Ascomycin, Immunosuppressant. Ascomycin (FK520) is a structurally complex macrolide with immunosuppressant activity. It is an ethyl analog of the known immune suppressant FK506 (Tacrolimus). Ascomycin acts by binding to a class of cytosolic proteins, the immunophilins, especially macrophilin-12 (FKBP-12). The immunophilin-FK520 complex inhibits calcineurin, a type 2B phosphatase (PP2B).
Ascomycin suppress the production of Th1 and Th2 cytokines in T lymphocytes, and preferentially inhibits the activation of mast cells (principal cells of the allergic response). In human basophils, it potently inhibited anti-IgE-induced histamine and cytokine release, and reduced IgE-dependent p38 MAPK activation. It seems that Ascomycin inhibit basophil degranulation at the initial phase of allergic skin reactions. Ascomycin derivatives are currently developed for the clinical treatment of dermatological diseases. Cell Signaling Activators and Inhibitors; Immunosuppressants. Protein Phosphatase Inhibitors; Protein Phosphatase Inhibitors (PP-2B (Calcineurin))