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Why can rejection begin soon after a transplanted organ is connected to the recipient’s body?

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Kidney transplant — transplant British surgeon Andrew Ready flushing a donated kidney during a transplant at Queen Elizabeth Hospital, Birmingham, England, 2006.

Rejection that begins almost immediately after a transplanted organ is connected to the recipient’s body is typically caused by antibody-mediated rejection.1

This rapid response occurs when the recipient already possesses preexisting antibodies that recognize the donor's antigens as foreign. These antibodies may have developed due to prior exposure to foreign antigens through blood transfusions, previous transplants, or pregnancy. Unlike cell-mediated rejection, which is driven by T lymphocytes and typically develops over days or months, antibody-mediated rejection happens within minutes or hours and is generally irreversible.1

To prevent such complications, medical professionals perform tissue typing and a direct crossmatch between the recipient’s serum and the donor’s lymphocytes to identify potential incompatibilities before the surgery takes place.2