Transplant immunologyorgan rejection - Essay Example

The problem of transplantation is extremely hot nowadays, since there appeared a new way of saving human lives. But there are still many problems concerning the procedure and the result of such surgery. The most harmful of them is transplant rejection, as rejection of transplant organs is the main barrier of transplantation today. "Transplant rejection is when a transplant recipient's immune system attacks a transplanted organ or tissue. Graft-versus-host-disease is a condition that can occur following bone marrow transplant.

A bone marrow transplant is a procedure to transplant healthy bone marrow into a patient whose bone marrow is not functioning properly"(Medical It occurs as a Encyclopedia, 2004,par.1). Rejection is normally a result of humoral and cell-mediated reactions of the recipient to some kinds of antigens contained by the donor tissue. These antigens are known as major histocompatibility complex (MHC) molecules. This type of molecules is connected to a human leukocyte antigen (HLA) complex molecules in humans.

"The recognition of these foreign MHC antigens initiates rejection, which occurs in two stages. During the first stage, known as sensitization, lymphocytes are alerted and respond to the foreign MHC molecules. Rapid proliferation occurs in this stage. In the second 'effector' stage, the graft is destroyed by several cellular and molecular mechanisms. Following pages represent breif explanations of these mechanisms"(Biomed, 2004, Par.1).There are four kinds of transplant rejection.

Hyperacute rejection emerges as a rule within the first 24 hours after operation. This reaction begins so rapidly that the tissue never becomes vascularized. It is characterized by skin rash, abnormal liver activity fever and large susceptibility to infections.Hyperacute rejection is affected by presence host antibodies that turn to antigens present in out blood,so usually hyperacute rejection can be avoided by screening for anti-graft antibodies. Acute rejection normally starts within first two weeks of transplantation, and most likely happens to some extent in all transplants.

"It is caused by mismatched HLA antigens that are present on all cells. HLA antigens are polymorphic therefore the chance of a perfect match is extremely rare. The T-cells cause the graft cells to lyse or produce cytokines that recruit other inflammatory cells, eventually causing necrosis of allograft tissue"( Biomed,2004, par. 5). The symptoms of acute rejections are the same as during the hyperacute one, but in this case they might be much weaker.The risk of acute rejection is weakened by immunosuppressive agents in maintenance therapy.

The sudden acute rejection is struggled by episodic treatment. High-dose corticosteroids and antibodies to T-cells are used to decrease the damage. Chronic rejection is kind of rejection which occurs months after years since the surgery was done. It's symptoms are graft arterial occlusions, which emerges from the "proliferation of smooth muscle cells and production of collagen by fibroblasts".(Biomed, 2004, par.6) Therefore, alternative treatment such as tissue engineering and xenotrnsplantation is an effort to overcome the perils of chronic rejection and rejectionin general.

Also I wold like to mention the transplant drugs. Purine analogs are similar to the purines used in DNA synthesis. They interfere with DNA and suppress immune system. Azathioprine (Imuran) is a widely-spread purine analog, used with abdomal transplantation (kidney, liver, pancreas). Corticisteroids Prednisone and prednisolone are better to use in the case of liver or kidney transplantation. Hard antibiotic Rapamycin is used when bone marrow of tissues are transplanted. "Unfortunately, these drugs also interfere with the many other tissues that depend on rapid cell division (e.g., lining of the intestine, hair follicles) so they have many unpleasant side effects.

Therefore, the search for agents that specifically target immune cells goes on"(Transplant Biology Encyclopedia, 2005, par.18). ABO blood type identification and HLA (tissue antigen) typing before the operation helps make sure to get a close match. Suppressing the immune system as a rule is necessary for the rest of the transplant recipient's life to prevent the tissue from being rejected in the future. The alternative way of transplantation called xenotransplantation is currently being developed.

Xenotransplantation is the replacement of an individual's ill organ with an organ taken from another species. Animals known as a source of organs for human use are certainly primates (because of their genetic similarities to humans) and pigs (because they are available). On the other hand, there is a large hazard of retrovirus infecions and so-called Porcine Endogonous Retroviruses (PERV), which might be lethal to human. Nevertheless,we hope that this alternative deccision will be reserched and properly improved, so that people will not die of defects in their organs any longer.

I believe scince doesn't stay the same and there also will be invented special medicine directed on lessening effects of rejection. Bibliography1) Biomed, 2004. Transplant rejection therapy. http://biomed.brown.edu/Courses/BI108/BI108_2004_Groups/Group04/Xenotransplantation.htm2) Medical Encyclopedia, 2004. http://www.nlm.nih.gov/medlineplus/ency/article/000815.htm3) Transplant Biology Encyclopedia, 2005. http://www.lhsc.on.ca/transplant/drugs.htm4) Transplantation, 2005 (in Wikipedia) http://en.wikipedia.org/wiki/Bone_marrow_transplant