231. The presence of anti-phosphatidylserine/prothrombin complex antibodies in cutaneous vasculitis: possible involvement in the pathogenesis

Background: We assessed the IgG and IgM prevalence of anti-phosphatidylserine/prothrombin complex (aPS/PT) antibodies (Abs) in patients with vasculitis using a novel commercial ELISA kit. To examine whether aPS/PT Abs were involved in the pathogenesis of cutaneous vasculitis, inbred wild-type rats were intravenously administered with a rat IgM class aPS/PT monoclonal Ab established previously or with rat immunoglobulins as controls. Then, the development of cutaneous vasculitis was determined by histopathological analyses. Methods: 1) Rats (n=4) were given a subcutaneous injection of 0, 2.5, 25, and 250 µg/ml cell-free histones on the back (300 µl/site). Two hours later, the skin was resected for immunostaining using a rat IgM class aPS/PT monoclonal Ab. Formalin-fixed, paraffin-embedded skin tissues were cut into 4 µm sections, and the sections were allowed to react with 1 µg/ml aPS/PT monoclonal Ab (rat IgM) followed by 2 µg/ml Alexa Fluor 594-conjugated goat anti-rat IgM Ab. 2) Rats (n=19) were given a subcutaneous injection of 250 µg/ml cell-free histones and then divided into four groups: Group A with an intravenous administration of 1.25 µg/g weight of the rat IgM class aPS/PT monoclonal Ab 2 hours after priming by histones (n=5; histone isc with aPS/PT iv), Group B with rat IgM (n=4; histone isc with IgM iv), Group C with rat IgG (n=5; histone isc with IgG iv), and Group D without immunoglobulin administration (n=5; histone isc). One week later, all rats were euthanized for histopathological analyses. Results: Serum IgM aPS/PT Ab levels were elevated in patients with systemic vasculitis with skin involvement and cutaneous arteritis compared to those in patients with systemic vasculitis without skin involvement and healthy controls. To express PS on the surface of vascular endothelium, these rats were given a subcutaneous injection of cell-free histones in advance. There was no significant difference in the serum levels of IgG aPS/PT Abs between the patients and healthy controls. Correspondingly, inbred ...