OBJECTIVETo understand the effects of the IL-1, TNF-alpha cytokines on the pathogenesis of periapical lesions by investigating its gene expression in rat.

METHODSThe model was established by surgically exposing mandibular molar teeth and left open to permit infection from the oral environment. The SD rats were killed at 1, 2, 3, 4 weeks and mandibular molar teeth X-ray were taken. In situ hybridization was used to test IL-1alpha, IL-1beta, TNF-alpha mRNA expression in periapical area and the kinds of positive cells were identified. Using image analysis system analyzed gene expression semi-quantified.

RESULTSIL-1alpha, IL-1beta and TNF-alpha mRNA were all expressed beginning at 1 week, peaked at 3 weeks, and declined somewhat at 4 weeks, but IL-1beta mRNA was expressed at much lower levels with the same kinetics (P<0.01). Most of the staining occurred in areas that had heavy inflammatory infiltrate, fibroblasts, or endothelial cells. There was a statistically significant correlations between the area of periapical lesion and the number of positively stained cells for IL-1alpha and for TNF-alpha (IL-1alpha: r=0.875, P<0.001; TNF-alpha: r=0.858, P<0.001), and between the number of positive cells for IL-1alpha and that of for TNF-alpha (r=0.969, P<0.001).

CONCLUSIONSIL-1alpha and TNF-alpha genes are highly expressed in developing periapical lesions in rat, which supports the hypothesis that these two cytokines play a key role in pulpal and periapical pathogenesis, including the concomitant bone destruction.