Regulation of T cell apoptosis

Proliferative expansion of lymphoid cells is required for effective immune responses against invading microorganisms, but after the infection is contr olled, the expanded effector cells must be eliminated to prevent non-adapti ve accumulation of cells. Higher vertebrates have developed extensive netwo rks of signal transduction pathways to ensure controlled activation and exp ansion of cells during immune responses and apoptotic deletion of lymphoid cells that are no longer needed at the end of immune responses. Extracellul ar signals received by cell surface receptors that trigger intracellular si gnaling cascades are essential elements that control both processes. These signal transduction pathways converge to regulate cell fate at both transcr iptional and post-transcriptional levels. Here we review the role of pathwa ys, especially those triggered by TNF receptor-related molecules, that dete rmine the fate of T cells during development and activation. In addition, w e introduce the possibility that these same pathways may be abnormally prog rammed and so lead to immune cell accumulation during inflammatory diseases such as asthma.