Sex hormones, such as estrogens, are believed to play a major role in gender-based differential immune competence and autoimmunity. One mechanism by which estrogens may influence the immune system is by regulating cytokine levels. We have recently reported that estrogen-treated wild type C57BL/6 mice have increased IFNgamma, mRNA and protein levels. This grant proposal is aimed at mechanistically studying how estrogen alters the production of lFNgamma and the molecular consequences of increased IFNgamma. Estrogen-induced IFNgamma is significant, since IFNgamma is a "master" cytokine with physiological effects on nearly all cells of the immune system: it is involved in resistance against intracellular infections, and in pathological effects of many autoimmune and inflammatory diseases. The hypothesis of this proposal is that increased IFNgamma in estrogen-treated mice is due to the promotion of increased numbers of specific IFNgamma secreting cells, an enhanced response to IFNgamma-promoting cytokines and/or co-stimulatory signals. A consequence of this increased IFNgamma will be altered cellular and molecular functions of IFNgamma target cells. This may be evident as increased expression of IFNgamma responsive genes and molecules, altered patterns of apoptosis and changes in susceptibility to autoimmunity. AIM (1) of this proposal will examine the molecular basis for estrogen-induced IFNgamma. AIM (2) will determine whether responsiveness of IFNgamma-target cells to IFNgamma is altered in estrogen-treated mice, with regard to STAT1 activation, IFNgamma-responsive genes, and expression of IRF-1, IRF-2, Cox-2, and MHC molecules. AIM (3) will investigate whether increased survival of lymphocytes from estrogen-treated mice is due to IFNgamma inducible nitric oxide, by using estrogen-treated wild type, IFNgamma knockout, and iNOS knockout mice. AIM (4) will address whether estrogen treated non-autoimmune mice are prone to develop selected types of induced-autoimmunity, and whether this is due to IFNgamma. This proposal is novel since it will provide a mechanistic-based understanding of how estrogen promotes IFNgamma and its consequences at molecular, cellular, and organismal levels. The proposal will benefit the future understanding of human health, especially with regard to gender-based immune diseases.