Date: Sunday, October 21, 2018
Session Title: 3S079 ACR Abstract: Antiphospholipid Syndrome (851–856)
Session Type: ACR Concurrent Abstract Session
Session Time: 2:30PM-4:00PM
Background/Purpose: Antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity and the presence of antiphospholipid antibodies (aPL). Phosphatidylserine-dependent antiprothrombin antibodies (aPS/PT) recognize the phosphatidylserine/prothrombin (PS/PT) complex, and are highly associated with APS. Recently, it has been reported that misfolded beta2-glycoprotein I (beta2-GPI) are transported to the cell surface by human leukocyte antigen (HLA) class II molecules and are targeted by autoantibodies in patients with APS [1, 2]. APS patients with anti-beta2-GPI are highly likely to share the thrombophilic pathophysiology with those with aPS/PT, therefore we hypothesized that misfolded prothrombin (PT), likewise beta2-GPI, are transported to the cell surface by HLA class II molecules in procoagulant cells, consequently being targeted by aPS/PT.
Methods: 1) The interaction of PT with HLA-DR was analyzed by flow cytometry (FCM) using PT / HLA-DR overexpressed HEK293T cells. 2) PT synthesis from monocyte was investigated in phorbol-12-myristate-13-acetate (PMA) treated THP-1 cells by western blotting (WB) and FCM. 3) Cell surface transportation of synthesized PT with HLA-DR was evaluated by FCM in PMA-treated THP-1 cells.
Results: 1) PT protein in the presence of transcripted HLA-DR was detected on the cell surface and PT/HLA-DR complex was recognized by a mouse monoclonal aPS/PT (231D). 2) PMA treated THP-1 cells synthetized PT which showed stronger binding to 231D than to control monoclonal anti-PT antibody, the latter recognizes PT in the absence of phosphatidylserine (Fig). 3) 231D binding to PT/HLA-DR complex was confirmed in THP-1 cells co-stimulated with PMA and interferon gamma. No binding was observed between control monoclonal anti-PT antibody and PT/HLA-DR complex.
Conclusion: Structurally altered PT is transported to the cell surface by HLA class II molecules in monocyte after PMA stimulation, indicating that PT/HLA-DR complexes may be targets for aPS/PT.
References:  Tanimura K, et al. Beta2-Glycoprotein I/HLA class II complexes are novel autoantigens in antiphospholipid syndrome. Blood 2015.  Arase N, et al. Novel autoantibody against the beta2-glycoprotein I/human leucocyte antigen-DR complex in patients with refractory cutaneous ulcers. Br J Dermatol 2018
Figure. Prothrombin expression in PMA treated THP-1 cells
To cite this abstract in AMA style:Ohnishi N, Fujieda Y, Hisada R, Nakamura H, Kato M, Oku K, Bohgaki T, Amengual O, Yasuda S, Arase H, Atsumi T. Antigenic Property of Prothrombin/HLA-DR Complex on Procoagulant Cells in Patients with Antiphospholipid Syndrome [abstract]. Arthritis Rheumatol. 2018; 70 (suppl 10). https://acrabstracts.org/abstract/antigenic-property-of-prothrombin-hla-dr-complex-on-procoagulant-cells-in-patients-with-antiphospholipid-syndrome/. Accessed January 21, 2020.
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