Background There is a large consensus regarding the association with APS clinical features of antiprothrombin antibodies, directed to phosphatidylserine/prothrombin complex.
Objectives As their diagnostic value remain matter to debate we designed a study to evaluate the prevalence of anti-phosphatidylserine/prothrombin (aPS/PT) in primary APS (PAPS) and their association with the conventional aPL.
Methods Plasma and serum samples were collected from 160 PAPS patients (137 females and 23 males, mean age = 44 years ±11.8 SD ranging between 18 and 77) attending Rheumatology Unit of Padua University. IgG/IgM aPS/PT antibodies were detected using commercial ELISA kits, kindly provided by INOVA Diagnostics, Inc. (San Diego, California, USA), following the manufacturer's instructions. IgG/IgM aCL and IgG/IgM antiβ2GPI antibodies were measured using “home-made” ELISA kits. LA was detected according to internationally accepted guidelines.
Results IgG aPS/PT antibodies alone were positive in 12 (7.5%), IgM alone in 41 (25.6%), and both IgG and IgM isotypes in 36 (22.5%) of PAPS patients. IgG aPS/PT antibodies were significantly associated with IgG aCL, IgG antiβ2GPI and LA (OR 11.8, 95% CI 4.7-29.5; OR 6, 95% CI 2.8-12.9 and OR 14.1, 95% CI 6.1-32; respectively). Instead, IgM aPS/PT antibodies were significantly associated only with LA (OR 6.9, 95% CI 3.7-12.9). The mean titres of IgG aPS/PT were significantly higher in IgG aCL positive (aCL+ve) vs IgG aCL negative (aCL-ve) in IgG antiβ2GPI positive (antiβ2GPI+ve) vs IgG antiβ2GPI negative (antiβ2GPI–ve) and in LA positive (LA+ve) vs LA negative (LA-ve) patients (p<0.0001 for all associations). The mean titres of IgM aPS/PT were significantly higher in IgM aCL+ve vs IgM aCL-ve in IgM antiβ2GPI+ve vs IgM antiβ2GPI-ve and in LA+ve vs LA-ve patients (p=0.02, p=0.02 and p<0.0001, respectively). Moreover, there was a significant correlation between IgG aPS/PT levels and IgG aCL, IgG antiβ2GPI levels and the presence of LA (rho=0.42, p<0.0001; rho=0.4, p<0.0001 and rho=0.5, p<0.0001, respectively). While IgM aPS/PT significantly correlate only with the presence of LA (rho=0.44, p<0.0001). We compare the prevalence of IgG and IgM aPS/PT antibodies in the different conventional aPL antibodies profile (triple vs double vs single aPL positivity). IgG aPS/PT is significantly frequent in triple than in double and in triple than in single positivity (OR 11, 95% CI 5.3-22.7; OR 19.9, 95% CI 8.4-47.4; respectively), but not in double vs single positivity. Even, IgM aPS/PT is significantly frequent in triple than in double and in triple than in single positivity (OR 5.8, 95% CI 3.2-10.9; OR 10, 95% CI 5.2-19.2, respectively), but not in double vs single positivity. Moreover, both IgG and IgM aPS/PT antibodies mean titres were significantly higher in triple aPL positivity than in triple aPL negative patients (p<0.0001 for both).
Conclusions As there was no correlation between IgM aPS/PT and IgM aCL and IgM antiβ2GPI, they might be considered a diagnostic tool for PAPS.
Disclosure of Interest : None declared