A previous study showed treatment with low dose theophylline upregulated total HDAC in peripheral blood monocytes and increased FEV1% predicted when combined with inhaled fluticasone propionate in patients with COPD compared with theophylline alone [28] consistent with our current findings where theophylline alone had no effect on HDAC2 but combined with prednisolone and/or very low dose cyclosporine A resulted in synergistic upregulation of HDAC2 and subsequent sensitivity to prednisolone. Here, HDAC9 is linked to chronic obstructive pulmonary disease.