Why does a patients body is less likely to reject an allograft if it comes from a close relatieve?

A patient's body is less likely to reject an allograft from a close relative due to the genetic similarity between the donor and recipient. Close relatives share more compatible human leukocyte antigen (HLA) markers, which play a crucial role in the immune system's recognition of foreign tissues. This reduced immunological mismatch lowers the likelihood of an adverse immune response, making the transplant more successful. Additionally, the presence of shared genetic traits may enhance tolerance to the transplanted tissue.