Understanding lipid antigen presentation in intestinal homeostasis and inflammation

Humans carry around 10 times more microorganisms in the intestine as total cells constituting our body. These microorganisms (predominantly bacteria) perform many important metabolic functions for example helping in the digestion of the food to allow the absorption of nutrients. However, to prevent uncontrolled overgrowth and dissemination of intestinal bacteria the human body had developed a great variety of strategies that allow bacterial containment within the intestine. As such, the human gastrointestinal tract houses the big bulk of the immune system, and many different cell types cooperate to maintain a healthy relationship with our gut flora. Importantly, alteration of this equilibrium can lead to the development of intestinal disorders like is the case of Inflammatory Bowel Disease (IBD) that affects 1 in 250 people in the UK. IBD comprises a mixture of life-long disorders that may be ameliorated with immunosuppressive drugs but not cured, with around 40% of patients being considered for surgery normally involving removal of the affected bowel. Added to this, IBD patients show up to 18% increased risk of colorectal cancer over 30 years post disease onset. Therefore understanding the factors that modulate the cross-talk between the intestinal flora and the immune cells is critical to identify new therapeutic targets for the treatment of intestinal diseases. This proposal centers on the understanding of the role of a population of immune cells, so called NKT cells, within the intestine, both in healthy conditions and during the development of IBD. NKT cells are known to be present in the gastrointestinal tract and they have been proposed to function in the containment of intestinal bacteria. In addition to this, NKT cells accumulate in the intestine of IBD patients where they may play a role in the initiation of the disease. However the mechanisms that regulate the activation of these cells and their role in the development of IBD remain unclear. We aim to deliver fundamental new insights into the mechanisms regulating NKT cell function within the intestine with the ultimate goal of manipulating this knowledge in our advantage to design new treatments for intestinal disorders.

The mammalian intestine contains a complex mixture of microorganisms that perform many metabolic functions and are critical for the establishment of tissue homeostasis. Consequently, the immune system has developed strategies to maintain the mutualistic relation with the microbiota while preventing bacterial spread. However, while the mucosal immune system is central for host protection, its aberrant activation and/or failure of regulation can lead to inflammatory and autoimmune diseases, as is the case of inflammatory bowel disease (IBD).
It is increasingly appreciated that the initiation and quality of tissue-associated immune responses are regulated by tissue-resident T cells of which NKT cells are clear examples. NKT cells are activated by lipid antigens presented by the surface molecule CD1. Upon activation, NKT cells secrete large amounts of cytokines and induce downstream activation of different cell types. Numerous studies support the role of NKT cells/CD1 in the maintenance of mucosal homeostasis and in the induction of IBD, although the mechanisms underlying these processes remain unclear. This proposal aims to understand the mechanisms regulating NKT cell function and CD1-lipid presentation in the intestine. We aim to build a comprehensive picture of NKT cell distribution and phenotype within gastro-intestinal compartments in homeostatic conditions. With this established, we will focus on the response of these cells to challenge and in the interactions with antigen presenting cells that will determine their activation during IBD induction. Additionally, we will explore the role of NKT cells in the generation of IgA, which is one of the main tools for the maintenance of intestinal homeostasis. These studies will provide a better understanding of the factors that modulate intestinal immunity, with the potential to improve therapies for patients suffering from intestinal inflammatory diseases and possibly a broader range of disorders.

The impact from this research can be integrated in two main areas:

(1) Academic impact:

a) Contribution towards science, generation of knowledge and worldwide academic advance: In recent years mucosal immunology has become an emerging area of investigation but still many questions remain regarding the regulation of homeostasis and immune protection. By deciphering the role of mucosal NKT cells and CD1-lipid presentation we aim to provide valuable insights into the mechanism that modulate immune responses within the intestine. This knowledge will be useful for scientists working in mucosal Immunology, but as well for those working in a broad range of disciplines where an emerging role for NKT cells is reported (i.e. autoimmunity, infectious diseases, tumour immunology).
A unique approach from the present study will be the direct visualization of mucosal immune cells within living tissues. During the last decade in vivo imaging of lymphoid tissues has contributed major new insights about the events underlying the generation of immune responses, but the use of this technique within the mucosa has been very limited. Our studies will provide the first set of data regarding NKT cell dynamics within the intestine, which may have important implications for our understanding of the role of these cells in mucosal immunity and will be of interest for the general Immunology community. Furthermore, the use of multi-photon microscopy for our project may involve the testing and optimization of a variety of components including different dyes (for cell labelling) or microscope filter sets. This knowledge can be used for scientists in a variety of disciplines and extended to their specific imaging systems.

b) Training of highly skilled researchers: the proposed project will provide both the postdoctoral fellow (requested in the current proposal) and the PhD student (funded by KCL) with scientific training in a variety of skills. Particularly significant will be the training in in vivo imaging techniques which use is still restricted to a limited number of labs worldwide. Moreover, working in cellular immunology can lead the fellows further research career to a variety of interesting follow-up projects, ranging from in vitro studies related with the mechanisms of immune cell activation to the study of different models of disease.

(2) Socio-economic impact:

Public health and welfare: One of the main focus of the current proposal will be understanding the mechanisms the lead to the development of Inflammatory Bowel Disease (IBD) with the ultimate aim of developing new therapies for the treatment of this disease. IBD comprise a mixture of intestinal inflammatory conditions affecting ~240000 people in the UK. These are long life conditions without a medical cure and therefore represent a big burden for the health care system. The role of NKT cells in ulcerative colitis (UC) is well established in both mouse and humans. NKT cells have been shown to be main producers IL-13 (that is highly secreted during UC) and a recombinant antibody directed against IL-13 (tralokinumab) is currently being tested in clinical trials. Therefore, understanding the factors that lead to NKT cell activation and subsequently to the development of IBD could help to identify new therapeutic targets for the treatment of intestinal diseases.
Additionally, this project aims to understand the factors that modulate the production of IgA and the selection of IgA repertoire. Regulation of antibody secretion and repertoire selection are very tightly controlled, since their deregulation may lead to the development of autoimmune diseases and cancer. Consequently, understanding the factors that control the selection of antibody repertoire may be important for the treatment of autoimmunity and for the design of vaccination strategies.