['Histone deacetylase (HDAC) is an enzyme that regulates chromatin structure and inflammatory gene expression. In patients with chronic obstructive pulmonary disease (COPD), while accumulating evidence indicates that the activity of HDAC is decreased in lung tissue alveolar macrophages, HDAC activity in peripheral inflammatory cells has not yet been evaluated in detail.', 'HDAC activities in peripheral blood mononuclear cells (PBMC) were investigated in patients with stable COPD (n = 26), non-smoking controls (n = 13), and smoking controls (n = 10), respectively. HDAC activity was measured using an HDAC Activity/Inhibitor Screening Assay Kit. Serum interleukine-8 (CXCL8) levels were determined by ELISA techniques. Lung function test was carried out according to the ATS/ERS guidelines.', 'Compared with healthy non-smokers, HDAC activity in the PBMCs of COPD patients was decreased by 40% (13.06 ± 5.95 vs. 21.39 ± 4.92 (μM/μg), p < 0.001). In patients with COPD, HDAC activity was negatively correlated to smoke intensity (r = -0.867, p < 0.001). In COPD patients who had smoked for more than 40 pack-years, HDAC activity in PBMC was 40% lower than that in COPD patients who had smoked fewer than 40 pack-years.Moreover, serum CXCL8 levels in patients with COPD were significantly higher than that in controls and were negatively correlated to HDAC activities.'] Is histone deacetylase activity decreased in peripheral blood monocytes in patients with COPD?