The dominant theory of Hippocrates was that of the four humours—that when the four humours were in balance health prevailed. Therefore, the main goal of the medical therapy was to restore humoral equilibrium.

We read with great interest the article by Hou et al,1 where an imbalance between protective and detrimental subgroups of T regulatory (Treg) cells in patients with COPD is showed. On the contrary with previous studies reporting no significant differences in CD4 foxp3+ T cells between patients with COPD and smokers,2 authors performed an elegant series of experiments and dissected Treg cells into three distinct subpopulations, denominated resting, active and cytokine-secreting Treg cells based on the intensity of foxp3+ expression and the secretion of proinflammatory cytokines including interferon and interleukin 17. As expected, subgroup analysis revealed an imbalance between different Treg subsets, including a downregulation of suppressive Treg cells and an...