To investigate the expression and significance of Toll-like receptor 9 (TLR9) and cyclooxygenase 2 (COX-2) in oral squamous cell carcinoma (OSCC) and paracancerous tissues.

A total of thirty-six patients with OSCC were selected, in which OSCC tissues and paracancerous tissues about 5 mm beyond the tumor boundary were obtained. The expression of TLR9 and COX-2 protein were detected by immunohistochemistry, and compared with 18 normal oral mucosa tissues. Image analysis was done to analyze the photos of the three kinds of tissues to calculate the average absorbance (A) value. The double-scoring semi-quantitative method was used to analyze the staining intensity of the specimens. The absorbance values of multiple groups were compared by One-Way analysis of variance, and the pairwise comparisons within the groups were done by LSD-t test; the positive rate of immunohistochemical staining among the three kinds of tissues was compared by chi-square test or Fisher′s exact probability method. The Spearman method was used to analyze the correlation of TLR9 and COX-2 expression in OSCC tissues and paracancerous tissues.

The average absorbance (A) values of TLR9 positive cells in OSCC, the paracancerous and normal tissues were 0.19 ± 0.06, 0.18 ± 0.05 and 0.13 ± 0.04, respectively, which was significant different (F = 8.022, P = 0.001) . Specifically, the average absorbance values of OSCC and paracancerous tissues were higher than that of normal oral mucosa tissues (t_OSCC = 3.99, P_OSCC<0.001, t_{paracancerous tissues} = 2.88, P_{paracancerous tissues} = 0.005) . The average A values of COX-2 positive cells in OSCC, the paracancerous and normal tissues were 0.20 ± 0.06, 0.18 ± 0.05 and 0.14 ± 0.04, respectively, which wassignificantly different (F = 7.716, P = 0.01) . The expression of COX-2 in OSCC tissue was higher than that in the paracancerous tissues (t = 2.00, P = 0.048) , and the expression of COX-2 in both OSCC and paracancerous tissues was higher than that in the normal oral mucosa tissues, which was statistically different (t_OSCC = 3.90, P_OSCC<0.001; t_{paracancerous tissue} = 2.25, P_{paracancerous tissue} = 0.027) . The positive rates of TLR9 and COX-2 in the three kinds of tissues were significantly different (χ^2TLR9 = 45.280, P_TLR9<0.001; χ²_COX-2 = 30.972, P_COX-2<0.001) . The positive rate of TLR9 in the cancerous and paracancerous tissues was higher than that of the normal oral mucosa tissues, and the difference is statistically significant (χ²_OSCC = 30.375, P_OSCC<0.001; χ²_{paracancerous tissues}=30.375, P_{paracancerous tissues}<0.001) .The positive rate of COX-2 in the cancerous and paracancerous tissues was higher than that in the normal oral mucosa tissues, which was statistically different (χ²_OSCC = 23.336, P_OSCC<0.001; χ²_{paracancerous tissues} = 17.763, P_{paracancerous tissues}<0.001) . The expressions of TLR9 and COX-2 in OSCC and paracancerous tissues were correlated (r_OSCC = 0.804, P_OSCC<0.001; r_{paracancerous tissues} = 0.533, P_{paracancerous tissues} = 0.001) .

TLR9 and COX-2 were highly expressed in OSCC and paracancerous tissues. TLR9 may play an important role in the occurrence and development of OSCC by regulating its downstream signal molecule COX-2.