Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.

Platelet Activation and Paradoxical Inhibition of ADP Induced Aggregation by Antiphospholipid Antibodies.

Oku4,  Kenji, Atsumi2,  Tatsuya, Amengual3,  Olga, Ieko1,  Masahiro, Furukawa6,  Shin, Kitakawa6,  Hirohiko, Hori6,  Yuji

Health Sciences University of Hokkaido
Hokkaido University Graduate School of Medicine Internal Medicine II, Sapporo, Japan
Hokkaido University Graduate School of Medicine Internal Medicine II
Hokkaido University Graduate School of Medicine Internal Medicine II, Kushiro Red Cross Hospital, Japan
Hokkaido UniversityGraduate School of Medicine Internal Medicine II
Kushiro Red Cross Hospital


Autoantibodies against beta2-glycoprotein I (b2GPI) and those against prothrombin are two major populations of antibodies found in patients with antiphospholipid syndrome (APS). The platelet activation and aggregation are crucial procedures in the development of arterial thrombosis. There are some reports suggesting a link between platelet activation and anti-b2GPI antibodies, but only little data are available regarding antiprothrombin antibodies and platelets. We previously showed that presence of IgG phosphatidylserine-dependent antiprothrombin antibodies (aPS/PT) was a strong risk of having arterial thrombosis in our cohort of 500 patients with autoimmune diseases, and that monoclonal aPS/PT affected ADP induced platelet aggregation in vitro (abstract 1594, ACR 2009).

In this study, we investigated further the in vitro behaviour of platelet exposed by aPS/PT and anti-b2GPI antibodies. Additionally, we quantitatively-analyzed CD62P, a surface marker of activated platelets and thromboxane B2(TXB2), a member of eicosanoid family molecules produced by activated platelets.


A monoclonal aPS/PT, 231D, that shared the properties with autoimmune aPS/PT, a human monoclonal anti-b2GPI antibody, EY2C9, and purified IgG from APS patients' sera were used for the following experiments. Normal platelets were treated with monoclonal antibodies or purified IgG. Conventional ADP or collagen induced platelet aggregation assay by turbidimetric method were performed using platelet riched plasma (PRP) spiked with monoclonal antibodies or purified IgG. To explore, in this system, the involvement of P2Y12, one of the ADP receptors on platelet controlling the secondary aggregation, we evaluated the activation of vasodilator stimulated phosphoprotein (VASP), using a standard assay. VASP represents P2Y12 inhibition as the intra-molecular signal protein. Positive ratio of CD62P was detected by two-colored flow-cytometry. TXB2 was quantitatively-analyzed by Enzyme-Linked ImmunoSorbent Assay (ELISA.).


ADP induced secondary platelet aggregation was significantly inhibited in 231D, EY2C9, and purified IgG affected PRP, whereas collagen induced platelet aggregation was not affected by any of the antibodies. VASP activities were significantly increased in 231D and EY2C9 treated platelets (p<0.01).

Both positive rates of CD62P and TXB2 levels were significantly raised on platelets treated with 231D or EY2C9 in the presence of their antigen.


The effects of monoclonal aPS/PT on platelets were similar to those of monoclonal anti-b2GPI antibodies and IgG fractions of APS patients' sera. Antiphospholipid antibodies activated platelets shown by CD62P expression and TXB2 production. Paradoxical inhibition of ADP induced platelet aggregation by antiphospholipid antibodies might be correlated with P2Y12 signal suppression. Those observations suggest that the platelet involvements with aPS/PT and anti-b2GPI are paradoxical and complex, leading to the heterogeneous clinical features of patients with APS.

To cite this abstract, please use the following information:
Oku, Kenji, Atsumi, Tatsuya, Amengual, Olga, Ieko, Masahiro, Furukawa, Shin, Kitakawa, Hirohiko, et al; Platelet Activation and Paradoxical Inhibition of ADP Induced Aggregation by Antiphospholipid Antibodies. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :10
DOI: 10.1002/art.27780

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