Cell proliferation and apoptosis in the immune system in the elderly.

Loss of the cell proliferative capability and involution of tissues and organs are among the most important phenomena that characterize the aging process. Some of the aged-linked immune dysfunctions could be partly due to a dysregulation of apoptotic processes and to a lower responsiveness of aged lymphoid cells to activation and proliferation signals. The main changes in proliferative activity and cell death during aging and their impact on the process of immunosenescence are discussed. In fact, a very important function that has been suggested to deteriorate with age and to play a major role in the aging process is the capability of cells from aged subjects to respond to mitogenic stimuli and, consequently, to undergo cell proliferation. However, the cellular activation processes are very complex and the proliferative responses can follow different interconnected signal transduction pathways, and only some of them appear to be modified during age. Moreover, cell growth, immunosenescence, and longevity are strictly interconnected and deeply related to programmed cell death or apoptosis. The cellular equilibrium between cell survival and proliferation, on the one hand, and programmed cell death, on the other hand, seems to be unbalanced with advancing age, although in each type of immune cell it could be differentially modulated, resulting in a variety of clinicopathological consequences. Thus, cell proliferation and cell death are two physiologically active phenomena closely linked and regulated and a failure of these mechanisms determines profound dysregulations of cell homeostasis with major consequences in immune functioning and the onset of autoimmune diseases and cancer, whose incidence appears to be increased in the elderly.