Autophagy protects against retinal cell death in mouse model of cytomegalovirus retinitis

BACKGROUND

Extensive death of uninfected bystander neuronal cells is an important component of the pathogenesis of cytomegalovirus retinitis (CMV). Our previous results have shown that there is a functional relationship between autophagy and apoptosis during MCMV infection of retinal pigment epithelium (RPE). The purpose of this study was to determine whether autophagy plays a significant role in the death of retinal cells during MCMV retinitis.

METHODS

The retinas of adult BALB/c mice were infected with MCMV via supraciliary injection. Rapamycin, a mTOR inhibitor, was injected to MCMV-infected BALB/c mice intraperitoneally. Immunohistochemistry and western blot were performed to observe the spread pattern of virus in retinas and the levels of targeted proteins. Plaque assay was performed to determine the virus titer in different groups. Since Atg5 is a key gene regulating autophagy, we bred Atg5^flox/flox; Nestin-Cre mice to deeply elucidate the role of autophagy during MCMV retinitis. Atg5^flox/flox; Nestin-Cre mice were genotyped and infected with MCMV. Immunohistochemistry was performed to observe the type of virus-infected cells and apoptosis in retinas during MCMV retinitis.

RESULTS

In MCMV mouse model, MCMV infection in outer nuclear layer (ONL) and inner nuclear layer (INL) in the retinas caused cleaved caspase 3 positive apoptosis, which is not co-localized with early antigen (EA) positive virus infected cells in rapamycin treated group. Rapamycin treatment increased the levels of LC3B-II by inhibiting mTOR and decreased the levels of cleaved caspase-3 during MCMV retinitis. However, virus propagation was not affected by rapamycin. In Atg5^flox/flox; Nestin-Cre mice, RPE and glial cells were the main targets of viral infection, and number of EA positive retinal cells and TUNEL positive retinal cells was significantly increased compared to Atg5^flox/+; Nestin-Cre mice though there was no difference of virus propagation between Atg5^flox/flox; Nestin-Cre mice and Atg5^flox/+; Nestin-Cre mice.

CONCLUSIONS

Autophagy protects retinal cells from MCMV infection induced apoptosis through mTOR-mediated signaling pathway.

Depletion of the Receptor-Interacting Protein Kinase 3 (RIP3) Decreases Photoreceptor Cell Death During the Early Stages of Ocular Murine Cytomegalovirus Infection

Purpose

The purpose of this study was to determine if the receptor-interacting protein kinase 3 (RIP3) plays a significant role in innate immune responses and death of bystander retinal neurons during murine cytomegalovirus (MCMV) retinal infection, by comparing the innate immune response and cell death in RIP3-depleted mice (Rip3^−/−) and Rip3^+/+ control mice.

Methods

Rip3^−/− and Rip3^+/+ mice were immunosuppressed (IS) and inoculated with MCMV via the supraciliary route. Virus-injected and mock-injected control eyes were removed at days 4, 7, and 10 post infection (p.i.) and markers of innate immunity and cell death were analyzed.

Results

Compared to Rip3^+/+ mice, significantly more MCMV was recovered and more MCMV-infected RPE cells were observed in injected eyes of Rip3^−/− mice at days 4 and 7 p.i. In contrast, fewer TUNEL-stained photoreceptors were observed in Rip3^−/− eyes than in Rip3^+/+ eyes at these times. Electron microscopy showed that significantly more apoptotic photoreceptor cells were present in Rip3^+/+ mice than in Rip3^−/− mice. Immunohistochemistry showed that the majority of TUNEL-stained photoreceptors died via mitochondrial flavoprotein apoptosis-inducing factor (AIF)-mediated, caspase 3–independent apoptosis. The majority of RIP3-expressing cells in infected eyes were RPE cells, microglia/macrophages, and glia, whereas retinal neurons contained much lower amounts of RIP3. Western blots showed significantly higher levels of activated nuclear factor–κB and caspase 1 were present in Rip3^+/+ eyes compared to Rip3^−/− eyes.

Conclusions

Our results suggest that RIP3 enhances innate immune responses against ocular MCMV infection via activation of the inflammasome and nuclear factor–κB, which also leads to inflammation and death of bystander cells by multiple pathways including apoptosis and necroptosis.

Role of Bax in death of uninfected retinal cells during murine cytomegalovirus retinitis

PURPOSE

Extensive death of uninfected bystander neuronal cells is an important component of the pathogenesis of cytomegalovirus retinitis. Our previous results have shown that caspase 3-dependent and -independent pathways are involved in death of uninfected bystander cells during murine cytomegalovirus (MCMV) retinitis and also that Bcl-2, an important inhibitor of apoptosis via the Bax-mediated mitochondrial pathway, is downregulated during this process. The purpose of this study was to determine whether Bax-mediated mitochondrial damage has a significant role in the death of uninfected retinal cells.

METHODS

BALB/c mice, Bax(-/-) mice, or Bax(+/+) mice were immunosuppressed with methylprednisolone and infected with 5 × 10(3) plaque-forming units (PFU) of the K181 strain of MCMV via the supraciliary route. Injected eyes were analyzed by plaque assay, electron microscopy, hematoxylin and eosin (H&E) staining, TUNEL assay, Western blot (for caspase 3, caspase 12, Bax, receptor interacting protein-1 [RIP1] and receptor interacting protein-3 [RIP3]), as well as immunohistochemical staining for MCMV early antigen and cleaved caspase 3.

RESULTS

Significantly more Bax was detected in mitochondrial fractions of MCMV-infected eyes than in mitochondrial fractions of mock-infected control eyes. Furthermore, the level of cleaved caspase 3 was significantly lower in MCMV-infected Bax(-/-) eyes than in MCMV-infected Bax(+/+) eyes. However, more caspase 3-independent cell death of uninfected bystander retinal cells and more cleaved RIP1 were observed in Bax(-/-) than in Bax(+/+) eyes.

CONCLUSIONS

During MCMV retinitis, Bax is activated and has an important role in death of uninfected bystander retinal cells by caspase 3-dependent apoptosis. Although the exact mechanism remains to be deciphered, active Bax might also prevent death of some types of uninfected retinal cells by a caspase 3-independent pathway.

Decrease of murine cytomegalovirus-induced retinitis by intravenous delivery of immediate early protein-3-specific siRNA

PURPOSE

Retinitis induced by both human and murine cytomegaloviruses following immunosuppression is characterized by progressive loss of retinal architecture, due to necrosis of virus-infected cells as well as widespread apoptosis of uninfected bystander cells. Because small inhibitory RNA molecules (siRNA) can reduce murine cytomegalovirus (MCMV) gene expression and thereby inhibit virus replication in vitro, we tested siRNAs directed against MCMV immediate early protein-3 (IE-3) to determine if MCMV-induced retinitis could be alleviated in vivo.

METHODS

Immunosuppressed Balb/c mice (2.0 mg methylprednisolone acetate every 3 days beginning on day -2) were infected with 5 × 10(3) pfu of the K181 strain of MCMV via the supraciliary route. At day 2 post infection, mice were treated with various doses of IE-3-specific siRNA ranging from 0.1 nmol to 10 nmol, in a volume of 20 μL PBS via tail vein injection. Injected eyes were collected at various times post inoculation and subjected to plaque assay for virus titer, MCMV antigen staining, H&E staining, TUNEL assay, and Western blot for MCMV IE-3 protein.

RESULTS

Small but significant amounts of fluorescently labeled IE-3-specific siRNA localized to the RPE layer 48 hours after intravenous injection. IE-3-specific siRNA significantly reduced virus titers at all concentrations tested (ranging from 0.1 nmol to 10 nmol), but the most potent effect of siRNA was observed at a dose of 1 nmol. We also observed that IE-3-specific siRNA produced a substantial decrease in MCMV titers and a substantial reduction in bystander cell apoptosis over the time course of virus infection.

CONCLUSIONS

Systemic administration of IE-3-specific siRNA could alleviate MCMV retinitis by inhibiting virus replication and subsequent death of uninfected retinal cells.

Alterations of retinal vasculature in cystathionine-Beta-synthase mutant mice, a model of hyperhomocysteinemia

PURPOSE

Mice with moderate/severe hyperhomocysteinemia due to deficiency or absence of the cbs gene encoding cystathionine-beta-synthase (CBS) have marked retinal disruption, ganglion cell loss, optic nerve mitochondrial dysfunction, and ERG defects; those with mild hyperhomocysteinemia have delayed retinal morphological/functional phenotype. Excess homocysteine is a risk factor for cardiovascular diseases; however, it is not known whether excess homocysteine alters retinal vasculature.

METHODS

Cbs(+/+), cbs(+/-), and cbs(-/-) mice (age ∼3 weeks) were subjected to angiography; retinas were harvested for cryosections, flat-mount preparations, or trypsin digestion and subjected to immunofluorescence microscopy to visualize vessels using isolectin-B4, to detect angiogenesis using anti-VEGF and anti-endoglin (anti-CD105) and activated glial cells (anti-glial fibrillary acidic protein [anti-GFAP]) and to investigate the blood-retinal barrier using the tight junction markers zonula occludens-1 (ZO-1) and occludin. Expression of vegf was determined by quantitative RT-PCR (qRT-PCR) and immunoblotting. Human retinal endothelial cells (HRECs) were treated with excess homocysteine to analyze permeability.

RESULTS

Angiography revealed vascular leakage in cbs(-/-) mice; immunohistochemical analysis demonstrated vascular patterns consistent with ischemia; isolectin-B4 labeling revealed a capillary-free zone centrally and new vessels with capillary tufts midperipherally. This was associated with increased vegf mRNA and protein, CD105, and GFAP in cbs(-/-) retinas concomitant with a marked decrease in ZO-1 and occludin. Homocysteine-treated HRECs showed increased permeability.

CONCLUSIONS

Severe elevation of homocysteine in cbs(-/-) mutant mice is accompanied by alterations in retinal vasculature (ischemia, neovascularization, and incompetent blood-retinal barrier). The marked disruption of retinal structure and decreased visual function reported in cbs(-/-) mice may reflect vasculopathy as well as neuropathy.

The effect of murine cytomegalovirus IE-3 specific shRNA is dependent on intragenic target site due to multiple transcription initiation sites

BACKGROUND

Murine cytomegalovirus (MCMV) is closely related to human cytomegalovirus (HCMV) which is responsible for a variety of diseases, including retinitis, in immunocompromised individuals. Small inhibitory RNA molecules directed against essential viral regulatory genes may prove clinically useful.

METHODS

Small hairpin RNAs (shRNAs) directed against the essential MCMV immediate early-3 gene (IE-3) were designed and tested in vitro at m.o.i.'s of 2 and 0.2 to determine if virus replication could be inhibited.

RESULTS

At m.o.i. = 2, a MCMV IE-3 specific shRNA specific for sequences at the beginning of exon 5 inhibited virus replication with a maximum decrease in virus titer of approximately two logs at day 5 p.i. Surprisingly, however, at m.o.i. = 0.2, the same shRNA enhanced virus replication. In the latter case, the main IE-3 product observed in infected cells was not the expected 88 kd full length IE-3 protein observed at high m.o.i. but rather a truncated 45 kd form of this protein. Rapid analysis of 5' cDNA ends (5' RACE) indicated that substantial differences exist in the transcript profile produced by the IE-3 gene at low and high m.o.i. early after infection and that multiple transcripts are produced under both conditions. One such transcript, which originated in exon 5 of the IE-3 gene, was located outside the region targeted by our shRNA and was the major transcript produced at low m.o.i. Targeting of this exon 5 transcript with a second shRNA resulted in inhibition of virus replication at both low and high m.o.i.

CONCLUSIONS

These studies indicate that IE-3 has a complex transcriptional profile and that shRNA targeting of this and other viral regulatory genes which produce multiple transcripts may have unexpected effects on virus replication.

Interferon-gamma, macrophages, and virus spread after HSV-1 injection

PURPOSE

After uniocular anterior chamber (AC) injection of HSV-1, the anterior segment of BALB/c mice becomes inflamed and infected; however, virus does not spread from the anterior segment to cause retinitis in the injected eye. The purpose of these studies was to determine whether interferon (IFN-)-γ and Mac-1(+) cells play a role in preventing direct anterior-to-posterior spread of HSV-1 in the injected eye.

METHODS

One AC of adult female BALB/c mice was injected with HSV-1 (KOS). The location of IFN-α, IFN-β, and IFN-γ in the injected eye was determined by immunofluorescence, and mRNA expression was quantified by qPCR. Injected eyes of IFN-γ knockout or clodronate-treated macrophage-depleted mice were examined to determine whether the absence of IFN-γ or Mac-1(+) macrophages affected the sites or timing of virus spread.

RESULTS

IFN-α, IFN-β, and IFN-γ were observed in the anterior segment of injected eyes through 72 hours and mRNA levels of IFN-β and IFN-γ were increased in virus-infected eyes 48 to 120 hours after infection. However, the absence of IFN-γ or macrophages did not affect either the sites or the timing of HSV-1 infection in injected eyes.

CONCLUSIONS

Protection of the retina of the injected eye does not depend on a single cell type or cytokine. In addition, in the eye, as in other sites of the body, there are redundancies in the innate response to virus infection.

Expression and iron-dependent regulation of succinate receptor GPR91 in retinal pigment epithelium

PURPOSE

GPR91, a succinate receptor, is expressed in retinal ganglion cells and induces vascular endothelial growth factor (VEGF) expression. RPE also expresses VEGF, but whether this cell expresses GPR91 is not known. Excessive iron is also proangiogenic, and hemochromatosis is associated with iron overload. Therefore, we examined the expression and iron-dependent regulation of GPR91 in the RPE.

METHODS

GPR91 expression was examined by RT-PCR and immunohistochemistry. Hemochromatosis mice, cytomegalovirus (CMV) infection of retina, expression of CMV-US2 in RPE, and exposure of RPE to ferric ammonium citrate (FAC) were used to examine the iron-dependent regulation of GPR91 expression. VEGF expression was quantified by qPCR. Knockdown of GPR91 in ARPE-19 cells was achieved with shRNA.

RESULTS

GPR91 was expressed in RPE but only in the apical membrane. Retinal expression of GPR91 was higher in hemochromatosis (Hfe(-/-)) mice than in wild-type (WT) mice. Primary RPE cells from Hfe(-/-) mice had increased GPR91 expression compared with WT RPE cells. Iron accumulation in cells induced by CMV infection, expression of CMV-US2, or treatment with FAC increased GPR91 expression. VEGF expression in the Hfe(-/-) mouse retina was increased at ages younger than 18 months, but the expression was downregulated at older ages. The involvement of GPR91 in succinate-induced expression of VEGF in RPE cells was confirmed with GPR91-specific shRNA.

CONCLUSIONS

GPR91 is expressed in the RPE with specific localization to the apical membrane, indicating that succinate in the subretinal space serves as the GPR91 agonist. Excessive iron in the retina and RPE enhances GPR91 expression; however, VEGF expression does not always parallel GPR91 expression.

Lack of TNF-alpha promotes caspase-3-independent apoptosis during murine cytomegalovirus retinitis

PURPOSE

Both caspase-dependent and caspase-independent apoptosis contribute to retinal damage during murine cytomegalovirus (MCMV) retinitis, and TNF-α is among the inducers of apoptosis. The aim of this study was to determine the contribution of TNF-α by studying virus replication and apoptosis in immunosuppressed (IS) TNF-α(-/-) mice.

METHODS

IS TNF-α(-/-) mice or wild-type mice were inoculated with MCMV by the supraciliary route. Injected eyes were examined by plaque assay, electron microscopy, Western blot analysis (caspase-3, caspase-8, caspase-12, Bid, NF-κB, cFlip, XIAP), staining for MCMV early antigen, and TUNEL assay.

RESULTS

Although the titer of MCMV was similar in both groups, significantly more apoptotic cells were observed in the retinas of IS TNF-α(-/-) mice than in those of wild-type mice. The level of active caspase-3 was similar in both groups; however, more activated proteins for genes involved in the mitochondrial pathway (cleaved caspase-8, tBid) and endoplasmic reticulum (ER) stress (cleaved caspase-12) and, though less active, NF-κB subunits and antiapoptotic proteins (XIAP and cFlip) were detected in the TNF-α(-/-) eyes compared with wild-type mice.

CONCLUSIONS

Although TNF-α is an inducer of apoptosis, the results of this study suggest that TNF-α is also antiapoptotic by the following mechanism: TNF-α activation of NF-κB promotes the production of the antiapoptosis genes, c-flip or XIAP, which, in turn, inhibit the activation of caspase-8 and the mitochondrial pathway or the activation of caspase-12 and ER stress.

Distribution of herpes simplex virus type 1 and varicella zoster virus in ganglia of the human head and neck

The distribution of the neurotropic alphaherpesviruses-herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) and varicella zoster virus (VZV)-was determined in autonomic and sensory ganglia of the head and neck obtained from formalin-fixed human cadavers. HSV-1 and VZV DNA were found in 18 of 58 and 16 of 58 trigeminal, 23 of 58 and 11 of 58 pterygopalatine, 25 of 60 and 14 of 60 ciliary, 25 of 48 and 11 of 48 geniculate, 15 of 50 and 8 of 50 otic, 14 of 47 and 4 of 47 submandibular, 18 of 58 and 10 of 58 superior cervical, and 12 of 36 and 1 of 36 nodose ganglia, respectively. HSV-2 was not detected at any site. Viral DNA positivity and location were independently distributed among autonomic and sensory ganglia of the human head and neck.

Infiltrating cells and IFNgamma production in the injected eye after uniocular anterior chamber inoculation of HSV-1

PURPOSE

After uniocular anterior chamber (AC) inoculation with HSV-1, the anterior segment of the injected eye becomes inflamed and infected; however, virus does not spread from the anterior segment and infect the retina of the injected eye. The purpose of this study was to identify early infiltrating cells and to determine whether infiltrating cells produce interferon (IFN)gamma.

METHODS

Euthymic, female, BALB/c mice were injected in one AC with 3 x 10(4) PFU of HSV-1 (KOS) in a volume of 2 microL. Mice from each group were killed at 12, 24, 36, 48, and 72 hours post injection (pi), the eyes were enucleated, and frozen sections were stained with antibodies specific for IFNgamma, Mac-1 (CD11b), CD49b, F4/80, CD4, CD8, and CD11c. The same antibodies were also used to stain single-cell suspensions of ocular cells for flow cytometry.

RESULTS

In the anterior segment of the injected eye, the ciliary body, and iris were virus infected and inflamed, and infiltrating cells increased throughout the period of observation. Mac-1(+), CD49b(+), and F4/80(+) cells colocalized with IFNgamma in the anterior segment as early as 12 hours pi, and the percentage of Mac-1(+) cells increased in the injected eye beginning at 24 hours pi and continued to 72 hours pi.

CONCLUSIONS

Taken together, these results demonstrate that Mac-1(+) cells are important IFNgamma-producing cells in the injected eye before day 3 and suggest that the IFNgamma produced by these cells is involved in inhibition of anterior to posterior spread of virus in the injected eye.

Neutrophils protect the retina of the injected eye from infection after anterior chamber inoculation of HSV-1 in BALB/c mice

PURPOSE

To determine whether infiltrating polymorphonuclear leukocytes PMNs play a role in preventing early direct anterior-to-posterior spread of herpes simplex virus (HSV)-1 and/or in preventing the spread of HSV-1 from the brain back to the retina of the injected eye after anterior chamber (AC) inoculation.

METHODS

BALB/c mice were treated with monoclonal antibody RB6-8C5 (Gr-1) against PMNs or control IgG and inoculated with HSV-1.

RESULTS

In Gr-1-treated mice, PMNs were depleted in the peripheral blood and in the HSV-1-infected eye. More virus (2-3 logs) was recovered from the inoculated eye of Gr-1 antibody-treated mice than from control mice. Immunohistochemistry revealed disseminated virus-infected cells in the junction between the anterior and the posterior segment and also in the posterior segment of the HSV-1-inoculated eye in Gr-1-treated mice. In control IgG-treated mice, virus-infected cells were observed only within the AC. More virus (3 logs) was recovered from the contralateral suprachiasmatic nucleus (SCN), and increased virus staining was observed in the ipsilateral optic nerve of Gr-1-treated mice compared with control mice. In Gr-1-treated mice, the central retina was virus-infected in a patchy fashion beginning on day 7 post infection (pi), and the infection progressed to involve the entire retina.

CONCLUSIONS

Since both direct anterior-to-posterior spread of virus and spread via the optic nerve occurred in PMN-depleted mice, these results suggest that PMNs play an important role both in limiting intraocular spread of virus in the injected eye and in controlling spread of the virus from the brain into the optic nerve and retina of the injected eye.

Murine cytomegalovirus infection and apoptosis in organotypic retinal cultures

PURPOSE

An organotypic retinal culture model was used to determine the pattern of murine cytomegalovirus (MCMV) infection and whether apoptosis is induced in MCMV-infected cultured retinas.

METHODS

Retinas harvested from C57BL/6 mice were individually cultured at 37 degrees C on 3-microm filter inserts placed in 24-well plates. Some retinas were infected with MCMV (5 x 10(5) PFU/well). At days 4, 7, and 11 after infection (pi), the culture medium and cultured retinas were collected for examination.

RESULTS

Replicating virus was recovered and viral early antigen (EA)- and late antigen (LA)-positive cells were observed in the MCMV-infected retinal cultures. Most MCMV-infected cells were glia and horizontal cells. Infection resulted in atrophy of the photoreceptor cells and cytomegaly. Apoptosis of uninfected bystander cells, including photoreceptor cells and horizontal cells, was observed. TNF-alpha was produced by activated microglia during MCMV infection of the retina. Mouse apoptosis microarray studies, caspase activity studies, and RT-PCR studies showed that the genes involved in both the death receptor-mediated apoptotic pathway and the mitochondrial pathway were upregulated.

CONCLUSIONS

Many aspects of MCMV infection of retinal cultures parallel those observed during MCMV retinitis in mice. Thus, this in vitro system may be used to explore the role of apoptosis of uninfected retinal cells and the contribution of cytokines and other modulators to the pathogenesis of CMV retinitis.

Tumor necrosis factor-alpha in cisplatin nephrotoxicity: a homebred foe?

A robust inflammatory response involving tumor necrosis factor-alpha (TNF-alpha) is induced during cisplatin nephrotoxicity. Using chimeric models, Reeves and colleagues now demonstrate that resident kidney cells, rather than infiltrating immune cells, are the major producers of TNF-alpha. Blockade of TNF-alpha attenuates inflammation and associated kidney injury.

Tumor necrosis factor-alpha-induced apoptosis in murine cytomegalovirus retinitis

PURPOSE

Previous results suggest that apoptosis is involved in the pathogenesis of murine cytomegalovirus (MCMV) retinitis. To explore the mechanism underlying retinal apoptosis in MCMV retinitis, this study was initiated to determine whether the tumor necrosis factor receptor (TNFR)1-TNF pathway is involved in apoptosis during MCMV retinitis.

METHODS

The left eyes of nonimmunosuppressed (non-IS) BALB/c mice, immunosuppressed (IS) BALB/c mice, TNFR1(-/-) C57BL/6 mice, and wild-type C57BL/6 mice were inoculated with MCMV k181 by way of the supraciliary route. On postinoculation days 3, 7, and 10, injected eyes of non-IS control and IS experimental mice were removed for RT-PCR for TNF-alpha and TNFR1. Protein expression of TNF-alpha, caspase-8, and caspase-3 was determined by staining frozen sections and performing Western blot analysis and quantitative ELISA. Apoptotic cells were identified by TUNEL labeling.

RESULTS

In IS BALB/c mice, TNF-alpha mRNA and protein were detected in MCMV-infected eyes throughout the infection. Activation of caspase-3 and caspase-8 was observed. Most of the TNF-alpha-expressing cells were MCMV-infected RPE cells or macrophages derived from RPE cells. TNF-alpha was observed in the area of apoptotic retinal cells, and the level of this cytokine corresponded to the extent of the retinal abnormality and to the number of apoptotic cells. In non-IS MCMV-infected BALB/c mice, TNF-alpha was expressed early in the retinas of MCMV-infected eyes, but its expression was decreased thereafter. TNFR1 mRNA was increased in IS and non-IS BALB/c after MCMV infection. More apoptotic cells were observed in the retinas of non-IS MCMV-infected wild-type C57BL/6 mice than in the retinas of non-IS TNFR(-/-) mice.

CONCLUSIONS

These results suggest that the TNFR1-TNF pathway is involved in the induction of apoptosis and the exacerbation of retinal abnormality during MCMV retinitis. Furthermore, because TNF-alpha and TNFR1 were present in IS and non-IS mice, TNF-alpha-induced retinal apoptosis during MCMV infection is not T-cell dependent.

Acute retinal necrosis

Acute retinal necrosis (ARN) is a rare disease that is usually caused by one of the three neurotropic human herpesviruses - herpes simplex virus type 1(HSV-1), HSV-2 and varicella-zoster virus (VZV). Although much is known about the clinical course of the disease and its treatment and about the viruses that cause it, comparatively little is known about its pathogenesis. This article will review the history of ARN, the typical clinical findings, and methods of diagnosis. Information from studies of the mouse model of ARN including development of anterior chamber-associated immune deviation (ACAID) and routes of spread will be reconsidered, and the combined information from human and mouse studies will be discussed to suggest mechanisms that contribute to the pathogenesis of ARN in human patients. Finally, puzzles and questions about the disease will be considered.

Lack of iNOS facilitates MCMV spread in the retina

PURPOSE

The purposes of this study were to identify iNOS-producing retinal cells and to determine whether lack of iNOS facilitates MCMV spread and replication in the retina.

METHODS

Immunosuppressed (IS) iNOS(-/-) mice or C57BL/6 (wild-type) mice were inoculated with 5 x 10(4) PFU of MCMV K181 strain (K181) via the supraciliary route. Injected eyes were collected at several times after inoculation and examined by plaque assay for replicating virus, RT-PCR for iNOS RNA, Western blot for iNOS protein and by staining for MCMV early antigen (EA), iNOS, and retinal cell antigens.

RESULTS

iNOS mRNA and iNOS proteins were expressed in the MCMV-injected eye of wild-type mice. Most iNOS-producing cells were F4/80-positive, including macrophages, RPE-derived macrophages, and resident microglia. Significantly higher titers of virus were recovered from the injected eyes, and more infected cells were detected in the retina of IS iNOS(-/-) mice than in IS wild-type mice. Retinal necrosis and loss of retinal architecture throughout the retina were noted in IS iNOS(-/-) mice, whereas cytomegalic cells and retinitis were present only in the peripheral retina of IS wild-type mice.

CONCLUSIONS

iNOS produced by macrophages, especially resident macrophages including microglia and RPE derived macrophages, plays an important role in limiting spread of MCMV in the retina.

Herpes simplex virus 1 infection induces the expression of proinflammatory cytokines, interferons and TLR7 in human corneal epithelial cells

Herpetic epithelial and stromal keratitis is a sight-threatening ocular infection. To study the role of the epithelium in the innate response to herpes simplex virus 1 (HSV-1) infection of the cornea, we used a telomerase-immortalized human corneal epithelial cell (HCEC) line, HUCL, and primary HCECs as a model and infected the cells with HSV-1 (KOS strain). HSV-1 infection of HCECs resulted in a two-phase activation of nuclear factor-kappaB (NF-kappaB), JNK and p38, with the first peak at 1-4 hr and a second peak at 8 hr. Concomitant with the first peak of activation, transcriptional expression of interleukin (IL)-6, IL-8, tumour necrosis factor (TNF)-alpha and interferon (IFN)-beta was rapidly induced in HSV-1-infected cells. HSV-1 infection also induced the production of IL-6, IL-8, and TNF-alpha in both HUCL cells and primary HCECs. Coincident with the second phase of NF-kappaB activation in HSV-1-infected HCECs, the expression of Toll-like receptor 7 (TLR7) was induced, whereas the level of TLR3 was greatly down-regulated. Thus, in response to HSV-1 infection, HCECs produce proinflammatory cytokines, leading to infiltration, and IFNs to enhance the antiviral activity in the cornea, probably through sequential activation of TLRs.

Tumor necrosis factor alpha and macrophages in the brain of herpes simplex virus type 1–infected BALB/c mice

After uniocular anterior chamber (AC) inoculation of herpes simplex virus type 1 (HSV-1), virus and TNF alpha (TNF-alpha) are detected in the suprachiasmatic nuclei (SCN). The goal of this study was to investigate the role of TNF-alpha and macrophages in the brain of HSV-1-infected BALB/c mice. Mice were treated with thalidomide for TNF-alpha inhibition or injected with clodronate liposomes to deplete macrophages, and the AC of one eye (ipsilateral) was injected with HSV-1 (KOS). The location of HSV-1, macrophages, and TNF-alpha was determined by fluorescence immunohistochemistry and the titer of virus was determined by plaque assay. Inhibition of TNF-alpha was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and depletion of macrophages was assessed by flow cytometry. In thalidomide-treated mice, TNF-alpha RNA levels were reduced in the SCN. Both SCN were infected by day 5 post inoculation (p.i.) and the titer of virus in the SCN contralateral to the side of injection was increased. The number of splenic macrophages was significantly reduced in clodronate-treated mice compared with controls. In macrophage-depleted mice, both SCN were infected at day 6 p.i. and the titer of virus in the SCN of these mice was increased at days 6 and 7 p.i. compared with controls. The titer of virus in the contralateral (uninoculated) eye of macrophage-depleted mice was increased at day 7 p.i. Fewer F4/80+ cells were observed in the SCN of macrophage-depleted mice. The results of these studies suggest that TNF-alpha plays a role in limiting virus replication in the SCN of euthymic BALB/c mice and that one source of TNF-alpha is macrophages.

Infection of retinal neurons during murine cytomegalovirus retinitis

PURPOSE

Previous results suggest that retinal neurons are infected early during murine cytomegalovirus (MCMV) infection of the inner retina. The purposes of this study were to identify which retinal neurons are infected and to determine the routes by which MCMV spreads in the retina.

METHODS

Immunosuppressed (IS) BALB/c mice were inoculated with 5 x 10(3) PFU of MCMV (k181) through the supraciliary route. Injected eyes were collected at several times after inoculation, sectioned, and examined by electron microscopy and by staining for retinal cell antigens and for MCMV early (EA) or late (LA) antigen.

RESULTS

MCMV-infected cells were observed in the choroid and RPE by day 3 after infection (PI) and in the inner retina beginning at day 5 PI. At this time, many horizontal and bipolar cells were MCMV-antigen-positive but only rare MCMV-infected amacrine cells (glycine positive or gamma-aminobutyric acid [GABA] positive) or MCMV-infected ganglion cells (NF positive) were observed in the inner retina. At day 10 PI, most virus-infected cells were glial fibrillary acidic protein (GFAP)- and GABA-positive glia. Virions were observed by electron microscopy in the choroid, RPE, and inner nuclear layer of the retina. Although virions were observed in the endothelium of the retinal vessels and the nearby retinal cells, the endothelial cell lining of the retinal vessels remained intact. Both apoptotic cells and necrotic cells were seen in the inner retina.

CONCLUSIONS

In the inner retina, horizontal and bipolar cells were the early (< or = day 7 PI) targets of MCMV infection. Virus spread from the RPE and the photoreceptor layer to the inner retina through infected Muller cells and within the inner retina horizontally through infected horizontal cells.

Cytokine profiles and inflammatory cells during HSV-1-induced acute retinal necrosis

PURPOSE

To investigate infiltrating cells, cytokines, and kinetics of cytokine expression during acute retinal necrosis (ARN) in the uninoculated eye after inoculation of herpes simplex virus (HSV)-1 into the anterior chamber of one eye of BALB/c mice.

METHODS

At different time points after inoculation of 2 x 10(4) plaque-forming units (PFU) HSV-1 (KOS strain) or an equivalent volume of Vero cell extract in cell culture medium, the uninoculated eyes were enucleated. RT-PCRs for TNFalpha, IFNgamma, and IL-4 and immunohistochemical staining were performed to identify infiltrating cells and cytokines. Cytometric bead array was used to measure the levels of TNFalpha, IFNgamma, and IL-4 protein.

RESULTS

CD4(+) T cells, F4/80(+) macrophages, Gr-1(+) polymorphonuclear cells (PMNs), and CD19(+) B cells were detected in the uninoculated eye of virus-infected mice. Furthermore, RPE65(+) retinal pigment epithelial (RPE) cells and activated Muller cells were also detected in the ARN lesion. TNFalpha, IFNgamma, and IL-4 mRNA and protein were upregulated during the evolution of ARN in HSV-1-infected contralateral eyes compared with levels in control subjects. Immunohistochemistry revealed that cytokines were produced by infiltrating cells as well as by resident retinal cells.

CONCLUSIONS

The results of these studies support the idea that T cells and cytokines are actively involved in HSV-1 retinitis. They also suggest that PMNs, B cells, and/or macrophages, as well as resident retinal cells, such as RPE and activated Muller cells, also play a role in the pathogenesis of HSV-1 retinitis.

Murine cytomegalovirus (MCMV) spreads to and replicates in the retina after endotoxin-induced disruption of the blood-retinal barrier of immunosuppressed BALB/c mice

The goal of this study was to determine whether disruption of the blood-retinal barrier (BRB) facilitates spread of MCMV to the retina in immunosuppressed (IS) BALB/c mice. IS mice were inoculated intravenously (i.v.) with murine cytomegalovirus (MCMV) or with macrophages infected with MCMV for 4 days in vitro. The BRB was disrupted by injection of sodium iodate (i.v.) or lipopolysaccharide (LPS, i.v. or anterior chamber). Frozen sections of ocular tissue were examined for MCMV antigens. The results showed that MCMV-infected cells were observed only in the choroid and ciliary body in IS mice with an intact BRB. After LPS injection, a few positive cells were observed in the retina of IS mice after i.v. injection of MCMV. In lipopolysaccharide (LPS)-treated IS mice, a few PKH-26-positive macrophages or MCMV-positive cells were observed in the retina at 1 or 2 days after injection of macrophages. No PKH-26-positive cells or virus-infected cells were noted in the retina of phosphate-buffered saline (PBS)-treated mice. Ten days after injection of virus-infected macrophages, MCMV-infected cells were observed in choroid and ciliary body of both LPS- and PBS-treated mice, but they were observed in the retina only in LPS-treated mice. The results support the idea that disruption of the BRB allows MCMV to spread to the retina of IS mice and that monocytes/macrophages disseminate MCMV to the retina in mice with a disrupted BRB. By extrapolation, damage to the BRB in immunosuppressed patients may facilitate spread of CMV-infected monocytes/macrophages to the retina.

Ocular Reactivation of MCMV after Immunosuppression of Latently Infected BALB/c Mice

PURPOSE

The purpose of this study was to identify the site(s) of MCMV latency and reactivation in the eye.

METHODS

Three months after supraciliary inoculation of 5 x 10(2) PFU of MCMV, BALB/c mice underwent immunosuppression with methylprednisolone and antibodies specific for CD4 T cells, CD8 T cells, and NK cells or with methylprednisolone alone. Control mice were infected but did not receive the immunosuppressants. After 2 or 3 weeks of immunosuppression, the mice were killed. Replicating virus and viral antigen were detected in the injected eyes, peripheral blood leukocytes (PBLs), and extraocular tissues by plaque assay and by staining for early antigen (EA) and beta-galactosidase (beta-gal), respectively.

RESULTS

In latently infected, nonimmunosuppressed control mice, replicating-virus-and viral-antigen-positive cells were not detected in the injected eyes or extraocular tissues. After immunosuppression with methylprednisolone and antibodies, EA and beta-gal were detected, and replicating virus was recovered from the injected eye and from several extraocular sites, including liver, lungs, salivary glands, and kidneys. No virus was recovered from PBLs. beta-Gal- or EA-positive cells were observed in the RPE of most mice, and a few virus-infected cells were also observed in the nuclear layers and ganglion cells. Microscopic changes, including retinal folding and detachment, photoreceptor atrophy, macrophage infiltration, and a few EA-positive cytomegalic cells, were observed in the injected eye of immunosuppressed mice.

CONCLUSIONS

After immunosuppression, MCMV reactivates in the injected eye and extraocular tissues, and RPE cells are the initial site of MCMV ocular reactivation in the eye. The timing of virus recovery from all sites suggests that MCMV observed in the injected eye is from in situ reactivation of virus and not from spread of virus from extraocular sites via infected PBLs.

DNA microarray analysis of the uninoculated eye following anterior chamber inoculation of HSV-1

PURPOSE

To use DNA microarray to analyze the expression patterns of genes in the uninoculated eye following uniocular anterior chamber inoculation of HSV-1.

METHODS

On Day 9 following inoculation of 2 x 10( 4) PFU of HSV-1 (KOS strain) or an equivalent volume of tissue culture medium into one anterior chamber of BALB/c mice, the uninoculated eyes were enucleated, pooled, and total RNA was isolated. cDNA was synthesized from the total RNA. The gene expression patterns were inferred based on the hybridization intensities of the probes on the cDNA array. The hybridization signals were globally normalized and filtered. The data were analyzed using hierarchical and gene tree clustering algorithms. Additional uninoculated eyes collected on Day 9 p.i. were stained for F4/80 and CD19.

RESULTS

Compared with the uninoculated eye of control mice, 3800 genes were upregulated at least twofold in the contralateral eye of HSV-1-infected mice. Among the 10 most upregulated genes, T cell-specific protein, MHC II antigen A, and MHC II k region locus 2 were upregulated 179-, 164-, and 162-fold, respectively. Ten T-cell receptor-related genes, 61 cytokine and chemokine genes, and 16 MHC genes were upregulated. Furthermore, 11 immunoglobulin and B cell genes and 11 macrophage-related genes were also upregulated. F4/80+ and CD19+ cells were observed on Day 9 p.i.

CONCLUSIONS

The DNA microarray results support the idea that T cells and immunomodulatory factors (cytokines, chemokines) are likely to be involved in HSV-1 retinitis. These results also suggest that B cells and/or macrophages play a role in the pathogenesis of HSV-1 retinitis.

Delayed spread and reduction in virus titer after anterior chamber inoculation of a recombinant of HSV-1 expressing IL-16

PURPOSE

The timing of T-cell infiltration of the hypothalamus is crucial in the prevention of bilateral retinitis in mice inoculated with HSV-1 through the anterior chamber (AC). In H129-infected mice, T-cells are recruited to the suprachiasmatic nuclei of the hypothalamus too late to protect infected mice from development of bilateral retinitis. The purpose of these studies was to determine whether alteration of T-cell recruitment to the hypothalamus would affect the timing and pattern of virus spread after AC inoculation.

METHODS

A recombinant of the H129 strain of HSV-1 expressing IL-16, a cytokine with lymphocytic and monocytic chemoattractant properties, was constructed, and mice were inoculated in the AC with H129wt, H129wt and H129/IL-16, or H129wt and H129/pGal10 (a recombinant virus containing vector only).

RESULTS

AC inoculation of BALB/c mice with H129wt and H129/IL-16 resulted in a delay of virus spread to the hypothalamus and the contralateral retina, and this delay correlated with decreased virus titers in infected tissues, compared with mice infected with H129wt or mice infected with H129wt and H129/pGal10. Although the number of infiltrating T-cells in the brains of mice infected with H129wt, H129wt and H129/IL-16, or H129wt and H129/pGal10 was similar, more Mac-1-positive cells were detected early (postinoculation day 2) in the injected eyes of mice infected with H129wt and H129/IL-16 than in mice infected with H129wt and/or H129wt and H129/pGal10.

CONCLUSIONS

These results suggest that early recruitment of Mac-1-positive cells to the injected eye may play a role in delaying virus spread in mice infected with H129wt and the IL-16-expressing recombinant virus. IL-16 delivery vectors could be exploited to prevent or delay HSV-1 infection of the hypothalamus, allowing development of the antiviral immune response and subsequent inhibition of virus spread into the optic nerve and retina.

Infiltration of T-lymphocytes in the brain after anterior chamber inoculation of a neurovirulent and neuroinvasive strain of HSV-1

Following anterior chamber (AC) inoculation of BALB/c mice with the KOS strain of herpes simplex virus type 1 (HSV-1), or with H129, a neuroinvasive and neurovirulent strain of HSV-1, both strains of virus spread from the injected eye through the brain to cause retinitis. However, KOS-infected mice develop retinitis in the uninoculated eye only, whereas H129-infected mice develop bilateral retinitis. Previous studies have shown that infiltrating T-cells in the suprachiasmatic nuclei (SCN) of the hypothalamus of KOS-infected mice concomitant with or before virus protect KOS-infected mice from ipsilateral retinitis. To determine the timing of T cell infiltration and cytokine production in the brain of H129-infected mice, adjacent, frozen sections of the brain were immunostained for virus, T-cells, IL-2, TNF-alpha or IFN-gamma. T-cells infiltrated the brains of H129-infected mice and cytokines were produced in infected tissues. However, virus spread to the optic nerve and retina of both the inoculated and uninoculated eye before T-cells and cytokines were detected in the SCN of H129-infected mice. These results suggest that infiltrating T-cells in the SCN of H129-infected mice may arrive too late to prevent the spread of virus into the optic nerves and retinas and thus prevent development of bilateral retinitis in infected mice.

Apoptosis in the retina during MCMV retinitis in immunosuppressed BALB/c mice

BACKGROUND

Cytomegalovirus (CMV) retinitis is the most common opportunistic ocular infection observed in immunosuppressed (IS) adult and pediatric patients. Due to the species restriction of the cytomegaloviruses, mice infected with murine CMV (MCMV) have been used to study the pathogenesis of CMV retinitis.

OBJECTIVES

The objectives of this study were to determine if retinal glial cells are the targets of MCMV infection and to determine which cells in the retina become apoptotic following inoculation of MCMV via the supraciliary route.

STUDY DESIGN

Adult female BALB/c mice were IS with methylprednisolone; one half of the mice were injected with MCMV and one half of the mice were injected with an equivalent volume of tissue culture medium via the supraciliary route. Animals were sacrificed and frozen sections of eyes were stained for MCMV early antigen, RPE65, CD45 or TUNEL; additional slides were double stained with combinations of the above reagents.

RESULTS AND CONCLUSIONS

The results indicate that most apoptotic cells in the retina were not virus infected, most apoptotic cells were not infiltrating CD45 positive leukocytes, and retinal glial cells were infected with MCMV but only late in infection. Together, these results suggest that retinal cells that undergo apoptosis during MCMV infection are neurons and that apoptosis of uninfected bystander cells is an important component of the pathogenesis of CMV retinitis.

Detection of herpes simplex virus type 1 in human ciliary ganglia

PURPOSE

To determine whether herpes simplex virus type 1 (HSV-1) DNA is present in the ciliary ganglion (CG).

METHODS

Fifty CG and 47 trigeminal ganglia (TG) were resected from 63 formalin-fixed cadavers between 56 and 98 years of age that had been embalmed within 12 hours of death. The donors had no known active HSV infection at the time of death. DNA was extracted from all ganglia by proteinase-K digestion (TG) or digestion by a mild lysis buffer (CG). DNA was amplified by polymerase chain reaction for sequences from human chromosome 18, D18S1259 (positive control), and from the HSV-1 DNA polymerase gene, U(L)30. The amplified DNA was separated by agarose gel electrophoresis, transferred to nylon membranes, and hybridized with the appropriate digoxigenin-labeled probe that was detected by alkaline phosphatase-conjugated monoclonal antibody.

RESULTS

The D18S1259 sequence was amplified from 47 TG and 30 CG samples. Of these samples, 32 (68.0%) of the 47 TG samples and 20 (66.6%) of the 30 CG samples were positive for the UL(30) HSV-1 sequence.

CONCLUSIONS

Using amplification of HSV-1 DNA as a surrogate marker of latency, the finding that the frequency of HSV-1 in the CG was approximately the same as that of the TG suggests that the CG may be an additional site of HSV-1 latency in humans. Active infection in or reactivation of HSV-1 from non-TG sites may explain why this virus is able to infect sites, such as the retina, that have no direct connections to the trigeminal nerve.

Rapid spread of a neurovirulent strain of HSV-1 through the CNS of BALB/c mice following anterior chamber inoculation

Following uniocular anterior chamber (AC) inoculation of BALB/c mice with the KOS strain of herpes simplex virus type 1 (HSV-1), virus spreads from the injected eye to the ipsilateral suprachiasmatic nucleus (SCN) in the central nervous system (CNS) to infect the optic nerve and retina of the contralateral eye, and mice develop retinitis in that eye only. In contrast, after AC inoculation of BALB/c mice with the H129 strain of HSV-1, mice develop bilateral retinitis. The pathway(s) by which H129 spreads to cause bilateral retinitis is not known. To determine the route and timing of H129 spread after AC inoculation, BALB/c mice were injected in the AC of the right eye with 5 x 10(3) PFU of H129. Brains from 30 mice were sectioned on a brain matrix and the amount of virus in the brain and eyes was determined by plaque assay. Frozen sections were prepared from the eyes, brain, and trigeminal ganglia of an additional 30 mice, and HSV-1 antigen was detected by immunohistochemistry. After AC inoculation, H129 follows a pathway similar to KOS in the CNS, but H129 appears to spread more rapidly than KOS within the CNS. Unlike KOS, H129 is able to infect brain stem nuclei and H129-infected mice developed neurological impairments in addition to bilateral retinitis. The results of these studies suggest that the ability of H129 to spread rapidly in the CNS allows early virus infection of retino-recipient nuclei proximal to the contralateral and ipsilateral optic nerves. Early infection of retino-recipient nuclei, such as the SCN may allow virus to spread into the retinas before a virus-specific immune response can be induced.

Acute retinal necrosis: insights into pathogenesis from the mouse model

Acute retinal necrosis (ARN) is a relatively rare syndrome that is caused by infection with one of several members of the human herpesvirus family. ARN usually occurs in otherwise healthy patients, although it has also been observed in immunocompromised individuals. It is characterized by retinal vasculitis and haemorrhaging, areas of retinal necrosis, vitreous and aqueous inflammation and optic neuritis. It may affect one or both eyes and frequently results in severely reduced vision or blindness in the affected eye. Results using the mouse model of ARN have provided insight into the pathogenesis of this disease. However, many unanswered questions remain, such as why does only a very small fraction of individuals infected with one or more herpesvirus develop ARN? Increased understanding of the interactions of herpesviruses with T cells and cytokines may enable the development of therapeutic strategies targeted specifically to control viral infection in the eye and/or brain.

Murine cytomegalovirus infection causes apoptosis of uninfected retinal cells

PURPOSE

To determine the role of apoptosis in prevention and/or exacerbation of retinal disease in a mouse model of cytomegalovirus retinitis.

METHODS

Immunocompetent or T-cell- depleted BALB/c mice were injected with murine cytomegalovirus (MCMV) by supraciliary injection. On sequential days after infection, mice were killed, and eyes were harvested for cryosectioning or for DNA extraction. Ocular sections were stained with monoclonal antibodies specific for MCMV or for T cells or used in the TdT-dUTP terminal nick-end labeling (TUNEL) assay to detect apoptotic cells.

RESULTS

In immunocompetent BALB/c mice, TUNEL assays revealed that a large area of the retina was apoptotic in relation to the relatively small number of MCMV-infected cells that were observed in the subjacent choroid and/or retinal pigment epithelium. In infected eyes from T-cell- depleted mice, there were more TUNEL-positive cells, and the areas of apoptosis were more extensive than in immunocompetent mice. These observations correlated with the increased extent of MCMV infection that is observed in the eyes of T-cell- depleted mice. However, irrespective of immune status, TUNEL-positive apoptotic cells were present mainly in areas of the retina overlying areas of MCMV-infected choroid and/or retinal pigment epithelium. More intense DNA laddering, indicative of increased apoptosis, was observed in the posterior segments of the eyes of T-cell- depleted mice after supraciliary inoculation with murine cytomegalovirus compared with less intense DNA laddering in the posterior segments of eyes of immunocompetent MCMV-infected mice.

CONCLUSIONS

The ability of the mouse's immune system to control MCMV infections in some tissues depends on induction of apoptosis in virus-infected cells. However, in the retina, cells undergoing apoptosis were not virus-infected, a finding that suggests that apoptosis of uninfected retinal cells may play a role in the pathogenesis of MCMV retinitis.

Natural killer cells prevent direct anterior-to-posterior spread of herpes simplex virus type 1 in the eye

PURPOSE

Anterior chamber (AC) inoculation of the KOS strain of herpes simplex virus type 1 (HSV-1) results in morphologic sparing of the ipsilateral retina, whereas the retina of the uninoculated contralateral eye becomes infected and undergoes acute retinal necrosis. Natural killer (NK) cells are an important component of the primary immune response to most virus infections. The purpose of this study was to determine whether NK cells are involved in preventing early direct anterior-to-posterior spread of HSV-1 after AC inoculation.

METHODS

Normal BALB/c mice were inoculated with 4 X 10(4) plaque-forming units (PFU) of the KOS strain of HSV-1 using the AC route. NK activity was measured in the spleen, the superficial cervical and submandibular lymph nodes, and the inoculated eye by lysis of chromium-labeled, NK-sensitive YAC-1 target cells. Histopathologic scoring and immunohistochemical staining for HSV-1 were performed in NK-depleted (injected intravenously with anti-asialo GM1) or mock-depleted (injected intravenously with normal rabbit serum) mice.

RESULTS

In mock-depleted mice, NK activity in the spleens, superficial cervical and submandibular lymph nodes, and inoculated eyes peaked at postinoculation (pi) day 5 and declined by pi day 7. Treatment with anti-asialo GM1 eliminated NK activity in the eye and at nonocular sites. The histopathologic scores at pi day 5 indicated more damage to the retinas of NK-depleted mice than to those of mock-depleted mice, and immunohistochemical staining for HSV-1 showed spread of the virus to the sensory retina only in NK-depleted mice.

CONCLUSIONS

NK cells were activated within 5 days after AC inoculation of the KOS strain of HSV-1. Activation of NK cells appears to play a role in preventing direct anterior-to-posterior spread of the virus in the inoculated eye which, in turn, protects the retina of this eye and helps to explain why the architecture of the retina of this eye is spared.

Protection against murine cytomegalovirus retinitis by adoptive transfer of virus-specific CD8+ T cells

PURPOSE

Human cytomegalovirus retinitis, the most common ophthalmic infection of AIDS patients, has been modeled in BALB/c mice infected with murine cytomegalovirus by the supraciliary route. A series of depletion and adoptive transfer studies was performed to determine whether adoptive transfer of T cells protects mice from retinitis caused by murine cytomegalovirus infection after supraciliary inoculation and to determine which subset of T cells is responsible for protection.

METHODS

BALB/c mice were thymectomized and T cell-depleted by injection of monoclonal antibodies to CD4, CD8, or both. Murine cytomegalovirus (9 x 10(2) plaque forming units [pfu]) was injected into the supraciliary space. Experimental animals received murine cytomegalovirus-specific T cells or subsets of T cells 2 hours before virus injection, whereas control animals received herpes simplex virus type 1-specific T cells by tail vein injection. Eight days after virus injection, retinal pathology was scored by histopathologic examination of hematoxylin and eosin-stained ocular sections.

RESULTS

CD8+ T cell depletion was sufficient for development of retinitis after supraciliary injection of murine cytomegalovirus. Adoptive transfer of murine cytomegalovirus-specific T cells, but not herpes simplex virus type 1-specific T cells, provided protection from retinitis. Additionally, separation of the murine cytomegalovirus-specific T cells into CD8+ and CD4+ subsets before adoptive transfer showed that the CD8+ fraction of the adoptive T cells was responsible for protection.

CONCLUSIONS

These results suggest that adoptive transfer of cytomegalovirus-specific T cells or T cell subsets might be used to treat or prevent cytomegalovirus retinitis in immunosuppressed human patients.

Is there a risk of cytomegalovirus transmission during in vitro fertilization with donated oocytes?

OBJECTIVE

To define the risk of human cytomegalovirus (HCMV) transmission from donated oocytes.

DESIGN

Prospective study.

SETTING

University IVF program.

PATIENT(S)

Sixty-seven couples undergoing 72 cycles of IVF-ET.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Serum from both partners (women: n = 71; men: n = 60) was obtained for detection of antibodies to HCMV. Semen before preparation (n = 53), sperm after preparation (Percoll gradient; n = 47), cervical mucus aspirated at the time of oocyte aspiration (n = 70), and uninseminated oocytes and embryos not suitable for cryopreservation (n = 568) were frozen in liquid nitrogen. Polymerase chain reaction was used for detection of HCMV (immediate early 1 gene) in all samples collected.

RESULT(S)

Serum antibodies to HCMV were found in 62% of the women and 37% of the men tested. Human cytomegalovirus DNA was detected in 25% of the ejaculates and in 19% of the cervical mucus samples. There was no amplification of HCMV DNA from oocytes or embryos.

CONCLUSION(S)

Because we were unable to amplify HCMV DNA from any of the oocytes or embryos, it seems unlikely that HCMV is transmissible through oocyte or embryo donation.

NK Cell Modulation of Murine Cytomegalovirus Retinitis

CMV retinitis, the most common ophthalmic infection of AIDS patients, causes blindness if left untreated. To study the role of NK cells in the modulation of CMV ocular infection, 9.0 × 102 plaque-forming units of the Smith strain of murine CMV (MCMV) was injected into the supraciliary space of the left eyes of BALB/c mice. Lysis of NK-sensitive target cells (YAC-1) by effectors from the draining lymph nodes peaked at day 5 postinfection, while the splenic cytolytic response was biphasic, with peaks at days 2 and 7 postinfection. Flow cytometry showed that NK cells (DX-5+) increased in spleens and eyes 5 days after supraciliary infection with MCMV compared with uninfected or mock-infected controls. Eight days after supraciliary injection with 9.0 × 102 plaque-forming units of MCMV, 7 of 10 NK-depleted mice developed retinitis compared with only 2 of 10 non-NK-depleted control mice. Poly(I-C) activation of NK cells in T cell-depleted animals protected mice from MCMV retinitis; only 2 of 10 mice in the poly(I-C)-treated group developed retinitis compared with 8 of 10 T cell-depleted, non-poly(I-C)-treated control mice. These results show the importance of NK cells in preventing MCMV retinitis and suggest that NK cells may also be involved in modulation of cytomegalovirus retinitis in human patients.

NK cell modulation of murine cytomegalovirus retinitis

CMV retinitis, the most common ophthalmic infection of AIDS patients, causes blindness if left untreated. To study the role of NK cells in the modulation of CMV ocular infection, 9.0 x 10(2) plaque-forming units of the Smith strain of murine CMV (MCMV) was injected into the supraciliary space of the left eyes of BALB/c mice. Lysis of NK-sensitive target cells (YAC-1) by effectors from the draining lymph nodes peaked at day 5 postinfection, while the splenic cytolytic response was biphasic, with peaks at days 2 and 7 postinfection. Flow cytometry showed that NK cells (DX-5+) increased in spleens and eyes 5 days after supraciliary infection with MCMV compared with uninfected or mock-infected controls. Eight days after supraciliary injection with 9.0 x 10(2) plaque-forming units of MCMV, 7 of 10 NK-depleted mice developed retinitis compared with only 2 of 10 non-NK-depleted control mice. Poly(I-C) activation of NK cells in T cell-depleted animals protected mice from MCMV retinitis; only 2 of 10 mice in the poly(I-C)-treated group developed retinitis compared with 8 of 10 T cell-depleted, non-poly(I-C)-treated control mice. These results show the importance of NK cells in preventing MCMV retinitis and suggest that NK cells may also be involved in modulation of cytomegalovirus retinitis in human patients.

T cells in the uninjected eye after anterior chamber inoculation of herpes simplex virus type 1

PURPOSE

To investigate T cell infiltration in the posterior segment of the uninjected eye after uniocular anterior chamber inoculation of HSV-1.

METHODS

The anterior chamber of one eye of euthymic BALB/c mice was injected with 1 x 10(4) plaque-forming units (PFU) to 2 x 10(4) PFU of herpes simplex virus type 1 (HSV-1; KOS strain). All mice were examined for retinitis on day 8 postinoculation (p.i.). Only mice with retinitis were retained and used in these experiments. Animals were killed on days 9, 11, 14, 21, 35, and 63 p.i. The uninjected eyes were removed. Some of the uninjected eyes were sectioned and stained for CD4+ and CD8+ cells using the avidin-biotinylated enzyme complex method. Infiltrating cells were collected from the remaining uninoculated eyes and stained using rat anti-mouse monoclonal antibodies specific for CD4+ or CD8+ T cells, and the percentage of CD4+ and CD8+ T cells was determined by flow cytometry.

RESULTS

At day 9 p.i. (acute retinitis), T cells were observed in the uvea but not in the retina of the contralateral eye. CD4+ and CD8+ cells were observed in the sensory retina coincident with the onset of retinal necrosis (day 11 p.i.), and CD4+ and CD8+ T cells continued to be detected in the remnants of the retina up to and including day 63 p.i. The maximum percentage of both CD4+ and CD8+ T cells was observed at day 21 p.i.

CONCLUSIONS

These results demonstrate that T cells enter the retina of the uninoculated eye during HSV-1 infection. The observation that T cells arrive in the sensory retina at the onset of retinal necrosis and not during acute retinitis and the peak of virus replication provides further evidence that T cells play a role in development of retinal necrosis. The result that T cells are observed in the uninjected eye as late as day 63 p.i. suggests that T cells might also have a role in the resolution phase of the disease.

Spread of HSV-1 to the suprachiasmatic nuclei and retina in T cell depleted BALB/c mice

Following uniocular anterior chamber inoculation of the KOS strain of HSV-1 in euthymic BALB/c mice, virus spreads from the injected eye to the brain, and from the brain to the optic nerve and retina of the uninjected eye by day 7 post inoculation (p.i.), but the optic nerve and retina of the injected eye are not infected with virus. Infection of the optic nerve and retina of the injected eye is observed only in athymic mice or in mice depleted of both CD4+ and CD8+ T cells. To determine the role of T cells in virus spread, adult female BALB/c mice were thymectomized and T cell depleted. Mice were co-injected with the KOS strain of HSV-1 and RH116, a thymidine kinase-negative mutant of KOS containing the Escherichia coli lac Z gene. Animals were sacrificed on days 3-7 p.i., and the eyes and brains were examined for blue-stained, virus-infected cells. A difference in the timing of virus infection was observed in the area of the suprachiasmatic nuclei only in mice depleted of both CD4+ and CD8+ T cells, and in this group, the contralateral suprachiasmatic nucleus was infected two days earlier. Since one route by which virus could infect the retina of the injected eye is via connections of the contralateral suprachiasmatic nucleus to the ipsilateral optic nerve, these findings suggest that (a) retinitis observed in the injected eyes of mice depleted of both CD4+ and CD8+ T cells results from virus infection of the contralateral suprachiasmatic nucleus followed by spread of virus to the ipsilateral optic nerve and retina and (b) early HSV-1 infection of the contralateral suprachiasmatic nucleus is prevented by a T cell dependent mechanism.

Immune effector cell (IEC)-mediated protection from HSV-1 retinitis occurs in the brain

Following uniocular anterior chamber inoculation of the KOS strain of HSV-1 into euthymic BALB/c mice, virus spreads from the injected eye to the brain and from the brain to the optic nerve and retina of the uninjected eye resulting in retinitis. Adoptive transfer of HSV-1-specific immune effector cells (IEC) within 24 h of anterior chamber inoculation of virus prevents retinitis. To determine where protection occurs, mice were injected with HSV-1 via the anterior chamber route, and fluorescently-labeled HSV-1-specific-IEC or ovalbumin-specific-lymph node cells were adoptively transferred intravenously. The eyes and brains of these mice were sectioned and examined for virus-infected cells and for fluorescently-labeled adoptively transferred cells. None of the mice in the group receiving an adoptive transfer of virus-specific IEC had evidence of virus infection of the ipsilateral suprachiasmatic nucleus (SCN), whereas the ipsilateral SCN of all of the mice in the control groups were virus-positive by day 5 P.I. Since virus spreads from the ipsilateral SCN to the contralateral optic nerve and retina to cause retinitis in the uninoculated eye, the results of these studies suggest IEC-mediated protection from HSV-1 retinitis occurs proximal to the ipsilateral SCN. Furthermore, since only HSV-1-specific IEC conferred protection and only these cells were observed in the brain, protection and trafficking of cells after adoptive transfer was virus-specific.

Adoptive transfer of murine cytomegalovirus-immune lymph node cells prevents retinitis in T-cell-depleted mice

PURPOSE

The purpose of this study was to determine whether adoptive transfer of murine cytomegalovirus (MCMV)-immune lymph node cells prevents retinitis in immunosuppressed mice.

METHODS

Adult BALB/c mice were thymectomized and T-cell depleted using rat monoclonal antibodies specific for mouse CD4+ and CD8+ T-cells. The level of rat immunoglobulin G in the treated mice was monitored by enzyme-linked immunosorbent assay. Immune cells were labeled with PKH26-GH immediately before adoptive transfer, and flow cytometry was used to determine the percentage of adoptively transferred T-cells (PKH+, fluorescein isothiocyanate [FITC+]) in the spleens of the recipient mice 3 days after transfer. The ability of adoptively transferred cells to protect from retinitis was studied in T-cell-depleted mice injected with MCMV through the supraciliary route. Mice received 4 x 10(7) in vitro-restimulated MCMV-immune cells, 4 x 10(7) freshly isolated MCMV-immune cells, 4 x 10(7) freshly isolated ovalbumin-immune cells, or no cells (control group).

RESULTS

The best time to balance depletion of endogenous T-cells with persistence of transferred cells was 3 weeks after T-cell depletion. Both restimulated and freshly isolated MCMV-immune cells conferred protection from retinitis. Freshly isolated ovalbumin-immune lymph node cells did not prevent retinitis, indicating that protection was virus-specific and merely was not because of transfer of antigen-activated lymph node cells.

CONCLUSIONS

Adoptive immunotherapy has been used to prevent cytomegalovirus (CMV) infection in patients who have undergone transplantation, and, by extrapolation, the results of these studies suggest that adoptive immunotherapy with human CMV-specific immune cells might be used to prevent or ameliorate CMV retinitis in immunocompromised patients.

Spread of murine cytomegalovirus to inner ocular structures following disruption of the blood-retina barrier in immunosuppressed BALB/c mice

PURPOSE

The aims of this study were to determine whether disruption of the blood-retina barrier (BRB) increases spread of murine cytomegalovirus (MCMV) to the eye after intraperitoneal inoculation and whether systemic immunosuppression influences the location of MCMV in the ocular compartment.

METHODS

The BRB of the left eye of normal and immunosuppressed mice was disrupted by supraciliary inoculation of tissue culture medium followed 2 hours later by intraperitoneal injection of MCMV. Plaque assay of homogenized ocular tissue was used to determine the frequency of virus-positive eyes and the titer of virus in the eyes. Beta-galactosidase staining of frozen sections was used to locate virus in the eyes.

RESULTS

In nonimmunosuppressed mice, the frequency of virus isolation, as well as the titer of virus, were significantly higher in eyes in which the BRB had been disrupted. Although the frequency of virus isolation was the same in both eyes of immunosuppressed mice, the titer of virus was significantly higher in the eye in which the BRB had been disrupted. The most striking result was that the location of virus was different in the nondisrupted eyes of immunosuppressed mice than it was in the disrupted eyes of immunosuppressed mice. In the former, virus was seen only in the outer ocular structures (conjunctiva, sclera, lacrimal gland), whereas in the latter, virus was observed in the retina and anterior segment (iris, ciliary body) as well as the outer ocular structures.

CONCLUSIONS

The results of these studies suggest that ocular damage followed by increased spread of virus to and within the eye during systemic infection with CMV may be one mechanism by which development of CMV retinitis is facilitated in patients with acquired immune deficiency syndrome.

Immunosuppression induces transcription of murine cytomegalovirus glycoprotein H in the eye and at non-ocular sites

In these studies, DNA PCR was used to identify sites of murine cytomegalovirus (MCMV) latency after inoculation of virus into the supraciliary space of the eye. Reverse transcription (RT) PCR for an immediate early gene and a late gene was used to identify putative sites of virus reactivation after methylprednisolone (steroid)-induced immunosuppression. Ten weeks after inoculation of 5 x 10(2) PFU of MCMV, BALB/c mice were immunosuppressed by intramuscular injection of steroid. Control mice were infected but not immunosuppressed. Two weeks after initiation of immunosuppression, mice were sacrificed. DNA and RNA extracted from homogenized tissues were amplified for immediate early gene 1 (IE1) and late gene, glycoprotein H (gH), DNA and mRNA by PCR and RT-PCR, respectively. Replicating virus was detected in homogenized ocular and non-ocular tissues by plaque assay. In the latently infected PBS-treated control group, viral DNA was detected in the inoculated eye and in several non-ocular tissues; IE1 mRNA was found in most of the DNA-positive tissues, while gH mRNA was amplified only in a few of the MCMV DNA-positive tissues from a single mouse. After immunosuppression, viral DNA and IE1 mRNA were detected at a higher frequency in various tissues of steroid-treated mice. gH mRNA was detected in a significantly higher number of the inoculated eyes, salivary glands and other non-ocular tissues of steroid-treated mice. After immunosuppression, low titers of infectious virus were recovered from the salivary glands of steroid-treated mice, but infectious virus was not recovered from the inoculated eye of either steroid-treated of non-immunosuppressed mice. The DNA PCR results suggest that after inoculation of 5 x 10(2) PFU of MCMV into the supraciliary space of euthymic BALB/c mice, virus becomes latent in the inoculated eye, salivary gland and other extraocular tissues. The RT-PCR results suggest that latent MCMV can be reactivated in multiple tissues by immunosuppression.

Discovery of a brain promoter from the human transferrin gene and its utilization for development of transgenic mice that express human apolipoprotein E alleles

Transgenic mice carrying heterologous genes directed by a 670-bp segment of the regulatory sequence from the human transferrin (TF) gene demonstrated high expression in brain. Mice carrying the chimeric 0.67kbTF-CAT gene expressed TF-CAT in neurons and glial cells of the nucleus basalis, the cerebrum, corpus callosum, cerebellum, and hippocampus. In brains from two independent TF-CAT transgenic founder lines, copy number of TF-CAT mRNA exceeded the number of mRNA transcripts encoding either mouse endogenous transferrin or mouse endogenous amyloid precursor protein. In two transgenic founder lines, the chloramphenicol acetyltransferase (CAT) protein synthesized from the TF-CAT mRNA was estimated to be 0.10-0.15% of the total soluble proteins of the brain. High expression observed in brain indicates that the 0.67kbTF promoter is a promising director of brain expression of heterologous genes. Therefore, the promoter has been used to express the three common human apolipoprotein E (apoE) alleles in transgenic mouse brains. The apoE alleles have been implicated in the expression of Alzheimer disease, and the human apoE isoforms are reported to interact with different affinities to the brain beta-amyloid and tau protein in vitro. Results of this study demonstrate high expression and production of human apoE proteins in transgenic mouse brains. The model may be used to characterize the interaction of human apoE isoforms with other brain proteins and provide information helpful in designing therapeutic strategies for Alzheimer disease.

T lymphocyte infiltration in the brain following anterior chamber inoculation of HSV-1

Following inoculation of the KOS strain of herpes simplex virus type 1 (HSV-1) into one anterior chamber of euthymic BALB/c mice, virus spreads from the injected eye to the central nervous system and from the central nervous system to the optic nerve and retina of only the uninoculated eye. In contrast, in athymic BALB/c mice or mice depleted of both CD4+ and CD8+ T cells, virus spreads to the optic nerve and retina of both the injected eye and the uninjected eye. To determine the location in the central nervous system where spread of virus to the optic nerve and retina of the injected eye is prevented, euthymic BALB/c mice were injected with a mixture of KOS and RH116, a mutant of KOS that contains the Escherichia coli beta-galactosidase (beta-gal) gene. Several animals were sacrificed each day; serial frozen sections of the brain were prepared and sequential sections were stained for beta-gal or for T cells. At all sites except the suprachiasmatic nuclei, virus and T cells arrived at approximately the same time. However, at day 5 post inoculation (PI), T cells were present in both the ipsilateral and the contralateral suprachiasmatic nuclei, but only the ipsilateral suprachiasmatic nucleus was virus-positive. Since virus spreads from the ipsilateral suprachiasmatic nucleus to the contralateral optic nerve, these results suggest that T cells infiltrating the area of the contralateral suprachiasmatic nucleus prior to the arrival of virus at this site prevent virus spread into the optic nerve of the inoculated eye.

Sjögren's syndrome: cytokine and Epstein-Barr viral gene expression within the conjunctival epithelium

PURPOSE

In primary Sjögren's syndrome (SS), ocular surface changes within the conjunctival epithelium include lymphocytic infiltration, squamous cell metaplasia, and a reduction in goblet cell number. These changes may be the simple result of increased mechanical abrasion secondary to dryness. Alternatively, they may represent a local response to ocular and/or systemic inflammatory processes, perhaps in response to Epstein-Barr viral (EBV) infection, an agent recently implicated in the etiology of SS. To determine whether inflammatory processes or local infection by EBV contribute to the ocular surface pathology of SS, we examined the expression of inflammatory cell surface markers, cytokines, and EBV gene products within the ocular conjunctiva of patients with SS.

METHODS

Ocular conjunctival tissue was isolated from patients with primary SS and nondry eye control patients by impression cytology or direct biopsy. These specimens were examined by immunofluorescence microscopy and reverse-transcriptase polymerase chain reaction (RT-PCR) for the expression of various markers.

RESULTS

The authors found the frequency of expression of HLA-DR (P < 0.0001), ICAM-1 (P < 0.035), and IL-6 (P < 0.0001) to be significantly elevated in patients with primary SS versus nondry eye control patients. The IL-2 receptor and cytokines IL-1 beta and IL-8 were each found to be expressed with relatively high frequency in both patient populations, whereas mRNAs encoding cytokines IL-2, IFN-gamma, GM-CSF, and TGF-beta were not reproducibly detectable in either population. Messenger RNA encoding a marker for passive-latent EBV infection (EBNA-1) was detected with high frequency in both SS and normal populations. The EBV IL-10 analog BCRF-1 was expressed with low frequency in the SS population; however, these levels were not significantly different from the control population. The expression of two other markers of EBV infection, latent membrane protein (LMP, a lytic and latent marker), and BZLF-1 (putative latent-lytic switch gene) was undetectable in either study population.

CONCLUSION

Based on the increased expression of the cell surface molecules HLA-DR and ICAM-1, and the inflammatory cytokine IL-6, the authors propose that local inflammatory processes contribute to the ocular surface changes and ocular surface dryness associated with primary SS.

Sparing of the ipsilateral retina after anterior chamber inoculation of HSV-1: requirement for either CD4+ or CD8+ T cells

PURPOSE

To determine whether CD4+ T cells, CD8+ T cells, or both CD4+ and CD8+ T cells are required for preservation of the ipsilateral retina after uniocular anterior chamber inoculation of herpes simplex virus type 1 (HSV-1).

METHODS

Adult-thymectomized BALB/c mice were T cell depleted by administration of anti-CD4 monoclonal antibody (mAb), anti-CD8 mAb, or anti-CD4 mAb and anti-CD8 mAb together. Control mice were thymectomized but were not T cell depleted. HSV-1 (KOS) was inoculated in one anterior chamber. At intervals after inoculation, the injected eyes were examined histopathologically or homogenized to determine the kinetics of infectious virus recovery. Additional groups of in vivo depleted mice were injected with wild type KOS and RH116 (a mutant of KOS containing the Escherichia coli beta-galactosidase gene) to determine whether viral genes were expressed in the retina in any of the mice.

RESULTS

In the inoculated eyes of mice depleted of both CD4+ and CD8+ T cells, there was a significantly higher incidence of acute destructive retinitis at days 9 and 14 postinoculation (PI), and the titer of virus recovered at day 14 PI was significantly higher. Viral gene expression in the retina and the optic nerve was observed after day 7 PI only in the group of mice depleted of both CD4+ and CD8+ cells. In contrast, acute destructive retinitis was not observed in nondepleted mice or in mice depleted of either CD4+ or CD8+ T cells alone, and virus recovery was not significantly different among these three groups of mice. No virus-infected cells were observed in the optic nerve or the sensory retina of nondepleted mice, of mice depleted of only CD4+ cells, or of mice depleted of only CD8+ cells.

CONCLUSION

The results of these studies suggest that either CD4+ or CD8+ T cells can spare the retina of the injected eye after uniocular anterior chamber inoculation of HSV-1. Because virus appeared after day 7 PI in the ipsilateral optic nerve and retina only in mice depleted of both CD4+ and CD8+ T cells, these results suggest that spread of virus to the ipsilateral retina occurs via the optic nerve and that either CD4+ or CD8+ T cells can prevent spread of virus to the inoculated eye resulting in sparing of the ipsilateral retina.