Mechanisms of Rejection and Tolerance In Transplantation

Abstract

Rejection remains the major barrier to successful transplantation. The immune response to an allograft is an ongoing dialogue between the innate and adaptive immune system; if left unchecked rejection of transplanted cells, tissues or organs occurs. Activation of the innate immune system, triggered as a consequence of tissue injury sustained during cell isolation or organ retrieval as well as ischaemia reperfusion, will initiate and amplify the adaptive response. T cells require a minimum of two signals for activation, antigen recognition and costimulation. The activation requirements of naïve T cells are more stringent than those of memory T cells. The majority of B cells require help from T cells to initiate antibody production. Antibodies reactive to donor HLA molecules, minor histocompatibility antigens, endothelial cells, red blood cells or autoantigens can trigger or contribute to rejection early as well as late after transplantation.