In vitro activity: Pimecrolimus blocks T-lymphocyte activation pathway by inhibiting calcineurin function. Pimecrolimus prevents the release of cytokines and pro-inflammatory mediators from mast cells. Pimecrolimus binds to macrophilin-12, the pimecrolimusmacrophilin complex then binds to the cytosolic enzyme calcineurin phosphatase. The pimecrolimus-macrophilin complex prevents the dephosphorylation of the cytoplasmic component of the nuclear factor of activated T cells by inhibiting the action of calcineurin. Pimecrolimus inhibits not only the transcription and synthesis of cytokines from mast cells, but also the release of preformed mediators serotonin and β-hexosaminidase by the inhibition of Fc∈-RI-mediated degranulation and secretion. Pimecrolimus treatment causes a strong down-regulation of the expression of mRNA for genes associated with the macrolactam target pathway and inflammation.

Cell Assay: Pimecrolimus is an immunophilin ligand, which binds specifically to the cytosolic receptor, immunophilin macrophilin-12. Pimecrolimus prevents the release of cytokines and pro-inflammatory mediators from mast cells. Pimecrolimus binds to macrophilin-12, the pimecrolimusmacrophilin complex then binds to the cytosolic enzyme calcineurin phosphatase. The pimecrolimus-macrophilin complex prevents the dephosphorylation of the cytoplasmic component of the nuclear factor of activated T cells by inhibiting the action of calcineurin. Pimecrolimus inhibits not only the transcription and synthesis of cytokines from mast cells, but also the release of preformed mediators serotonin and β-hexosaminidase by the inhibition of Fcε-RI-mediated degranulation and secretion. Pimecrolimus treatment causes a strong down-regulation of the expression of mRNA for genes associated with the macrolactam target pathway and inflammation. Pimecrolimus is found to be as effective as cyclosporine A following oral ingestion and slightly superior after subcutaneous administration in mice. Pimecrolimus contrasts cyclosporine A and tacrolimus by inhibiting ongoing secondary inflammatory response, but not impairing the primary immune response in allergic contact dermatitis in mice. Pimecrolimus is as effective as the high-potency corticosteroid clobetasol-17-propionate in a pig model of allergic contact dermatitis (ACD). Pimecrolimus also effectively reduces skin inflammation and pruritus in hypomagnesemic hairless rats, a model that mimics acute signs of atopic dermatitis