Activated protein C resistance in patients with anti-beta 2 glycoprotein I antibodies

To evaluate if the presence of anti-beta 2GPI antibodies (a beta 2GPI) is associated with activated protein C resistance (APC-R) phenotype, we performed the APC-R APTT-based assay in 74 plasma samples from patients with antiphospholipid antibodies (aPL). Samples were diluted 1:5 in factor V-deficient plasma. Lupus anticoagulant (LA), anticardiolipin antibodies (aCL) and a beta 2GPI (IgG and IgM) were also performed. A control group of 22 healthy volunteers was used. The prevalence of reduced APC-R ratio in patients with aPL was significantly higher than in normal controls (31.1 vs 4.5%, P < 0.05) and the mean APC-R ratio was lower (mean +/- SD; 2.32 +/- 0.40 vs 2.55 +/- 0.21, P < 0.02). There were no differences in the prevalence of APC-R and the ratio values between LA(+) and LA(-). Among the LA(+), the aCL(+) had a higher prevalence of APC-R than the aCL(-) (P < 0.01) and lower APC-R ratios (P < 0.01). The latter group was no different to normal controls. Anti-beta 2GPI antibodies were associated with a higher prevalence of APC-R (50.0 vs 19.6%, P < 0.001), and lower APC-R ratios (2.15 +/- 0.41 vs 2.42 +/- 0.35, P < 0.005), compared with a beta 2GPI(-). In conclusion, the acquired APC-R in patients with aPL seems to be associated with aCL and a beta 2GPI rather than an in vitro interference by LA.