What role does cyclophilin play in the function of cyclosporine?

Cyclophilin plays a crucial role in the mechanism of action of cyclosporine by binding to the drug itself. This binding forms a complex that inhibits the activity of calcineurin, a calcium/calmodulin-dependent phosphatase. Calcineurin is essential for the activation of T cells and the subsequent production of interleukin-2 (IL-2), a key cytokine in the immune response.

By inhibiting calcineurin, the cyclophilin-cyclosporine complex effectively prevents the dephosphorylation of Nuclear Factor of Activated T-cells (NFAT), which is crucial for IL-2 gene transcription. As such, the overall effect of cyclosporine is immunosuppression, which is vital in preventing transplant rejection and treating autoimmune diseases.

Other options, such as facilitating calcineurin activation, promoting NFAT degradation, and enhancing IL-2 production, do not accurately represent the function and effects of cyclophilin-cyclosporine interaction. The primary function is to inhibit calcineurin, thereby blocking the immune response mediated by T cell activation.