Regulation of ocular immune responses

Challenges to Gene Editing Approaches in the Retina

Retinal gene therapy has recently been at the cutting edge of clinical development in the diverse field of genetic therapies. The retina is an attractive target for genetic therapies such as gene editing due to the distinctive anatomical and immunological features of the eye, known as immune privilege, so that inherited retinal diseases (IRDs) have been studied in several clinical studies. Thus, rapid strides are being made toward developing targeted treatments for IRDs. Gene editing in the retina faces a group of heterogenous challenges, including editing efficiencies, off-target effects, the anatomy of the target organ, immune responses, inactivation, and identifying optimal application methods. As clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas) based technologies are at the forefront of current gene editing advances, their specific editing efficiency challenges and potential off-target effects were assessed. The immune privilege of the eye reduces the likelihood of systemic immune responses following retinal gene therapy, but possible immune responses must not be discounted. Immune responses to gene editing in the retina may be humoral or cell mediated, with immunologically active cells, including microglia, implicated in facilitating possible immune responses to gene editing. Immunogenicity of gene therapeutics may also lead to the inactivation of edited cells, reducing potential therapeutic benefits. This review outlines the broad spectrum of potential challenges currently facing retinal gene editing, with the goal of facilitating further advances in the safety and efficacy of gene editing therapies.

Differential and Altered Spatial Distribution of Complement Expression in Age-Related Macular Degeneration

Purpose

Dysregulation of the alternative complement pathway is a major pathogenic mechanism in age-related macular degeneration. We investigated whether locally synthesized complement components contribute to AMD by profiling complement expression in postmortem eyes with and without AMD.

Methods

AMD severity grade 1 to 4 was determined by analysis of postmortem acquired fundus images and hematoxylin and eosin stained histological sections. TaqMan (donor eyes n = 39) and RNAscope/in situ hybridization (n = 10) were performed to detect complement mRNA. Meso scale discovery assay and Western blot (n = 31) were used to measure complement protein levels.

Results

The levels of complement mRNA and protein expression were approximately 15- to 100-fold (P < 0.0001–0.001) higher in macular retinal pigment epithelium (RPE)/choroid tissue than in neural retina, regardless of AMD grade status. Complement mRNA and protein levels were modestly elevated in vitreous and the macular neural retina in eyes with geographic atrophy (GA), but not in eyes with early or intermediate AMD, compared to normal eyes. Alternative and classical pathway complement mRNAs (C3, CFB, CFH, CFI, C1QA) identified by RNAscope were conspicuous in areas of atrophy; in those areas C3 mRNA was observed in a subset of IBA1⁺ microglia or macrophages.

Conclusions

We verified that RPE/choroid contains most ocular complement; thus RPE/choroid rather than the neural retina or vitreous is likely to be the key site for complement inhibition to treat GA or earlier stage of the disease. Outer retinal local production of complement mRNAs along with evidence of increased complement activation is a feature of GA.

Maintaining T cell tolerance of alloantigens: Lessons from animal studies

Achieving host immune tolerance of allogeneic transplants represents the ultimate challenge in clinical transplantation. It has become clear that different cells and mechanisms participate in acquisition versus maintenance of allograft tolerance. Indeed, manipulations which prevent tolerance induction often fail to abrogate tolerance once it has been established. Hence, elucidation of the immunological mechanisms underlying maintenance of T cell tolerance to alloantigens is essential for the development of novel interventions that preserve a robust and long lasting state of allograft tolerance that relies on T cell deletion in addition to intra-graft suppression of inflammatory immune responses. In this review, we discuss some essential elements of the mechanisms involved in the maintenance of naturally occurring or experimentally induced allograft tolerance, including the newly described role of antigen cross-dressing mediated by extracellular vesicles.

Macrophages and Uveitis in Experimental Animal Models

Resident and infiltrated macrophages play relevant roles in uveitis as effectors of innate immunity and inductors of acquired immunity. They are major effectors of tissue damage in uveitis and are also considered to be potent antigen-presenting cells. In the last few years, experimental animal models of uveitis have enabled us to enhance our understanding of the leading role of macrophages in eye inflammation processes, including macrophage polarization in experimental autoimmune uveoretinitis and the major role of Toll-like receptor 4 in endotoxin-induced uveitis. This improved knowledge should guide advantageous iterative research to establish mechanisms and possible therapeutic targets for human uveitis resolution.

Differential gene expression in anatomical compartments of the human eye

DNA microarrays (representing approximately 30,000 human genes) were used to analyze gene expression in six different human eye compartments, revealing candidate genes for diseases affecting the cornea, lens and retina.

Background

The human eye is composed of multiple compartments, diverse in form, function, and embryologic origin, that work in concert to provide us with our sense of sight. We set out to systematically characterize the global gene expression patterns that specify the distinctive characteristics of the various eye compartments.

Results

We used DNA microarrays representing approximately 30,000 human genes to analyze gene expression in the cornea, lens, iris, ciliary body, retina, and optic nerve. The distinctive patterns of expression in each compartment could be interpreted in relation to the physiology and cellular composition of each tissue. Notably, the sets of genes selectively expressed in the retina and in the lens were particularly large and diverse. Genes with roles in immune defense, particularly complement components, were expressed at especially high levels in the anterior segment tissues. We also found consistent differences between the gene expression patterns of the macula and peripheral retina, paralleling the differences in cell layer densities between these regions. Based on the hypothesis that genes responsible for diseases that affect a particular eye compartment are likely to be selectively expressed in that compartment, we compared our gene expression signatures with genetic mapping studies to identify candidate genes for diseases affecting the cornea, lens, and retina.

Conclusion

Through genome-scale gene expression profiling, we were able to discover distinct gene expression 'signatures' for each eye compartment and identified candidate disease genes that can serve as a reference database for investigating the physiology and pathophysiology of the eye.

The relative contributions of each subset of ocular infiltrated cells in experimental choroidal neovascularisation

AIM

Choroidal neovascularisation (CNV) is a major cause of blindness in adults. The aim of this study was to investigate the role of infiltrating cells in the development of experimental CNV.

METHODS

CNV was induced in C57BL/6 (B6) mice by laser photocoagulation (PC). After PC, the numbers of each subset of infiltrated cells were analysed by flow cytometry at multiple time points. Each subset (except for macrophages) was depleted by the specific antibodies in vivo. Thereafter, the area of CNV was compared between the control B6 mice and the specific antibody treated mice 7 days after PC. The CNV formation in neutrophil depleted CC chemokine receptor-2 (CCR2) knockout mice was also examined to minimise the effects of macrophages.

RESULTS

In the early phase of CNV formation, a large number of neutrophils and macrophages infiltrated to the eyes. Natural killer (NK) cells and T lymphocytes were barely detected while no B lymphocytes were detected. The CNV areas did not significantly change compared between the control B6 mice and the specific antibody treated mice. However, the neutrophil depleted CCR2KO mice resulted in a reduction of CNV.

CONCLUSION

Although lymphocytes and NK cells had little effect on CNV formation, neutrophils partially contributed to CNV in the absence of macrophages.

The pattern of interleukin-12 and T-helper types 1 and 2 cytokine expression in herniated lumbar disc tissue

STUDY DESIGN

A study was conducted to investigate the expression of cytokines related to the immune reaction in herniated lumbar disc tissues.

OBJECTIVE

To investigate the immunologic status of lumbar disc tissue and the type of immune reaction that occurs in response to lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

It has been proposed that herniated lumbar disc tissue causes an immune reaction. Various inflammatory cells, proinflammatory cytokines, antibodies, and immunoglobulins have been identified in and around herniated lumbar disc tissue. Recently, it has been reported that lumbar disc tissue may be another potential immune-privileged site in the human body.

METHODS

This study included 40 herniated lumbar disc tissues: 20 contained and 20 noncontained discs. The concentrations of interleukin-12, T-helper Type 1, interferon-gamma (IFN-gamma), and Th2 (IL-4) cytokines were determined by enzyme-linked immunosorbent assay, respectively. The results were compared between the two groups.

RESULTS

The concentrations of interleukin-12 and interferon-gamma were higher in the noncontained discs than in the contained discs: 28.3 +/- 10.7 pg/mL vs 9.2 +/- 4.2 pg/mL (P = 0.001) and 4.7 +/- 5.0 pg/mL vs 2.3 +/- 3.8 pg/mL (P = 0.029), respectively. On the contrary, the concentration of IL-4 was higher in the contained discs than in the noncontained discs: 24.3 +/- 20.1 pg/mL vs 1.9 +/- 4.5 pg/mL; P= 0.001. The degrees of interleukin-12 and interferon-gamma expression were negatively correlated with that of IL-4 (n = 40): correlation coefficient, -0.671 (P = 0.001) and correlation coefficient, -0.344 (P = 0.03), respectively.

CONCLUSIONS

The findings suggest that preferential expression of Th2 cytokines by disc cells, as shown in contained discs, is another factor contributing to the immune privileged status of lumbar disc tissue. The exposure of lumbar disc tissue to the epidural space may increase the concentration of interleukin-12 in herniated lumbar disc tissue, changing the pattern of T-helper Types 1 and 2 cytokine expression.

Bacterial endophthalmitis: epidemiology, therapeutics, and bacterium-host interactions

Endophthalmitis is a severe inflammation of the interior of the eye caused by the introduction of contaminating microorganisms following trauma, surgery, or hematogenous spread from a distant infection site. Despite appropriate therapeutic intervention, bacterial endophthalmitis frequently results in visual loss, if not loss of the eye itself. Although the pathogenicity of bacterial endophthalmitis has historically been linked with toxin production during infection, a paucity of information exists as to the exact mechanisms of retinal toxicity and the triggers for induction of the intraocular immune response. Recently, research has begun to examine the bacterial and host molecular and cellular events that contribute to ocular damage during endophthalmitis. This review focuses on the causative agents and therapeutic challenges of bacterial endophthalmitis and provides current data from the analysis of the role of bacterial virulence factors and host inflammatory interactions in the pathogenesis of eye infections. Based on these and related studies, a hypothetical model for the molecular pathogenesis of bacterial endophthalmitis is proposed. Identifying and understanding the basic mechanisms of these bacterium-host interactions will provide the foundation for which novel, information-based therapeutic agents are developed in order to prevent vision loss during endophthalmitis.

Persistence of acanthamoeba antigen following acanthamoeba keratitis

AIM

To investigate the hypothesis that persistent corneal and scleral inflammation following acanthamoeba keratitis is not always caused by active amoebic infection but can be due to persisting acanthamoebic antigens

METHODS

24 lamellar corneal biopsy and penetrating keratoplasty specimens were obtained from 14 consecutive patients at various stages of their disease and divided for microscopy and culture. Histological sections were immunostained and screened for the presence of Acanthamoeba cysts by light microscopy. Cultures were carried out using partly homogenised tissues on non-nutrient agar seeded with E coli. Clinical data were obtained retrospectively from the case notes of these patients.

RESULTS

Of the 24 specimens, 20 were obtained from eyes that were clinically inflamed at the time of surgery. Acanthamoeba cysts were present in 16 (80%) of these 20 specimens, while only five (25%) were culture positive. Acanthamoeba cysts were found to persist for up to 31 months after antiamoebic treatment.

CONCLUSION

These findings support the hypothesis that Acanthamoeba cysts can remain in corneal tissue for an extended period of time following acanthamoeba keratitis and may cause persistent corneal and scleral inflammation in the absence of active amoebic infection. In view of these findings, prolonged intensive antiamoebic therapy may be inappropriate when the inflammation is due to retained antigen rather than to viable organisms

Ocular immune privilege: a review

The definition of the term 'immune privilege' has evolved over the last century. Current usage refers to a state within a particular organ or tissue in which elements of normal immunity are absent. The fact that this deficiency is thought to be generally beneficial has compelled others to go a step further and venture that immune privilege acts to minimize expression of immunopathology. The purpose of this article is to review which parts of the eye hold immune privileged status, what mechanisms contribute to it, and what clinical benefits may have driven the development of these unique immune environments. The article ends with an examination of recent studies which have sought to use components of ocular immune privilege to prevent systemic autoimmune disease.