Autoimmune and other diseases frequently manifest a sexual disparity that is often attributed to hormonal differences. This explanation does not account for the difference in frequency rather than severity between the sexes; nor does it explain the frequent failure of hormonal countervention to alleviate a problem. We propose that inherent biological differences between otherwise identical male and female cells can be a source of the disparity. Such a possibility has been studied only minimally. We have found in initial studies, which are consistent with the few publications available, that there is a marked difference between male and female cells in their responses to cell death inducing stimuli. We will analyze this possibility by collecting cells from several tissues (liver, brain, thymus, heart) of embryonic mice, sexing the embryos and noting both their position in the uterus and the sex of their neighbors. We will culture these cells in primary culture and challenge them with a range of cell death inducing stimuli, including commonly used laboratory challenges such as H2O2 and ethanol, physiological challenges such as TNF-alpha, Fas and Fas ligand, and glucocorticoids, and medically relevant chemotherapeutic agents. We will assess the dose- and time-dependent sensitivity of the male and female cells to these several challenges. This assessment will include direct observation of the viability of the cells as well as analysis of which aspects of cell death respond differentially: activation of ceramide 2nd messenger signaling, caspase and lysosome activity, and degradation of chromatin and DNA. Starting with the eatliest embroyos that we can sex, we will extend the studies to include later embryos, newborns, juveniles, and pubertal animals, to determine whether the in vivo differences can be accounted for by initial genetic differences or whether they arise only after exposure to sex hormones. In these experiments we will also be able to determine the extent to which hormone-derived differences persist in the absence of hormones. These experiments represent both a direct inquiry into the mechanism of gender related difference in disease and an entry point for this investigator to the field of gender differences in autoimmune disease.