had primary, and 30 had s econdary APS related to systemic lupus erythematosus (SLE). The remaining 3 7 patients had SLE without APS. Anti-beta(2)-GPI antibodies of IgG, IgA and IgM isotypes were present in 84.8%, 59.3% arid 51.5% of patients with APS. Both the frequency and the level of each isotype were significantly higher in patients with APS. This association was very strong for IgA (P = 0.0004 for the antibody frequency and P < 0.0001 for the antibody level), as well as for IgG type antibodies (P < 0.0001 and P < 0.0001), whereas it was wea ker for IgM (P=0.01 and P=0.04). A strong relationship was demonstrated bet ween increased IgA anti-beta(2)-GPI antibody levels and a history of venous thrombosis, thrombocytopenia, heart valve disease, livedo reticularis and epilepsy. Ige anti-beta(2)-GPI antibodies were associated with the presence of lupus anticoagulant (LA) in addition to the main features of APS. Howev er, antibodies of IgM isotype were related only to thrombocytopenia and hea rt valve disease. We recommend the evaluation of anti-beta(2)-GPI antibodie s of IgA isotype in addition to IgG in patients with clinical suspicion of APS.