β2 glycoprotein I containing immune-complexes in lupus patients: association with thrombocytopenia and lipoprotein (a) levels

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Abstract
In this study we determined the prevalence and clinical associations of immune-complexescontaining beta-2-glycoprotein I (b2GPI) in randomly selected SLE patients. We studied 38 consecutive SLE patients attending the Rheumatology Unit. Previous arterial or venous-thrombosis were documented by the appropriate diagnostic test. Lipid profile including total cholesterol, LDL, VLDL, HDL and Lp(a) levels were determined from the sera of the fasting patients. Antibodies to cardiolipin, oxidized LDL and b2GPI were detected employing ELISA. b2GPI containing IgG immune-complexes were assayed by using a dot-blot assay. Fourteen SLE patients (36.8%) were found to be positive for the presence of IgG anti-b2GPI antibodies. Ten of the SLE patients (26.3%) were found to have high levels of b2GPI containing immune-complexes. There was a positive correlation between b2GPI-IC levels and the occurrence of thrombocytopenia in the patients (P < 0.05). Furthermore, patients with SLE and venous thrombosis had higher levels of b2GPI-IC when compared with thrombosis-free patients or with healthy controls (P < 0.05). Patients with higher Lp(a) levels (> 50 mg/dl) possessed higher levels of b2GPI-IC as compared with patients with lower Lp(a) concentration (< 20 mg/dl) (P < 0.05). These results suggest that IC-containing b2GPI can help in defining a subpopulation of SLE patients with increased risk of thrombocytopenia and further aid in resolving mechanisms of immune-mediated tissue damage.