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MV Kumar, CN Nagineni, JJ Hooks, B Detrick; Expression of Toll-Like Receptors in Human Retinal Pigment Epithelial Cells . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1563.
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Purpose: Toll-Like Receptors (TLR) are involved in the innate immune response associated with microbial pathogens. We investigated and compared the gene expression and cytoplasmic protein levels of TLRs in human retinal pigment epithelial cells (HRPE) and human monocyte cells. Methods: HRPE cell cultures were stimulated with LPS (Salmonella typhosa) at 1µg/ml and/ or interferon-gamma (IFN-γ) 100 U/ml for 6 hours. Total RNA prepared from control unstimulated and stimulated cells were used for analysis of the steady state levels of the TLR mRNA by RT-PCR. By using monoclonal antibodies against TLR-2 and TLR-4, the presence of these proteins were evaluated by immunofluorescence. The human monocyte cell line (U937) was used as a control cell line. Results: TLR 1 and 2 were expressed in unstimulated HRPE and were not significantly affected by either LPS or IFN-γ. In contrast, gene expression of TLR-3 and 4 were up regulated by both IFN-γ and LPS. The most prominent enhancement of TLR gene expression in HRPE was seen with TLR-3. Low levels of gene expression of TLR-5 and 9 were observed in unstimulated cells and were not altered after LPS and/ or IFN-γ treatment. The relative intensities of the basal levels of TLR gene expression in HRPE was in decreasing order, TLR- 2, 3, 1, 4, 9 and 5 where as in U937 cells it was TLR 4,5,2,1,9 and 3. In contrast, the constitutive expression of TLR 5 and 3 are different in HRPE and U937cells. HRPE showed enhanced cytoplasmic staining for TLR-2 and TLR-4 in cells treated with IFN-γ. Conclusion: The differential expression of TLRs in HRPE and U937 cells suggest that retinal cells and monocytes respond uniquely to microbial products. IFN-γ, which is elevated during inflammatory and infectious diseases, can up regulate selective TLRs in HRPE and may thereby participate in immunopathogenic processes.
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