Why is a patient's body less likely to reject an allograft if it comes from a close relative?

A patient's body is less likely to reject an allograft from a close relative due to the increased genetic similarity between the donor and recipient. Close relatives share a higher percentage of their human leukocyte antigens (HLAs), which are crucial for the immune system's recognition of self versus non-self. This similarity reduces the likelihood of the recipient's immune system identifying the graft as foreign, thereby decreasing the chances of rejection and improving graft acceptance.