[Effects of Enterococcus faecalis supernatants on inflammatory responses of human periodontal ligament cells under pressure].

Objective: To study the effect of various concentrations of Enterococcus faecalis (Ef) supernatants on human periodontal ligament cell (hPDLC) and the inflammatory response of hPDLC under static pressure. Methods: The method of methyl thiazolyl tetrazolium (MTT) was used to detect the effect of various concentrations of Ef supernatants on the proliferation of hPDLCs and the flow cytometry was used to detect the expression of Toll-like receptor 2 (TLR-2) on the surface of hPDLC after 24-hour-stimulation of Ef supernatant. Furthermore, the hPDLCs were divided into non inducing group without Ef supernatant and inducing group with 5% Ef supernatant, and hPDLCs in each group were loaded with 0, 49 and 196 Pa static pressures respectively. The expressions of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) mRNA and protein were detected by reverse transcription-PCR (RT-PCR) and enzyme linked immunosorbent assay (ELISA) after 24 hours. Results: MTT results showed that the supernatant of Ef with concentratio n ≥5% could significantly inhibit the proliferation activity of hPDLCs at 48 hours of cell culture ( P< 0.05). Flow cytometry showed that the positive cell rates of TLR-2 increased with increasing volume fractions of the Ef supernatants. The values were (2.12±0.07)%, (2.41±0.32)%, (2.65±0.27)%, (4.76±0.46)%, (9.91±0.92)% and (12.01±1.35)%, respectively. The differences were statistically significant when the concentrations≥5% ( P< 0.05). There were no significant differences in the expressions of IL-1β and TNF-α mRNA between the non inducing group and the control group under the pressure of 49 Pa ( P> 0.05). However, there were significant differences in the expressions of IL-1β and TNF-α mRNA between the non inducing group and the control group under the pressure of 196 Pa ( P< 0.05), while the expressions of IL-1β and TNF-α in the inducing group were significantly lower than that in the control group under the pressures of 49 and 196 Pa ( P< 0.05). Compared with the control group, the mRNA expression was significantly increased ( P< 0.05). The result of ELISA was consistent with that of PCR. Conclusions: High concentration of Ef supernatant could inhibit the proliferation of hPDLC. Ef supernatant might promote the expression of TLR-2 on the surface of hPDLC. Excessive mechanical pressure induced the inflammatory response of hPDLC. The presence of inflammatory mediators could lead to the intolerance of hPDLC to pressures and small pressure could aggravate the inflammatory response.