As mentioned above, the dynamics of the network elements can be described by a set of ODEs. Here, the ODEs involve the following 18 variables: M1, M2, DC, T1, T2, T8, T17, and Tg represent the densities of M1, M2, DC, Th1, Th2, CD8+T, Th17, and Treg cells (in units of cell numbers in a cubic millimeter of tissue), respectively, whereas I4, I6, I10, I12, I17, I21, Iα, Iγ, and Iβ denote concentrations of the cytokines, IL-4, IL-6, IL-10, IL-12, IL-17, IL-21,TNF-α, IFN-γ, and TGF-β. The variable, TD, is defined as a ratio (in terms of a percentage) of damaged tissue to the whole lung parenchymal tissue (normal tissue plus damaged tissue). This TD definition is similar to that of destructive index (DI) [46–47] and can be measured experimentally. While a TD value of 0–30% is considered normal, a TD value larger than 30% is associated with COPD .