Alloreactivity and apoptosis in graft rejection and transplantation tolerance

Weissmann wrote as early as 1889 that higher organisms contain within thems elves the germs of death [1]. However, the term, programmed cell death, or apoptosis as it is now known, was defined much later [2]. Thus, it was long recognized that damaged and old cells are eliminated within the body, but the underlying mechanisms are only now beginning to emerge. Apoptosis appea rs central to the process of negative selection of developing T-cells in th e thymus. In regard to organ transplantation, apoptosis contributes to graf t rejection and the establishment of graft tolerance. Thus, understanding t he regulatory mechanisms of apoptosis may help establish a new protocol for the induction of transplantation tolerance.