Final answer:
Tissues are immunologically 'typed' before an organ transplant to ensure that the donor and recipient have a close match in their MHC proteins. Matching the MHC proteins reduces the chances of organ rejection.
Step-by-step explanation:
Tissues are immunologically 'typed' before an organ transplant to make sure that the donor and recipient match as closely as possible in their MHC (major histocompatibility complex) proteins. The MHC proteins are cell surface glycoproteins that distinguish self from non-self in body tissues and organs. Matching the MHC proteins between the donor and recipient reduces the chances of organ rejection and increases the success of the transplant.