BACKGROUND: β2-Glycoprotein I (β2GPI) represents the major antigenic target for antiphospholipid antibodies (aPL), with domain 1 (D1) being identified as a risk factor for thrombosis and pregnancy complications in APS. We aimed to analyse the ability of aPL, and particularly anti-D1 β2GPI, to stimulate prothrombotic and proinflammatory activity of immune cells in vitro. METHODS: Peripheral blood mononuclear cells (PBMCs) from 11 healthy individuals were incubated with: (1) "anti-D1(+)"-pooled plasma derived from patients suspected of having APS contained anticardiolipin antibodies (aCL), lupus anticoagulant (LA), anti-β2GPI and anti-D1 β2GPI; (2) "anti-D1(-)"-pooled plasma from patients suspected of having APS contained aCL, LA, anti-β2GPI, and negative for anti-D1 β2GPI; (3) "seronegative"-negative for aPL. RESULTS: The presence of anti-D1(+) and anti-D1(-) plasma resulted in increased HLA-DR and CD11b on monocytes. While only anti-D1(+) plasma markedly increased the percentage and median fluorescence intensity (MFI) of CD142 (tissue factor, TF) on monocytes in comparison with those cultured with anti-D1(-) and seronegative plasma. Anti-D1(+) plasma resulted in increased percentage and MFI of activation marker CD69 on NK and T cytotoxic cells. Expression of IgG receptor FcγRIII(CD16) on monocytes and NK cells was down-regulated by the anti-D1(+) plasma. CONCLUSIONS: Taking together, our study shows the ability of patient-derived aPL to induce immune cell activation and TF expression on monocytes. For the first time, we demonstrated the influence of anti-D1 β2GPI on the activation status of monocytes, NK and cytotoxic T cells. Our findings further support a crucial role of D1 epitope in the promotion of thrombosis and obstetrical complications in APS.

Department of Hemato oncology Faculty of Medicine and Dentistry Palacky University Olomouc and Faculty Hospital Olomouc Czech Republic

Department of Immunology Faculty of Medicine and Dentistry Palacky University Olomouc and Faculty Hospital Olomouc Czech Republic

Laboratory of Molecular and Cellular Immunology Institute of Molecular Biology NAS RA 7 Hasratyan St 0014 Yerevan Armenia

Laboratory of Molecular and Cellular Immunology Institute of Molecular Biology NAS RA 7 Hasratyan St 0014 Yerevan Armenia Department of Immunology Faculty of Medicine and Dentistry Palacky University Olomouc and Faculty Hospital Olomouc Czech Republic

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