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D. Bok, G.S. Hageman, J. Hu, L. Hancox, Y. Wang; Expression and functional analyses of toll–like receptors in human retinal pigment epithelial cells . Invest. Ophthalmol. Vis. Sci. 2004;45(13):636.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Retinal pigment epithelial (RPE) cells may be involved in local immune responses that participate in the pathogenesis of some retina–related diseases such as age–related macular degeneration. In this study we investigated the expression of toll–like receptors (TLRs) in RPE cells and the response of RPE cells to TLR ligand stimulation. Methods: Human fetal RPE cells were grown to confluence and a high state of differentiation on porous Millicell filters and treated with various TLR ligands (LPS for TLR4; synthetic lipopeptide, peptidoglycan and lipoteichoic acid for TLR2). The expression of TLR members (TLR1–10) in fetal RPE and adult donor RPE cells was examined by reverse transcription (RT)–PCR or Western blot analysis. Cytokine (MIP3α, IL1ß, IL6, IP10) expression in RPE cells was monitored by semi–quantitative RT–PCR or ELISA. RPE cell growth was determined by a metabolic colorometric assay. Results: All ten TLR family member genes were transcribed in fetal RPE cells grown on either flask or filters. RPE cells from various adult donors manifested different combinations of TLR expression. TLR2 expression in fetal RPE cells were confirmed by Western blot, but not detectable by flow cytometry. All TLR ligands increased mRNA levels of IL6, IL1ß and MIP3α. ELISA of RPE culture medium indicated that IL6 expression upregulation was dependent on ligand concentration. Comparison between IL6 concentrations in apical or basal chambers of RPE filters showed that cytokine secretion was directional, and RPE cells responded to apical or basal stimulation with differential dynamics. TLR2 ligands did not induce apoptosis in, or change the growth pattern of, RPE cells. No alteration of TLR expression was detected in TLR ligand treated RPE cells. Conclusion: RPE cells from adult human and fetal donor eyes express TLR family members. Functional assays demonstrate that RPE cells respond to TLR ligand stimulation as indicated by inflammatory cytokine expression. RPE cells respond to TLR ligands and secrete cytokines in a polarized fashion. As such, we propose that RPE cells may respond to local infectious stimuli through TLR signaling pathways in vivo.
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