This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Asthma, Subject name: Pharmacology
[{'content': 'Mechanism of action of theophylline in bronchial asthma is: \nSelect and explain. \nA. Phosphodiesterase 4 inhibition, B. Beta2 agonism, C. Anticholinergic action, D. Inhibition of mucociliary clearance', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (A) Phosphodiesterase 4 inhibition(Ref: Katzung 11th/e p345; KDT 8th/e p245)Theophylline is used in bronchial asthma. Its mechanism of action is:Inhibition of phosphodiesterases particularly PDE-4.Antagonism of adenosine receptors.Enhancement of histone deacetylation. Acetylation of histone is required for activation of inflammatory gene transcription. By inhibiting this process, low-dose theophylline may restore responsiveness to corticosteroids.', 'role': 'assistant'}]