Attachment of Treponema pallidum to human brain microvascular endothelial cells in vitro: an experimental study

Abstract

Objective To observe the attachment of Treponema pallidum to human brain microvascular endothelial cells (HBMECs) in vitro. Methods Some primary cultured HBMECs were inoculated into in 24-well plates to be cocultured with the suspension of T. pallidum at a concentration of 1.6 × 107 treponemes/ml. After 0.5, 2 and 4 hours of co-culture, scanning electron microscopy was conducted to observe the attachment of T. pallidum to HBMECs. Some HBMECs were cocultured with the presence of T. pallidum suspensions at different concentrations (4 × 106, 8 × 106, 1.6 × 107 treponemes/ml) for 2, 4, 6 and 16 hours, then, dark-field microscopy was performed to count the number of treponemes that attached to single HBMECs. Statistical analysis was carried out by using repeated-measures analysis of variance. Results As scanning electron microscopy showed, treponemes gathered at some regions on the surface of HBMECs when they attached to HBMECs. In addition, T. pallidum partly merged with the membrane of HBMECs at the site of attachment. After co-culture with T. pallidum suspensions, the number of treponemes that attached to single HBMECs was significantly different among different time points (F= 387.72, P< 0.001) and among different concentrations of T. pallidum suspensions (F= 593.23, P< 0.001) , with an interaction effect between the concentration of T. pallidum suspensions and incubation period (F= 98.74, P< 0.001). Concretely speaking, the number of treponemes that attached to single HBMECs increased over time until 6 hours after the start of coculture, then showed a decreasing trend, and reached the nadir value at 16 hours. Conclusion T. pallidum can adhere to cultured HBMECs in vitro, likely by the merger of its end with the membrane of HBMECs at some regions. Key words: Treponema pallidum; Endothelial cells; Microvessels; Human brain microvascular endothelial cells