[Down-regulation of Toll-like receptor 4 is related to the tolerance to lipopolysaccharide in rat alveolar macrophages].

OBJECTIVE: To explore the change of expression of Toll-like receptor 4 (TLR(4)) related to the tolerance to lipopolysaccharide (LPS) in rat alveolar macrophages. METHODS: Alveolar macrophages obtained from 30 Wistar male rats were randomly divided into a control group, a LPS single-dose stimulation group and a LPS double-dose stimulation group. IL-10 and IL-18 mRNA in alveolar macrophages and the level of TNF-alpha, as indexes of LPS tolerance, were measured by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and enzyme linked immunoads orbeen assay (ELISA), respectively. The expression of TLR(4) was detected by Western Blot. RESULTS: The level of TNF-alpha, and the mRNA for IL-10 and IL-18, and the protein of TLR(4) in the alveolar macrophages stimulated with single-dose LPS (100 ng/ml) were highly increased as compared with the control group [(0.760 +/- 0.030) micro g/L, 2.18 +/- 0.09, 1.83 +/- 0.07, 2.060 +/- 0.060, 148.3 +/- 1.4 vs (0.450 +/- 0.010) micro g/L, 1.16 +/- 0.04, 0.97 +/- 0.03, 1.320 +/- 0.020, 58.1 +/- 0.4 (P < 0.01)], while they were significantly decreased in the alveolar macrophages after re-stimulation with double-dose LPS (100 ng/ml and 500 ng/ml). CONCLUSIONS: (1) The tolerance to LPS in alveolar macrophages can be induced by re-stimulation with LPS. (2) The down-regulated expression of TLR(4) is related to tolerance to LPS.