What term describes when transplanted organ is attacked by the recipient's immune system?

• A. Rejection
• B. Infection
• C. Allergic reaction
• D. Autoimmune disease

Answer: (A)

When a transplanted organ is attacked by the recipient's immune system, the process is called rejection. The donor organ carries non-self antigens, especially differences in HLA, that trigger the recipient’s immune cells to recognize the graft as foreign and mount an attack. This immune response harms the graft tissue and can lead to loss of function if not controlled. Rejection can occur quickly as hyperacute rejection due to preformed antibodies, or develop over days to weeks as acute rejection driven by T cells and antibodies, and it can progress over months to years as chronic rejection with ongoing vascular damage. Immunosuppressive therapy aims to prevent this attack by dampening T cell activation and antibody production. Infections involve pathogens, allergic reactions are hypersensitivity to environmental substances, and autoimmune disease is the immune system targeting the body’s own tissues—none describe the graft-specific immune attack on a transplanted organ.