TRISTAN, TORCH, and other randomized, placebo-controlled clinical trials have proven that SFC therapy for improves lung function and quality of life of patients with COPD, reduces the risk of acute exacerbation of symptoms [13, 15, 20, 21], and decreases the rate of decline in FEV1 values . In our study and other reports, SFC therapy improved pre-FEV1 values and St. George's Respiratory Questionnaire (SGRQ) scores , reduced the risk of acute exacerbation of COPD, reduced dyspnea according to the MMRC scale, and increased the in the 6-min walk distance. For example, Barners et al. found that SFC significantly improved pre-FEV1 values , and Celli et al. found that SFC decreased the rate of FEV1 decrease in COPD patients . Our results and those of others indicate that long-term SFC administration can improve clinical endpoints. However, the mechanism underlying the effects of SFC therapy on COPD is unclear.
COPD is defined as an "abnormal inflammatory response" disease . Therefore, development of anti-inflammatory treatments for COPD is extremely important. It has been suggested that SFC may have anti-inflammatory effects on COPD. However, there is still significant controversy regarding this subject . Barnes et al. found that SFC therapy can significantly reduce the numbers of CD8+ or CD4+ T cells in the bronchial mucosa, but has no effect on the number of CD68+ cells (monocytes/macrophages). More importantly, their study was the first to show that SFC therapy reduced the number of neutrophils in induced sputum . Our findings are consistent with those of their report. Bourbeau et al. found that the numbers of CD8+ cells and CD68+ macrophages were reduced by treatment with SFC compared to that with a placebo, but not by treatment with FC alone. SFC therapy did not significantly change neutrophil numbers relative to placebo . However, there were only 9 cases of SFC therapy in the group investigated by Bourbeau et al., which may weaken the viability of their conclusion due to the small sample size.
Our study also confirmed that SFC therapy significantly reduced the levels of two important inflammation markers, IL-8 and TNF-α, in induced sputum. IL-8 is a chemotactic factor of leukocytes and lymphocytes. Neutrophils and CD8+ T lymphocytes are major inflammatory effector cells in COPD. IL-8 may activate neutrophils, thereby mediating the inflammatory response in COPD . Treatment with salmeterol/FC (100/1000 μg daily) for 3 months has been reported to significantly reduce the level of IL-8 in induced sputum . Meanwhile, cigarette extracts were shown to stimulate neutrophils and macrophages to release IL-8 in vitro, and this response could be inhibited by FC in a dose-dependent manner. Furthermore, the anti-inflammatory effect of FC could be enhanced by salmeterol, suggesting that salmeterol and FC have synergistic anti-inflammatory effects . Similar synergistic effects of these drugs on IL-8 levels were also reported . IL-8 seems to account, to some extent, for the effects of SFC on neutrophils.
TNF-α is mainly produced by monocytes and macrophages after infection. TNF-α can induce monocytes/macrophages to produce IL-8, which activates neutrophils and stimulates them to undergo chemotaxis. Activated neutrophils can release large amounts of reactive oxygen species, proteolytic enzymes, lipids, and cytokines, which further aggravate lung injury . In COPD pathogenesis, TNF-α can also stimulate epithelial cells to release monocytes/macrophage- or neutrophil-derived chemotactic factors , leading to injury and remodeling of lung tissue. Many studies have confirmed that the degree of TNF-α elevation in the peripheral blood of COPD patients is closely related to the severity of COPD symptoms [30–32]. Baners et al. reported that SFC reduced the expression of TNF-α in the bronchial mucosa of COPD patients . In addition, we found that SFC reduced the levels of TNF-α and IL-8 in the peripheral blood of COPD patients.
We also identified a significant decrease in IL-17A levels in induced sputum after SFC therapy. IL-17A, secreted by Th17 cells, induces airway epithelial cells to release IL-8 and granulocyte macrophage colony-stimulating factor (GM-CSF). GM-CSF stimulates neutrophils and macrophages to proliferate and undergo chemotaxis, and thus activates the inflammatory response in COPD. IL-17A can also induce the release of matrix metalloproteinase (MMP)-9, which is involved in emphysema [33–35]. It was previously found that the number of cells expressing IL-17A in the bronchial mucosa was significantly increased in COPD patients . Our data also suggest that lower levels of IL-17A after SFC therapy may be associated with the reduced number of neutrophils in induced sputum.
More importantly, we also found that the proportion of Foxp3+Tregs as a percentage of total CD4+ T cells in the peripheral blood of COPD patients was significantly smaller than that in the healthy subjects, and could be elevated significantly by SFC therapy. Foxp3+ Tregs are a subpopulation of T cells that have anti-inflammatory and immunoregulatory effects, and thereby maintain T cell homeostasis and tolerance to self-antigens [37, 38]. Correlations have been found between dysfunction of Tregs and the pathogenesis of asthma and rheumatoid and other autoimmune diseases [39, 40]. Recently, Burcelo et al. found that the number of Foxp3+Tregs in COPD patients was significantly lower than that in smokers without COPD, but showed no difference relative to healthy subjects, which is difficult to explain. It has been found that the number of Foxp3+Tregs in the peripheral blood of children with asthma decreased but did not reach a significant difference compared to that in the control subjects. However, CD4+CD25+ T cells in the lungs of these patients were significantly reduced in number. CD4+CD25+ T cell numbers in peripheral blood can be significantly increased after treatment with inhaled corticosteroids (ICS), such as FC . About the relationship between Th 17 cells (producing IL-17A) and Foxp3+Tregs, natural Foxp3+Tregs inhibited Th2 polarization and Th17-driven lung inflammation in BALB/c mice [42, 43]. Anti-IL-17 treatment had significantly fewer Th1 cells and more Treg after lymph node infusion in aplastic anemia . CD4+Foxp3+ Tregs were able to control Th17 and Th17+Th1 cells in an IL-10-dependent manner in mice colitis . CD39+ Regulatory T cells suppress generation and differentiation of Th17 cells in human malignant pleural effusion .
These findings are consistent with our observations in COPD patients, suggesting that ICS treatment can increase Foxp3+Treg cell numbers to some extent. Foxp3+Tregs may also contribute to the anti-inflammatory effects of ICS/long-acting beta agonist (LABA) combination therapy. In addition, we found significant negative correlation between the number of Foxp3+Tregs in the peripheral blood and IL-17 levels, suggesting that Foxp3+Tregs may negatively regulate the differentiation of Th17 cells and IL-17 production. On the other hand, it was also reported that there was an increase in Tregs in COPD patients, his regulation of inflammation depended on the between pro- and anti- inflammatory influences . Therefore, the more evidence and the connection regarding Th17 cells, IL-17 and Tregs in COPD need further study in the future.
Our study demonstrates that SFC therapy has significant anti-inflammatory effects and improves clinical symptoms of COPD. SFC administration reduced the levels of inflammation markers in sputum and peripheral blood, and reduced the number of neutrophils in induced sputum. These effects may be related to decreased levels of IL-8 and IL-17 in induced sputum and the recovery of normal Foxp3+Treg cell numbers in the peripheral blood. The anti-inflammatory effects of SFC may contribute to its efficacy in the treatment of COPD.