Regulatory T cells in the blood of patients with chronic obstructive pulmonary disease (COPD): A systematic review and meta-analysis

Background: Chronic obstructive pulmonary disease (COPD) ranks among the leading causes of mortality and morbidity worldwide. Due to the lack of effective treatments for COPD, targeting regulatory T-cells (Treg) has recently attracted considerable attention. Therefore, we conducted a systematic review and meta-analysis to review all of the existing data about the percentage of Treg cells in peripheral blood samples of COPD patients to discover the potential role of these cells in finding new treatments for these patients. Methods: We explored SCOPUS, PubMed, and Web of Science databases using search terms like "Chronic obstructive pulmonary disease", "Emphysema", "suppressive lymphocyte", and "Regulatory T Cell". Data regarding the number of COPD patients and healthy subjects, Treg cell identification, definition of Treg cell markers, and the percentage of Tregs in COPD patients and controls, in addition to smoking, and clinical status of COPD patients were extracted. Results: The overall assessment showed no significant difference in the frequency of Treg cells between COPD patients and healthy subjects. No remarkable difference in Treg frequencies was observed in subgroup analysis based on the markers used to define Tregs, the clinical state of COPD patients, and the patient's smoking history. Based on our results, smoking reduces the level of Treg cells in the body. The frequency of CD4+CD25+FoxP3+ Tregs was considerably lower in the blood of smokers than in non-smoking healthy individuals. Conclusion: The overall result of this meta-analysis points out the importance of smoking in the prevalence of peripheral blood Treg cells.