As discussed above, TD can be generated by S , M1 [24–26] and T8 , respectively. Iγ and I17 also cause TD . These TD generation processes are all down-regulated by I10 . As mentioned earlier, in the lung parenchyma the process for MMP-induced TD generation is also inhibited by Iβ . Equation describing the TD dynamics thus is dTDdt=k12S(1−TD)11+(I10K10)2+k13M1(1−TD)11+(I10K11)2+k14T8(1−TD)11+(I10K12)2+k15(IγK14)2+(I17K15)21+(IγK13)2+(I17K14)2+(I10K15)2+(IβK16)2−dTDTD(12) where TD is defined by damaged tissue/(normal tissue+damaged tissue)×100% and tissue repair is involved indirectly in the last term in Eq 12.