Abstract: Zhang Ruili, Wang Qianqiu. Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing 210042, China Corresponding author: Wang Qianqiu, Email: wangqq@ncstdlc.org 【Abstract】 Objective To evaluate the effect of Treponema pallidum membrane protein Tpp47 on vascular endothelial cells. Methods Human umbilical vein endothelial cells （HUVECs） were classified into multiple groups to be cultured with various concentrations （50, 100, 200, 400 and 800 μg/L） of the recombinant protein Tpp47 or lipopolysaccharide （LPS） for different durations （3, 6, 12, 24 and 48 hours）. Then, enzyme-linked immunosorbent assay （ELISA） was performed to determine the levels of intercellular cell adhesion molecule-1 （ICAM-1） and E-selectin in the culture supernatant of, fluorescence-based real-time quantitative PCR to quantify the mRNA expressions of ICAM-1 and E-selectin in, HUVECs. The 3-（4,5-dimethylthiazol-2-yl）-2,5 diphenyl tetrazolium bromide （MTT） assay was used to evaluate the proliferation activity of HUVECs treated with Tpp47 （400 μg/L） and LPS （200 μg/L） respectively for 24 hours. To estimate the effect on adhesion ability, some HUVECs were pretreated with Tpp47 （400 μg/L） and LPS （200 μg/L） respectively for 24 hours followed by coculture with THP-1 human monocytic leukaemia cells for 6 hours, then, the adhesion of HUVECs to THP-1 cells was visualized by fluorescence microscopy. The cells receiving no treatment served as the blank control. Results A significant increase was observed in the supernatant level （expressed as the absorbance value at 450 nm） of ICAM-1 for HUVECs treated with Tpp47 of 400 μg/L for 24 hours （1.28 ± 0.03 vs. 0.90 ± 0.01, t = 18.28, P < 0.05） and that of E-selectin for HUVECs treated with Tpp47 of 400 μg/L for 12 hours （0.51 ± 0.01 vs. 0.13 ± 0.03, t = 18.19, P < 0.05） compared with untreated HUVECs. The adhesion rate to THP-1 cells was significantly higher in HUVECs pretreated with Tpp47 for 24 hours than in untreated HUVECs （56.1% ± 1.9% vs. 16.3% ± 2.1%, χ2 = 12.65, P < 0.05）. The cell proliferation rate was 19.5% ± 1.7% in HUVECs treated with Tpp47, significantly higher than that in untreated HUVECs （10.0% ± 3.1%, χ2 = 3.92, P < 0.05）, but lower than that in those treated with LPS （41.2% ± 3.7%, χ2 = 10.42, P < 0.05）. Conclusions The recombinant membrane protein Tpp47 could enhance HUVECs to proliferate and adhere to monocytic THP-1 cells, suggesting a certain role of Tpp47 in the pathogenesis of syphilis.

Key words: Treponema pallidum, Cell adhesion molecules, E-selectin, Tpp47, Human umbilical vein endothelial cells, Monocytic THP-1 cells