Why are transplanted organs rejected?

 Transplanted organs are rejected because of the presence of special protein molecules present in the body of every individual. Called antibodies, these molecules can easily recognize a foreign body by a substance called antigens produced by the later.

  As the organ to be transplanted is obtained from another individual, it may contain several antigens not found in the patient. So, when transplanted, the patients’ body makes antibodies to fight the foreign antigens present in the transplanted organ. In this process, the donor organ is destroyed or simply rejected. Chances of rejection can be reduced by tissue matching as in case of blood transfusion or by using an organ from a sibling or from a close relative of the patient. Also, drugs given after the transplantation help in suppressing the body’s protective response and thus prevent rejection.