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

Abstract

Objective: The Fas/Fas ligand (FasL) system has been assigned a pivotal role in the establishment and maintenance of peripheral tolerance, and mice having defects in the Fas/FasL system are known to develop lupus-like symptoms. However, it remains unclear whether the Fas/FasL system is involved in the pathogenesis of systemic lupus erythematosus (SLE) 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 autoantibodies were detected by Western blot analysis using the recombinant extracellular domain of human FasL as the antigen. Apoptosis of Fas-expressing Jurkat cells, induced by recombinant soluble FasL (sFasL) in the presence of anti-FasL autoantibodies, was assessed by DNA staining with propidium iodide, followed by flow cytometric analysis. Apoptosis of Jurkat cells by cell-bound FasL was assessed by 2-color analysis, involving TUNEL staining with fluorescein isothiocyanate-dUTP and 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 inhibited both sFasL-mediated and cell-bound FasL-mediated apoptosis of Fas-expressing Jurkat cells. Thus, it is plausible that anti-FasL autoantibodies in patients with SLE disturb the establishment and maintenance of peripheral tolerance in vivo by inhibiting the Fas/FasL-mediated elimination of autoreactive lymphocytes.

Conclusion: These results suggest that anti-FasL autoantibodies that inhibit Fas/FasL-mediated apoptosis are involved, at least in part, in immune abnormalities and may possibly be involved in the pathogenesis of SLE.