ChEBI: Tacrolimus (anhydrous) is a macrolide lactam containing a 23-membered lactone ring, originally isolated from the fermentation broth of a Japanese soil sample that contained the bacteria Streptomyces tsukubaensis. It has a role as an immunosuppressive agent and a bacterial metabolite.NCI Thesaurus (NCIt): Anhydrous from of tacrolimus, a macrolide isolated from Streptomyces tsukubaensis. Tacrolimus binds to the FKBP-12 protein and forms a complex with calcium-dependent proteins, thereby inhibiting calcineurin phosphatase activity and resulting in decreased cytokine production. This agent exhibits potent immunosuppressive activity in vivo and prevents the activation of T-lymphocytes in response to antigenic or mitogenic stimulation. Tacrolimus possesses similar immunosuppressive properties to cyclosporine, but is more potent.