Why does a patients body is 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 greater genetic similarity between them. Close relatives share more identical human leukocyte antigens (HLAs), which are crucial for the immune system's recognition of foreign tissues. This genetic match reduces the likelihood of an immune response against the transplanted tissue, decreasing the chances of rejection. Additionally, the presence of shared antigens can promote tolerance, further enhancing the compatibility of the graft.