The Lions Eye Institute has a long history of cutting edge research. Our immunology research centre is unique in the world and combines a highly acclaimed general immunology program with a unique ocular immunology program.
The central focus of the general immunology research in Professor Mariapia Degli-Esposti’s group at LEI is to determine the key cellular and molecular interactions that occur in response to viral infection. In recent years this research has provided important contributions to understanding how the immune system responds to infection and how, in turn, pathogens manipulate host immunity to improve their chances of survival. Mouse cytomegalovirus (MCMV) is used as a model virus infection, due to its similarity in structure and biology with the human cytomegalovirus (HCMV).
During the last 5 years Professor Degli-Esposti has established a new program in ocular immunology with the purpose of understanding immune responses in the eye and design new therapies for sight threatening diseases which have an immune component. Professor Degli-Esposti has developed an international collaboration with Professor John Forrester, whom is now an adjunct Professor at the University of Western Australia, to work on the cause of uveitis using a novel mouse model – the only one in the world that closely mimics human disease.
- General Immunology
Improving adaptive anti-viral responses: a key to eliminating persistent viral infection
HCMV establishes a persistent infection, and although in a healthy subject infection is generally asymptomatic, infection of immunocompromised hosts leads to severe disease. Using the MCMV-infection model, recent studies have shown that MCMV-susceptible and MCMV-resistant mouse strains have functional differences in the efficacy of the antiviral CD4+ and CD8+ T cell responses and in the ability to control persistent virus. These studies provided evidence to indicate that antiviral T cell responses are negatively affected by natural killer (NK) cells. Our data indicate that the NK cell-mediated elimination of virus-infected dendritic cells (DC) may be the key event in this process. Ongoing studies will address how T cells control persistent infection and how their anti-viral activity can be restored therapeutically. This research will help us understand viral pathogenesis and importantly will provide valuable information for the improved treatment of chronic viral infections and the generation of more efficacious vaccines.
Mechanisms of viral induced immunosuppression: effects on monocyte-DC-NK networks
CMV infection has been associated with impaired host immunity in man and mouse. HCMV induced immunosuppression results in adverse clinical outcomes due to secondary infections with unrelated pathogens. Understanding the mechanism involved in the induction of immunosuppression is the first step towards developing better therapies. This research aims to define the effects of MCMV infection on cells belonging to the innate immune system, and how this affects the transient, but profound, viral induced immunosuppression. In particular, this research aims to address how MCMV infection may interfere with the functions and interactions of the key innate effectors (DC, NK cells and monocytes/macrophages) on many levels, including the activity of these cells, the maintenance of mature and precursor populations at various physiological sites, and the development of such populations. How such virally-affected DC interact with other arms of innate immunity, such as NK cells, may be critical in viral induced immunosuppression.
To replicate efficiently viruses have evolved means to inhibit or interfere with apoptosis, which is the orderly removal of unwanted or infected cells by the host. The study of viral anti-apoptotic proteins has not only enhanced our understanding of the processes regulating viral replication, and thus their role in causing human diseases, but has also provided insights into the processes that normally regulate apoptotic pathways. CMV utilises several distinct mechanisms to inhibit the premature death of virally infected cells. For example, CMV can interfere with death receptor signalling, utilising the extrinsic apoptotic pathway, a process for which at least two viral genes have been identified. CMVs also have the capacity to interfere with the intrinsic apoptotic pathway by preventing mitochondrial permeabilization. Given the central role played by Bax and Bak in promoting cellular destruction, it is not surprising that many viruses have evolved strategies to inhibit their activation. We, and others, have determined that the product of the MCMV m38.5 open reading frame (ORF) inhibits Bax, but not Bak. Particularly, we found that m38.5 prevents apoptosis in infected leukocytes, thereby ensuring efficient dissemination of the virus to the salivary glands. In addition to encoding an inhibitor of Bax, we have identified the m41.1 protein as being a potent inhibitor of Bak. Ongoing research is focused on determining how these inhibitors contribute to viral fitness. Understanding how these proteins inhibit Bax and Bak has the potential to aid in the development of drugs that will be effective in treating diseases such as cancer.
The focus of the viral immunology group’s research is on providing insights into novel mechanisms of viral immune evasion. Research has shown that natural killer (NK) cells are key immune effectors in the control of cytomegalovirus infection. Viral replication is regulated by host genes that encode NK cell receptors. In the mouse, Ly49H recognizes the cytomegalovirus encoded m157 protein that is expressed on infected cells and triggers their elimination. However, the virus can escape NK cell immunosurveillance by the emergence of mutants that engage inhibitory NK cell receptors. Analysis of the nature and outcome of these interactions with viral proteins through inhibitory and activating NK cell receptors enhances our understanding of anti-viral immune responses. More broadly, investigating the regulation of NK cell function will aid in the development of drugs targeting this process with the ultimate outcome of improving anti-viral immune responses.
Graft versus host disease (GVHD)
Cytomegalovirus represents the most predictable and problematical infection after bone marrow transfer, with approximately 70% of patients experiencing viral reactivation. Historically, CMV was a major cause of post-transplant mortality, with approximately 25% of CMV-seropositive recipients developing CMV-related disease within 3 months post-transplantation.
Although most transplant centres have adopted strict monitoring, preemptive antiviral therapies and prophylactic strategies to prevent CMV disease, these approaches still have a number of short-comings. Therapy requires prolonged administration of toxic anti-viral drugs and life-threatening CMV disease still develops in 10% of patients.
We recently developed a mouse model to study the effects of allogeneic bone marrow transplantation and GVHD on the immunological control of CMV, as well as determining whether CMV infection alters the magnitude and progress of GVHD. Primary infection of bone marrow recipients mimics the reactivation of CMV. Our results show that CMV infection exacerbates clinical disease. At the same time there is a significant reduction in the control of viral replication associated with the generation of a suboptimal anti-viral CD8+ T cell response and a profound defect in antigen-presenting cells. Our aim is to ultimately design effective therapies to prevent complications from infection in transplant patients.
- Ocular Immunology
Inflammatory ocular disease (uveitis) is an autoimmune disease that affects the eye, damaging the retina and causing blindness. Uveitis mainly occurs in the 20-50 year age group, and can affect one or both eyes. Uveitis is an important problem and accounts for 10% of blindness in people of working age in the western world. Little is known about the cause of uveitis and it remains one of the most important unsolved problems in ophthalmology. We are investigating the development of autoimmune uveitis using a novel transgenic mouse model. This model allows us to closely track activation of the auto-reactive CD4+ T cells prior to the onset of disease as well as after they induce damage to the retina. Our recent experiments have revealed that autoreactive CD4+ T cells are readily activated before disease, however once disease develops, they become unresponsive. Our aim is to learn more about the mechanism that mediates this peripheral tolerance, whether it is a transient state or not, and how it is induced by the onset of tissue destruction in the eye.
Viral infection and the eye
Following on from our studies characterising the effects of subretinal infection with MCMV, we have found that systemic infection also influences immune cells within the eye despite the absence of direct infection. We are now investigating this phenomenon and have identified a crucial role for IFN-gamma in this process. This research will provide us with new insights on the level of immune surveillance that takes place within the eye.