Immune regulator vitamin A and T cell death

Proper regulation of T cell death is of vital importance for the function of the immune system. Positive and negative selection of developing T cells in the thymus ensures the survival of only those T cells that can recognize peptides presented by self-MHC molecules and at the same time not respond to self-antigens, and thus, T cell death within the thymus is instrumental in shaping the mature T cell repertoire. The death of activated peripheral T cells is crucial for processes such as down-modulation of immune responses after clearance of infectious agents, peripheral tolerance, and maintenance of immune-privileged sites. These processes are largely proceeding due to the enhanced susceptibility of activated T cells to spontaneous, activation-, and Fas-induced apoptosis. The active metabolite of the immune regulator vitamin A, retinoic acid, has been reported to influence various types of apoptotic processes in both thymocytes and activated peripheral T cells. This chapter gives an overview of, and discusses the reported effects of vitamin A on spontaneous and activation-induced cell death of thymocytes and mature T cells, as well as on Fas-induced T cell death.