The cornea IV immunology, infection, neovascularization, and surgery chapter 1: Corneal immunology

PURPOSE

of Review: This review offers an informed and up-to-date insight on the immune profile of the cornea and the factors that govern the regulation of such a unique immune environment.

SUMMARY

The cornea is a unique tissue that performs the specialized task of allowing light to penetrate for visual interpretation. To accomplish this, the ocular surface requires a distinct immune environment that is achieved through unique structural, cellular and molecular factors. Not only must the cornea be able to fend off invasive infectious agents but also control the inflammatory response as to avoid collateral, and potentially blinding damage; particularly of post-mitotic cells such as the corneal endothelium. To combat infections, both innate and adaptive arms of the inflammatory immune response are at play in the cornea. Dendritic cells play a critical role in coordinating both these responses in order to fend off infections. On the other side of the spectrum, the ocular surface is also endowed with a variety of anatomic and physiologic components that aid in regulating the immune response to prevent excessive, potentially damaging, inflammation. This attenuation of the immune response is termed immune privilege. The balance between pro and anti-inflammatory reactions is key for preservation of the functional integrity of the cornea.

RECENT FINDINGS

The understanding of the molecular and cellular factors governing corneal immunology and its response to antigens is a growing field. Dendritic cells in the normal cornea play a crucial role in combating infections and coordinating the inflammatory arms of the immune response, particularly through coordination with T-helper cells. The role of neuropeptides is recently becoming more highlighted with different factors working on both sides of the inflammatory balance.

Ocular Manifestations of Emerging Flaviviruses and the Blood-Retinal Barrier

Despite flaviviruses remaining the leading cause of systemic human infections worldwide, ocular manifestations of these mosquito-transmitted viruses are considered relatively uncommon in part due to under-reporting. However, recent outbreaks of Zika virus (ZIKV) implicated in causing multiple ocular abnormalities, such as conjunctivitis, retinal hemorrhages, chorioretinal atrophy, posterior uveitis, optic neuritis, and maculopathies, has rejuvenated a significant interest in understanding the pathogenesis of flaviviruses, including ZIKV, in the eye. In this review, first, we summarize the current knowledge of the major flaviviruses (Dengue, West Nile, Yellow Fever, and Japanese Encephalitis) reported to cause ocular manifestations in humans with emphasis on recent ZIKV outbreaks. Second, being an immune privilege organ, the eye is protected from systemic infections by the presence of blood-retinal barriers (BRB). Hence, we discuss how flaviviruses modulate retinal innate response and breach the protective BRB to cause ocular or retinal pathology. Finally, we describe recently identified infection signatures of ZIKV and discuss whether these system biology-predicted genes or signaling pathways (e.g., cellular metabolism) could contribute to the pathogenesis of ocular manifestations and assist in the development of ocular antiviral therapies against ZIKV and other flaviviruses.

Herpes simplex virus-1 infects the olfactory bulb shortly following ocular infection and exhibits a long-term inflammatory profile in the form of effector and HSV-1-specific T cells

BACKGROUND

Herpes simplex virus 1 (HSV-1) infection can result in a life-threatening condition known as herpes simplex encephalitis (HSE). Trafficking patterns by which the virus reaches the central nervous system (CNS) following ocular infection are unresolved. We evaluated early viral dissemination pathways following ocular infection that involve trafficking to the olfactory bulb (OB). Additionally, we have characterized the capacity of HSV-1 to establish latency within OB tissue and profiled the local T lymphocyte response over the course of the acute infection into latency.

METHODS

Scarified corneas of C57BL/6 or reporter-inducible Rosa mice (RosaTd/Tm) were inoculated with HSV-1 and assessed for viral dissemination into the peripheral nervous system (PNS) and CNS by RT-PCR and confocal microscopy. T cells and the resident microglia activation signatures were analyzed by flow cytometry. T cell effector function in the form of IFN-γ secretion was measured by T cells isolated from OB in comparison to T cells from other nervous system sites known to harbor HSV-1-specific memory T cells.

RESULTS

Following ocular infection, HSV-1 viral titers from nasal secretions were detected as early as 48 h through 8 days post infection (8 DPI). HSV-1 gene expression was expressed as early as 2 days following ocular infection in the OB and was consistent with an enhanced expression in the ophthalmic, maxillary, and mandibular branch of the trigeminal nerve ganglia (TG). Rosa fluorescence protein expression (RFP+) representing HSV-1-infected cells from RosaTd/Tm mice was detected in the OB before other areas of the CNS (2 DPI). Additionally, during acute infection, most infected cells appeared to be anatomically distributed within the OB rather than other regions of the CNS. During latency (i.e., 30 DPI and beyond) despite no detectable infectious virus or lytic gene expression and low levels of latency associated transcripts, total effector (CD44+ CD62-) CD4+ T, CD8+ T, HSV-1-specific CD8+ T cells, and MHC class II positive resident microglia numbers continued to increase. CD4+ and CD8+ T cell populations isolated from the OB during latency were capable of responding to PMA/ionomycin in the production of IFN-γ similar to T cells from other tissue that possess latent virus including the TG and brain stem.

CONCLUSIONS

It is currently understood that HSV-1 traffics to the TG following ocular infection. We have identified a second conduit by which HSV-1 can directly access the CNS bypassing the brain stem. We have also recognized that the OB is unique in that during HSV-1 latency, latency-associated transcripts levels were marginally above uninfected controls. Despite these findings, the local immune response mimicked the phenotype of an active infection during latency.

Quantitative Trait Locus Based Virulence Determinant Mapping of the HSV-1 Genome in Murine Ocular Infection: Genes Involved in Viral Regulatory and Innate Immune Networks Contribute to Virulence

Herpes simplex virus type 1 causes mucocutaneous lesions, and is the leading cause of infectious blindness in the United States. Animal studies have shown that the severity of HSV-1 ocular disease is influenced by three main factors; innate immunity, host immune response and viral strain. We previously showed that mixed infection with two avirulent HSV-1 strains (OD4 and CJ994) resulted in recombinants that exhibit a range of disease phenotypes from severe to avirulent, suggesting epistatic interactions were involved. The goal of this study was to develop a quantitative trait locus (QTL) analysis of HSV-1 ocular virulence determinants and to identify virulence associated SNPs. Blepharitis and stromal keratitis quantitative scores were characterized for 40 OD4:CJ994 recombinants. Viral titers in the eye were also measured. Virulence quantitative trait locus mapping (vQTLmap) was performed using the Lasso, Random Forest, and Ridge regression methods to identify significant phenotypically meaningful regions for each ocular disease parameter. The most predictive Ridge regression model identified several phenotypically meaningful SNPs for blepharitis and stromal keratitis. Notably, phenotypically meaningful nonsynonymous variations were detected in the UL24, UL29 (ICP8), UL41 (VHS), UL53 (gK), UL54 (ICP27), UL56, ICP4, US1 (ICP22), US3 and gG genes. Network analysis revealed that many of these variations were in HSV-1 regulatory networks and viral genes that affect innate immunity. Several genes previously implicated in virulence were identified, validating this approach, while other genes were novel. Several novel polymorphisms were also identified in these genes. This approach provides a framework that will be useful for identifying virulence genes in other pathogenic viruses, as well as epistatic effects that affect HSV-1 ocular virulence.

In addition to causing recurrent labial lesions, herpes simplex virus type 1 (HSV-1) is also the primary source of infectious blindness in the United States. Animal studies have shown that the severity of infection is influenced by several factors, including viral strain. Conventional studies investigating the genetics of viral virulence have focused on characterizing a naturally occurring strain, and engineering mutations into viruses. The purpose of this study was to develop a quantitative trait locus (QTL) computational analysis of HSV-1 genome to identify ocular virulence determinants and associated viral SNPs. Notably, phenotypically meaningful variations were detected in the UL24, UL29 (ICP8), UL41 (VHS), UL53 (gK), UL54 (ICP27), UL56, ICP4, US1 (ICP22), US3 and gG genes. Several genes previously implicated in virulence were identified, validating this approach, while other genes were novel. This is the first time a QTL based approach has been applied to a herpesvirus and it will also be valuable in future virulence, epistasis, and protein-protein interaction studies.

[Battle with herpes for 37 years]

Herpes simplex virus type 1(HSV-1) remains latent in the human trigeminal ganglion after primarily infecting the cornea and conjunctiva. Mental stress, heat stimulation, ultraviolet ray and immunosuppression are among the reactivating factors of HSV-1, which can lead to epithelial herpetic keratitis, stromal herpetic keratitis, and other complications. I have been working with HSV-1 for a long time, concentrating especially on its latency and reactivation. I would like to introduce some of the recent research results. 1. Herpetic keratitis cases at the Department of Ophthalmology, Kinki University. There were 129 eyes of 128 patients who visited the Cornea Service in our university hospitals at Osayasayama, Sakai and Nara over 13 years and were diagnosed with herpetic keratitis and followed up for at least one year. They were investigated as to the type of herpetic keratitis at the initial visit and its recurrence. Initial types of herpetic keratitis and number of eyes of each type were: Epithelial type, 65 eyes (50%); Stromal type, 30 eyes (23%); Combined epithelial and stromal types, 18 eyes (14%). Recurrence was seen in 47% of the total 129 eyes. Recurrent cases of the epithelial type were mostly epithelial type. Frequently recurrent cases of the stromal type presented with repeated epithelial, stromal, and combined types. 2. Effects of antiherpetics on mouse epithelial herpetic keratitis. Acyclovir (ACV) eye ointment is usually prescribed for several weeks to treat human epithelial herpetic keratitis. Our question is: Is this long administration really necessary? To find the answer to this question, we investigated time-dependent effects of antiherpetics on mouse epithelial herpetic keratitis. Mouse corneas were infected with HSV-1 and either ACV eye ointment, oral valaciclovir (VACV) or oral famciclovir (FCV) was administered. No virus was detected in the tear fluid examined by viral culture 4 days after start of ACV eye ointment or oral VACV and 6 days after start of oral FCV. Real-time PCR revealed significant decrease of HSV DNA copy number in the eyeball or trigeminal ganglion compared to saline instillation 4 and 6 days after start. These results suggest that antivirals for 5 days could sufficiently decrease the HSV amount in the ocular surface and eyeball. 3. Corneal latency. In order to prove latency of HSV in the human cornea, virological and molecular biological techniques were used to ensure the following 3 prerequisites. 1) Positive HSV DNA in the human cornea. 2) Negative homogenate, positive explant. 3) Only latency-associated transcript (LAT) detected and transcriptional products of other virus genes (α, β, γ) not detected in the cornea. As a result, all the 3 prerequisites have been satisfied in the 3 corneas that had a past history of herpetic keratitis. This result suggests that HSV could remain latent in the human cornea. 4. Detection of HSV-1, HHV-6, and HHV-7 DNA in the anterior segment and aqueous humor using multiplex real-time PCR. Multiplex real-time PCR was applied for the first time ever in opththalmology to human herpes virus 6 (HHV-6) and 7(HHV-7). Samples taken from tear fluid before and 3 days after phacoemulsification and aspiration (PEA) or penetrating keratoplasty (PKP), and aqueous humor aspirated during PEA were used. The results of multiplex real-time PCR showed HSV-1, HHV-6 and HHV-7 DNA present in tear fluid both before and after PEA or PKP. 5. Gene expression when reactivation is suppressed. Nuclear factor-κB (NF-κB) has recently been reported to be involved in reactivation of HSV-1. IkappaB kinase-β (IKK2) inhibitors, which inhibit the activity of NF-κB, were used to examine gene expression during HSV reactivation in a mouse model. Significant decrease of HSV DNA copy number was observed at the trigeminal ganglion with real-time PCR in a group which was given IKK2 inhibitors intraperitoneally. Microarray method demonstrated 2-fold or more increased expression of 1812 probe. By Pathway analysis, eased immunosuppressive effects were observed in the group which was given IKK2 inhibitor intraperitoneally. 6. Immunoresponse involved in herpetic keratitis. Chemokine expression profiles in human corneal herpetic cases and mouse herpetic keratitis were analyzed. The results were similar to previously published reports: Cxcl9, Cxcl10, Ccl5, which are Th1 type chemokines, and Ccl20, a Th17 type chemokine, were observed to increase. On the other hand, Th2 type chemokine did not show an increase. Immunoresponse occurred mainly in the trigeminal ganglion. With these results, we suggest herpetic keratitis could be prevented by actively inducing Th17 type immunoresponse.

Microbiota-driven immune cellular maturation is essential for antibody-mediated adaptive immunity to Staphylococcus aureus infection in the eye

As an immune-privileged site, the eye, and particularly the outer corneal surface, lacks resident mature immune effector cells. Physical barriers and innate mediators are the best-described effectors of immunity in the cornea. When the barriers are breached, infection can result in rapid tissue destruction, leading to loss of visual acuity and frank blindness. To determine the cellular and molecular components needed for effective adaptive immunity on the corneal surface, we investigated which immune system effectors were required for protection against Staphylococcus aureus corneal infections in mice, which are a serious cause of human eye infections. Both systemically injected and topically applied antibodies to the conserved cell surface polysaccharide poly-N-acetylglucosamine (PNAG) were effective at mediating reductions in corneal pathology and bacterial levels. Additional host factors impacting protection included intercellular adhesion molecule 1 (ICAM-1)-dependent polymorphonuclear leukocyte (PMN) recruitment, functional CD4(+) T cells, signaling via the interleukin-17 (IL-17) receptor, and IL-22 production. In germfree mice, there was no protective efficacy of antibody to PNAG due to the lack of LY6G(+) inflammatory cell coeffector recruitment to the cornea. Protection was manifest after 3 weeks of exposure to conventional mice and acquisition of a resident microbiota. We conclude that in the anterior eye, ICAM-1-mediated PMN recruitment to the infected cornea along with endogenous microbiota-matured CD4(+) T cells producing both IL-17 and IL-22 is required for antibody to PNAG to protect against S. aureus infection.

Effect of highly active antiretroviral therapy (HAART) on the natural history of ocular manifestations in HIV-infected children

PURPOSE

To determine the effect of highly active antiretroviral therapy (HAART) on the natural history of ocular manifestations in HIV-infected children.

METHODS

All of the HIV-infected children attending the Institute of Pediatrics, University of Milan, Milan, Italy, between 1982 and 2004 were studied. Every 3 months, they were physically examined and underwent indirect fundoscopy conducted by an experienced ophthalmologist; if diagnosed as having eye disease, they were evaluated by the ophthalmologist every week while on specific therapy and monthly thereafter. The clinical and laboratory findings before and after the introduction of HAART were compared.

RESULTS

The cohort consisted of 117 HIV-infected children (61 males), with a follow-up ranging from 0.09 to 22.31 years (median, 16.33 years). A total of nine cases of ocular involvement (7.7%) were diagnosed between 1983 and 1994, before the introduction of HAART. All nine children died 4-24 months (median, 15 months) after the diagnosis of ophthalmic disease. No case of ocular involvement was observed after the introduction of HAART (P=0.011 vs. before HAART).

CONCLUSION

The introduction of HAART has had a significant impact on the natural history of ocular manifestations in HIV-infected children, thus suggesting that a reduction in the frequency of ophthalmologic follow-up should be considered for HAART-treated HIV-infected children with immune reconstitution and no visual symptom.

The frequency of Chlamydia trachomatis major outer membrane protein-specific CD8+ T lymphocytes in active trachoma is associated with current ocular infection

Chlamydia-specific cytotoxic T lymphocytes are able to control model infections but may be implicated in disease pathogenesis. HLA-A2 peptide tetramers to Chlamydia trachomatis major outer membrane protein 258-266 (MOMP258-266) and MOMP260-268 were used to characterize HLA class I-restricted CD8+ T cells in Gambian children aged 4 to 15 years with clinical signs of active trachoma and/or infection with C. trachomatis. The frequencies of circulating HLA-A2 tetramer binding cells (TBC) were determined in whole blood samples by flow cytometric analysis. Initial screening of subjects with an anti-HLA-A2 antibody confirmed the presence of either HLA-A2 or HLA-A28. These were subsequently further divided by molecular subtyping. The C. trachomatis-specific HLA-A2 peptide tetramers were able to bind T cells with receptors from subjects which were restricted by either the HLA-A2 or the HLA-A28 restriction element. In this population, the median value of C. trachomatis-specific CD8+ T cells was 0.02%, with frequencies of up to 3.71% of CD8+ T cells reactive with a single tetramer in a minority of subjects. TBC were detected more often in subjects who were infected at the ocular surface, and their presence was associated with infection episodes of longer duration. Detection of C. trachomatis-specific TBC was not associated with the presence of disease or with the estimated load of ocular C. trachomatis infection at the time of sample collection. High frequencies of C. trachomatis-specific cells did not predict subsequent appearance or resolution of the clinical disease signs of active trachoma.

Circulating anti-galectin-1 antibodies are associated with the severity of ocular disease in autoimmune and infectious uveitis

PURPOSE

Galectin (Gal)-1, an endogenous lectin found at sites of immune privilege, plays a critical role in the regulation of the immune response. Therapeutic administration of Gal-1 or its genetic delivery suppresses chronic inflammation in experimental models of autoimmunity. The purpose of this work was to investigate the occurrence of circulating anti-Gal-1 antibodies in patients with autoimmune and infectious uveitis as potential determinant factors of disease progression.

METHODS

IgG, IgE, and IgA anti-Gal-1 antibodies were assessed by ELISA and Western blot in sera from patients with autoimmune (n = 47) and infectious (n = 15) uveitis compared with healthy control subjects (n = 30). The frequency of anti-Gal-1 antibodies was examined in patients experiencing poor clinical outcome (n = 21) or good evolution (n = 9). Anti-Gal-1 antibodies were eluted by incubating patient sera with nitrocellulose filters adsorbed with rGal-1. The ability of these antibodies to recognize retinal tissue was assessed by ELISA, Western blot, and immunohistochemistry.

RESULTS

IgE, IgG, and IgA anti-Gal-1 antibodies were increased in sera from patients with autoimmune uveitis (P < 0.001 vs. controls) and toxoplasmic retinochoroiditis (P < 0.001). The level of anti-Gal-1 IgE and IgG antibodies was associated with progressive disease and poor outcome in autoimmune and infectious uveitis. Furthermore, these antibodies strongly immunoreacted with retinal lysates and recognized retinal structures mainly photoreceptors in retinal sections.

CONCLUSIONS

Anti-retinal Gal-1 antibodies are present in sera from patients with uveitis and can be associated with the progression of ocular disease, suggesting their potential use in follow-up observations of these patients.

Toll-like receptors in ocular immunity and the immunopathogenesis of inflammatory eye disease

Microbial agents have an important role in the pathogenesis of various inflammatory eye diseases, such as uveitis and keratitis. Microbial infections of the eye such as microbial keratitis, ocular onchocerciasis, bacterial endophthalmitis, viral retinitis, and other infectious uveitis are unfortunately common. In addition, microbial agents have been implicated in the pathogenesis of "non-infectious" immune mediated diseases such as HLA-B27 associated acute anterior uveitis. Toll-like receptors (TLR) are a family of pattern recognition receptors that initiates rapid host innate immune response to microbial components known as pathogen associated molecular patterns, which are unique to a given class of microbes, such as lipopolysaccharide of Gram negative bacteria. Recent in vitro and in vivo studies have demonstrated the expression and function of TLRs in the eye, with significant implications for better understanding of ocular immunity and the pathogenesis of inflammatory eye diseases affecting the cornea, uvea, and retina.

Toll-like receptors and the eye

PURPOSE OF REVIEW

This review will describe the structure, expression/distribution and functional activity of Toll-like receptors, in particular in the ocular structures. It will also discuss innate and adaptive immune responses, by exploring the possible modulation/regulation of innate and adaptive immunity by Toll-like receptors, in view of recent findings observed in the ocular surface.

RECENT FINDINGS

Current knowledge indicates that Toll-like receptors represent essential elements in host defence against pathogens, a prerequisite to the induction of adaptive immune responses. The expression/distribution of Toll-like receptors in the healthy eye highlights the possible function of Toll-like receptors in both innate and adaptive responses during pathological conditions of the ocular surface.

SUMMARY

Recent findings have greatly increased the knowledge of the possible role of Toll-like receptors in innate and adaptive immune responses. Toll-like receptors seem to play different roles in a wide range of activities of the immune system, and might represent an exclusive link between innate and adaptive responses under pathological conditions. Recent studies in ophthalmology have highlighted the role of Toll-like receptors in infections (keratitis) as well as in allergic states of the ocular surface. This review thus describes the relationship between Toll-like receptors and the main immune/structural cells taking part in inflammatory disorders. Understanding the complex mechanisms underlying Toll-like receptor localization and function will provide additional data that might help devise novel therapeutic approaches involving Toll-like receptors and their agonists, in an attempt to modulate the biased immune system.

Consequences of CXCL10 and IL-6 induction by the murine IFN-alpha1 transgene in ocular herpes simplex virus type 1 infection

Herpes simplex virus type 1 infection of the mouse eye results in an impressive inflammatory response culminating in the death of the animal or the establishment of a "latent" infection depending on a number of ill-defined variables that include components of the innate and adaptive immune system. The application of type I interferon transgenes has been found to antagonize viral replication and spread from the eye to the nervous system. Associated with the in situ transfection of the cornea is the upregulation of two inflammatory molecules, interleukin-6 and CXCL10. In this article, we will further examine the contribution these molecules may have in the host response to ocular infection with herpes simplex virus type 1.

No apparent association between periocular and ocular microcolonization and the degree of inflammation in patients with atopic keratoconjunctivitis

BACKGROUND

The cause of the chronic inflammation in atopic keratoconjunctivitis (AKC), the ocular manifestation of atopic eczema/dermatitis syndrome, is largely unknown.

OBJECTIVE

To investigate the possibility that microorganisms may be important in the inflammatory activity in AKC.

METHODS

Fifteen patients with AKC participated in the study. The presence of aerobic bacteria and fungi was related to the severity of clinical signs, the numbers of inflammatory cells in tears and conjunctival biopsies, and the concentration of various cytokines in tears. In addition, serological evidence for IgE sensitization to Staphylococcus aureus B antigen and Malassezia sympodialis antigen was investigated. Twelve healthy subjects were included for control purposes.

RESULTS

The patients exhibited moderate clinical signs of AKC. No relation was found between the severity of AKC and the presence of microorganisms, despite the fact that S. aureus was frequently isolated. AKC patients showed significantly higher levels of IFN-gamma, TNF-alpha (tumour necrosis factor-alpha), IL-2, IL-4, IL-5 and IL-10 than controls. An association was found between conjunctival signs and the levels of all cytokines except IL-5.

CONCLUSION

We found no evidence to suggest that periocular and ocular microcolonization are related to inflammatory parameters in AKC. However, confirmation of the present results in a longitudinal study with repeated clinical examinations and samplings in the same individual is required before the contribution of S. aureus to on-going inflammation in AKC can be dismissed.

[A study of total IgE in inflammatory pathologies of the eye anterior segment]

The paper contains data on comparative research of the IgE content in blood serum and lachrymal fluid in patients with ophthalmoherpes and with other inflammatory diseases of the eye. A higher IgE level was found in blood serum and lachrymal fluid in cases of ophthalmoherpes as well as in lachrymal fluid in cases of allergic, Chlamydia and fungus diseases of the eye. The data obtained can be used in the diagnostics of allergic eye diseases as well as in elaborating complex treatment methods for herpetic, Chlamydia and fungus lesions of the anterior eye segment. A detection of the local allergenic effect of acaricide drugs exerted on the conjunctiva and eyelids makes it obligatory to consider the above fact while treating patients with demodectic blepharoconjunctivitis.

Immune defense at the ocular surface

The ocular surface is constantly exposed to a wide array of microorganisms. The ability of the outer ocular system to recognize pathogens as foreign and eliminate them is critical to retain corneal transparency, hence preservation of sight. Therefore, a combination of mechanical, anatomical, and immunological defense mechanisms has evolved to protect the outer eye. These host defense mechanisms are classified as either a native, nonspecific defense or a specifically acquired immunological defense requiring previous exposure to an antigen and the development of specific immunity. Sight-threatening immunopathology with autologous cell damage also can take place after these reactions. This article discusses the innate and acquired corneal elements of the immune defense at the ocular surface. The relative roles of the various factors contributing to prevention of eye infection remain to be fully defined.

[Ocular infections of the elderly]

A CLINICAL ASPECT DEPENDING ON THE PHYSIOPATHOGENESIS: Ocular infections are a frequent motive for ophthalmological consultations in geriatric settings because of the mechanical factors related to age (modifications in palpebral dynamics and lacrymal function) and in local and general immune factors leading to the rapid and/or more severe development of infections. The mechanism of microbial contamination of the eye also determines the clinical damage: predominantly local (dirty hands, traumas) with involvement of the surface tissues (conjunctive and cornea) or general, hematogenic or neurogenic, frequently at the origin of more internal infections (iris, choroid, retina, optical nerve). CONJUNCTIVITIS AND KERATITIS: These provoke reddening of the eyes, tears and above all pain when the corneal epithelium is involved. Microbiological samples are useful in cases of severe, presumably infectious keratitis or conjunctivitis. Two emergency situations must be distinguished: any suspicion of herpes for which local corticosteroids are contraindicated and keratitis or conjunctivitis with the use of lenses, often due to Gram negative bacilli, amoeba or fungus, the treatment of which is intensive and the prognosis often severe. OPHTHALMOLOGICAL HERPES ZOSTER: The rapid diagnosis and introduction of efficient doses of antivirals reduces the initial pain, the ocular complications of herpes zoster and post-zoster pain. The latter, when it exists, requires specialized management. ACUTE UVEITIS: A context of intra-ocular inflammation in an elderly patient must always evoke a pseudo-uveitis syndrome, the principle cause of which is lymphoma. Conversely, an uveitis occurring in the days or weeks following ocular surgery, including cataract, must be considered as suggestive of a post-surgical infection and rapidly referred to a specialist. ACUTE DACRYOCYSTITIS: Is manifested by a hard and painful tumefaction below the internal angle of the eye. Following collection, it requires draining through an in incision in the skin, washing and packing of the sac, and systemic antibiotherapy. The preventive treatment of recurrences requires open dacryocystorhinostomy or via endonasal endoscopy.

Ocular immune privilege and the impact of intraocular inflammation

Immune privilege, a characteristic of the internal compartments of the eye, is a physiologic mechanism that is designed to provide the eye with protection against pathogens while protecting the delicate visual axis from the sight-destroying potential of immunogenic inflammation. It is assumed that the presence of intraocular inflammation is incompatible with the existence of immune privilege. The validity of this assumption has been tested in four animal models of intraocular inflammation-systemic and local endotoxin-induced uveitis (EIU), mycobacterial adjuvant-induced uveitis (MAIU), and experimental autoimmune uveitis (EAU). Immune privilege was assessed in inflamed eyes by growth of intracamerally injected allogeneic tumor cells, by the capacity to support immune deviation following intracameral injection of antigen (ovalbumin, OVA), by assaying protein, leukocyte, and selected cytokine content of aqueous humor (AqH), and by capacity of inflamed AqH to suppress T cell activation in vitro. The results indicate that, irrespective of the type of inflammation, tumor cells formed progressively growing tumors in inflamed eyes. Moreover, OVA injected into the anterior chamber of eyes inflamed by MAIU and EAU failed to induce immune deviation. AqH from inflamed eyes reflected breakdown of the blood:ocular barrier as well as transient loss of its immunosuppressive properties. Immunosuppressive microenvironments routinely reemerged in inflamed eyes, and the immunosuppressive agent present under these circumstances in AqH was active TGF beta2. It is concluded that immune privilege is surprisingly resistant to abolition by intraocular inflammation, and that maintenance of immune privilege in the face of ongoing inflammation depends upon the emergence of progressive and partially different immunosuppressive mechanisms.

Twenty-five-year panorama of corneal immunology: emerging concepts in the immunopathogenesis of microbial keratitis, peripheral ulcerative keratitis, and corneal transplant rejection

PURPOSE

To describe the most recent advances in our understanding of the cellular and molecular mechanisms involved in the immunopathogenesis of corneal immunoinflammatory disorders including microbial keratitis, peripheral ulcerative keratitis. and allograft rejection.

METHODS

Review of the published peer-reviewed literature that has contributed significantly to our modern understanding of corneal immunology. In addition, the authors have summarized the information in conceptual diagrams that highlight the critical cellular and molecular pathways that lead to corneal immune responses in the two most thoroughly studied corneal immune disorders, herpes simplex keratitis (HSK) and transplant rejection.

RESULTS

In spite of the wide array of molecular and cellular factors that mediate corneal immunity, critical mechanistic facets are shared by the various corneal immunoinflammatory disorders. These include activation and migration of local antigen-presenting cells (APCs), including Langerhans cells (LCs), upregulation in pleiotropic proinflammatory cytokines such as interleukin-1 (IL-1) and tumor necrosis factor-alfa (TNF-alpha) that can mediate a wide array of immune functions in addition to up-regulating protease expression. and chemokines that play a critical role on the one hand in attracting nonantigen-specific inflammatory cells such as neutrophils and on the other in attracting CD4+ T helper type 1 (Th1) cells that mediate most of the destruction in the cornea.

CONCLUSIONS

In the last 25 years, we have seen our field develop from a descriptive stage into a new phase where the fundamental processes that mediate and effect corneal immunity are being accurately deciphered. It is anticipated that this new knowledge will allow development of specific molecular and genetic therapeutic strategies that could target critical steps in the immunopathogenesis of disease without the untoward side-effects of nonspecific generalized immune suppression that still remains the standard of care today.

The importance of specific IgG and IgE autoantibodies to retinal S antigen, total serum IgE, and sCD23 levels in autoimmune and infectious uveitis

Autoimmunity plays an important role in the development of uveitis. The uveitis are linked to Th1 or Th2 lymphocyte activation. We studied 41 patients with uveitis, divided into autoimmune uveitis (n = 32) and infectious uveitis (n = 9), 30 normal controls, and 20 asthmatic atopic without ocular diseases. The infectious uveitis patients were separated into bacterial (n = 6) and toxoplasmic (n = 3) retinochoroiditis. We measured IgE and sCD23 serum levels and specific IgG and IgE to retinal S antigen by ELISA tests. The IgE levels were 500 +/- 325 kU/L in autoimmune uveitis, 57 +/- 35 kU/L in bacterial uveitis, 280 +/- 38 kU/L in toxoplasmic retinochoroiditis, 75 +/- 32 kU/L in the controls, and 557 +/- 243 kU/L in atopics (P < 0.0005). The sCD23 levels were 10.4 +/- 5.4 ng/ml in autoimmune uveitis, 3.7 +/- 1.17 ng/ml in bacterial uveitis, 6.76 +/- 1.36 ng/ml in toxoplasmic retinochoroiditis, 3.4 +/- 1 ng/ml in controls, and 8.35 +/- 2.2 ng/ml in atopic patients (P < 0.005). The specific IgG to retinal S antigen was positive in 27 of 32 cases, and the specific IgE to retinal S antigen was positive in 22 of 32 autoimmune uveitis. The bacterial uveitis patients as well as the controls were negative for both autoantibodies to retinal S antigen. The toxoplasmic retinochoroiditis patients presented specific IgG and IgE to retinal S antigen in two of three cases, respectively, one of them with overlap of both antibodies. These results suggest the importance of specific IgG and IgE to retinal S antigen in autoimmune uveitis, which, along with higher IgE and sCD23 levels, reveal Th2 activation.

Pseudomonas aeruginosa orbital phlegmon in a patient treated for myelodysplastic syndrome with concomitant Sjögren's syndrome

Pseudomonas aeruginosa orbital infections have been described very rarely in patients with neutropenia after chemotherapy. We report the case of a woman with the unusual association of Sjögren's disease and myelodysplasia, who suffered from a Pseudomonas aeruginosa orbital phlegmon after chemotherapy for her myelodysplastic syndrome. Partial intestinal antibiotic decontamination with ciprofloxacine did not prevent the infection. She was treated successfully with intravenous ceftazidime, netilmicin and granulocyte-colony stimulating factor (G-CSF). The normalization of the granulocyte count seems to play a crucial role for recovery. We present the clinical and radiological findings, discuss the therapy and review the literature concerning ocular infections due to Pseudomonas. Other infections due to this germ in immunocompromised hosts are briefly reviewed.

[Physiological protective mechanisms of the eye]

The physiological mechanisms for the protection of the eye are only partly known. It becomes increasingly evident that the eye is supervised by and included in the immune system of the body. The physiological protection system of the eye consists of a mechanical and an immunological component. The lacrimal gland plays a key role for the immune system of the anterior segment. It is part of the MALT system, and the characterisation of the special ocular components of this system-including possible homing receptors-will give important informations. Research of the ocular immune system has disclosed various special features, like the anterior chamber associated immune deviation (ACAID). The distribution of antigen presenting cells and its localization, but also the distribution of T- and B-lymphocytes is an important factor for limiting ocular inflammation. The phenomenon of 'apoptosis' seems to have an important role in maintenance of the ACAID. The cornea is nearly free of cells, and infiltrating antigen presenting cells may prevent ACAID. Research regarding mechanisms which are used to tuned these various cells will give answers to the questions how the cornea contains its optical transparency, how corneal transplant rejection works, how the eye participates in systemic disorders and may also define the role of a possible dysfunction of antigen presenting cells of the retinal pigment epithelium in senile maculopathy.

Protective effects of interferon-gamma in intraocular herpes simplex type 1 infection do not depend on major histocompatibility complex class I or class II expression

Intraocular infection with herpes simplex virus type I strain F (HSV-1) induces bilateral retinitis, the expression of both MHC class I and II molecules and activation of CD4 and CD8 cells. To investigate the role of MHC upregulation in IFN-gamma mediated antiviral effects in intraocular infection with HSV-1, we infected MHC deficient mice and mice with an additional ectopic site of IFN-gamma production in their retina (rho gamma) intravitreally with HSV-1 into one eye. Protective effects of IFN-gamma in intraocular HSV-1 infection were notable as sparing of the contralateral non-inoculated eye from retinitis, and were not dependent on MHC class I and class II expression, thus limiting the importance of MHC expression for the outcome of viral infection in vivo.

[Physiopathologic mechanisms behind eye symptoms in primary tumors of the pineal body]

Primary tumors of the pineal body can produce dyscoordinative movements of the eye, pupillary dilatation, paralysis of adduction during convergence and nystagmus. Obstruction of the aqueduct can cause hydrocephalus, increased intracranial pressure and papilledema. Diabetes insipidus may be a presenting symptom. Pinealocytes and the photoreceptors of the eye contain several autoantigens. In man, the best known is the S-antigen. This antigen can be detected in the cerebrospinal fluid of patients with primary tumors of the pineal body. The S-antigen, and possibly other related autoantigens, can elicit an autoimmune mediated reaction causing inflammatory eye symptoms. This recently described paraneoplastic neurologic syndrome shares properties in common with other known cancer-associated ophthalmologic syndromes characterised by rapid development of eye symptoms, rapid loss of sight and by eye manifestations prior to evident appearance of symptoms related to primary tumor growth. A primary tumor of the pineal body should be considered in patients where a monosymptomatic uveoretinitis presents without associated provoking factors. Furthermore, analyses of S-antigen in the spinal fluid can be useful in the clinical diagnosis of the same primary tumors.

[Ocular infections in immunodepressed patients]

Two kinds of immunosuppression must be distinguished: malignant diseases on one hand, and acquired immunodeficiency syndrome on the other hand. Ocular infections can involve any part of the eye and they can lead to blindness. They usually attest of a systemic infection. Their treatment consist of an induction course to provide complete healing of the lesions, immediately followed by a maintenance course to prevent relapses. Retinitis are the most common posterior involvement, especially the retinitis due to cytomegalovirus and Toxoplasma gondii. Zoster ophtalmicus is the most common anterior involvement. Mucormycosis is rare but very severe. A closed collaboration between ophtalmologists and internists is mandatory to provide the most appropriate management of these infections.