CD4 and pulmonary fibrosis: Notably, CD4+ T cells in cluster T9 expressed high levels of KLF6 that positively regulates the expression of TGFβ and molecules in the TGFβ pathway (47), AREG (amphiregulin) that is involved in pulmonary fibrosis (48), and CXCR4 that may promote T-cell migration to the lung (49).