What is the primary site of action for cyclosporine?

Cyclosporine primarily acts on T cells, which is crucial for its immunosuppressive effects. This drug inhibits the activation of T cells by interfering with the signal transduction pathways that are necessary for T cell activation and proliferation. Specifically, cyclosporine binds to cyclophilin inside the T cells, and this complex inhibits the activity of calcineurin, an enzyme that is essential for activating the transcription factor NFAT (nuclear factor of activated T cells). This inhibition prevents the production of interleukin-2 (IL-2), a key cytokine for T cell growth and differentiation.

While other immune cells, such as B cells, macrophages, and neutrophils, play roles in the immune response, cyclosporine’s primary action is on T cells, making them the central focus for its therapeutic effects. The inhibition of T cell function leads to a reduction in the immune response, which is particularly valuable in preventing organ transplant rejection and treating autoimmune conditions.