1. ¹Department of Ophthalmology, Kresge Eye Institute, Wayne State University School of Medicine, Detroit, MI, USA
2. ²Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, MI, USA
3. ³Department of Biomedical Sciences, University of Detroit Mercy School of Dentistry, Detroit, MI, USA

Correspondence: Professor F-SX Yu, Kresge Eye Institute/Department of Ophthalmology, Wayne State University School of Medicine, 4717 St Antoine Blvd, Detroit, MI 48201, USA. E-mail: fyu@med.wayne.edu

Received 20 June 2008; Revised 11 September 2008; Accepted 12 September 2008; Published online 21 October 2008.

Abstract

In the present study we tested the responsiveness of human corneal epithelial cells (HCECs) and corneal fibroblasts to lipopolysaccharide (LPS), a Toll-like receptor (TLR) 4 ligand. Purified Pseudomonas aeruginosa LPS was used to stimulate telomerase-immortalized HCECs (HUCL) and stromal fibroblast (THK) cell lines. Exposure of cells to LPS induced a time-dependent activation of NF-B in THK but not in HUCL cells, as assessed by an increase in IB- phosphorylation and degradation. Concomitant with NF-B activation, LPS-treated THK cells, but not HUCL cells, produced a significantly larger number of cytokines than control untreated cells. A cell surface biotinylation assay revealed that HUCL cells express TLR4 intracellularly, whereas TLR5 is expressed on the cell surface. Furthermore, reverse transcriptase-PCR analysis revealed that HUCL and primary HCECs, in contrast to THK cells, do not express myeloid differentiation (MD)-2. Thus, our results demonstrate that the LPS unresponsiveness of HCECs might be due to deficient expression of MD-2, an essential component for LPS-TLR4 signaling.