mTOR-driven glycolysis governs induction of innate immune responses by bronchial epithelial cells exposed to the bacterial component flagellin.

Human bronchial epithelial (HBE) cells play an essential role during bacterial infections of the airways by sensing pathogens and orchestrating protective immune responses. We here sought to determine which metabolic pathways are utilized by HBE cells to mount innate immune responses upon exposure to a relevant bacterial agonist. Stimulation of HBE cells by the bacterial component flagellin triggered activation of the mTOR pathway resulting in an increased glycolytic flux that sustained the secretory activity of immune mediators by HBE cells. The mTOR inhibitor rapamycin impeded glycolysis and limited flagellin-induced secretion of immune mediators. The role of the mTOR pathway was recapitulated in vivo in a mouse model of flagellin-triggered lung innate immune responses. These data demonstrate that metabolic reprogramming via the mTOR pathway modulates activation of the respiratory epithelium, identifying mTOR as a potential therapeutic target to modulate mucosal immunity in the context of bacterial infections.

General, but not myeloid or type II lung epithelial cell, myeloid differentiation factor 88 deficiency abrogates house dust mite induced allergic lung inflammation.

Asthma is a highly prevalent chronic allergic inflammatory disease of the airways affecting people worldwide. House dust mite (HDM) is the most common allergen implicated in human allergic asthma. HDM-induced allergic responses are thought to depend upon activation of pathways involving Toll-like receptors and their adaptor protein myeloid differentiation factor 88 (MyD88). We sought here to determine the role of MyD88 in myeloid and type II lung epithelial cells in the development of asthma-like allergic disease using a mouse model. Repeated exposure to HDM caused allergic responses in control mice characterized by influx of eosinophils into the bronchoalveolar space and lung tissue, lung pathology and mucus production and protein leak into bronchoalveolar lavage fluid. All these responses were abrogated in mice with a general deficiency of MyD88 but unaltered in mice with MyD88 deficiency, specifically in myeloid or type II lung epithelial cells. We conclude that cells other than myeloid or type II lung epithelial cells are responsible for MyD88-dependent HDM-induced allergic airway inflammation.

Osteopontin promotes host defense during Klebsiella pneumoniae-induced pneumonia.

Klebsiella pneumoniae is a common cause of nosocomial pneumonia. Osteopontin (OPN) is a phosphorylated glycoprotein involved in inflammatory processes, some of which is mediated by CD44. The aim of this study was to determine the role of OPN during K. pneumoniae-induced pneumonia. Wild-type (WT) and OPN knockout (KO) mice were intranasally infected with 104 colony forming units of K. pneumoniae, or administered Klebsiella lipopolysaccharides (LPS). In addition, recombinant OPN (rOPN) was intranasally administered to WT and CD44 KO mice. During Klebsiella pneumonia, WT mice displayed elevated pulmonary and plasma OPN levels. OPN KO and WT mice showed similar pulmonary bacterial loads 6 h after infection; thereafter, Klebsiella loads were higher in lungs of OPN KO mice and the mortality rate in this group was higher than in WT mice. Early neutrophil recruitment into the bronchoalveolar space was impaired in the absence of OPN after intrapulmonary delivery of either Klebsiella bacteria or Klebsiella LPS. Moreover, rOPN induced neutrophil migration into the bronchoalveolar space, independent from CD44. In vitro, OPN did not affect K. pneumoniae growth or neutrophil function. In conclusion, OPN levels were rapidly increased in the bronchoalveolar space during K. pneumoniae pneumonia, where OPN serves a chemotactic function towards neutrophils, thereby facilitating an effective innate immune response.

Recent insights into the pathogenesis of bacterial sepsis.

Sepsis is a very heterogeneous clinical syndrome broadly defined as the systemic host response to an infection. Until very recently, the prevailing concept of the pathogenesis of sepsis was that mortality is the consequence of an uncontrolled hyperinf lammatory response of the host. The disappointing results of nearly 40 years of anti-inflammatory strategies and the development of animal models that more closely mimic clinical sepsis have led to the reconsideration of the pathophysiology of sepsis. Sepsis is now considered a misbalance between proinflammatory reactions (designed to kill invading pathogens but at the same time responsible for tissue damage) and anti-inflammatory responses (designed to limit excessive inflammation, but at the same time making the host more vulnerable for secondary infections). This review discusses key components of the pro- and anti-inflammatory response to sepsis, listing potential novel interventional strategies along the way.

Effect of acute hyperglycaemia and/or hyperinsulinaemia on proinflammatory gene expression, cytokine production and neutrophil function in humans.

AIMS: Type 2 diabetes is frequently associated with infectious complications. Swift activation of leucocytes is important for an adequate immune response. We determined the selective effects of hyperglycaemia and hyperinsulinaemia on lipopolysaccharide (LPS)-induced proinflammatory gene expression and cytokine production in leucocytes and on neutrophil functions. METHODS: Six healthy humans were studied on four occasions for 6 h during: (i) lower insulinaemic euglycaemic clamp, (ii) lower insulinaemic hyperglycaemic clamp, (iii) hyperinsulinaemic euglycaemic clamp, and (iv) hyperinsulinaemic hyperglycaemic clamp. Target levels of plasma glucose were 12.0 mmol/l (hyperglycaemic clamps) or 5.0 mmol/l (euglycaemic clamps). Target plasma insulin levels were 400 pmol/l (hyperinsulinaemic clamps) or 100 pmol/l (lower insulinaemic clamps). RESULTS: Hyperglycaemia reduced LPS-induced mRNA expression of nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor alpha (NFKBIA), interleukin-1 alpha (IL1A) and chemokine (C-C motif) ligand 3 (CCL3), whereas during hyperinsulinaemia enhanced mRNA levels occurred in six out of eight measured inflammation-related genes, irrespective of plasma glucose levels. Combined hyperglycaemia and hyperinsulinaemia led to enhanced IL1A, interleukin-1 beta (IL1B) and CCL3 mRNA levels upon LPS stimulation. Neither hyperglycaemia nor hyperinsulinaemia altered cytokine protein production, neutrophil migration, phagocytic capacity or oxidative burst activity. CONCLUSIONS: These results suggest that short-term hyperglycaemia and hyperinsulinaemia influence the expression of several inflammatory genes in an opposite direction, that the acute effects of hyperinsulinaemia on inflammatory mRNA levels may be stronger than those of hyperglycaemia, and that the effects of insulin, in particular, may be relevant in the concurrent presence of hyperglycaemia.

Toll-like receptor mRNA levels in alveolar macrophages after inhalation of endotoxin.

Toll-like receptors (TLRs) are pattern-recognition receptors that have been implicated in the initiation of innate immune responses upon the first encounter with invading pathogens. The airways are frequently exposed to various types of lipopolysaccharide (LPS) from the environment or from pathogens. The current study was designed to determine the effect of LPS on TLR gene expression in human alveolar macrophages in vivo. In total, 16 healthy subjects were enrolled in a single-blinded, placebo-controlled study. Subjects inhaled 100 microg LPS or normal saline (n = 8 per group). Measurements were performed in alveolar macrophages purified from bronchoalveolar lavage fluid obtained 6 h post-challenge. Inhalation of LPS by healthy human volunteers resulted in enhanced alveolar macrophage expression of mRNAs encoding TLRs 1, 2, 7, 8 and CD14, and reduced expression of mRNAs encoding TLR4 and lymphocyte antigen 96. In conclusion, lipopolysaccharide differentially influences the toll-like receptor mRNA expression profile in human alveolar macrophages in vivo.

Vagus nerve stimulation inhibits activation of coagulation and fibrinolysis during endotoxemia in rats.

BACKGROUND: Sepsis and endotoxemia are associated with concurrent activation of inflammation and the hemostatic mechanism, which both contribute to organ dysfunction and death. Electrical vagus nerve stimulation (VNS) has been found to inhibit tumor necrosis factor (TNF)-alpha release during endotoxemia in rodents. OBJECTIVE: To determine the effect of VNS on activation of coagulation and fibrinolysis. METHODS: Rats received a sublethal i.v. dose of lipopolysaccharide (LPS) after electrical VNS or sham stimulation. Activation of coagulation and fibrinolysis, as well as cytokine release, was measured before LPS injection and 2, 4 and 6 h thereafter. RESULTS: LPS induced activation of the coagulation system (increases in the plasma concentrations of thrombin-antithrombin complexes and D-dimer, and a decrease in antithrombin) and biphasic changes in the fibrinolytic system [early rises of plasminogen activator activity and tissue-type plasminogen activator, followed by a delayed increase in plasminogen activator inhibitor type 1 (PAI-1)]. VNS strongly inhibited all LPS-induced procoagulant responses and more modestly attenuated the fibrinolytic response. In addition, VNS attenuated the LPS-induced increases in plasma and splenic concentrations of the proinflammatory cytokines TNF-alpha and interleukin-6 (IL-6), while not influencing the release of the anti-inflammatory cytokine IL-10. CONCLUSION: These data illustrate a thus far unrecognized effect of VNS and suggest that the cholinergic anti-inflammatory pathway not only impacts on inflammation but also on the coagulant-anticoagulant balance.

Analysis of the cellular infiltrate in the iris during experimental autoimmune encephalomyelitis.

PURPOSE: Previous studies have shown that experimental autoimmune encephalomyelitis (EAE) and anterior uveitis (AU) develop in Lewis rats immunized with myelin basic protein (MBP). The purpose of this study was to characterize the dynamics, distribution, and phenotype of infiltrating cells in the iris during EAE-associated AU. METHODS: Lewis rats were immunized with MBP emulsified in complete Freund's adjuvant (CFA) or with CFA alone. Cellular infiltration of the iris was analyzed at various time points by immunohistochemistry of wholemounts, flow cytometry, and immunoelectron microscopy, by using monoclonal antibodies specific for monocytes/macrophages (ED1), T lymphocytes (R73, W3.25, OX8), T-cell activation markers (OX39, OX40), granulocytes (HIS48), major histocompatibility complex (MHC) class II (OX6), and neurofilament (2H3). RESULTS: MBP-immunized rats showed development of characteristic monophasic EAE, followed, after resolution of paralysis, by mild self-limited AU. Initially, focal infiltrates of round MHC class II(+) and ED1(+) cells were found in the iris. During the course of AU, the midiris became massively infiltrated with ED1(+) monocytes-macrophages, R73(+) T cells, granulocytes (HIS48(+)), and MHC class II(+) cells. The influx of T cells consisted of CD4(+) and CD8(+) cells, of which only a small fraction (<14 and 11%, respectively) expressed activation markers. The infiltrating cells accumulated in proximity to myelinated and nonmyelinated nerve bundles and in the vicinity of blood vessels in the iris. No evidence was found for demyelination or nerve degradation. Neither EAE nor AU developed in CFA-treated control rats. CONCLUSIONS: These data show that EAE-associated AU is characterized by a transient mixed cellular infiltrate consisting of monocytes-macrophages, granulocytes, and CD4 and CD8 T cells. The preferential accumulation of inflammatory cells in the vicinity of nerve fibers suggests that AU in this model may result from autoreactivity to nerve antigens.

Breakdown of tolerance to a neo-self antigen in double transgenic mice in which B cells present the antigen.

Transgenic (Tg) mice expressing a foreign Ag, hen egg lysozyme (HEL), under control of the alphaA-crystallin promoter ("HEL-Tg" mice) develop immunotolerance to HEL attributed to the expression of HEL in their thymus. In this paper we analyzed the immune response in double (Dbl)-Tg mice generated by mating the HEL-Tg mice with Tg mice that express HEL Abs on their B cells ("Ig-Tg" mice). The B cell compartment of the Dbl-Tg mice was unaffected by the HEL presence and was essentially identical to that of the Ig-Tg mice. A partial breakdown of tolerance was seen in the T cell response to HEL of the Dbl-Tg mice, i.e., their lymphocyte proliferative response against HEL was remarkably higher than that of the HEL-Tg mice. T-lymphocytes of both Dbl-Tg and Ig-Tg mice responded to HEL at concentrations drastically lower than those found stimulatory to lymphocytes of the wild-type controls. Cell mixing experiments demonstrated that 1) the lymphocyte response against low concentrations of HEL is due to the exceedingly efficient Ag presenting capacity of the Ab expressing B cells and 2) breakdown of tolerance in Dbl-Tg mice can also be attributed to the APC capacity of B cells, that sensitize in vivo and stimulate in vitro populations of T cells with low affinity toward HEL, assumed to be escapees of thymic deletion. These results thus indicate that T cell tolerance can be partially overcome by the highly potent Ag presenting capacity of Ab expressing B cells.

Changes in cytokine mRNA levels in experimental corneal allografts after local clodronate-liposome treatment.

PURPOSE: Corneal allograft rejection in rats can be prevented by subconjunctival injections of liposomes containing dichloromethylene diphosphonate (clodronate-LIP), which selectively eliminate macrophages. In this study, the effect of clodronate-LIP treatment on cytokine mRNA levels in corneal allografts was examined. METHODS: AO rats received corneal grafts of PVG rats. Rats were either not treated or injected subconjunctivally with clodronate-LIP on the day of transplantation and on postoperative days (PODs) 2, 4, 6, and 8. RNA was isolated from the graft and rim of corneas at different times after transplantation and from normal controls. Interleukin (IL)-1beta, IL-1 receptor antagonist (IL-1RA), IL-2, IL-4, IL-6, IL-10, IL-12p40, tumor necrosis factor (TNF)-alpha, TNF-beta/lymphotoxin (LT), interferon (IFN)-gamma, monocyte chemotactic protein 1 (MCP-1), and macrophage inflammatory protein 2 (MIP-2) mRNA levels were analyzed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Corneal rejection, observed in all untreated rats by POD 12, was associated with increased mRNA levels of all cytokines investigated in grafts and rims. Clodronate-LIP treatment prevented allograft rejection and strongly decreased the levels of IL-1beta, IL-1RA, IL-2, IL-4, IL-6, IL-10, IFN-gamma, TNF-beta/LT, MCP-1, and MIP-2 mRNA in grafts and IL-1 beta, IL-2, IL-4, IL-6, and IFN-gamma mRNA in rims. Interleukin-12p40 mRNA levels were unaltered in clodronate-treated rats, except for a transient increase in grafts at POD 3. TNF-alpha mRNA levels were increased by clodronate-LIP in grafts and rims early after transplantation (PODs 3 and 7). Despite a normal appearance, long-term accepted corneal grafts (POD 100) contained mRNA for IL-10, IL-12p40, TNF-alpha, MCP-1, and MIP-2. CONCLUSIONS: Clodronate-liposome treatment markedly altered the mRNA levels of all cytokines investigated in corneal allografts. These results may explain in part the mechanism by which clodronate-LIP treatment prevents corneal allograft rejection.

Analysis of the secretion pattern of monocyte chemotactic protein-1 (MCP-1) and transforming growth factor-beta 2 (TGF-beta2) by human retinal pigment epithelial cells.

Retinal pigment epithelial (RPE) cells, situated between the neurosensory retina and the vascularized choroid, form part of the blood-eye barrier and are important for homeostasis of the outer retina. These cells are able to produce a variety of cytokines which may play a role in the maintenance of the immunosuppressive milieu inside the eye and in intraocular inflammatory responses. In the present study, we investigated whether RPE cells secreted the anti-inflammatory cytokine TGF-beta2 and the proinflammatory cytokine MCP-1 in a polarized manner. Monolayers of human donor RPE cells were cultured on transwell filters. Secretion of TGF-beta2 and MCP-1 at either the apical or basal side of the RPE cell monolayers, that were not treated or stimulated with IL-1beta (200 U/ml), was analysed by ELISA. All three cell lines examined had a different TGF-beta2 secretion pattern. In two of the three donor RPE cell lines tested, TGF-beta2 secretion was polarized, but not in the same direction. TGF-beta2 secretion was not up-regulated by stimulation with IL-1beta. In contrast, IL-1beta strongly induced MCP-1 secretion preferentially into the basal compartment of all RPE monolayers tested. These data indicate that human RPE cells are able to secrete TGF-beta2 and MCP-1 in a polarized fashion. Our results suggest that MCP-1 can be secreted by RPE cells in the direction of choroidal vessels during inflammatory responses in the posterior part of the eye, which may limit damage to the neurosensory retina.

Experimental autoimmune keratitis induced in rats by anti-cornea T-cell lines.

PURPOSE: Idiopathic inflammation of the cornea, keratitis, has been proposed to result from an autoimmune process, but thus far no convenient animal model of keratitis exists. An attempt was made to establish an animal model for keratitis, to investigate possible autoimmune mechanisms. METHODS: T-cell lines were established from lymph node cells removed from rats immunized with bovine corneal epithelium (BCE) extract. After restimulation in vitro with BCE or a specific corneal antigen, the cells were transferred by intraperitoneal injection into naive rats, rats subjected to total body irradiation, or rats in which only one eye was irradiated. RESULTS: Neither direct immunization with corneal antigens nor transfer of activated anti-corneal T-cells into naive rats gave any signs of keratitis. Irradiation alone did not induce corneal inflammation. Transfer of corneal-specific activated T cells into irradiated rats produced keratitis starting around day 4 and culminating around day 8. The disease was self-limiting and the severity dependent on the dose and site of radiation. Keratitis was characterized by corneal haze, conjunctival and episcleral hyperemia, episcleral hemorrhages, chemosis, corneal infiltrates, and vascularization. Immunohistochemistry showed T-cell and macrophage infiltration of epithelium and stroma in the affected corneas. CONCLUSIONS: Thus, keratitis may be produced by T cells reactive to corneal antigens, provided that the target tissue has been made susceptible by irradiation. The effectiveness of T-cell vaccination in preventing adoptive keratitis suggests that systemic as well as local tissue factors may regulate the disease process.

Interleukin 10 treatment does not prolong experimental corneal allograft survival.

In view of the known anti-inflammatory activities of interleukin (IL) 10, we investigated whether the administration of recombinant murine IL-10 prolonged corneal graft survival. A major histocompatibility complex mismatched rat model with AO rats as recipients of PVG donor corneas was used. A total of 39 corneal allografts was included in this study and divided into 7 groups for different treatments. Group I (n = 6), II (n = 8), III (n = 6) and IV (n = 7) were injected subconjunctivally with saline (control), 0. 5 ng, 5 ng or 50 ng of IL-10, respectively, on the day of transplantation and then on postoperative days (POD) 2, 4, 6, 8 and 10. Group V (n = 4) and group VI (n = 4) were injected intraperitoneally with saline (control) or 1 microg of IL-10, respectively, on the day before surgery, the day of grafting and then on POD 2, 4 and 6. Finally, group VII (n = 4) was injected with both subconjuctival 5 ng of IL-10 and intraperitoneal 1 microg of IL-10 on the same days as the previous groups. The median days for corneal rejection in the various groups were: group I, 11.3 +/- 0.9; group II, 11.5 +/- 0.9; group III, 11.6 +/- 0.8, and group IV, 10 +/- 1.0. Statistical analysis revealed a trend towards rejection (p = 0.08) in group IV (compared to group I). In groups V and VI, corneal rejection was evident on day 12 and in group VII the median time for rejection was 10.5 +/- 0.8 days. These results indicate that IL-10 treatment does not prolong corneal allograft survival and may even accelerate rejection.

Expression of multiple forms of IL-1 receptor antagonist (IL-1ra) by human retinal pigment epithelial cells: identification of a new IL-1ra exon.

The eye is considered an immunologically privileged organ and is separated from the rest of the body by blood-ocular barriers. Part of the blood-retina barrier consists of the retinal pigment epithelium (RPE). In addition to the physical barrier which the monolayer of RPE cells forms, these cells contribute to ocular immune privilege by producing anti-inflammatory molecules that down-regulate potential damaging immune reactions. In this study the mRNA expression of IL-1 receptor antagonist (IL-1ra) by RPE cells was studied in 15 donor-derived cell lines. Expression of both the intracellular and secreted IL-1ra was detected in unstimulated and IL-1beta- or phorbol 12-myristate 13-acetate-exposed RPE. Analysis of IL-1ra protein in RPE cell lysates and cell culture supernatants indicated that these cells produce mainly intracellular IL-1ra. No correlation between IL-1ra expression levels and the IL-1ra gene polymorphism could be detected. In addition to the two known intracellular IL-1ra variants (intracellular IL-1ra type I and type II) evidence is provided for the expression of a hitherto unknown splice variant of the IL-1ra mRNA by RPE cells. Expression was not confined to RPE cells and could also be detected in cultured human fibroblasts and macrophages. This variant, which we have tentatively named intracellular IL-1ra type III, encodes a C-terminally truncated protein of only 27 amino acids.

Interferon gamma immunoreactivity in iris nerve fibres during endotoxin induced uveitis in the rat.

AIMS: Previous studies have implied that interferon gamma (IFN-gamma) is involved in the pathogenesis of endotoxin induced uveitis (EIU) in the rat. This study investigated the source of IFN-gamma in the iris during EIU. METHODS: Whole mounts of iris were isolated from Lewis rats before and at different times (from 4 hours to 14 days) after foot pad injection of 200 micrograms Salmonella typhimurium lipopolysaccharide (LPS). Immunohistological analysis was performed using monoclonal antibodies (mAbs) specific to rat IFN-gamma (DB12 and DB13). mAbs specific to monocytes, macrophages, and dendritic cells and MHC class II were used to asses the inflammatory response in the eye (ED-1, ED-2, and OX-6). An antibody specific to neurofilaments (2H3) was used to stain nerve fibres in the normal iris. RESULTS: LPS administration induced acute intraocular inflammation, characterised by a massive infiltration of monocytes/macrophages and increased numbers of MHC class II positive cells in the iris. IFN-gamma immunoreactive cells were not detected in iris whole mounts of control rats. Strikingly, IFN-gamma immunoreactivity was found in fibres from 4 hours until 10 days after LPS injection, with the most intense staining at 48-72 hours. Other DB12 or DB13 positive cells were not detected in the iris. The pattern of DB12 and DB13 staining in the inflamed iris was similar to the 2H3 staining of neurons in the iris of control rats. CONCLUSION: These results show that systemic LPS administration induces IFN-gamma immunoreactivity in iris fibres and suggest that iris nerve fibres may be a source of IFN-gamma during EIU. The IFN-gamma immunoreactive material in the iris nerve fibres may be identical to neuronal IFN-gamma.

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-1beta (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.

Immunohistochemical studies on the endotoxin-induced uveitis.

OBJECTIVE: To investigate the longitudinal changes of macrophages and major histocompatibility complex (MHC) class II-positive cells in the iris and ciliary body of Lewis rats after lipopolysaccharide (LPS) injection. METHODS: Immunohistochemistry was performed using monoclonal antibodies to monocytes and macrophages (ED1) and MHC class II-positive cells (OX6) on wholemounts of the iris and ciliary body in endotoxin-induced uveitis (EIU). RESULTS: A network of macrophages (ED1+ cell) and MHC class II-positive cells, was present in the iris and ciliary body of normal Lewis rats. Most cells in the iris and ciliary body displayed dendritiform appearance. A severe involvement of the iris and ciliary body, as evidenced by a rapid influx of monocytes and macrophages and remarkable increase of MHC class II-positive cells, was observed after LPS injection. CONCLUSIONS: A network of macrophages and MHC class II-positive cells in the iris and ciliary body may play an important role in immune surveillance. LPS injection induces a severe inflammation in the anterior segment of the eye, which may serve as a model for acute anterior uveitis in human.

Macrophages and MHC class II positive cells in the choroid during endotoxin induced uveitis.

AIMS/BACKGROUND: Endotoxin induced uveitis has been regarded as a model for acute anterior uveitis and until now little was known about choroidal involvement. The aim of this study was to investigate changes in macrophages and MHC class II positive cells in the choroid of Lewis rats during endotoxin induced uveitis. METHODS: Choroid-sclera wholemounts were isolated from normal Lewis rats and at different time points--4, 8, 16, 24, 48, 72, and 96 hours, and 7, 10, and 14 days after a footpad injection of 200 micrograms of lipopolysaccharide (LPS). Immunohistochemistry was performed using the monoclonal antibodies ED1 (monocytes, macrophages, dendritic cells), and OX6 (MHC class II antigen). RESULTS: In normal rats, two layers of macrophages were identified in the choroid; a layer located immediately beneath the retinal pigment epithelium (RPE) and a layer bordering the sclera. The density of ED1 positive cells in the layer bordering the RPE cells was 902 (SD 132) cells/mm2 whereas the scleral layer had a cell density of 389 (73) cells/mm2. Based on morphology, positive cells could be divided into two main categories; pleomorphic/round cells and dendritiform cells with varying appearances, with the latter being predominant in normal eyes. A network of MHC class II positive dendritic cells was found in the choroid, beneath the RPE, with a density of 659 (96) cells/mm2. No MHC class II positive cells were found in the macrophage layer bordering the sclera. LPS injection caused a massive influx of ED1 positive macrophages in the area below the RPE cells but did not result in an influx of macrophages at the scleral side of the choroid. The infiltrate reached a maximum at 16 hours following LPS injection and decreased at 96 hours. The morphology of the infiltrating cells was pleomorphic/round at early stages of inflammation and changed into a dendritiform cell population later. The number of MHC class II positive cells on the anterior side of the choroid increased 8 hours after injection and reached a peak at 72-96 hours. MHC class II positive cells were not observed in the vicinity of the sclera at any time after LPS injection. Both resident and MHC class II positive dendritic cell numbers returned to normal values at day 14 following LPS injection. CONCLUSIONS: These results indicate that the choroid is severely inflamed after systemic LPS administration to Lewis rats and suggests that endotoxin induced uveitis may serve as a model for generalised uveitis in humans.

Cytokine mRNA expression during experimental corneal allograft rejection.

Allograft rejection is the main cause of corneal graft failure. T lymphocytes and macrophages have been implied to be involved in corneal rejection, but little is known about the molecular mechanism in this process. In this study, cytokine mRNA expression in the cornea was analysed during experimental corneal transplantation. The donor and acceptor corneas of two groups of rats were studied after receiving an allo- (PVG to AO rat) or autograft (AO rat). For controls, central buttons and peripheral corneal rings of the non-transplanted contralateral eyes were used. At different post-operative days (1, 3, 7, 12 and 19), the corneas were removed and subjected to mRNA isolation. All corneal samples underwent semi-quantitative reverse transcriptase-polymerase chain reaction analysis for interleukin-1 beta, interleukin-1, receptor antagonist, interleukin-2, interleukin-4, interleukin-6, interleukin-10, tumor necrosis factor-alpha, interferon-gamma, monocyte chemotactic protein-1 and macrophage inflammatory protein-2 mRNA expression. Corneal rejection, characterized by opaque corneas with prominent neovascularization, was always diagnosed around day 12. Contralateral, non-grafted corneas showed constitutive mRNA expression for interleukin-1 receptor antagonist and in a few samples also monocyte chemotactic protein-1 and macrophage inflammatory protein-2 mRNA was found. Both allo- and autografts expressed mRNA for the cytokines found in contralateral, non-grafted tissue, as well as for interleukin-1 beta, interleukin-6, interleukin-10 and tumor necrosis factor-alpha. In allografts, the mRNA levels for these cytokines remained constant throughout all post-operative days, with increased interleukin-6 mRNA expression after post-operative day 12. The analysis of the autografts revealed high cytokine mRNA levels until post-operative day 3 or 7, which decreased from then on, except for interleukin-1 receptor antagonist. mRNA for interleukin-2, interleukin-4 and interferon-gamma was not observed in autografts at any time point and in allografts, until post-operative day 12. Interleukin-2 and interferon-gamma mRNA showed maximal expression on POD 12, while in autografts, a marked decrease was observed after POD 3. IL-10 mRNA levels decreased immediately after POD 1 in autografted eyes. For TNF-alpha, an increased mRNA expression starting on POD 7 was found in recipient rings of allografted eyes, while in autografts a weak expression was seen in some samples. MIP-2 transcription increased on PAD 12, while in autografts, its expression was not markedly different from that detected in the contralateral, non-grafted peripheral cornea.