Britannica Sources used in this answer

Why are tissue grafts from another species usually rejected quickly?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

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

Tissue grafts from another species, known as xenotransplantation, are typically rejected rapidly because the human immune system perceives the foreign cells as a threat, much like it would a virus or bacteria.1

The rapid rejection of such grafts is primarily driven by antibody-mediated responses. This occurs when the recipient already possesses preexisting antibodies that recognize antigens on the surface of the donor tissue. Unlike cell-mediated rejection, which develops over days or months as T lymphocytes infiltrate the graft, antibody-mediated rejection happens within minutes or hours and is generally irreversible. Because the biological differences between species are vast, the immune system identifies these tissues as "nonself" with extreme efficiency, triggering a coordinated assault by B lymphocytes, T cells, and other immune components to destroy the foreign matter.2