... T cells Function Declines Ernst et al. (1990), Miller (1996), Garcia and Miller (1997), Pawelec et al. (1999) Aukrust et al. (1996), Kim and Nel (2005) Naïve CD4 + T cells IL-2 production Reduced Meydani et al. (1990), Engwerda et al. (1996), Linton et al. (1996Linton et al. ( , 2005, Kurashima and Utsuyama (1997) Regulatory T cells Increased Sharma et al. (2006) Montecino- Rodriguez et al., 1998;Aspinall and Andrew, 2000;Andrew and Aspinall, 2001) but also for potential therapeutic approaches in human patients (Napolitano et al., 2002;Henson et al., 2004;Sutherland et al., 2005;Herndler-Brandstetter et al., 2008). Homeostatic proliferation, induced either by aging-dependent or disease-associated thymic involution and lymphopenia, has, vice versa, been made responsible for a higher incidence of autoimmunity in humans (Mishra and Kammer, 1998;Douek et al., 2003;Piliero et al., 2004;Jameson, 2005;Thewissen et al., 2005;Giovannetti et al., 2008), as it results in the clonal expansion of memory (-like) T cells that reduce the diversity of the available TCR repertoire (Berzins et al., 2002;Kovaiou et al., 2005;Herndler-Brandstetter et al., 2008). ...