Anti-beta 2-glycoprotein I antibody isotype and IgG subclass in antiphospholipid syndrome patients

Beta 2-glycoprotein I (beta 2-GPI) is an antigenic target recognised by ant iphospholipid antibodies found in association with the antiphospholipid syn drome (APS). In this study, the prevalence of Immunoglobulin M (IgM) and Ig A anti-beta 2-GPT antibodies was examined in APS patients and compared with Ige antibodies. In addition the value of measuring antibody isotypes and I gG subclass was investigated in the laboratory diagnosis of APS. A solid ph ase enzyme linked immunosorbent assay was established to measure IgG, IgM a nd IgA and IgG subclass antibodies to beta 2-GPI in patients with APS and a variety of other thrombotic and non-thrombotic disorders. Raised levels of IgM anti-beta 2-GPI antibodies were observed in 65% of patients with APS, 21% with systemic lupus erythematosus (SLE), 23% with rheumatoid factor, 4% with stroke, 5% carotid artery stenosis (CAS), 17% with a biological false positive serology for syphilis, 43% with infectious mononucleosis (IM) and 27% with human immunodeficiency virus (HIV). The median value for IgM anti bodies to beta 2-GPI for all these groups ranged from 2 to 7 arbitrary unit s (AU). Elevated levels of IgA antibodies to beta 2-GPI were found in patie nts with APS (47%), SLE (13%), rheumatoid factor (26%), CAS (48%), stroke ( 25%), VDRL false positive serology for syphilis (33%), IM (47%) and HIV (7% ). The median value of IgA antibodies to beta 2-GPI in all of these groups ranged from 2 to 4 AU. Conversely the median value for IgG anti-beta 2-GPI in APS patients was 112 AU compared to 1-4AU in the other conditions examin ed. The presence of IgM and IgA antibodies to beta 2-GPI was much less spec ific and sensitive for APS than IgG, with raised levels of these isotypes s een in a variety of thrombotic and non-thrombotic disorders. Elevated level s of IgG1, 1gG2, IgG3 and IgG4 antibodies to beta 2-GPI were detected in AP S patients. While all four IgG anti-beta(2)-GPI antibody subclasses were re presented in APS patients there appeared to be a significant overall skewin g towards to the IgG2 subclass.