FAS (CD95,APO-1) ANTIGEN EXPRESSION AND FUNCTION IN MURINE MAST-CELLS

As an extension of the observation that mast cells undergo apoptosis f ollowing growth factor deprivation, we hypothesized that mast cells mi ght also undergo apoptosis in response to activation through Fas Ag (C D95, APO-1), thus providing arm additional pathway that could contribu te to the regulation of mast cell numbers, Surface expression of Fas A g was studied by flow cytometry, and apoptotic changes following treat ment with anti-fas mAb were analyzed using flow cytometric analysis of PI uptake and TUNEL staining, DNA electrophoresis, and electron micro scopy. Murine bone marrow-cultured mast cells (BMCMC) and peritoneal m ast cells, as well as two mast cell lines (C57 and MCP-5), constitutiv ely expressed Fas Ag. Aggregation of Fas ag with anti-Fas mAb resulted in the characteristic changes of apoptosis in C57 mast cells, BMCMC w ere resistant to anti-fas mAk, alone, but after the addition of actino mycin D also exhibited apoptosis in response to anti-Fas treatment. In addition, actinomycin D alone induced apoptosis. Stent cell factor, T GF-beta, and Fc epsilon RI aggregation enhanced Fas expression, Howeve r, Fas-mediated apoptosis was not augmented by Fc epsilon RI aggregati on, and stem cell factor and TGF-beta partially protected BMCMC agains t Fas-mediated cytotoxicity, Finally, C57 mast cells were highly susce ptible tea killing by a Fas ligand-bearing CTL hybridoma, white BMCMC were relatively resistant, consistent with the results using anti-Fas mAb. Thus, induction of mast cell apoptosis by activation of the Fas p athway provides an additional mechanism by which mast cell numbers may be regulated in biologic systems.