Using polysome – bound mRNA profiling (actively translated mRNA) we have analyzed different phases of the immune response, including the in vivo analysis of the initial activation phase, the subsequent differentiation of CD8+ cells to cells with a Tc1, Tc2, Tc1L or Tcnull phenotypes and the subsequent phase characterized by the apoptosis of the vast majority of cells triggered by deprivation of growth factor. This extensive analysis allowed us to identify groups of genes with a regulated expression in specific phases of the immune response, which allows to hypothesize that they may play a relevant role in them. A subgroup of these genes has been already verified (using either northern blot, western blot or FACS analysis) and some candidate genes have been chosen for a functional analysis.