Mechanism of action of theophylline in bronchial asthma is :: (A) Phosphodiesterase 4 inhibition, (B) Beta2 agonism, (C) Anticholinergic action, (D) Inhibition of mucociliary clearance
Answer is A. 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.