[Mechanisms of allograft rejection]

Recent studies have considerably altered our understanding of allograft rejection mechanisms. The new approaches concern rejection targets, effector mechanisms, the triggering of the immune response and the genetic control of the immune response. Rejection targets now regarded as most important are antigenic epitopes such as "tissue specific" antigens, vascular endothelium antigen, skin Epa antigen and the minor histocompatibility antigen H-Y. Effector mechanisms seem to be restricted almost to the lymphocyte Th helper subset rather than to the Tc cytotoxic subset. The triggering of the immune response is mainly effected by certain cells, e.g. dendritic cells and Langerhans cells, or by lymphokines, such as interleukin 2. Finally, the genetic control of the response to alloantigens, previously demonstrated for less complex systems, is now known to exist in allograft rejection.