Lacy-Hulbert & Stuart Laboratories
Top Row: Lynda Stuart, Adam Lacy-Hulbert, Kerri Thomas, David Kugler
Bottom Row: Mridu Acharya, Kyle Sha, Fiona Raso, Caroline Stefani, Kim Decker
The immune system provides us with many layers of defense against infection by bacteria, viruses and other microbes. These range from highly specialized ‘adaptive’ immune responses, which include antibodies and killer T cells that recognize specific microbial components through ‘innate’ immune mechanisms that are designed to react to macromolecules shared by many microbes, to barrier mechanisms, which physically prevent infection in the skin, lung, gut and other mucosal surfaces. The Lacy-Hulbert and Stuart Laboratories work closely together to understand how these different aspects of the immune system cooperate to identify and combat potentially infectious organisms while preventing immune attack against innocuous microbes or the body’s own self. The research is currently focused in three main areas:
Distinguishing Pathogens From Self
The cells of the innate immune system, particularly specialized phagocytes such as dendritic cells (DCs) and macrophages, represent a ‘first line’ of surveillance and defense against infection. Major advances over the past 20 years have led to the identification of an armory of receptors that recognize common microbial components and stimulate cytokine release, which in turn promote adaptive immune responses. However, many of these microbial components are shared by innocuous or commensal microbes that are present in large numbers in the intestine and other sites in the body. Furthermore, it is now clear that these same receptors can be triggered by self-derived macromolecules, such as nucleic acids, lipids and polysaccharides. We believe that inappropriate activation of the innate immune system by self-associated components may be a major driving force behind many autoimmune or chronic inflammatory diseases. Research in the labs is directed at understanding how innate immune cells recognize and distinguish self from pathogens, and respond accordingly.
A major focus of the laboratory’s work in this area is the recognition of cells that die by apoptosis or other mechanisms. Apoptosis is a ‘silent’ form of cell death, used for removal of cells that are damaged or no longer needed. Cells that initiate apoptosis are rapidly removed by phagocytes or neighboring cells. The lab team has shown that when dendritic cells phagocytose apoptotic cells, they adopt a ‘regulatory’ phenotype that promotes immune tolerance. The researchers believe that this mechanism allows the immune system to constantly survey self antigens and maintain immune tolerance. Current research is focused on understanding how recognition of apoptotic cells modifies innate immune signaling to promote immune tolerance, and how defects in this process may lead to autoimmune diseases such as systemic lupus erythematosus (SLE).
Work in the Stuart lab is also identifying additional mechanisms for recognition of pathogens. Pathogenic bacteria are distinguished from closely related non-infectious strains by the expression of ‘virulence factors’. These are proteins that target host cell functions to aid infection and colonization. In plants, it has been proposed that the cells can sense the action of these virulence factors and initiate immune responses to combat infection. Several years ago the lab showed, for the first time, that metazoans (fruit flies and mammals) use analogous mechanisms to sense pathogens and trigger innate immune signaling pathways. Ongoing research is aimed at identifying more of these mechanisms, and understanding how they promote immune defense.
Finding out how innate immune cells recognize potential targets and respond appropriately is essential to the understanding of both defense against infection and autoimmunity.
Regulation of Immune Responses to Self and Self-Associated Antigens
Macrophages and dendritic cells (DCs) also play essential regulatory roles in preventing auto-reactive immune responses. One such mechanism is through the generation of regulatory T cells (Tregs). Differentiation of T cells into Tregs requires the cytokine TGF-b, which is normally synthesized in an inactive or latent form. The lab has shown that DCs and macrophages are required to activate TGF-b before it can signal to T cells, and this requires the expression of a specific cell surface receptor, alpha-v beta 8 integrin (avb8) on DCs. Deletion of avb8 from DCs in mice causes a failure of generation of Tregs in the periphery, which leads to intestinal inflammation, resembling inflammatory bowel disease (IBD). This same mechanism is also required for generation of a second population of T cells, Th17 cells, which are also dependent on TGF-b signaling, and av-deficient mice are protected from Th17-mediated autoimmune diseases, such as mouse models of multiple sclerosis. Currently the lab is working to understand how DCs come to express avb8, how this triggers TGF-b activation, and whether targeting this process may provide a therapeutic strategy for inflammatory bowel disease, multiple sclerosis or other autoimmune diseases.
Forward Genetics to Identify New Mechanisms in Immunity and Host Defense
The understanding of innate immunity and host defense is incomplete, and there are many mechanisms and components to be discovered. To help in this process, the lab has developed forward genetic techniques using transposon mutagenesis and high throughput gene sequencing, which can be used to probe immune mechanisms in mammalian cells. An important feature of this system is the ability to perform large scale gain- and loss-of-function screens simultaneously across the genome in multiple cell types. The initial system was validated in a screen for resistance to cytotoxic cancer drugs, but the current focus is in host defense and immunity. Currently, the lab is using this approach to identify mechanisms of resistance to viral infections, with a major focus on Ebola virus. From this screen we are identifying genes that confer resistance to virus entry or replication, with the ultimate aim of identifying or developing drugs that could be used to prevent viral infection.
Work in the laboratories has been funded by the National Institutes of Health, The Crohn’s and Colitis Foundation of America, The Wellcome Trust and The Seattle Foundation.
Adam Lacy-Hulbert, PhD
Lynda Stuart, MD, PhD
Mridu Acharya, Research Assistant Member
Ky Sha, Postdoctoral Fellow
Anna Bruchez, Postdoctoral Fellow
Caroline Stefani, Postdoctoral Fellow
David Kugler, Postdoctoral Fellow
Kimberly Decker, Postdoctoral Fellow
Fiona Raso, Technician
Lea Gaucherand, Technician