Transplantation :
transplantation is the procedure involving the removal of a bodily organ or tissue from one person , and the insertion of that organ or tissue into another person to replace a damaged organ or tissue .
definition of terms :
1- allograft- transplant from one individual to another (synonymous with homograft).
2- hetrotopic graft - transplant placed in a site different than the organ s normal location .
3- orthotopic graft - transplant placed in its normal anatomical site .
4- syngentic graft (isograft)- transplant between identical twins.
5- xenograft - transplant between different species.
organ transplantationis now well established as an effective treatment for selected patients with end-stage organ failure. transplantation of the kidney ,liver , pancreas, heart and lungs are all routine procedures , and transplantation of the small intestine is becoming more widely practiced . currently , transplant activity is limited only by the shortage of cadaveric organs .
transplantation barriers :
1- genetic disparity between the donor and the recipient .
2- histocompatibility antigen as they constitute the target for rejection . the genes coding for these antigens are referred to as histocompatibility genes . there are more than 30, histocompatibility genesand they cause rejection at different rate .
The law of transplantation :
the transplat situation is unique in that foreign MHS molecules can directly activate T cells . conventional tcell responses against foreign protein require that such antigen are process into peptides and presented on the surface of the recipient APC , in association with MHS molecules .
- host versus graft responses cause transplant rejection if the graft carrier any antigen that are not present in the recipient . will be rejected.
- Graft versus host reaction result when donor lymphcytes attach the graft recipient .
This situation ine bone marrow transplantation in which graft versus host disease (GVHD) is induced by the immunolgically competent Tcells being transplanted into allogenic recipients whic are unable to reject them, the inability may due to :
1- The genetic difference between the donor and the recipient .
2- A lack of immunocompetence (through immaturity or immunosuppressive) of the recipient . In this situation the immunocompitent Tcell transplantation with bone marrow can attack the recipient .