Why does the body reject new kidney?

The body may reject a new kidney due to an immune response, where the immune system recognizes the transplanted organ as foreign. This is often influenced by differences in human leukocyte antigen (HLA) markers between the donor and recipient. If the immune response is strong, it can lead to acute rejection, while chronic rejection occurs over time due to ongoing immune activity. Immunosuppressive medications are typically used post-transplant to help prevent this rejection.