Expression of Fas but not Fas ligand on fetal pig β cells

Background: The aim of this study was to determine whether fetal pig insulin-producing cells, a potential source of transplantable tissue for the treatment of type 1 diabetes, are affected by the Fas-FasL interaction, one of the cytotoxic pathways involved in T-cell-mediated autoimmune destruction of pancreatic beta cells. Methods: Expression of Fas/FasL on fetal pig beta cells was assessed by immunohistochemistry, flow cytometry, Western blot, and RT-PCR. Apoptosis of fetal pig beta cells induced by soluble FasL (sFasL) or anti-Fas antibody (APO-1) was detected by flow cytometry using PI. Expression of FLIP on fetal pig pancreatic tissue was detected by immunofluorescent staining and Western blot. Results: Fas was expressed on fetal pig pancreatic cells, both beta and non-beta cells, and the level of expression could be upregulated by exposure to human interleukin-1beta (IL1beta) 2000 pg/ml for 24 h. In contrast, FasL was not detected on fetal pig pancreatic cells but could be induced on both beta and non-beta cells when the cells were treated with IL1beta. Fas persisted on fetal pig beta cells transplanted as islet-like cell clusters into severe combined immunodeficient mice, with expression of this antigen at all times examined, 1 day, 2, 3 and 4 weeks. FasL was absent. Despite the presence of Fas on fetal pig beta cells, addition of sFasL or anti-Fas antibody failed to induce apoptosis of the fetal pig beta cells. In contrast, pig lymphocytes, which express Fas, were destroyed by addition of both sFasL and APO-1. A possible reason for this is the expression on the fetal pig pancreatic cells of FLIP, an inhibitor of Fas-induced apoptosis. Conclusions: Fetal pig beta cells are resistant to Fas-FasL destruction. Our data imply that fetal pig beta cells transplanted into humans with type 1 diabetes may not be destroyed by activated T cells through the Fas-FasL-mediated pathway.