Why is cyclosporin A often used in individuals who have received tissue transplants?

• A. It helps prevent infections.
• B. It suppresses the recipient's immune response against the transplant.
• C. It selectively kills the transplanted tissue's immune cells.
• D. It increases the number of B cells in the body.

Answer: (B)

Preventing graft rejection hinges on dampening the host’s immune response, especially T-cell activation. Cyclosporin A blocks calcineurin in T lymphocytes, which stops transcription of interleukin-2 and other cytokines needed for T-cell activation and proliferation. With T cells less able to respond to donor antigens, the transplanted tissue is less likely to be attacked, improving graft survival. It’s not used to prevent infections—in fact, immunosuppression can raise infection risk. It also doesn’t selectively kill immune cells in the transplanted tissue, nor does it increase B cell numbers; its primary effect is to suppress T-cell activity via the calcineurin pathway.