Effect of nintedanib on PDGF-BB- (A, B), bFGF- (C, D), and VEGF- (E, F) induced fibroblast proliferation compared with serum-free RPMI (control) in fibroblasts derived from IPF lungs (A, C, E) and non-fibrotic control lungs (B, D, F). Primary human lung fibroblasts derived from IPF patients and from non-fibrotic lungs were pre-incubated for 30 minutes with increasing concentrations of nintedanib (0.001, 0.01, 0.1, and 1 μM), before adding PDGF-BB (10 ng/ml), bFGF (10 ng/ml), and VEGF (10 ng/ml) for 48 hours. Serum-free RPMI served as control. Cell growth was assessed by manual cell counting, and values are presented as mean ± SEM of triplicate independent experiments performed in 4 different cell lines, expressed as relative proliferation compared to control (serum-free RPMI medium) which was set to 100%. *p < 0.05.