Final answer:
Organ transplants are often rejected when the donor's MHC molecules are not compatible with the recipient's, causing the immune system to attack the transplant. A precise match of these molecules is essential for successful transplantation, and even with a match, immunosuppressive drugs are usually required. MSCs in cellular allografts may help in reducing the immune response.
Step-by-step explanation:
Why Organ Transplants from Incompatible Donors Are Rejected
Organ transplants can be critical life-saving procedures, but their success is heavily dependent on the compatibility of MHC molecules between the donor and the recipient. MHC molecules are responsible for distinguishing self-cells from non-self-cells in the body. During transplantation, if the recipient's immune system recognizes the donor's MHC molecules as foreign, it will launch a cytotoxic T-cell response leading to organ rejection.
A match in these molecules is vital because MHC polymorphisms are extensive, which means there's a massive variety of MHC gene combinations within the human population. Transplant recipients usually need immunosuppressive drugs to reduce the rejection risk, as even a well-matched organ may be prone to rejection due to slight differences in gene products that are involved in immune responses. Cellular allografts may contain mesenchymal stem cells (MSCs), which are multipotent cells that could potentially reduce the immune system's response against transplanted tissues.