INHIBITION OF FAS FAS LIGAND-MEDIATED APOPTOTIC CELL-DEATH OF LYMPHOCYTES IN-VITRO BY CIRCULATING ANTI-FAS LIGAND AUTOANTIBODIES IN PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS/

Objective. The Fas/Fas ligand (FasL) system has been assigned a pivota l role in the establishment and maintenance of peripheral tolerance, a nd mice having defects in the Fas/FasL system are known to develop lup us-like symptoms. However, it remains unclear whether the Fas/FasL sys tem is involved in the pathogenesis of systemic lupus erythematosus (S LE) in humans. This study examined whether there are circulating anti- FasL autoantibodies in the peripheral blood of patients with SLE that would interfere with Fas/FasL-mediated apoptosis. Methods. Anti-FasL a utoantibodies were detected by Western blot analysis using the recombi nant extracellular domain of human FasL as the antigen. Apoptosis of F as-expressing Jurkat cells, induced by recombinant soluble FasL (sFasL ) in the presence of anti-FasL autoantibodies, was assessed by DNA sta ining with propidium iodide, followed by flow cytometric analysis. Apo ptosis of Jurkat cells by cell-bound FasL was assessed by 2-color anal ysis, involving TUNEL staining with fluorescein isothiocyanate-dUTP an d phycoerythrin-labeled anti-CD3 monoclonal antibodies. Results. Among the 21 patients with SLE, 7 had IgG-isotype anti-FasL autoantibodies in their circulating blood. In addition, these autoantibodies inhibite d both sFasL-mediated and cell-bound FasL-mediated apoptosis of Fas-ex pressing Jurkat cells. Thus, it is plausible that anti-FasL autoantibo dies in patients with SLE disturb the establishment and maintenance of peripheral tolerance in vivo by inhibiting the Fas/FasL-mediated elim ination of autoreactive lymphocytes. Conclusion. These results suggest that anti-FasL autoantibodies that inhibit Fas/FasL-mediated apoptosi s are involved, at least in part, in immune abnormalities and may poss ibly be involved in the pathogenesis of SLE.