Polarized secretion of IL-6 and IL-8 by human retinal pigment epithelial cells

A number of cell types situated along interfaces of various tissues and organs such as the peritoneum and the intestine have been shown to secrete inflammatory cytokines in a polarized fashion. Retinal pigment epithelial (RPE) cells are positioned at the interface between the vascularized choroid and the avascular retina, forming part of the blood–retina barrier. These cells are potent producers of inflammatory cytokines and are therefore considered to play an important role in the pathogenesis of ocular inflammation. Whether cytokine secretion by these cells also follows a vectorial pattern is not yet known, and was therefore the subject of this study. Monolayers of human RPE cells (primary cultures and the ARPE-19 cell line) cultured on transwell filters were stimulated to produce IL-6 and IL-8 by adding IL-1β (100 U/ml) to either the upper or the lower compartment. After stimulation, the human RPE cell lines showed polarized secretion of IL-6 and IL-8 towards the basal side, irrespective of the side of stimulation. The ARPE-19 cell line also secreted IL-6 and IL-8 in a polarized fashion towards the basal side after basal stimulation; polarized secretion was, however, not apparent after apical stimulation. The observation that human RPE cells secrete IL-6 and IL-8 in a polarized fashion towards the choroid may represent a mechanism to prevent damage to the adjacent fragile retinal tissue.     

Monocyte chemotactic protein gene expression by cytokine-treated human retinal pigment epithelial cells

Inflammation involving the retina and choroid is a common clinical problem, but the mechanisms that elicit and maintain ocular inflammation remain poorly understood. Interposed between the sensory retina and the systemic blood circulation within the choroid is the neural-derived retinal pigment epithelium (RPE), which forms part of the blood-retina barrier. The RPE is actively phagocytic and shares several features with mononuclear phagocytes of bone marrow origin, including the production of a neutrophil chemotactic factor, interleukin 8, after stimulation with interleukin 1 beta (IL-1 beta) or tumor necrosis factor alpha (TNF-alpha). Because monocyte-derived macrophages are present in retinal lesions of many common and blinding diseases, we monitored human RPE cells or monocyte chemotactic protein (MCP) mRNA expression and activity following cytokine stimulation. Cultured human RPE cells were left unstimulated or exposed to recombinant human IL-1 beta, TNF-alpha, or lipopolysaccharide. MCP mRNA expression in RPE cells and biologically active MCP in RPE cell supernatants were present 1 hour after stimulation and maintained for 24 hours. Conditioned media from RPE cells stimulated with 20 ng/ml of IL-1 beta or TNF-alpha for 24 hours contained biologically active monocyte chemotactic activity that rose rapidly from baseline levels over 4 hours and plateaued over the subsequent 20 hours. RPE chemotactic activity was dose dependent using concentrations of these cytokines ranging from 20 pg/ml to 20 ng/ml of 4-hour assays. Time- and concentration-dependent expression of RPE cell MCP mRNA was also found in the same cultures. Peak MCP mRNA expression occurred after 8 hours of stimulation with IL-1 beta or TNF-alpha. Maximal steady-state MCP mRNA expression occurred at 20 ng/ml for IL-1 beta. Immunohistochemical staining using specific anti-MCP antibodies resulted in distinctive RPE cell staining, confirming the presence of MCP in human RPE cells. These findings demonstrate that cytokine-stimulated RPE cells may evoke or augment mononuclear phagocyte-mediated ocular inflammation by synthesizing MCP.     

Class II antigen expression and gamma interferon modulation of monocytes and retinal pigment epithelial cells from patients with retinitis pigmentosa

Monocytes from retinitis pigmentosa patients express diminished amounts of class II (HLA-DR) antigens in comparison to normal individuals, normal siblings of retinitis pigmentosa patients, glaucoma patients, and macular degeneration patients. This observation is correlated with a subnormal production of IFN-gamma, a potent regulator of class II antigen expression. When monocytes from retinitis pigmentosa patients are treated with IFN-gamma, the decreased expression of HLA-DR on the cell surface is restored to levels found on monocytes from normal individuals. HLA-DR antigens were detected on the surfaces of human retinal pigment epithelial cells grown in vitro and the expression of these antigens can be enhanced following IFN-gamma treatment. These data demonstrate an altered expression and regulation of class II, HLA-DR, antigens in a human eye disease. Since class II antigens and IFN-gamma are currently known to be necessary regulating proteins for efficient immune reactivity, these findings may indicate an immune disturbance in retinitis pigmentosa patients. Alternatively, this alteration may have nonimmune implications. For example, these studies may demonstrate an imbalance in systemic regulatory control systems and hence raise the possibility that these or related regulatory proteins and cell surface receptors may be instrumental in maintaining retinal integrity.     

Lack of FasL expression in cultured human retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cells have been proposed to play a part in maintaining the eye as an immune privileged organ. However, our knowledge of the implicated mechanism is still sparse. Fas ligand (FasL) expression of RPE cells is generally recognized to be essential for the immune privilege of the eye, but due to contradictory published results, it is unclear whether RPE cells express this molecule. The purpose of this study was to investigate the expression of FasL in RPE cells in vitro and in vivo. Cultured human fetal and adult RPE cells were examined by flow cytometry, Western blotting, RT-PCR and RNase Protection assay for FasL expression. Additionally, sections of ocular tissue were stained for FasL by immunohistochemistry. None of the used methods indicated FasL expression in cultured fetal or adult RPE cells of various passages. However, RPE cells in vivo, as judged from tissue sections, were positive for FasL, indicating a discrepancy between RPE cells in vitro and in vivo with regard to this molecule.     

Neutrophil chemotactic factor (IL-8) gene expression by cytokine-treated retinal pigment epithelial cells.

The neural-derived retinal pigment epithelium (RPE) underlies the sensory retina and is central to both retinal homeostasis and many common retinal diseases. Retinal pigment epithelium cells are actively phagocytic and share several features with macrophages that have recently been shown to produce a neutrophil chemotactic factor (NCF), also known as interleukin-8, after cytokine stimulation. Because RPE cell responses to cytokines are largely unknown, human RPE cell NCF production was monitored after interleukin-1-beta (IL-1 beta), tumor necrosis factor-alpha, or lipopolysaccharide stimulation. RPE NCF mRNA expression and RPE production of biologically active NCF was time and concentration dependent. Maximal NCF mRNA expression occurred at 20 ng/ml for IL-1 beta. Messenger RNA expression in RPE cells and biologically active NCF in RPE cell supernatants were found 1 hour after stimulation and were maintained for 24 hours. These findings demonstrate that cytokine-stimulated RPE cells may evoke or augment neutrophil-mediated inflammation by synthesizing NCF, a cytokine that may be important in ocular disease mechanisms.     

Bordetella pertussis adenylate cyclase-hemolysin induces interleukin-6 secretion by human tracheal epithelial cells

After interaction with tracheal epithelial cells, Bordetella pertussis induces the secretion of interleukin-6. This secretion is dependent on the expression of adenylate cyclase-hemolysin by the bacterium but not on the expression of other characterized bacterial toxins or adhesins. This finding confirms the important role of adenylate cyclase-hemolysin in the pathogenicity of the bacterium.     

Transforming growth factor-beta enhances interleukin-6 secretion by intestinal epithelial cells.

Recent reports have suggested that transforming growth factor-beta (TGF-beta) may have an important role in IgA immune responses, e.g. induction of surface IgM+ B cells to commit to IgA. TGF-beta is also an important regulatory cytokine for the maturation of intestinal epithelial cells. Using the IEC-6 rat intestinal epithelial cell line as a model system, TGF-beta 1 was found to enhance interleukin-6 (IL-6) secretion by the IEC-6 cells. The IL-6 was produced in a dose-dependent manner and secretion could be specifically inhibited by an anti-TGF-beta 1 antibody. IL-6 production by the IEC-6 cells was confirmed by using a rabbit anti-mouse IL-6 antibody which completely neutralized the IL-6 present in the IEC-6 cell supernatant. The enhancement of IL-6 secretion was found to involve a low-level enhancement in the expression of RNA for IL-6. The induction of IL-6 secretion was also reversible when TGF-beta was removed. These results suggest that the action of TGF-beta on intestinal epithelial cells may play an important role in immune responses at the intestinal mucosa.     

Regulation of natural antibiotic expression by inflammatory mediators and mimics of infection in human endometrial epithelial cells

The natural antibiotic molecules, beta-defensins 1 and 2 (HBD1/2) and secretory leukocyte protease inhibitor (SLPI), have an important role in mucosal defence and are present in the uterus. This study details their regulation in primary endometrial epithelial cells and in two endometrial cell lines (MFE/HES). Cells were treated with proinflammatory molecules and mimics of infection [lipopolysaccharide (LPS) and lipoteichoic acid (LTA)]. mRNA for HBD1, HBD2 and SLPI was detected in primary endometrial epithelial cells using real-time quantitative PCR. HBD1 mRNA was present at very low levels preventing conclusive study of its regulation. However, HBD2 mRNA expression was increased by interferon-gamma, interleukin (IL)-1beta alone and IL-1beta+tumour necrosis factor (TNF)-alpha. SLPI mRNA was not affected by proinflammatory mediators, although protein levels fell in the presence of IL-1beta+TNFalpha. LPS had little effect on antimicrobial expression. However, there was a trend towards increased expression with LTA treatment for 4-8 h. Antimicrobial expression in endometrial cell lines was similar to that in primary cells, although SLPI was increased by IL-1beta+TNFalpha treatment. These results suggest that in endometrium some natural antibiotics (e.g. SLPI) may be constitutively expressed providing a basal level of protection, while others (e.g. HBD2) are inducible allowing maximal antimicrobial activity during infection. Natural antimicrobials will have an important role in endometrium in protecting against infection.     

Preeclampsia-related inflammatory cytokines regulate interleukin-6 expression in human decidual cells

Preeclampsia, a common pregnancy disorder associated with an increase in systemic inflammation, is the leading cause of maternal and fetal morbidity and mortality throughout the world. It is associated with shallow extravillous trophoblast invasion of the decidua, leading to uteroplacental blood flow that is inadequate for the developing fetal-placental unit. In preeclamptic women, interleukin-6 (IL-6) levels in plasma, but not placenta, are elevated, prompting evaluation of the decidua as a potential source of this excess, circulating IL-6. The current study found significantly higher immunohistochemical staining for IL-6 in decidual cells from preeclamptic versus preterm, gestational age-matched control placentas. Pro-inflammatory cytokines associated with the genesis of preeclampsia (i.e., tumor necrosis factor-alpha and interleukin-1beta) enhanced IL-6 mRNA levels and increased secreted IL-6 levels in first trimester leukocyte-free decidual cell incubations, as measured by real time quantitative RT-PCR, ELISA, and Western blotting. Therefore, decidual cell-derived IL-6 may contribute to excess circulating IL-6 levels that can promote both endothelial cell dysfunction (and subsequent vascular dysfunction) and the pathogenesis of preeclampsia whereas locally elevated IL-6 levels may contribute to an excess of decidual macrophages implicated in shallow extravillous trophoblast invasion of the decidua.     

Glucocorticoid enhances gamma interferon effects on human monocyte antigen expression and ADCC.

The expression of HLA-DR antigen by highly enriched human monocytes cultured in serum free medium was found to be markedly elevated by human recombinant gamma interferon (IFN-gamma). This effect was maximal after 48 h in culture with 300 mu/ml IFN-gamma. Class I MHC antigen also increased with IFN-gamma treatment. By contrast, binding of a myeloid-specific monoclonal antibody, AML-2-23, was dramatically decreased by IFN-gamma. The augmentation of MHC antigens was not ablated by an immunosuppressive concentration (2 X 10(-7) M) of the glucocorticoid dexamethasone (DEX). In fact, both the enhancement of Class I and Class II MHC antigen expression and the suppression of AML-2-23 antigen by IFN-gamma were often more profound in the presence of DEX. IFN-gamma treatment also resulted in elevated monocyte effector function, as measured by antibody dependent cellular cytotoxicity (ADCC). This functional activation was not inhibited by DEX. On the contrary, DEX slightly augmented IFN-gamma effects on ADCC. This contrasts with other reports that glucocorticoids inhibit monocyte responsiveness to lymphokines, and suggests that the interplay between lymphokines and the glucocorticoid hormones may be more complex than previously thought.     

Two-photon excited autofluorescence imaging of human retinal pigment epithelial cells

Degeneration of retinal pigment epithelial (RPE) cells severely impairs the visual function of retina photoreceptors. However, little is known about the events that trigger the death of RPE cells at the subcellular level. Two-photon excited autofluorescence (TPEF) imaging of RPE cells proves to be well suited to investigate both the morphological and the spectral characteristics of the human RPE cells. The dominant fluorophores of autofluorescence derive from lipofuscin (LF) granules that accumulate in the cytoplasm of the RPE cells with increasing age. Spectral TPEF imaging reveals the existence of abnormal LF granules with blue shifted autofluorescence in RPE cells of aging patients and brings new insights into the complicated composition of the LF granules. Based on a proposed two-photon laser scanning ophthalmoscope, TPEF imaging of the living retina may be valuable for diagnostic and pathological studies of age related eye diseases.     

灯盏花素对人视网膜色素上皮细胞和糖尿病大鼠视网膜VEGF表达的影响

目的:观察灯盏花素对高糖环境下人视网膜色素上皮细胞株ARPE-19中VEGF、VEGFR2和pERK蛋白的表达及对2型糖尿病大鼠视网膜VEGF表达的影响。方法:培养ARPE-19细胞,分为对照组、灯盏花素组、高糖组和高糖+灯盏花素组,ELISA检测VEGF的分泌水平,Western blot检测细胞VEGF、VEGFR2和p-ERK的蛋白水平;取正常大鼠,随机分为正常对照组、灯盏花素组、糖尿病模型组和糖尿病灯盏花素治疗组,16周后取各组大鼠眼球,观察大鼠视网膜的病理变化并评分,免疫组化观察VEGF的表达情况。结果:(1)细胞实验结果显示,灯盏花素组VEGF、VEGFR2和p-ERK的蛋白水平与正常对照组比较均减低(P0.05);高糖组细胞上述蛋白水平与正常对照组比较均增加(P0.05);高糖+灯盏花素组上述蛋白水平与高糖组比较表达均减少(P0.05);(2)大鼠视网膜病理学评分显示糖尿病组与正常对照组、糖尿病灯盏花素治疗组相比差异显著,灯盏花素组与正常对照组相比差异无统计学意义。糖尿病大鼠与正常对照组、灯盏花素组相比,视网膜VEGF的表达增加;糖尿病灯盏花素治疗组中VEGF的表达较糖尿病组有所降低(P0.05)。结论:灯盏花素可以降低ARPE-19细胞VEGF、VEGFR2和p-ERK的蛋白表达水平,抑制糖尿病大鼠视网膜VEGF的表达,提示灯盏花素可能通过降低糖尿病大鼠视网膜细胞和组织中VEGF的表达,缓解其糖尿病视网膜病变进程。     

Differential cytokine expression of human retinal pigment epithelial cells in response to stimulation by C5a

Human retinal pigment epithelial (RPE) cells form part of the blood-retina barrier where they potentially can regulate leucocyte function. RPE cells are known to secrete several cytokines in response to stimulation by other cytokines. Anaphylatoxin C5a, a potent inflammatory mediator produced during complement activation, binds to G-protein coupled C5a receptors (C5aR) on monocytes/macrophages and releases various cytokines from the cells. We previously reported that the human RPE cell line ARPE-19 possesses C5aR and expresses IL-8 mRNA in response to C5a stimulation. In this study, we used a primary human RPE cell line (RPE43) and found that C5a induces increased expression of IL-1beta, IL-6, MCP-1 and GM-CSF mRNAs as well as IL-8 mRNA. ARPE-19 cells showed similar increases in the same cytokines. Interestingly, the kinetics of expression of the various cytokines differed. These results provide further evidence that C5a stimulation of RPE cells may play a role in regulating leucocyte function during ocular inflammation in which there is complement activation.     

Thrombin induces Sp1-mediated antiviral effects in cytomegalovirus-infected human retinal pigment epithelial cells

Human cytomegalovirus (HCMV) retinitis causing retinal detachment and destruction of the blood-retina barrier is closely related to retinal hemorrhage/coagulation. However, the effects of procoagulants on HCMV (re)activation in retinal cells have not been investigated yet. Therefore, we studied whether thrombin modulates the expression of HCMV immediate early (IE) and late (L) genes in cultured human retinal pigment epithelial cells (RPE). Thrombin specifically stimulated the protease-activated receptor-1 (PAR-1) on RPE and, surprisingly, inhibited basal and 12,0-tetradecanoylphorbol 13-acetate-stimulated HCMV IE gene expression in infected RPE. On the other hand, HCMV strongly induced Sp1 DNA binding activity, which was prevented by thrombin/PAR1-mediated Sp1 hyperphosphorylation. Our data suggest that thrombin/PAR-1 may inhibit Sp1-dependent HCMV replication, which might be an important regulatory mechanism for HCMV persistence and replication in RPE.     

Modulation of CD4 antigen expression on human gingival Langerhans cells by gamma interferon.

Human gingival organ culture was used to test the hypothesis that gamma interferon (gamma-IFN), which induces HLA-DR and HLA-DQ antigens on Langerhans cells, modulates CD4 antigen expression on these same cells. Before culture, the density of CD4+ cells in the gingival epithelium was 12.7% +/- 3.8% of the density of CD1+ cells. gamma-IFN (200 IU/ml) enhanced CD4 expression such that at 24 h, all CD1+ cells also expressed CD4. Prostaglandin E2, which in isolation had no effect, partially abrogated the stimulatory effect of gamma-IFN on CD4 expression. These results imply that gamma-IFN and prostaglandin E2 are two signals which regulate CD4 expression on gingival Langerhans cells.     

Enhancing effect of cholera toxin on interleukin-6 secretion by IEC-6 intestinal epithelial cells: mode of action and augmenting effect of inflammatory cytokines.

Oral administration of cholera toxin (CT) induces a strong mucosal immune response to CT as well as having a potent adjuvant effect. Since one of the first cell types to encounter CT during cholera infection or after oral administration is the epithelial cell, we studied the effect of CT on interleukin-6 (IL-6) secretion by the rat intestinal epithelial cell line IEC-6. CT was found to rapidly enhance IL-6 secretion and IL-6 gene expression by these cells. The addition of dibutyryl cyclic AMP (cAMP) to cultures of IEC-6 cells had little effect on IL-6 secretion, yet mRNA levels were elevated, suggesting that the response may have been regulated by cAMP. Purified B subunit of CT did not significantly enhance IL-6 secretion or mRNA expression. CT and transforming growth factor beta 1 synergistically enhanced IL-6 secretion in IEC-6 cells. The addition of CT with either IL-1 beta or tumor necrosis factor alpha gave even greater synergistic enhancement of IL-6 secretion, and dibutyryl cAMP could mimic CT's synergy with IL-1 beta. These results indicate that the intestinal epithelial cell is capable of secreting high levels of IL-6 after encountering CT, especially in the presence of inflammatory cytokines. This high level of IL-6 secretion could be a very important component of the mucosal immune response to CT and may also account for a portion of the adjuvant effect of CT.