Patients with antiphospholipid syndrome (APS) have a hypercoagulable condition associated with the presence of antiphospholipid autoantibodies (aPL). Consensus antibodies for diagnosis are lupus anticoagulant, anti-beta2 glycoprotein I (B2GPI) and anticardiolipin (IgG or IgM). Circulating immunocomplexes (CIC) of B2GPI associated with IgM or IgG were reported. Isolated IgA aB2GPI antibodies have achieved high diagnostic value although specific CIC of B2GPI bounded to IgA (B2A-CIC) has still not been described. CIC detection assays are mainly based on interaction with complement and are not appropriate to detect B2A-CIC because IgA does not fix complement using the classical pathway.
Sera from healthy blood donors (N= 247) and from patients with thrombosis background and isolate positive for IgA aB2GPI (N = 68) were studied in a case-control study. Two methods were applied, these being a capture ELISA to quantify specific B2A-CIC and quantification of total IgA anti-B2GPI after dissociating CIC.
B2A-CIC values in APS-patients were 19.27 ± 2.6 AU vs 6.1 ± 0.4 AU in blood donors (p < 0.001). There were 36.4% B2A-CIC positive patients (cutoff 21 AU) versus 5.5% in blood donors (p < 0.001). Dissociated IgA aB2GPI levels (total IgA aB2GPI) were 146.8 ± 10.8 IU/mL in patients vs. 22.4 IU/mL in controls (p < 0.001). B2A-CIC was independent of B2GPI and autoantibodies IgA aB2GPI serum levels.
B2A-CIC can be identified and quantified in an easy and reproducible manner using two complement-independent methods. The use of these tests in prospective studies will allow better understanding of the prognosis and outcome of patients.