OBJECTIVETo investigate the expression of the Toll-like receptor-4 (TLR-4) in temporo-mandibular joint synovitis in rats, and to discuss the correlation between the expression of TLR-4 and the synovitis.

METHODSSixty male wistar rats were randomly divided into five groups, 12 each. Group A was the control group in which the rats were given normal diet.In Group B, the rats' bilateral masseter muscles were cut off (masseter resection group). In Group C, An cast metal crown were bonded on the mandibular right first molar of each rat (occlusal interference group). In Group D, occlusal pad were bonded on maxillary molars of each rat (occlusal dimension increase group). In Group E, rats' bilateral masseter muscles were re-sected and occlusal pads were bonded on their maxillary molars (masseter resection and occlusal dimension increase group). Pathological changes of synovium were observed using hematoxylin and eosin (HE) stains and pathology scores were evaluated. The expression of TLR- 4 were determined by immunohistochemical stains, and the expression of TLR-4 mRNA were determined by real-time PCR. The correlation between the expression of TLR-4, TLR-4 mRNA and the pathological score were analyzed using Spearman analysis.

RESULTSThe pathological scores of Group A-E were 0.5 ± 0.5, 2.5 ± 1.0, 2.7 ± 1.0, 3.0 ± 0.9, 5.3 ± 1.2 respectively. The expression of TLR-4 were (3.2 ± 1.5)%, (16.± 2.6)%, (15.8 ± 2.1)%, (17.5 ± 2.4)%, (38.2 ± 4.4) %. The expression of TLR-4 mRNA were 1.07 ± 0.09, 2.12 ± 0.33, 2.07 ± 0.29, 2.17 ± 0.34, 4.53 ± 0.46. Compared with group A, groups B- E showed significant higher pathology score (P < 0.05) and increased expression of both TLR-4 (P < 0.05) and TLR-4 mRNA (P < 0.05). An significant positive correlation was found between the expression of TLR- 4 and the pathology score (r = 0.785, P < 0.05), and between the expression of TLR- 4 mRNA and the pathology score (r = 0.720, P < 0.05).

CONCLUSIONSTLR-4 may be closely associated with the development of the synovitis of TMJ of rats.