HLA system in solid organ transplantation part 8

Allostimulation during the process of solid organ transplantation

In immune response against transplants, the activation of effector T cells and B cells, as well as the activation of the innate defence system, are crucial for the establishment of transplant rejection. T helper cells are activated upon binding foreign MHC molecules or their processed peptides bound to recipient MHC molecules, and they orchestrate both the alloreactive immune response and the innate response against the transplant. Likewise, cytotoxic T cells, becoming activated in similar fashion, are the main effectors of lysis of allogeneic parenchymal cells, in the way they eliminate  virally-infected or neoplastic cells. On the other hands, B cells are activated to produce alloantibodies upon recognizing conformational epitopes on foreign MHC molecules directly through their B cell receptor; usually requiring T cell help for proper activation, generation of memory B cells, immunoglobulin isotype switching and maturation of the affinity   of their alloantibodies. But not all the immune response deployed in response  to the transplant organ is destructive. Regulatory T (Treg) cells, the master immune moderators, are also activated during  during an immune allocation. T reg cells may play a role in re-establising immune homeostasis, and perhaps also in promoting the long-term operational acceptance of the transplanted organ.