Abstract
Intercellular adhesion molecul-1 (ICAM-1) is a transmembrane glycoprotein belonging to the immunoglobulin superfamily of adhesion molecules and plays perdominant roles in recruitment and trafficking of leucocytes to sites of inflammation. ICAM-1 expression in intestinal epithelial cells (IECs) is enhanced by several stimuli, such as proinflammatory cytokines, bacterial infections or pathogen-associated molecular patterns. One of these stimuli, double-stranded RNA (dsRNA), is a by-product of viral replication and can be recognized by its cognate receptor Toll-like receptor 3 (TLR-3). In spite of expression of both TLR-3 and ICAM-1 in IECs, correlation between TLR-3-signalling and ICAM-1 expression has never been examined in IECs. In the present study, we investigated whether poly I:C, an analogue of dsRNA, can stimulate the expression of ICAM-1 in IEC line, HT-29. Poly I:C-stimulation up-regulated the expression of ICAM-1 mRNA by real-time polymerase chain reaction. Enhanced expression of ICAM-1 was confirmed in protein level by immunofluoresense cell staining and enzyme-linked immunosorbent assay by measuring the released soluble ICAM-1 in culture supernatant. As the stimulation effect was reduced by pre-treatment of the cells with anti-TLR-3 antibody, poly I:C-binding signal was thought to be sensed by TLR-3 on the surface of HT-29. The results of luciferase assay and nuclear factor kappa-b (NF-kappaB) inhibitor treatment experiments indicated that the downstream signal was mainly transduced by transcription factor, NF-kappaB. All these results demonstrated the connection between TLR-3 signalling and ICAM-1 expression in HT-29 cells and indicated the importance of coordinated function of both innate and adaptive immunity against viral infections.