How do Migratory Dendritic Cell Populations Control Immune Responses in the Intestine?

The intestine has a surface area nearly one hundred times greater than the skin, and is exposed to many potentially dangerous micro-organisms. It requires effective immune responses to protect the intestine from infections, and the correct type of immune response must be made to control the different types of pathogen that may be encountered. On the other hand, immune responses must not be made against the large numbers of harmless bacteria and abundant food proteins that are also present in the intestine. When an inappropriate response occurs it can have serious consequences, leading to inflammatory bowel diseases or food allergy.
A critical cell for controlling immune responses is the dendritic cell (DC). Many DCs are found in the intestine, where they actively gather information about their local environment, including about whether any micro-organisms have managed to cross the thin barrier of cells that separates food and "friendly bacteria" from the tissues of the body. Following a period of residence in the intestine of approximately 20 days, DCs migrate, in lymph, carrying information about the intestine to the immune cells in the local (mesenteric) lymph nodes (MLN). On reaching the MLN, DCs interact with T cells, key immune effector cells. This interaction not only controls whether an immune response will occur, but also determines which type of response will be generated. Understanding how DCs control these processes is important for the design of oral vaccines or prevention of inflammatory bowel diseases. However, the study of migrating DCs has been difficult because they cannot easily be separated or identified among the other cells in the MLNs and intestine. The best way to collect cells that are certain to be migrating DCs is by surgery, which is used to directly collect the DC-containing lymph. Previously this surgery has mostly been performed in large animals. We developed humane surgical techniques to collect migrating DCs from mice, and can therefore now use a wide variety of immunological techniques to analyse the DCs' functions. In our previous work, we have used these techniques to identify four different types of migrating intestinal DC, each of which generates different immune responses after interacting with T cells. Before we carried out these studies, it was thought that two of these DC types were unable to migrate from the intestine.
With this application, we aim to continue our investigations into these different types of migrating DCs, and discover how their properties may be manipulated to control immune responses in the intestine- either to improve the efficiency of oral vaccines, or to help prevent or control intestinal inflammatory disease. Specifically, we will investigate how DCs control three different types of T cell immune responses in the intestine, using mouse models of these immune responses. We will examine the changes in the DCs that occur in each of the models, and also whether particular DC types are necessary or sufficient for inducing each of these responses. Finally, we will use these data to develop approaches for therapeutic modulation of intestinal immune responses.
In summary: we have developed a unique array of techniques for the analysis of the functions of migrating intestinal DCs, and have used these to discover exciting new populations of cells with specific immunological functions. We will built on this strong foundation to discover how these DCs control the development of T cell responses in the intestine, and use these data to develop strategies for manipulating the intestinal immune response.

The intestinal immune system must maintain a delicate balance, retaining the ability to make appropriate responses to invading pathogens while also preventing unwanted and damaging responses against harmless commensal organisms and food antigens. Dendritic cells (DCs) acquire antigen in the intestinal lamina propria and continually migrate, via lymph, from the intestine to the mesenteric lymph nodes (MLNs), where they prime T cells and direct their differentiation. They are required for the initiation of intestinal immune responses, and are thought to control the polarisation of the responding T cells.
Understanding the control of these responses is central for the development of oral vaccines, and for therapies to prevent or control inflammatory bowel diseases. Study of the immunology of migrating DCs has been hampered by the fact that they consist of a number of functionally different subsets that are difficult to definitively identify in intestinal tissues or in the MLN. Because DCs are exquisitely sensitive to their local environment, there are also significant challenges in purifying the DC subsets from intestinal tissues without altering their functions. For these reasons, the properties of migrating DCs are best studied after purification from the lymph of rats and larger animals. However, investigations in these species are hampered by a lack of immunological reagents, inbred strains, and transgenic animals.
To investigate how migrating DCs interact with T cells and control intestinal T cell responses, we have previously developed techniques for purifying migrating intestinal DCs from murine thoracic duct lymph in the mouse, and for intra-lymphatic injection of cells. We will use these techniques to examine the functions of specific subsets of migrating DCs in initiating and polarising responses from cytotoxic T cells, Th1/17, and Th2 cells, to enable development of methods for targeting specific DC subsets and thus controlling intestinal T cell responses.

The central aim of this project is to generate results of importance to a wide range of clinicians and academics working on an important, but poorly understood topics in modern medicine. Our goal is to identify new cellular mechanisms that hold the key to the control of intestinal immune responses, which are the key to preventing and treating intestinal infections throughout the developed and developing world. The economic and psychological impact of these infections is enormous, preventing affected individuals leading a normal life and placing a heavy burden on health services and families alike. Understanding the basis of intestinal immunity would enable a major improvement in quality of life for all these individuals.
Our expertise in the purification and analysis of dendritic cell populations is of benefit to the private sector, where collection of carefully-defined cell populations is critical for the generation of high quality transcriptomic and deep sequencing data. SM has recently entered into a contract (~$450,000 USD over 3 years) with a partner company in the USA to provide specific samples of cells from patients and animals undergoing active immune responses, and appropriate controls, to identify potential novel therapeutic targets and biomarkers of disease.
In the medium term, these discoveries should also inform clinical practice, as we anticipate that they will help identify factors contributing to the development of inflammation in Ankylosing Spondylitis, though our parallel clinical research projects. Our previous work on the basic biology of migrating DCs, which identified subsets of migrating intestinal DCs in rodents, led directly to the identification of a defect in specific DC population in transgenic animals expressing the human HLA-B27 transgene. These animals provide a model for the development of inflammation in Spondylarthropathy; we have now used the data to design studies of DCs in patients with Ankylosing Spondylitis, and have recently identified analogous defects in the patients. We anticipate that the experiments in this application will also generate results that may be exploited by clinicians, both in the UK and Internationally.