The balance between different immunological stimuli is essential in the progression and stabilization of atherosclerotic plaques. Immune regulation has been suggested as potential target for the treatment of atherosclerotic disease. We sought to determine whether treatment with pentoxifylline, a phosphodiesterase inhibitor with immunomodulating properties, could reduce the pro-inflammatory response observed in patients with acute coronary syndromes (ACS) and increase anti-inflammatory activity. In a double-blind, prospective, placebo-controlled study, 64 patients with ACS were randomized to receive pentoxifylline 400 mg TID or placebo for 6 months. Analysis of the pro-inflammatory markers, C-reactive protein (CRP), interleukin (IL)-6, IL-12, interferon-gamma and tumor necrosis factor (TNF)-α and the anti-inflammatory cytokines, transforming growth factor (TGF)-β1 and IL-10 were done at baseline, 1 and 6 months. Pentoxifylline treatment significantly reduced the adjusted levels of CRP and TNF-α compared to placebo after 6 months (P = 0.04 and P < 0.01, respectively). IL-12 increase was significantly less pronounced with pentoxifylline (P = 0.04). The levels of the anti-inflammatory cytokine, IL-10, also declined significantly less in the pentoxifylline group compared to placebo (P < 0.01) with a trend towards a higher increase of TGF-β1 in the former group (P = 0.16). Pentoxifylline reduces pro-inflammatory and increases anti-inflammatory response in patients with ACS and may have beneficial clinical effects on cardiovascular events. © 2006 Elsevier Ireland Ltd. 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