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Graham R. Wallace, Lie Liu, Elizabeth A. Walker, Radhika Susarla, Iwona Bujalska, Jawaher Al-Salem, Paul J. Tomlins, Antal Rot, Philip I. Murray, Saaeha Rauz; Pre-receptor Regulation of Glucocorticoid Effects by Immunoregulatory Components in Human Corneal Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4363.
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© ARVO (1962-2015); The Authors (2016-present)
Toll like receptors (TLR) are a family of pattern recognition molecules that act as first line of defense against a variety of pathogens. Although exogenous glucocorticoids (GCs) are widely used in the treatment for ocular infections to curb the inflammatory response to limit tissue damage, cell specific GC (cortisol) production via the enzyme 11-beta hydroxysteroid dehydrogenase type 1 (11β-HSD1) may contribute to the immune privileged status of the ocular surface, either alone or via innate immune responses mediated by TLR pathways. In this study, TLR and GC pathways were characterised in human corneal epithelial cells (HCEC) and fibroblasts (HKF).
Primary (P)HCEC and HKF were cultured from redundant corneal-scleral transplant tissue, and macrophage populations (M1, M2) were generated from peripheral blood mononuclear cells (M1: GM-CSF and M2: M-CSF). TLR, 11β-HSD1, glucocorticoid receptor (GR) and Hexose-6-phosphate dehydrogenase (H6PDH) expression and interaction was defined by a combination of conventional RT-PCR, conversion assays for 11β-HSD1 activity, cytokine ELISA/luminex bead assays, and macrophage migration assays.
Both PHCEC and HKF expressed all TLR with the exception of TLR6 and TLR8. 11β-HSD1, GR, H6PDH were expressed in all cell types and these were capable of generating cortisol (M1>HKF>M2>PHCEC). Stimulation of the corneal cells with the TLR3 and 4 agonists induced maximal cytokine and chemokine production (TLR3, PHCEC= MCP1, IL6, CXCL10, IFNγ, TNFα; TLR 4, HKF= RANTES, CXCL10, VEGF, IFNγ), but TLR agonists 1-9 did not affect 11β-HSD1 bioactivity in either of the cell types. TLR3 and 4 stimulation of the corneal cell monolayers induced macrophage migration in both cell types (HKF>PHCEC), but this was most striking after LPS stimulation of the HKF and poly I:C stimulation of PHCEC with associated induction in M1 cortisol bioavailability. Furthermore, GCs (cortisol, dexamethasone) dampened cytokine production in the HKF, but not in the PHCEC.
PHCECs and HKFs have the potential to respond to microbial pathogens through TLR-mediated pathways, resulting in the production of cytokines and chemokines. They are also capable of intracellular production of GCs via the enzyme 11β-HSD1, which has an impact in regulating the ocular-surface defenses and immune response
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