Experimental coronavirus retinopathy (ECOR): retinal degeneration susceptible mice have an augmented interferon and chemokine (CXCL9, CXCL10) response early after virus infection

Mouse hepatitis virus induces a biphasic disease in BALB/c mice that consists of an acute retinitis followed by progression to a chronic retinal degeneration with autoimmune reactivity. Retinal degeneration resistant CD-1 mice do not develop the late phase. What host factors contribute to the distinct responses to the virus are unknown. Herein, we show that IFN-α, IFN-β and IFN-γ act in concert as part of the innate immune response to the retinal infection. At day 2, high serum levels of IFN-γ, CXCL9 and CXCL10, were detected in BALB/c mice. Moreover, elevated levels of CXCL9 and CXCL10 gene expression were detected in retinal tissue. Although IFN-γ and the chemokines were detected in CD-1 mice, they were at significantly lower levels compared to BALB/c mice. These augmented innate responses observed correlated with the development of autoimmune reactivity and retinal degeneration and thus may contribute to the pathogenic processes.

Interferon-beta and adhesion molecules (E-selectin and s-intracellular adhesion molecule-1) are detected in sera from patients with retinal vasculitis and are induced in retinal vascular endothelial cells by Toll-like receptor 3 signalling

Retinal vasculitis is a major component of ocular inflammation that plays a role in retinal tissue damage in patients with idiopathic uveitis and Behçet's disease. Here we show that type 1 interferons (IFN alpha/beta) were not detected in sera from normal individuals but were identified in up to 46% of the sera from retinal vasculitis patients. The predominant form of IFN observed was IFN-beta, which was detected in 39% of Behçet's disease patients and 47% of idiopathic uveitis patients. Seven patients whose sera contained IFN-beta were monitored prospectively. IFN-beta was shown to be present for 6-12 months in all seven of the sera samples tested. Furthermore, the adhesion molecule profile identified in this study was strikingly different when Behçet's and uveitis patient sera were compared to sera from normal controls. Sera from Behçet's disease patients contained significantly elevated levels of the soluble adhesion molecules, sE-selectin and s-intracellular adhesion molecule-1 (sICAM-1), whereas sera from patients with idiopathic uveitis contained significantly increased sE-selectin. In vitro studies evaluating the cell source of these cytokines revealed that polyriboinosinic polyribocytidylic acid (poly I:C) activated retinal vascular endothelial cells produce sE-selectin, sICAM-1 and IFN-beta. Production of these molecules was inhibited by pretreatment with anti-Toll-like receptor 3 (TLR-3) antibody. In conclusion, IFN-beta, sE-selectin and sICAM-1 are elevated in patients with retinal vasculitis and are induced in retinal vascular endothelial cells in vitro by activating the innate immune system through TLR-3. Further analysis of innate immune signalling may prove to be a novel target for future studies on pathogenic mechanisms and therapeutic approaches in retinal vasculitis.

Interferon-gamma differentially regulates TGF-beta1 and TGF-beta2 expression in human retinal pigment epithelial cells through JAK-STAT pathway

Retinal pigment epithelium (RPE) and transforming growth factor-beta (TGF-beta) have been shown to be involved in various retinal diseases. We have studied the role of inflammatory cytokines on the expression and secretion of TGF-beta in human RPE cells (HRPE). Confluent cultures of HRPE derived from donor eyes were used. RT-PCR analyses showed that TNF-alpha and IL-1beta increased the mRNA levels of both TGF-beta1 and TGF-beta2. IFN-gamma enhanced constitutively expressed, as well as, TNF-alpha-and IL-1beta-induced TGF-beta1 mRNA levels but decreased TGF-beta2 mRNA. The effects of these cytokines on TGF-beta1 and TGF-beta2 secretion correlated with the mRNA levels. TGF-beta1 was always produced as the latent form while 21-31% of TGF-beta2 was in the active form. IFN-gamma reduced the production of active form of TGF-beta2 to 4-9%. TGF-beta3 secretion was not detectable under any of the conditions. The Real-Time PCR analysis of TGF-beta mRNAs confirmed the observed results. The TGF-beta1 and TGF-beta2 secretion was induced by TGF-beta2 and TGF-beta1, respectively. Under these conditions, the contrasting effects of IFN-gamma on TGF-beta1 and TGF-beta2 secretion were also observed. JAK inhibitor selectively inhibited IFN-gamma induced TGF-beta1 secretion and mRNA levels while reversing the inhibitory effects of IFN-gamma on TGF-beta2. Analyses of transcription factor activity strongly indicated the role of STAT-1 but not NFkappaB, C-Myc, C-Jun, SP-1, MEF-2. Our data demonstrate that IFN-gamma differentially regulates constitutively expressed, as well as, cytokine-induced TGF-beta1 and TGF-beta2 mRNA levels and secretion of TGF-betas by HRPE.

Autoantibodies to p75/LEDGF, a cell survival factor, found in patients with atypical retinal degeneration

We have identified a group of patients with an atypical retinal degeneration having anti-retinal autoantibodies in their sera. This select population is characterized by a progressively severe loss of vision associated with a decrease in photoreceptor function, abnormal pigmentation of the retinal pigment epithelium and a negative family history of retinal dystrophy. Immunohistochemical analysis on mouse retinal tissues with sera from this group of patients demonstrated high titers of anti-retinal antibodies (320 to 1,280). Anti-retinal reactivity at these levels was not detected in sera from normal individuals, or from patients with uveitis or known genetic retinal degenerations. One antigen that was identified from a retina cDNA library with sera from a patient with atypical retinal degeneration was lens epithelium-derived growth factor (LEDGF). Western blot analysis revealed that sera from all three patients demonstrated reactivity to p75/LEDGF, a survival factor that protects cells from oxidative, thermal and UV damage. In conclusion, we have found a novel group of patients with a retinal degeneration of non-paraneoplastic, non-familial origin demonstrating immunoreactivity to an autoantigen, p75/LEDGF, heretofore not associated with this disease. Finally, identification of specific anti-retinal antibodies may have applications in the diagnosis and management of retinal degeneration.

Herpes simplex virus 1 (HSV-1) DNA and immune complex (HSV-1–human IgG) elicit vigorous interleukin 6 release from infected corneal cells via Toll-like receptors

Toll-like receptor 3 (TLR-3) and TLR-9 gene expression and interleukin 6 (IL-6) secretion were studied in corneal cells with components of herpes simplex virus (HSV). Human corneal epithelial cells (HCEs) and primary human corneal fibroblasts (HCRFs) were infected with live HSV or UV-inactivated HSV (UV-HSV), transfected with HSV DNA or treated with HSV–anti-HSV IgG immune complexes. Gene expression of TLR-3 and -9 was analysed by real-time PCR. Supernatants were assayed for IL-6 by ELISA. Incubation of HCEs and HCRFs with live HSV-1, UV-HSV and HSV DNA resulted in augmented TLR-3 and -9 gene expression and IL-6 release. Moreover, infected or transfected HCRFs released greater amounts of IL-6 than did HCEs. As virus is frequently in the form of neutralized virus immune complexes, the ability of these immune complexes to interact with TLRs and trigger IL-6 production was evaluated. Here, it is shown that HSV–anti-HSV IgG complexes were as potent as HSV DNA in their ability to induce IL-6. Treatment of HCRFs transfected with HSV DNA with the TLR-9-inhibitory oligomer iODN, anti-TLR-3 antibody or phosphatidylinositol 3-kinase inhibitor indicated that IL-6 release from HCRFs was mediated by TLR-3 and -9 gene expression. These results demonstrated that neutralized HSV immune complexes were as potent as HSV DNA in enhancing IL-6 release from corneal fibroblasts. These phenomena were mediated via augmented TLR-3 and -9 gene expression.

Human cytomegalovirus induced cyclooxygenase-2 in human retinal pigment epithelial cells augments viral replication through a prostaglandin pathway

Cytomegalovirus (CMV) retinitis is characterized by alterations in retinal cell function and host responses to virus replication. The goal of this study was to evaluate the induction of cyclooxygenase-2 (COX-2) and prostaglandin (PGE) in CMV infected human retinal pigment epithelial (RPE) cells and to determine their effect on virus replication. CMV immediate early (IE) protein and COX-2 proteins were identified in RPE cells in retinal tissue sections from patients with CMV retinitis. COX-2 mRNA and protein were induced after CMV infection of human RPE cell cultures. CMV infection of RPE cells induced translocation of NF-kappaB from the cytoplasm to the nucleus. PGE1 and PGE2 were significantly (p<0.001) increased in human RPE cell cultures infected with CMV. Inhibition of CMV IE gene by antisense oligonucleotides abrogated induction of mRNA for COX-2 and protein synthesis of COX-2 and PGE2. PGE enhanced CMV plaque formation and real time PCR analysis revealed that PGE treatment significantly increased CMV DNA copy numbers. These studies demonstrate that when CMV replicates within human RPE cells, COX-2 induction augments virus replication via the PGE pathway. The induction of COX-2 and PGE during retinal CMV infection may augment virus replication and alter a variety of retinal physiological responses.

Retinal degeneration in experimental coronavirus retinopathy (ECOR) is associated with increased TNF-alpha, soluble TNFR2 and altered TNF-alpha signaling

Experimental coronavirus retinopathy (ECOR) is a virally triggered model of retinal degeneration composed of both genetic and autoimmune components. Since TNF-alpha plays a role in immune-mediated processes we evaluated the levels of TNF-alpha/TNF-alpha receptors and the downstream signaling molecule nitric oxide (NO) during disease in both retinal degeneration susceptible BALB/c and degeneration resistant CD-1 mice. Following coronavirus injection, TNF-alpha mRNA was detected at higher levels within the retinas, and concentrations of TNF-alpha (p<0.005) and sTNFR1 (p<0.0005) proteins were increased within the sera of BALB/c but not CD-1 mice. While concentrations of sTNFR2 proteins were elevated in both BALB/c (p<0.00005) and CD-1 (p<0.005) mice compared to controls, concentrations were higher in BALB/c mice (p<0.0005). Gene expression of iNOS while initially high in BALB/c mice decreased during the acute phase of infection, while it increased in CD-1 mice. These trends are attributable to differences in monocyte TNFR2 release (p<0.0005) between the strains since sTNFR2 decreased (p<0.01) levels of NO production. These studies demonstrate that retinal degeneration following viral infection is associated with increased release of TNF-alpha/TNF receptors combined with a down-regulation of NO. Furthermore they suggest that these molecules are involved in alterations in immune response leading to autoimmune reactivity.

Expression of PDGF and their receptors in human retinal pigment epithelial cells and fibroblasts: regulation by TGF-beta

Platelet derived growth factors (PDGF) are known to be associated with vitreoretinal disorders such as proliferative vitreoretinopathy (PVR). We have studied the expression of PDGF and their receptors in human retinal pigment epithelial cells (HRPE) and choroid fibroblasts (HCHF), and the regulation of PDGF and its receptors by various cytokines and growth factors. RT-PCR analyses showed enhanced expression of PDGF-A and PDGF-B mRNA in HRPE treated with TGF-beta, but not with other cytokines. A minimal increase was observed in PDGF-A mRNA in TGF-beta treated HCHF cells. PDGF-R alpha mRNA, which was expressed prominently in HCHF and at very low levels in HRPE, was not affected by any of the agents. PDGF-R beta was not detectable in either HRPE or HCHF. HRPE secreted PDGF-AA and AB constitutively, and this secretion was significantly enhanced by TGF-beta. In contrast, HCHF cultures did not secrete detectable levels of any of the three isoforms of PDGF (AA, AB, BB). All three human recombinant PDGF isoforms enhanced HCHF cell proliferation significantly, while only a minimal increase was observed in HRPE. PDGF isoforms also induced HCHF cell elongation and promoted migration of HCHF in an in vitro wound assay. The results presented in this study demonstrate that TGF-beta activated RPE cells produce PDGF that may act on fibroblasts and other mesenchyme derived cells which express PDGF receptors. These studies indicate that the promotion of the proliferation and migration of mesenchymal cells by RPE cell derived PDGF may facilitate the formation of fibrovascular tissues associated with PVR.

Innate immunity in the retina: Toll-like receptor (TLR) signaling in human retinal pigment epithelial cells

Toll-like receptors (TLRs) are crucial components of innate immunity that participate in host defense against microbial pathogens. We evaluated the expression and function of TLRs in human retinal pigment epithelial (RPE) cells. Real time PCR analysis revealed gene expression for TLRs 1–7, 9, and 10 in RPE cells. TLRs 1 and 3 were the most highly expressed TLRs. Protein expression for TLRs 2, 3, and 4 was observed on RPE cells and this expression was augmented by treatment with poly I:C or interferon-γ (IFN-γ). TLR 3 is the receptor for dsRNA, an intermediate of virus replication. Because RPE cells express TLR 3 and are frequently the site of virus replication within the retina, we evaluated TLR 3 signaling. RPE cells treated with poly I:C produced IFN-β but not IFN-α, and this was inhibited by the treatment of RPE cells with anti-TLR 3 antibody. Human recombinant IFN-β was shown to be biologically active on RPE cells by inhibiting viral replication. Poly I:C treatment of RPE resulted in an increase in the production of IL-6, IL-8, MCP-1, and sICAM-1. The presence of TLRs on RPE cells and the resultant TLR signaling in RPE cells suggest that these molecules may play an important role in innate and adaptive immune responses within the retina.

Transforming growth factor-beta induces expression of vascular endothelial growth factor in human retinal pigment epithelial cells: involvement of mitogen-activated protein kinases

Vascular endothelial growth factor (VEGF) is a major agent in choroidal and retinal neovascularization, events associated with age-related macular degeneration (AMD) and diabetic retinopathy. Retinal pigment epithelium (RPE), strategically located between retina and choroid, plays a critical role in retinal disorders. We have examined the effects of various growth factors on the expression and secretion of VEGF by human retinal pigment epithelial cell cultures (HRPE). RT-PCR analyses revealed the presence of three isoforms of mRNA corresponding to VEGF 121, 165, and 189 that were up regulated by TGF-beta1. TGF-beta1, beta2, and beta3 were the potent inducers of VEGF secretion by HRPE cells whereas bFGF, PDGF, TGF-alpha, and GM-CSF had no effects. TGF-beta receptor type II antibody significantly reversed induction of VEGF secretion by TGF-beta. In contrast activin, inhibin and BMP, members of TGF-beta super family, had no effects on VEGF expression in HRPE. VEGF mRNA levels and protein secretion induced by TGF-beta were significantly inhibited by SB203580 and U0126, inhibitors of MAP kinases, but not by staurosporine and PDTC, protein kinase C and NF-kappaB pathway inhibitors, respectively. TGF-beta also induced VEGF expression by fibroblasts derived from human choroid of eye. TGF-beta induction of VEGF secretion by RPE and choroid cells may play a significant role in choroidal neovascularization (CNV) in AMD. Since the secretion of VEGF by HRPE is regulated by MAP kinase pathways, MAP kinase inhibitors may have potential use as therapeutic agents for CNV in AMD.

The critical role of IFN-gamma in experimental coronavirus retinopathy

PURPOSE

Experimental coronavirus retinopathy (ECOR) is an animal model of progressive retinal disease that is first manifest as an acute retinal inflammation followed by chronic, immune-associated retinal degeneration in genetically susceptible, BALB/c mice. In retinal degeneration-resistant CD-1 mice, only the acute infection is seen. In the present study, interferon (IFN)-gamma production during ECOR was studied and its role evaluated in the clearance of infectious virus from the retina.

METHODS

BALB/c, CD-1, and IFN-gamma-deficient (IFN-gamma gko) mice were inoculated with the JHM strain of murine coronavirus by the intravitreal route. Mouse eyes were evaluated for infiltrating cells and major histocompatibility complex (MHC) expression by immunocytochemical staining. Isolated retinas were analyzed for IFN-gamma mRNA by RT-PCR, and sera were evaluated for IFN-gamma protein by ELISA assays.

RESULTS

Virus infection in BALB/c mice was associated with an increase in the incidence and levels of systemic IFN-gamma. Moreover, IFN-gamma mRNA was detected within the retinas of infected animals during the acute phase of the disease but was not detected in normal or mock-injected animals. IFN-gamma mRNA was detected at the time of T-cell infiltration, and earlier studies have shown that this is temporally related to granzyme B gene expression and the clearance of infectious virus from the retina. Retinal IFN-gamma mRNA was also associated with the upregulation of MHC class I and II molecules within the retina. When this infection occurred in IFN-gamma gko mice, the virus was unchecked, and the infection led to death.

CONCLUSIONS

These studies indicate that generation of IFN-gamma by cells infiltrating the retina is an essential part of an immune mechanism responsible for noncytolytic clearance of infectious virus from the retina.

Differential expression of chemokines by human retinal pigment epithelial cells infected with cytomegalovirus

PURPOSE

To evaluate the effects of human cytomegalovirus (HCMV) infection on chemokine gene expression and secretion by human retinal pigment epithelial (HRPE) cell cultures.

METHODS

HRPE cells were infected with HCMV (strain AD169) at an MOI of 5. Culture supernatants, collected at various postinoculation days, were used for the analyses of chemokines by ELISA. The steady state levels of chemokine and chemokine receptor mRNA were analyzed by RT-PCR. Effects of interferon and MCP-1 on HCMV replication in HRPE cells were evaluated by plaque assays.

RESULTS

HRPE cells infected with HCMV exhibited characteristic cytopathic effects. The reduction in the levels of monocyte chemotactic protein (MCP)-1 and -3 mRNA in HCMV-infected HRPE cells was observed in comparison to uninfected HRPE cells. In contrast, HCMV infection enhanced IL-8 mRNA levels, whereas regulated on activation normal T-cell expressed and secreted (RANTES) mRNA was not detectable in either control or infected HRPE cells. A significant decrease in MCP-1 (P < 0.01) and MCP-3 (P < 0.05), but a significant increase in IL-8 (P < 0.05), protein secretion was observed. Expression of the chemokine receptors CCR2, specific for MCP-1, and CXCR1 and CXCR2, specific for IL-8, were not altered by HCMV infection. Treatment of HRPE cultures with MCP-1 had no significant effect on HCMV replication in HRPE cells.

CONCLUSIONS

HCMV infection in HRPE cells resulted in the modulation of MCP-1, MCP-3, and IL-8. Because chemokines facilitate the activation of leukocytes and their migration to the sites of inflammation, the modulation of chemokine production by the virus suggests a role for chemokines in immune evasion and/or immunopathogenesis of CMV retinitis.

Transforming growth factor-beta expression in human retinal pigment epithelial cells is enhanced by Toxoplasma gondii: a possible role in the immunopathogenesis of retinochoroiditis

Retinochoroiditis caused by Toxoplasma gondii infection results in inflammation and necrosis of the retina. We have used human retinal pigment epithelial cultures (HRPE) as an in vitro model to investigate the role of TGF-beta in T. gondii-induced retinochoroiditis. RT-PCR analyses showed enhanced steady state levels of TGF-beta1 and TGF-beta2 mRNA in T. gondii-infected HRPE. Uninfected HRPE secrete TGF-beta1 in a latent form while 10-30% of the secreted TGF-beta2 was in the active form. T. gondii infection induced a significant increase (P < 0.01) in total TGF-beta1 and TGF-beta2 secretion by HRPE. In addition, soluble extracts of T. gondii (ST) stimulated secretion of both TGF-beta1 and TGF-beta2 significantly (P < 0.01). Interestingly, T. gondii infection as well as ST of the parasites completely inhibited secretion of the active form of TGF-beta2. Studies evaluating the effect of TGF-beta on T. gondii replication in HRPE revealed that TGF-beta enhanced parasite replication. The interactions between host retinal cells and T. gondii may play an active role in the pathogenesis of retinochoroiditis.

Blood-retinal barrier breakdown in experimental coronavirus retinopathy: association with viral antigen, inflammation, and VEGF in sensitive and resistant strains

Intraocular coronavirus inoculation results in a biphasic retinal disease in susceptible mice (BALB/c) characterized by an acute inflammatory response, followed by retinal degeneration associated with autoimmune reactivity. Resistant mice (CD-1), when similarly inoculated, only develop the early phase of the disease. Blood-retinal barrier (BRB) breakdown occurs in the early phase in both strains, coincident with the onset of inflammation. As the inflammation subsides, the extent of retinal vascular leakage is decreased, indicating that BRB breakdown in experimental coronavirus retinopathy (ECOR) is primarily due to inflammation rather than to retinal cell destruction. Vascular endothelial growth factor (VEGF) is upregulated only in susceptible mice during the secondary (retinal degeneration) phase.

Cyclooxygenase-2 gene expression and regulation in human retinal pigment epithelial cells

PURPOSE

Cyclooxygenases (COX) orchestrate a variety of homeostatic processes and participate in various pathophysiological conditions. The retinal pigment epithelium (RPE) cell performs a variety of regulatory functions within the retina. The conditions under which COX-1 and COX-2 are expressed and upregulated in human RPE (HRPE) cells were determined.

METHODS

COX gene expression was examined using RT-PCR analysis of untreated HRPE cultures or cultures exposed to bacterial lipopolysaccharide or various cytokines. COX proteins were detected by immunohistochemistry and Western blot analysis. Prostaglandin (PG) production was analyzed by EIA.

RESULTS

Examination of untreated RPE cells revealed the presence of COX-2 mRNA and the absence of COX-1 mRNA. Moreover, cytokine stimulation more readily enhanced COX-2 gene expression than COX-1 gene expression. IL-1 beta, the most potent inducer of COX-2, also resulted in detection of COX-2 protein by immunocytochemical staining and Western blot analysis. There was a direct relationship between both the appearance and amount of COX-2 mRNA and protein synthesis and the degree of PG synthesis by RPE cells. Furthermore, COX inhibitors significantly decreased PG production. Pretreatment of RPE cells with a NF-kappa B inhibitor, PDTC, resulted in dose-dependent decrease in IL-1 beta-induced COX-2 gene expression and PG production.

CONCLUSIONS

COX-2 was the predominant isoform of cyclooxygenase in untreated HRPE cells. When HRPE cells were treated with proinflammatory cytokines, COX-2 gene expression and synthesis of PGs were enhanced. NF-kappa B mediated the induction of COX-2 gene expression in HRPE cells. These studies indicate that RPE cells may participate in normal and pathologic retinal conditions through the induction of COX-2.

Inhibition of human cytomegalovirus replication in a human retinal epithelial cell model by antisense oligonucleotides

PURPOSE

The antiviral activity of first and second generation antisense oligonucleotides on human cytomegalovirus (CMV) replication was evaluated in two cell systems, the traditional system on human fibroblasts and on human retinal pigment epithelial (HRPE) cell culture system.

METHODS

To evaluate CMV replication strategies within the retina, an HRPE cell system permissive to CMV replication was developed. In this study, the antiviral activity of the antisense oligonucleotides, ISIS 2922 (Vitraven) and ISIS 13312, was evaluated in the traditional fibroblast antiviral assay and in the HRPE cell system. Antiviral activity was measured by evaluating inhibition of virus induced cytopathic effect, virus plaque formation, and virus gene expression.

RESULTS

Both oligonucleotides produced concentration-dependent inhibition of CMV cytopathic effect and CMV plaque formation in both human RPE cells and a human fibroblast cell line, MRC-5. The oligonucleotide, ISIS 2922, demonstrated a mean 50% inhibitory concentration (IC(50)) of 0.04 and 0.24 microM in HRPE and MRC-5 cells, respectively. The second-generation oligonucleotide, ISIS 13312, yielded similar results with IC(50) levels of 0.05 and 0.3 microM in HRPE and MRC-5 cells, respectively. Similar findings were obtained with a CMV clinical isolate. In addition, initiation of effective oligonucleotide treatment could be introduced 6 days after CMV infection in HRPE cells, whereas, in the fibroblast cell line, oligonucleotide treatment was only effective up to 3 days after infection. Semiquantitative RT-PCR analysis demonstrated significant inhibition of CMV intermediate early and late mRNAs by both oligonucleotides.

CONCLUSIONS

These studies demonstrate that HRPE cells were significantly more sensitive than fibroblasts to the antiviral actions of ISIS 2922 and ISIS 13312. Moreover, the data indicate that the anti-CMV potency of the two oligonucleotides was similar. The enhanced potency of these oligonucleotides in HRPE cells may be associated with a delay in viral gene transcription and slow viral replication and spread in these cells.

The role of apoptosis within the retina of coronavirus-infected mice

PURPOSE

To evaluate the possible roles of apoptosis in the murine retinopathy induced by coronavirus.

METHODS

Mice were inoculated with virus intravitreally. Mouse eyes harvested at varying times after inoculation were evaluated for apoptotic and immunologic events by hematoxylin and eosin staining, immunohistochemical staining, in situ terminal deoxynucleotidyltransferase dUTP nick-end labeling (TUNEL) assay, and electron microscopy. Isolated retinas were analyzed for infectious virus and for expression of apoptosis-associated genes.

RESULTS

The number of apoptotic events was significantly elevated in infected eyes from BALB/c and CD-1 mouse strains, reaching a maximum at days 6 through 10, and returning to normal levels at day 20. The majority of apoptotic cells were observed in the outer nuclear layer of the infected retina. In contrast, few apoptotic cells were observed in normal or mock-injected mouse eyes. Apoptotic events within the retina were associated with the presence of viral antigen, infiltration of CD8(+) T cells, and clearance of infectious virus. Reverse transcription-polymerase chain reaction (RT-PCR) analysis identified the upregulation of Fas ligand (FasL) and granzyme B mRNAs within the infected retinas. The development of apoptosis, regulative gene expression, and viral clearance were similar in both retinal degeneration-susceptible (BALB/c) and -resistant (CD-1) mice.

CONCLUSIONS

Retinal apoptosis was associated with retinal inflammation, a decrease in infectious virus, and upregulation of genes associated with CTL killing. These studies indicate that retinal apoptosis may be one of the host mechanisms that contribute to limiting this retinal infection.

Toxoplasma gondii infection induces gene expression and secretion of interleukin 1 (IL-1), IL-6, granulocyte-macrophage colony-stimulating factor, and intercellular adhesion molecule 1 by human retinal pigment epithelial cells

We have used human retinal pigment epithelial (HRPE) cultures to investigate the primary cellular responses of retinal resident cells to intracellular Toxoplasma gondii replication. At 4 days postinoculation, when all of the cells were infected, the secretion of interleukin 1beta (IL-1beta), IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and intercellular adhesion molecule 1 (ICAM-1) was augmented by 23-, 10-, 8-, and 5-fold, respectively, over the control. Northern and reverse transcriptase PCR analyses showed significant upregulation of steady-state levels of mRNA for IL-1beta, IL-6, GM-CSF, and ICAM-1. The secretion of these molecules by HRPE cells may play a critical immunoregulatory role in the pathophysiological processes associated with T. gondii-induced retinochoroiditis.

Detection of cytomegalovirus proteins by flow cytometry in the blood of patients undergoing hematopoietic stem cell transplantation

Cytomegalovirus (CMV) infection and associated diseases continue to be a major complication encountered by patients undergoing high-dose chemoradiotherapy and hematopoietic stem cell transplantation (HSCT). A number of studies revealed that identification of CMV in the blood of HSCT patients was a predictor of future CMV disease. The purpose of this study was to determine if CMV proteins detected by flow cytometry could be a rapid and more quantitative way to monitor CMV infections and CMV antigenemia in HSCT patients. Preliminary studies showed that CMV immediate early (IE), early (E), and late (L) tegument proteins were specifically identified in CMV-infected cell lines and not in uninfected cells. We evaluated CMV antigen detection by flow cytometry in blood samples collected before and after transplantation in 56 serially collected blood samples from 17 HSCT patients and CMV protein expression was compared to CMV isolation. CMV IE and E proteins were not detected in any of the samples analyzed. However, CMV L protein detection by flow cytometry correlated with virus isolation in serially collected blood samples. Samples from 14 patients were evaluated by both techniques, at the same time intervals. There was a 100% correlation (8/8) between the lack of CMV antigen detection by flow cytometry and the failure to isolate infectious virus. Moreover, 5 of 6 patients who were positive for CMV L antigen by flow cytometry also were positive by virus isolation techniques. When flow cytometry and virus isolation did not detect CMV antigen on the same day, CMV positivity was first detected by flow cytometry. Then, 1-2 weeks later, positive virus isolation was documented. This study indicates that flow cytometric identification of CMV antigenemia correlates with isolation of CMV in HSCT patients and may be a predictive test for the rapid detection of CMV in the blood.

Mechanisms of interferon-induced inhibition of Toxoplasma gondii replication in human retinal pigment epithelial cells

Inflammation associated with retinochoroiditis is a major complication of ocular toxoplasmosis in infants and immunocompetent individuals. Moreover, Toxoplasma gondii-induced retinal disease causes serious complications in patients with AIDS and transplant patients. The retinal pigment epithelial (RPE) cell is an important regulatory cell within the retina and is one of the cells infected with T. gondii in in vivo. We have developed a human RPE (HRPE) cell in vitro model system to evaluate T. gondii replication and the regulation of this replication by cytokines. T. gondii replication was quantitated by counting the foci of infection (plaque formation) and the numbers of tachyzoites released into the supernatant fluids. Pretreatment of cultures with recombinant human tumor necrosis factor alpha, alpha interferon (IFN-alpha), IFN-beta, or IFN-gamma for 24 h prior to inoculation inhibited T. gondii replication in a dose-dependent manner. Of these cytokines, IFN-gamma was the most potent, and T. gondii replication was completely inhibited at a concentration of 100 U/ml. The anti-toxoplasmotic activity of IFN-gamma was significantly blocked by monoclonal antibody to IFN-gamma. Treatment of the cultures with IFN-gamma from day 1 or 2 postinoculation with T. gondii also offered protection against the parasite. The anti-toxoplasmotic activity of tumor necrosis factor alpha or IFN-alpha, -beta, or -gamma in these cultures was found to be independent of the nitric oxide (NO) pathway, since NO production was not found in HRPE cells treated with these cytokines. However, addition of tryptophan to IFN-gamma-treated cells significantly reversed the inhibitory effects of IFN-gamma, suggesting that IFN-gamma acts by depleting cellular tryptophan. This effect was further confirmed by reverse transcription-PCR and Northern (RNA) blot analysis, which indicated induction of indoleamine 2,3-dioxygenase (IDO), an enzyme that converts tryptophan to kynurenine. These results indicated that interferons inhibited T. gondii replication in HRPE by NO-independent but IDO-dependent mechanisms. This in vitro model of T. gondii replication in HRPE may be useful in evaluating the effects of cytokines and drugs on T. gondii replication within the retina.