Summary
We have investigated the effect of purified immunoglobulin G (IgG) on endothelial
cell functions in 16 patients with lupus anticoagulant, 9 of whom had systemic lupus
erythematosus (SLE). Spontaneous or thrombin-stimulated secretion of prostacyclin
(PGI2) by cultured human endothelial cells from umbilical cord vein (HUVEC) was not inhibited
by the patient’s IgG. Nor was spontaneous release of tissue plasminogen activator
(t-PA) or of its inhibitor (PAI) modified in the presence of patient’s IgG.
The rate of activation of purified protein C (PC) by HUVEC in the presence of thrombin
was significantly lowered by patient’s IgG or Fab’ fragment (inhibition of 43%). Neutralization
of this effect was obtained by incubation of a greater quantity of phospholipids (phosphatidylcholine,
phosphatidylserine) with the patient’s IgG. Activation of PC was also performed using
purified rabbit thrombomodulin (TM) and a similar inhibition of the patient IgG was
observed (inhibition of 48%) but the activation of Gla-domainless PC was not modified.
Key words
Lupus anticoagulant - Endothelial cells - Protein C - Thrombomodulin - Prostacyclin
