Final answer:
Anti-thymocyte globulin is a medication used to suppress the immune system by targeting T cells, thereby preventing organ transplant rejection or treating immune-mediated organ damage.
Step-by-step explanation:
Anti-thymocyte globulin (ATG) is an immunosuppressive drug used, most commonly, to prevent rejection in organ transplantation and to treat certain conditions of immune-mediated organ damage. This drug is a mixture of antibodies, created by immunizing animals such as rabbits or horses with human thymocytes. These antibodies then target mainly T cells in the human body, which are central to the immune response and can cause transplant rejection. ATG leads to the depletion of T cells, preventing them from attacking the transplanted organ. It does this by binding to the T cells, causing cell lysis, blocking their function, or leading to their removal by other parts of the immune system. The aim of using ATG is to achieve a state of immunosuppression where the body's immune system is weakened enough to accept the transplanted organ but still able to defend against infections.