In vitro studies of antiphospholipid antibodies and its cofactor, β2-glycoprotein I, show negligible effects on endothelial cell mediated protein C activation - Oosting, J D; Derksen, R HWM; Hackeng, T M; van Vliet, M; Preissner, K T; Bouma, B N; de Groot, P G (Thromb Haemost, 1991)