Final answer:
Heart transplant acute rejection is diagnosed by endomyocardial biopsy, occurring weeks to months after transplantation, and involves monitoring for immune response against the donor's MHC molecules.
Step-by-step explanation:
Acute rejection in heart transplant patients is a significant concern and is diagnosed by endomyocardial biopsy (C) following transplantation. It does not happen immediately after transplant, nor is it characterized solely by angina and decreased exercise tolerance. Instead, acute rejection typically occurs within a few weeks to a few months post-transplant and can involve a variety of symptoms, including heart failure. Endomyocardial biopsy is the gold standard for diagnosing acute rejection by examining tissue samples for signs of immune response, such as infiltration by T lymphocytes. Pathologists look for evidence of cellular damage or the presence of immune cells that are indicative of an active rejection.
Unlike blood transfusions, where the immediate immune response can lead to a rapid and severe reaction to incompatible blood types, heart transplant rejection is mediated by the recipient's immune response to the
donor's MHC molecules
and the immunogenicity of the graft itself. Ongoing
immunosuppressive therapy
is often required to decrease the risk of rejection.