TGFB1 and idiopathic interstitial pneumonia: Moreover, Th2 is a major subpopulation in IPF, which excretes interleukin 4 (IL-4), interleukin 5 (IL-5), interleukin 13 (IL-13), and TGF-β that are responsible for M2 macrophage recruitment and direct fibroblast activation [59].