The aim of our studies is to define the intracellular processes linking TCR stimulation to T lymphocyte cell death. To this end, we have utilized the mouse T cell hybridoma 3DO. Like normal self-reactive T cells undergoing negative selection, 3DO undergoes programmed cell death when stimulated with an anti-T cell receptor (TCR) monoclonal antibody. We reasoned that TCR-induced cell death could be blocked by transfected cDNAs expressing: 1) adequate levels of specific antisense RNAs or dominant negative mutants for apoptotic genes; and 2) producing anti-apoptotic proteins. To test this hypothesis, we have constructed cDNA libraries into eukaryotic expression vectors using a mRNA source enriched in apoptotic genes. The libraries were transiently transfected into 3DO. The transfected cells have been stimulated with an anti-TCR antibody to trigger programmed cell death and the living cells were recovered and lysed to isolate transfected plasmids. Using the functional selection system described, we have isolated several cDNA clones, designated Apoptosis Linked Genes (ALG-1/6), able to inhibit TCR-induced cell death. Two of these genes, ALG-2 and ALG-3, have been studied in depth. To further define the molecular mechanisms by which these two proteins regulate programmed cell death we used the yeast two-hybrid system to identify proteins that interact with either ALG-2 or Presenilins. With this system, we have isolated and characterized an ALG-2 Interacting Protein (AIP), and a Presenilin associated protein (PAP).Recently, we have also defined the mechanisms by which ALG-4 regulates apoptosis. Moreover, sequence analysis of ALG-7 has prompted us to study the role of sphingolipids in TCR-signaling. - T cell receptor, T cell activation, programmed cell death, Alzheimer?s Disease.