INCREASED EXPRESSION OF INDUCIBLE CYCLOOXYGENASE-2 IN HUMAN ENDOTHELIAL-CELLS BY ANTIPHOSPHOLIPID ANTIBODIES

The effect of IgGs from 4 patients with antiphospholipid antibodies an d elevated excretion of urinary 11-dehydro-thromboxane B-2 was evaluat ed on the production of prostacyclin by human endothelial cells in cul ture. After 6 h incubation, there was no change in 6-keto-prostaglandi n F-1 alpha in the supernatant. However patients' IgGs induced a marke d increase in cyclooxygenase (Cox) activity compared to IgGs from 2 no rmal individuals or a commercial pool of IgGs from normal donors, test ed by adding exogenous arachidonic acid. Western blot analysis of the cellular Cox content using antibodies specific for the different forms of the enzymes revealed that patients' IgGs stimulated the synthesis of the newly described inducible Cox-2 without affecting the constitut ive Cox-1. This effect was partially neutralized by preincubating the IgGs with phospholipids. The induction was dependent on the amount of IgGs; it was visible at 2 h and persisted up to 24 h. Analysis of mRNA levels showed a pattern of variation in good agreement with the resul ts obtained for protein. The protein kinase inhibitor H-7 or long-term incubation of cells with PMA strongly reduced the induction. These re sults suggest that antiphospholipid antibodies may not prevent the pot ential of the vascular cells from generating higher amounts of prostac yclin in response to acute episodes of thrombosis.