A natural macrocyclic lactone produced by the bacterium Streptomyces hygroscopicus, with immunosuppressant properties. In cells, sirolimus binds to the immunophilin, FK Binding Protein-12 (FKBP-12) to generate an immunosuppressive complex that binds to and inhibits the activation of the mammalian Target Of Rapamycin (mTOR), a key regulatory kinase. This results in inhibition of T lymphocyte activation and proliferation that occurs in response to antigenic and cytokine (IL-2, IL-4, and IL-15) stimulation and inhibits antibody production. (NCI04)
