Organ rejection occurs when the body's immune system identifies a transplanted organ, such as a kidney or heart, as foreign. This happens because the immune system is designed to protect the body from harmful substances, including bacteria and viruses. When an organ from a donor is introduced, the recipient's body may attack it, leading to inflammation and damage. To prevent organ rejection, patients often take immunosuppressive medications. These drugs help suppress the immune response, allowing the body to accept the new organ. However, long-term use of these medications can increase the risk of infections and other complications, making careful monitoring essential for transplant recipients.