Tacrolimus is a macrolid compound with a macrocyclic ring structure. It binds to a distinct family of intracellular proteins, the FK506 binding proteins and inhibits a large variety of Ca2+ dependent intracellular activities. 
Effects on T lymphocytes are the following:
-	inhibition of TCR-CD3 or antigen-induced proliferation, IL-2 production and IL-3, IL-4, IFN- transcription
-	inhibition of CD2-induced proliferation and IL-2 production
-	inhibition of lectins, CD28, phorbol 12-myristate 13-acetate, IL-2-induced proliferation
Tacrolimus also ihibites -surface Ig and lipopolisaccaride-induced proliferation of B lymphocytes, degranulation of mast cells, CTL and basophils in response to appropriate stimuli, proliferation of fibroblast in response to mitogen agents.