This revised competing renewal is designed to test the hypothesis that an immunoregulatory network involving apolipoprotein (apo) E exists between macrophages and lymphocytes. These studies focus on two cell types found in the atherosclerotic lesion, cholesteryl ester-loaded macrophages and activated T-lymphocytes, and their secreted products, apo E and interferon gamma (IFNgamma). We have determined that macrophages produce apo E in response to cholesteryl ester loading, and that this apo E inhibits T-lymphocyte activation. T-lymphocytes within atherosclerotic lesions produce IFNgamma, which protects against progression of lesion development. The hypothesis that apo E, produced locally in lesions as a consequence of macrophage foam cell formation, promotes atherosclerosis because it inhibits lymphocyte function will be tested by accomplishing three specific aims. The first aim is to demonstrate both in vitro and in vivo that apo E modulates T-lymphocyte expression of IFNgamma. These studies will be done in vitro with human peripheral blood, mononuclear cells, and with tissues from the C57BL/6 apo E-deficient mice. Both IFNgamma protein and mRNA will be measured. Studies in vivo will make use of transplanted bone marrow cells from wild type mice into irradiated E-deficient host mice. This model will permit us to study macrophage- specific expression of apo E in atherosclerotic lesions in mice that lack hepatic expression of apo E. The second aim is to determine if HDL modulates the capacity of apo E to inhibit T-cell function. The second aim also will be studied both in vitro and in vivo and will make use of human peripheral blood, mononuclear cells as well as double mutant, apo E- and apo AI-deficient transgenic mice. The third aim is to characterize the interaction between apo E and T-lymphocytes that mediates the inhibitory activity of apo E. Candidate receptors including lymphocyte LDL receptors, LRP receptors, VLDL receptors, and glycosaminoglycans will be studied. Development of atherosclerotic lesions is a complex long term event that involves multiple cells and soluble mediators in a dynamic environment. A proper understanding of this disease will require integral studies that characterize how different cells induce, amplify, and/or antagonize the function of neighboring cells. When completed, these studies will greatly enhance our understanding within the environment of the vessel wall the role of both macrophages and lymphocytes and their products, apo E and IFNgamma in the progression or regression of atherosclerosis.