The costimulatory and differentiating activity of soluble class I MHC antigens for an autologous thymocyte population

T Cell Receptor (TCR)-induced Death of Immature CD4+CD8+ Thymocytes by Two Distinct Mechanisms Differing in Their Requirement for CD28 Costimulation: Implications for Negative Selection in the Thymus

“…In mature T cells, TCR signals do not directly induce an apoptotic program, but rather act indirectly by upregulating surface expression of members of the TNF family, specifically fas ligand (fasL) and TNF ( 32 – 34 ). These proteins bind to fas or TNF receptor (TNFR) which mediate apoptosis through death domains expressed in their cytosolic regions ( 35 ). This mechanism of apoptosis necessarily results in death of both TCR-stimulated T cells and neighboring (or bystander) cells expressing fas or TNFR.…”