Relationship between anti-phospholipid and anti-endothelial cell antibodies: Further characterization of the reactivity on resting and cytokine-activated endothelial cells

Sera positive for autoimmune anti-phospholipid antibodies were studied by a cell surface radioimmunoassay for their cross-reactivity with resting or activated human endothelial cells. The endothelial cell activation by interleukin 1β, gamma-interferon, lipopolysaccharide or phorbol-12 myristate-13 acetate did not affect the cross-reactivity. Comparable findings were also found by testing anti-cardiolopin affinity purified preparations. Taken together these data indicate that endothelial cell activation is not sufficient per se to modulate the expression of antigenic determinants recognizable by the anti-phospholipid antibodies. However, anti-cardiolipin affinity purified preparations displayed enhanced cell binding after cell membrane perturbation by paraformaldehyde fixation, suggesting that an alteration in endothelial cell integrity might further trigger the reaction of circulating anti-phospholipid antibodies with vessel walls in vivo.