The rejection of transplanted organs is primarily due to the immune system's response to foreign tissues, particularly related to different MHC I molecules between donors and recipients.
Different MHC I molecules between donor and recipient cells can lead to rejection of a transplanted organ or tissue due to the recipient's immune system recognizing the donor tissue as foreign and triggering an immune response. This rejection process involves major histocompatibility complex markers MHC I and MHC II, specifically human leukocyte antigens (HLAs), playing a critical role.
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