<prompt> Mechanism of action of theophylline in bronchial asthma is :Phosphodiesterase 4 inhibitionBeta2 agonismAnticholinergic actionInhibition of mucociliary clearance  <response>: 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. 