Anti-phosphatidylserine/prothrombin antibodies: An additional diagnostic marker for APS?

Francesca Pregnolato, Cecilia B. Chighizola, Susan Encabo, Zakera Shums, Gary L. Norman, Armando Tripodi, Veena Chantarangkul, Tiziana Bertero, Valeria De Micheli, Maria Orietta Borghi, Pier Luigi Meroni

Research output: Contribution to journalArticlepeer-review


Among the diagnostic assays for anti-phospholipid syndrome (APS), lupus anticoagulant (LA) is the strongest predictor of thrombosis; however, it presents several limitations as interference with anticoagulant therapy and poor inter-laboratory agreement. Two-thirds of LA activity is apparently due to antibodies against prothrombin (PT), usually detectable by ELISA. Binding of PT to phosphatidylserine (PS) has been shown to enhance solid-phase anti-PT assay sensitivity. To determine the prevalence of antibodies against PS/PT (aPS/PT) in APS, we tested the semiquantitative QUANTA Lite® aPS/PT ELISA in a cohort of 80 APS patients. The prevalence of aPS/PT was 81.3 %, rising to 87.6 % when considering LA-positive subjects only. We observed a strong correlation between aPS/PT and LA (p = 0.006). To note, APS patients with thrombotic manifestations displayed significantly higher IgG aPS/PT titers compared to 20 aPL asymptomatic carriers (p = 0.012). To rule out a possible cross-reactivity of anti-β2 glycoprotein I antibodies (aβ2GPI) with PS/PT complex, we tested two monoclonal aβ2GPI antibodies and an affinity-purified (AP) polyclonal aβ2GPI IgG obtained from the serum of a patient reacting against both β2GPI and PS/PT. The two monoclonal antibodies did not show any reactivity against PS/PT complex, similarly the AP IgGs did not react toward PS/PT antigen while preserved their aβ2GPI activity. Our findings suggest that aPS/PT are a definite antibody population in APS. Moreover, the good correlation between aPS/PT ELISA and LA may support its use as a surrogate test for LA, particularly useful to overcome the technical limitations of the functional assay.

Original languageEnglish
Pages (from-to)432-438
Number of pages7
JournalImmunologic Research
Issue number2-3
Publication statusPublished - Jul 2013


  • Anti-phosphatidylserine/prothrombin antibodies
  • Anti-phospholipid antibodies
  • Anti-phospholipid antibody syndrome
  • Lupus anticoagulant

ASJC Scopus subject areas

  • Immunology


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