This project aims at understanding the selective events and physiological mechanisms which contribute to the structuring of the peripheral T cell repertoire as a consequence of antigen encounter. Based on recent experimental data obtained by us and by others, we propose a working hypothesis according to which, upon antigen encounter in the periphery, a strong selection process occurs among the responding T cells: a large fraction of T cells die while a minor population survive, revert to small lymphocytes and give rise to memory T cells. The ratio between these two fractions within each T cell response is function of the intensity and abundance of antigenic stimuli and of some intrinsic physiologic properties of each responder T cell. Our experiments aim at dissecting the intimate physiological changes during the transition from virgin to memory or anergic T cells which lead to the appearance of the "resistant memory phenotype". To this end we will analyze the status of the TCR/CD3 signalling complex, the expression of Ca2+ and K+ channels, the sequestration of Ca2+ in individual cells, expression of phosphotases (in particular CD45), the expression of protein kinases (in particular protein kinase C), tyrosine kinases lck and fyn, and patterns of bcl-2 expression. These physiological parameters will be studied on various T cell populations induced in vivo (in neonatally and adult thymectomized mice) and in vitro by either endogenous superantigens (Mls) or conventional non- self antigens (polypeptides). Biologically, with the help of these T cell populations we will address the problem of memory T cell selection and expression versus peripheral deletion and/or anergy. In all these studies we will use a variety of cellular immunology, protein chemistry, and molecular biology techniques. By understanding the molecular mechanisms which contribute to the differential features of virgin, anergic and memory T cells we hope to construct a testable physiological model which would explain our observations on the antigen driven transition of T cells to "Ca2+ resistant" phenotypes. Thus as a long-term goal we hope to be able to manipulate the system according to the information obtained from the above mentioned measurements. Such studies could involve genetic manipulation or protein microinjection into cells with representative phenotypes. In the long-term these studies may reveal avenues for therapeutic intervention to enhance or suppress immune function.