Figure 8. TNF-α released by BEAS-2B cells induces CC16 production and secretion from CC16+ cells. BEAS-2B cell conditioned medium (DEP-BEAS-2B) is prepared, and used to culture CC16+ cells. The TNF-α level in the culture medium of ctrl, DEP-BEAS-2B, and rTNF-α group is 0, 0.81 and 3 ng/ml, respectively. CC16+ cells are cultured in these media for 48 h. Then CC16 mRNA expression (A) and level in culture supernatants (B) are detected by RT-PCR and ELISA assay. (C) CC16-TNF-α negative feedback loop between Clara cells and normal airway epithelial cells protects against DEP exposure-induced injury. Red upside down T line drawing indicates inhibitive action. Blue line with arrowhead drawing indicates driving role. *P < 0.05, **P < 0.01 and ***P < 0.001 vs. Ctrl.