Graft rejection after an organ transplant is due mainly to

1. The body is able to differentiate self from nonself. 2. A graft from another individual carries nonself markers. 3. The cell mediated immune response is responsible for graft rejection. 4. This is why tissue matching and blood group matching are done before any transplant. 5. Even after matching, the patient takes immunosuppressants for life. _Source: syllabus Biology Ch7 'Human Health and Disease', section 7.2.2_