The concomitant presence of lupus anticoagulant, anticardiolipin and anti-beta2-glycoprotein i antibodies could be associated with acquired activated protein c resistance in non-systemic lupus erythematosus patients.

Abstract

Nojima et al (2002) recently reported the co-existence of lupus anticoagulant (LA) and anti-prothrombin antibodies as a risk factor for the prevalence of acquired activated protein C resistance (APCR) in systemic lupus erythematosus (SLE) patients, which was furthermore associated with venous thromboembolism. The acquired APCR phenotype occurs in the absence of the factor V (FV) Leiden mutation and has been described among patients with antiphospholipid antibodies (APA). There is no clear information about which antibodies are involved in this phenotype. However, an in vitro effect of the anti-β2-glycoprotein I (αβ2GPI) antibodies on the response to activated protein C (APC) has been described (Matsuda et al, 1995; Martinuzzo et al, 1996; Galli et al, 1998). The in vivo effect of the APA is less evident. The acquired APCR phenotype has been associated with LA but not with anticardiolipin antibodies (ACA) in children with SLE (Male et al, 2001). Our preliminary data in non-SLE patients with LA activity suggest, as stated by Nojima et al (2002) for SLE patients, that the sole presence of LA may not be enough to account for the acquired APCR. This is in agreement with the results of Martinuzzo et al (1996), showing that a low response to APC seemed to be directly associated with αβ2GPI and/or ACA, irrespective of the presence of another APA, like LA. We evaluated whether the presence of ACA immunoglobulin (Ig)G and αβ2GPI IgG was associated with acquired APCR in 24 LA patients with primary antiphospholipid syndrome and the following clinical features: venous (n = 12) or arterial (n = 6) thrombosis and fetal wastage (n = 6). LA was detected in the patients' plasma by the dilute Russell's viper venom time (Sigma) and the activated partial thromboplastin time (aPTT) (PTT-LA; Diagnostica Stago), in addition with mixing studies and neutralization procedures, according to criteria of the Scientific and Standards Committees of the International Society on Thrombosis and Haemostasis. An enzyme-linked immunosorbent assay was performed for the detection of ACA IgG (the binding site) and αβ2GPI IgG (Varelisa; Elias). Patients were divided into ACA+/αβ2GPI+ and ACA–/αβ2GPI– groups. The APCR was evaluated using aPTT-based assays: the original (APCRoriginal; Coatest APC resistance-S; Chromogenix) and the modified (APCRmodified; Coatest APC resistance-V; Chromogenix) tests were performed in order to detect the acquired APCR. The resistance related to FV Leiden or another genetic cause involving FV could affect both systems, unlike the acquired APCR that mainly affects the original test (Gennari et al, 2000). All (10/10) ACA+/αβ2GPI+ samples showed abnormal APCRoriginal results, displaying a mean ratio significantly lower than the ACA–/αβ2GPI– group (Table I). A similar pattern, but to a lesser extent, was observed with the APCRmodified technique. In five out of 10 samples, the effect on the APC response could not be diluted out (Table I), suggesting that these antibodies may be so ‘powerful’ that even the dilution in FV-depleted plasma could not normalize the phenotype. Moreover, an effect of either αβ2GPI or ACA on the protein C pathway could be suspected, as an inverse correlation between the APCRoriginal ratio and the antibody titres (rSpearmanαβ2GPI = −0·87; P < 0·0001; rSpearman ACA = −0·88; P = 0·0003) was found. Nojima et al (2002) showed that the co-existence of anti-prothrombin and LA was the most significant risk factor for the prevalence of acquired APCR, but the association of αβ2GPI and LA also appeared to be a significant risk factor. Anti-prothrombin antibodies were not tested in our samples; however, the co-existence of LA with αβ2GPI and ACA in non-SLE patients seemed to be associated with the acquired APCR phenomenon. In addition to the previous reports, our results suggest that, irrespective of the underlying disease, the presence of different APA may be necessary for the appearance of the acquired APCR phenomenon.