Analysing antibacterial immunity from two sides: host versus pathogen

Bacterial infections represent a major problem to human health; often causing life-threatening diseases and persistent infections that can require extensive treatment with antibiotics. Salmonella causes a range of disease in humans, from gastro-enteritis to typhoid fever and is also prevalent in animals such as cattle, which can have serious economic consequences as well as public health implications.

Normally, upon infection, host cells respond to bacterial products, activating a cascade of events that culminate in the production of molecules that trigger a robust immune defence programme to inactivate the bacteria. Many bacteria, including Salmonella, manipulate these host responses by the action of so-called virulence factors, producing a complex interaction between the host immune response and the incoming pathogen. This project on the one hand aims to understand how bacterial virulence factors produced and transported into host cells alter the outcome of infection to the advantage of the pathogen. We have identified several virulence factors that modulate host cell responses and we will now characterise their mechanism of action in detail. Deciphering how these virulence factors influence immune signalling cascades during infection provides valuable insight into what makes the bacteria pathogenic, provides important information on host processes that are targeted by the pathogen and is likely to provide valuable information for vaccine design and novel therapeutics.

To complement this, research efforts are required to understand in molecular detail novel host mechanisms that restrict bacterial pathogens. Therefore, this project will also investigate the role of a family of host molecules (a group of proteins) that are called TRIMs. Research efforts have focused on TRIM function during viral infection but few have been studied in detail and the family remains poorly characterised during bacterial infection. Despite this, several lines of evidence suggest they have important functions upon host infection with bacteria. Therefore, I shall study how this group of proteins responds to bacterial infection and determine whether they can restrict the growth of bacteria within cells. These findings will reveal new functions for these proteins, many of which when mutated cause disease. Ultimately, with the improved understanding of host immune responses we are better informed on the best methods to combat bacterial infection. This is an important consideration given the rapidly developing rise in antibiotic resistant bacterial species.

Innate immunity provides a first line of defence against pathogens and is essential for inducing the adaptive arm of immunity and ultimately, pathogen clearance. Numerous pathogens, including the intracellular bacterium Salmonella enterica, serovars of which cause gastroenteritis and typhoid fever, interfere with innate immune responses, contributing to pathogenicity. My overall goal is to investigate the complex host-pathogen interactions that mediate the outcome of infection. Using a multidisciplinary approach encompassing proteomics, cell biology and structural biology, I will elucidate the molecular mechanisms by which virulence "effector" proteins, delivered across host membranes via type-3-secretion systems, contribute to innate immune modulation and ultimately the pathology of infection.

To complement this, I will study the host family of TRIM E3 ligases, the majority of which transfer ubiquitin to substrates. TRIMs function in a variety of core host cell processes including; cell differentiation, inflammation and innate immune signalling and mutations in a number of TRIMs are associated with diverse diseases. However, their role in antibacterial immunity is poorly characterised. I will investigate their regulation, sub-cellular localisation and function during bacterial infection.

Together, this study on fundamental bioscience will provide valuable insight into the pathophysiology of bacterial infections and provide key information on innate immune signalling pathways as well as having potential clinical and/or therapeutic applications in the future. All of this is important with respect to the rising risk of antibiotic resistant pathogens, including Salmonella.

This research will have far-reaching impact beyond the Salmonella and TRIM academic fields.

1. General public- This proposal falls under the remit of the BBSRC's vision into improving the health and wellbeing of humans. Salmonella is one of the most common zoonotic diseases, spreading between animals and humans. It causes significant socioeconomic and health implications throughout the world, especially in Sub-Saharan Africa where non-typhoidal strains of Salmonella cause high rates of death in patients who are mal nourished, HIV positive or infected with malaria. Fundamental biomedical research that increases the understanding of Salmonella virulence mechanisms and host innate immune signalling pathways that attenuate bacterial infection will, in the long term, have impact on the general public, both with respect to health and economics. In addition I will add to this by partaking in specific programmes for public engagement such as the "Superbug Zone" which disseminates the CMBI research on bacterial pathogens and "Soapbox Science" which promotes women scientists and the research they conduct.

2. Junior Researchers- I will ensure that the staff and students I supervise will develop a wide range of technical expertise from protein affinity purification to mouse work, flow cytometry and confocal microscopy. In addition, lab members will develop critical skills for planning and executing experiments that are ethical and rigorous in design. Moreover, I will help them develop transferable skills that include written and oral communication both to expert and general audiences, organisation and literature investigation.

3. Young scientists- During the award I aim to engage the next generation on the importance of antimicrobial resistance and bacterial infections on human health. I will do this is by generating excitement about science through speaking to schoolchildren about my research, providing advice on studying science at school and university and hosting sixth form students for short laboratory experiences, which I've done before.

4. Biotechnology and pharmaceutical companies- One aim of my project is to understand at a molecular level the role of Salmonella virulence proteins in modulating host immune responses. In the longer term, this could attract R&D investment and inform research by companies that are interested in developing novel drugs for inhibiting bacteria, using bacteria to deliver therapeutics or in vaccine development. In addition, my research into TRIM E3 ligases may be of therapeutic interest. Abnormalities in numerous TRIMs are associated with human diseases, for example cancer, inflammatory diseases, neuronal function and infectious diseases. My research aims to catalogue the function of TRIMs in antibacterial immunity and uncover new functions, which will inform the biology of TRIM-associated diseases. In the longer term, this could impact clinicians, potentially producing diagnostic tools and will help identify which TRIMs are candidates for novel therapeutic manipulation for treating diseases that impact on the health and wellbeing of humans. In this respect, TRIM-edicine investigates TRIM72 among other proteins for therapeutic approaches to target cellular pathways altered in disease, highlighting that such ideas are not too far-reaching. Whilst it is not possible to predict with certainty whether intellectual property will emerge from the planned work, any potential commercialisation and exploitation of scientific knowledge will be protected properly by patents through Imperial College and its technology transfer company Innovations.

5. Academic beneficiaries- These are detailed in another section but in brief I will disseminate my research to broad audiences by attending both national and international conferences and workshops, partaking in various research networks (e.g. London Inflammation Network) and by forming new collaborations with scientists in diverse fields.