Tissue expression of Toll-like receptors 2 and 4 in sporadic human colorectal cancer

BACKGROUND: Toll-like receptors (TLRs) play an important role in innate immunity by sensing a variety of pathogens and inducing acquired immunity. To test our hypothesis that dysregulation of innate immune responses acts to trigger carcinogenesis, we studied the expression of TLR2 and 4 in sporadic human colorectal cancer tissue. METHODS: In specimens of cancerous and noncancerous colorectal tissue obtained at surgery, mRNA expression levels of TLR2 and 4 were quantified by TaqMan real-time polymerase chain reaction and compared between the two types of tissue. To confirm TLR2 and TLR4 protein expression levels, immunohistochemical analysis was performed using the same samples. RESULTS: TLR2 mRNA expression was significantly higher in cancerous tissue than in noncancerous tissue, while TLR4 mRNA expression did not differ significantly. Immunohistochemical analysis revealed stronger staining for TLR2 in cancerous mucosal epithelial cells than in noncancerous tissue. Staining for TLR4 in the lamina propria of the mucosa was equally weakly positive in noncancerous tissue and cancerous tissue. This TLR-specific difference in expression suggested that such expression does not only reflect a local inflammatory response to cancer infiltration, i.e., if this was the case, both TLR2 and 4 expression would probably be up-regulated. Our results suggest that TLR2 expression might be involved in sporadic colorectal carcinogenesis, whereas TLR4 is not.