Cyclosporin acts by inhibiting the proliferation of:

Mechanism of action of cyclosporine Normally when antigen presenting cell (e.g. macrophage) present antigen to Helper T cell, there is activation of T cell by sequential intracellular eventsFirst calcium ions, after binding to calmodulin activate a membrane serine / threonine phosphatase called calcineurin. Calcineurin activates nuclear factor of activated T cells (NFAT) by dephosphorylation. Activated NFAT migrates to nucleus and induce transcription of cytokines IL-2 and other cytokinase. IL-2 activates T cells and cause proliferation of T cells. Cyclosporine enters target cells and bind to cyclophilin (an immunophilin). This cyclosporine – cyclophilin complex inactivates calcineurin IL-2 trascripitan and proliferation of T cells