EXPRESSION AND FUNCTION OF FAS ON CELLS DAMAGED BY GAMMA-IRRADIATION IN B6 AND B6 LPR MICE/

Fas (CD95) is a cell surface protein that mediates apoptosis, lpr is a mutation of the Fas gene caused by a retroviral insertion resulting i n premature termination of transcription and aberrant splicing of Fas mRNA, Mice homozygous for the lpr gene develop lymphoproliferation and produce autoantibodies closely resembling those of human systemic lup us erythematosus, While lpr mice have been reported to express low lev els of normally spliced Pas mRNA, it is unknown whether they express f unctional Pas protein, Here we show that splenocytes from lpr mice tha t have been damaged by gamma-irradiation expressed Pas protein, Pas wa s upregulated on irradiated B6 cells and could be detected on B6/lpr c ells undergoing apoptosis following in vitro culture. Detection of Pas on live lpr cells was demonstrable when apoptosis was blocked by zinc . In a short term chimera system, Pas was shown to play a role, in viv o, in the disposition of radiation-injured cells from both normal and lpr mice. The addition of anti-Pas Ab to in vitro cultures resulted in an increase in apoptosis in both B6 and B6/lpr cells, Detection of in tact Pas message and low levels of Pas protein in Ipi mice has led to the consideration of lpr as a leaky mutation. This study demonstrates that lpr mice can produce functional Pas protein. This system is also appropriate for identifying the in vivo role of Fas/FasL in apoptosis following other cell manipulations.