Why do organ transplants trigger an immune response in a recipient? (A) Antigens in the recipient’s body recognise the organ as foreign - HSC - SSCE Biology - Question 13 - 2012 - Paper 1

Organ transplants trigger an immune response because the recipient’s immune system recognizes the antigens present on the transplanted organ as foreign. This recognition process is primarily carried out by the recipient's white blood cells, which identify these antigens as different from the body's own tissues. If the immune cells detect anything that does not belong to the body — in this case, the transplanted organ — they activate an immune response aimed at attacking and rejecting the foreign tissue.