Mechanisms of programmed cell death of effector T lymphocytes

T cell adequate function is critical for defense against pathogens. Transient disruption of T cell homeostasis occurs when primarily naive cells undergo antigen-driven expansion and acquire effector functions. Effector T cells then either undergo programmed cell death (PCD, it occurs usually as massive apoptosis during the contraction phase of the immune response) or survive to become memory cells. Two main pathways of effector T cell PCD are discussed in the review: activation induced cell death (AICD), which is a form of extrinsic apoptosis, and neglect-induced death (NID), which is an intrinsic one. Initial studies using in vitro models supported a role of AICD, mostly initiated by TCR receptor triggering in immune contraction. However, it was not finally supported by either recent in vivo experiments or current review authors' clinical studies concerning primed T cell apoptosis in chronic inflammatory lower airway diseases. Actually, Bcl-2 family members seem to be critical for the culling of T cell responses. The antiapoptotic molecule Bcl-2 and its proapoptotic antagonist Bcl-2, both under upstream control of autocrine interleukin-2, are the most probable candidates for regulators of T cell contraction. Other possible mechanisms regulating the process of contraction such as death receptor ligation, the impact of cytokines, as well as the importance of transcription factor NF-κB, are discussed. Additionally, attention is turned to the potential role of T cell survival/apoptosis regulation in future therapies of some diseases, including tumors and lung fibrosis.