This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Which of the following act through helper T cells? \nSelect and explain. \nA. Cyclosporine, B. Azathioprine, C. Cytarabine, D. Cycloserine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Mechanism of action of:\n\nCyclosporine - Through T helper cells (by inhibiting calcineurin)\nAzathioprine - Inhibits de novo purine synthesis and damages DNA. It selectively affects cytolytic T lymphocytes.\nCytarabine - Inhibits DNA synthesis in S-phase.\nCycloserine - Inhibits bacterial cell wall synthesis.', 'role': 'assistant'}]