CD4 + CD25 high CD127 – regulatory T

Chronic obstructive pulmonary disease (COPD) is a progressive lung disorder characterized by poorly reversible airway obstruction. Tobacco smoking is the main etiological factor inducing oxidative stress and an abnormal inflammatory response leading to mucociliary dysfunction, airway wall thickening and pulmonary parenchymal changes [1]. COPD pathogenesis remains largely unknown and it appears to be the result of smoke exposure and host/defense interaction. In balancing the efficient recognition of pathogens and the control of immune tolerance, regulatory T-cells (Tregs) play a key role. Different subtypes of Tregs exist. While the forkhead box P3 transcription factor (FOXP3) is the hallmark of regulatory function, interleukin (IL)-2 receptor ?-chain (also known as CD25) is a cell surface marker commonly used to distinguish among regulatory (CD25^high), activated (CD25^int), and naive (CD25^low) T-cells in humans [2]. Liu et al. have demonstrated that the downregulation of the ?-chain of the IL-7 receptor (CD127) on the majority of the CD4⁺FOXP3⁺ T-cells distinguishes Tregs from activated T-cells. Low CD127 expression, combined with high expression of CD25, therefore enables better isolation and purification of Treg populations among CD4⁺CD25⁺ T-cells. In functional assays, CD4⁺CD25^highCD127^low T-cells are highly suppressive [3].

Contrasting evidences have been reported concerning different subtypes of CD4⁺FOXP3⁺ T-cells in COPD. Plumb et al. assessed the presence of CD4⁺FOXP3⁺ Tregs in surgically resected lung tissues from COPD patients, smokers with normal lung function and healthy non smokers showing an increased number of CD4⁺FOXP3⁺ cells in lymphocyte follicles in lung parenchyma of moderate COPD patients [4]. Roos-Engstrand et al., analyzing the bronchoalveolar lavage fluid (BALF), showed no significant differences in CD4⁺CD25⁺ cells between COPD patients and the other healthy smokers and non smokers subjects. Among CD4⁺ T-cells expressing CD25, smokers with normal lung function had significantly decreased percentage of FOXP3 expression compared with those who never smoked. Moreover, the authors found that ex-smokers COPD patients expressed a decreased percentage of CD127⁺ cells in BALF compared to smoking COPD patients and the expression of CD127 on CD4⁺CD25⁺ T-cells was increased in smokers with normal lung function, with respect to non-smokers [5]. Compared with never smokers, smokers with normal respiratory function presented a greater number of regulatory T-cells, absent in COPD subjects [6]. Further, an increased proportion of Tregs in the BALF was found in smokers with COPD compared to the control group [7]. Recently, Lane et al. have found that smokers without COPD have increased numbers of CD4⁺CD25⁺FOXP3⁺ Tregs in the large airways [8]. Besides, another study demonstrated impaired Treg-mediated suppression of CD4⁺ T-cell activation in a group of COPD patients with high body mass index and similar proportions of CD4⁺FOXP3⁺ T-cells in COPD patients compared to controls [9].

Tregs have also been explored in peripheral blood. Xiong et al. showed that CD4⁺CD25⁺, CD4⁺ Treg, CD8⁺CD25⁺ and CD8⁺ Tregs were expressed in the peripheral blood of patients with acute exacerbations of COPD with a significant correlation with age, disease’s course, smoking index, quantity of white cells, and blood pH, while no correlations were found between these cells and IL-10 [10]. Barcelò et al. showed no significant differences in peripheral blood samples among healthy smokers, no-smokers and COPD patients, concerning CD4⁺CD25⁺ T-cells [6].

Overall, these data underline a not well understood role of Treg population in the pathogenesis of COPD and further investigations are needed to evaluate the potential effect of drugs on Tregs. Bronchodilators, such as long-acting ?₂-agonists, and inhaled corticosteroids, used in combination, are the recommended treatment for moderate and severe COPD patients with frequent exacerbations. It has been demostrated that glucocorticoids are able to restore the balance between inflammatory and regulatory cells, increasing the proportion of FOXP3⁺ Treg cells [11, 12] but, to date, not many studies assessed the effects of ß₂-agonists in combination with corticosteroids on these lymphocytes [13].

The aim of our study was to evaluate the relative percentage of CD4⁺CD25^highCD127^– Tregs in the peripheral blood of current and former smoker COPD patients and healthy volunteers. Furthermore, the in vitro effect of different concentrations of an inhaled corticosteroid (budesonide) and a long-acting ?₂-agonist (formoterol), alone and combined, in modulating CD4⁺CD25^highCD127^– Tregs cell population has been investigated.