Final answer:
The immune system, particularly T lymphocytes, rejects a transplanted organ by targeting the donor's MHC molecules, which are recognized as foreign. Immunosuppressive drugs are used to prevent this, but they come with risks of increased infection.
Step-by-step explanation:
The immune system is directly responsible for the rejection of a transplanted organ. When an organ is transplanted from an incompatible donor, the recipient's immune system recognizes the donor's MHC molecules as foreign. The MHC (Major Histocompatibility Complex) molecules on cells play a crucial role in the immune system's recognition of self versus non-self. Different MHC molecules between donor and recipient trigger the recipient's immune response leading to organ rejection. This reaction is primarily mediated by the recipient's T lymphocytes, which attack the transplanted tissue, perceiving it as a threat similar to pathogens. To prevent this, transplant recipients often require immunosuppressive drugs that lower the body's immune response, but these drugs can lead to increased susceptibility to infections and other complications. Organ transplants are a significant development in medical science, but matching the MHC molecules of donor and recipient is paramount to reduce the risk of rejection.
Substances produced in the body responsible for the rejection of a transplanted organ are antibodies and cytotoxic T cells that target the foreign MHC molecules on the donated organ.
Transplant rejection occurs when the recipient's immune system identifies the transplanted organ as foreign due to differences in MHC molecules. After organ transplantation, the immune cells, particularly T lymphocytes, recognize these MHC molecules not matching the recipient's own and initiate an attack. This immune response is intended to protect the body from potential threats but, in the case of transplantation, results in the destruction of the beneficial transplanted organ. Immunosuppressive therapy is typically administered to reduce the immune response and lower the risk of organ rejection.