KLF2 is an anti-inflammatory molecule26, and has an important role in maintaining endothelial function. TNFα-induced monocyte adhesion to ECs was then performed to evaluate the anti-inflammatory effect of TA in HCAECs and HUVECs. As shown in Fig. 4A,B, TNFα significantly induced monocyte adhesion to HCAECs compared with vehicle, while TA treatment significantly reversed TNFα-induced monocyte adhesion (Fig. 4A,B). In order to exclude cell viability affects monocyte adhesion by TA. We performed cell viability assay in HCAECs and HUVECs to evaluate the possible toxicity of TA. We found that TA at 10 µM did not cause obvious toxicity at the same condition with cell adhesion assay (data not shown).Figure 4TA attenuated monocyte adhesion to ECs. (A,B) HCAECs were pretreated with vehicle (DMSO) or TA (10.0 µM) for 12 h, and then exposed to TNFα (10 ng/ml) or vehicle (PBS) for an additional 6 h. Then, THP-1 monocytes were added for 30 min. (A) Images were taken from representative optical fields showing endothelial cells (cobblestone shape) and adhering THP-1 monocytes (small, round cells) in the co-culture. (B) THP-1 cells in panel A were counted and statistically analyzed. *p < 0.05, **p < 0.01, n = 4. (C–E) HUVECs were transfected with siRNA (control siRNA) or siKLF2 (KLF2 siRNA) for 48 h. Then the cells were pretreated vehicle (DMSO) or TA (10.0 µM) for 12 h, and then exposed to TNFα (10 ng/ml) or vehicle (PBS) for an additional 6 h. Then, THP-1 monocytes were added for 30 min. (C) The levels of KLF2 mRNA in ECs treated with control siRNA and KLF2 siRNA were analyzed by q-PCR. (D) Images were taken from representative optical fields showing endothelial cells (cobblestone shape) and adhering THP-1 monocytes (small, round cells) in the co-culture. (E) THP-1 cells in panel C were counted and statistically analyzed. One way ANOVA was used to analyze the data. *p < 0.05, **p < 0.01, n = 3.