Detection of serum β2-GPI–Lp(a) complexes in patients with systemic lupus erythematosus

BackgroundCirculating β2-glycoprotein-I-oxidized low-density lipoprotein (β2-GPI–ox-LDL) complexes have been found in patients with systemic lupus erythematosus (SLE) and other autoimmune diseases as a contributor to the development of autoimmune-mediated atherosclerosis. In vitro study showed that β2-GPI also bound with high affinity to atherogenic lipoprotein (a) [Lp(a)] which shares structural similarity to LDL. We examined the existence and clinical significance of serum complexes of β2-GPI with Lp(a) in SLE patients.MethodsA “sandwich” ELISA was developed for measuring serum concentrations of β2-GPI–Lp(a) complexes, using rabbit anti-human β2-GPI antibody as capturing antibody, and quantitating with antibody against apo(a). Forty-seven SLE patients and 42 healthy controls were studied.ResultsBoth Lp(a) (400 ± 213 mg/l vs. 181 ± 70 mg/l) and ox-Lp(a) (27.07 ± 22.30 mg/l vs. 8.20 ± 4.55 mg/l) concentrations were higher in SLE patients than in controls (P < 0.0001). β2-GPI–Lp(a) complexes were detectable in both controls and SLE. The complexes levels in SLE were higher than in controls (0.96 ± 0.41 U/ml vs. 0.59 ± 0.20 U/ml, P < 0.0001) and was positively correlated with ox-Lp(a) (P < 0.001).ConclusionsWe report the existence of β2-GPI–Lp(a) complexes in both controls and SLE patients. The complexes levels increase in SLE.