What does tacrolimus do in the body?

Tacrolimus suppresses the immune system by inhibiting calcineurin, an enzyme that activates T cells, a type of white blood cell involved in immune defense. When a person receives an organ transplant, their immune system may identify the new organ as a foreign threat and attempt to attack it. By blocking calcineurin, tacrolimus reduces T-cell activity, helping to prevent the body from rejecting the transplanted organ. View original source