Anti-endothelial cell antibodies to the endothelial hybridoma cell line (EAhy926) in systemic lupus erythematosus patients with antiphospholipid antibodies

The endothelial hybridoma (EAhy926) cell line was employed to clarify whether antiphospholipid antibodies (aPA) lupus anticoagulant (LA), antiprothrombin antibody (aPT) and/or anticardiolipin antibody (aCL)] and anti-endothelial cell antibodies (AECA) are identical, and establish whether β₂-glycoprotein I (β₂-GPI) is needed for reactivity of aPA to endothelial cells. Ig-G AECA was positive in 9/30 SLE patients with aPA (30.0%) and 10/22 SLE patients negative for aPA (45.5%). Ig-M AECA was positive in one SLE patient with aPA and one SLE patient without aPA. AECA-positivity was not significantly different among unfixed, TNF-stimulated and fixed EAhy926. The influence of β₂-GPI on the reactivity of serum to EAhy926 was minimal, and absorption experiments of serum with cardiolipin-liposome/β₂-GPI or phosphatidylserine-liposome/prothrombin gave little evidence of cross-reactivity of aPA and AECA. The results of our study suggest that aPA and AECA may have partially cross-reacted, but were different antibodies. However, further study is needed to clarify the clinico-pathological significance of AECA.