A mathematical and biophysical analysis of salmonella macrophage interactions

Salmonella enterica causes a wide range of diseases in many animals. Economic losses to the farming industry through Salmonella infection are potentially very high, but also important is the fact that a number of serovars that infect animals can also cause food poisoning and gastroenteritis in humans. Salmonella infect specialised immune cells (macrophages) where the bacteria reside within an intracellular compartment called the salmonella-containing vacuole. Within the macrophage the bacteria may be killed, may hide, may grow and can cause the cell to die. The interaction between macrophages and salmonellae is critically important to the progression of disease. Controlling the numbers of bacteria within the macrophage is an important step in enabling the host to stop the bacteria growing and to survive infection. Many mechanisms involved in the interaction between Salmonella and macrophages are unclear. In particular little is known about how the macrophage physically interacts with the cell. The macrophage detects the presence of bacteria through specialised proteins called Pattern Recognition Receptors (PRRs) which induce macrophage responses to help the host control a salmonella infection. In this project I will use mathematical models to predict how PRR activity effects the process by which Salmonella infect macrophages and then test these theoretical assumptions using biological experiments. I will use physical techniques to investigate whether PRRs influence how Salmonella associate with macrophages. In the final part of the project I will compare how PRR activity affects the global response of macrophages to infection. This project will increase our understanding of how Salmonella infect macrophages and may deliver new targets for developing drugs to treat the diseases caused by these pathogens.

A crucial aspect of the pathogenesis of invasive Salmonella infections is the ability of the pathogen to invade and survive within phagocytes. Pattern Recognition Receptors (PRRs) on macrophages allow the host to detect pathogens. Many different PRRs detect Salmonella serovars yet the physiological role for most of these proteins in the host response to infection is unclear. Different Salmonella serovars produce bacterial proteins that modulate PRR signaling. The macrophage response to infection involves PRR signaling in concert with the activity of salmonellae factors, but the precise balance of how this occurs is unknown. The question I am therefore asking in this research proposal is what is the contribution of PRRs and bacterial factors to the macrophage control of salmonellosis? This project will use biological, physical and mathematical techniques to study the fundamental mechanisms by which Salmonella enterica serovar Typhimurium (STm) infects macrophages and to determine whether PRRs influence these processes. Iterations of experimental analysis and mathematical models will be used to determine how PRRs affect the process of macrophage infection by STm. Biophysical analysis will be used to determine whether PRRs affect the physical interaction between STm and the macrophage. The final part of this project will be to compare the signaling networks activated by bacterial ligands (such as STm lipopolysaccharide and flagellin) with live STm in macrophages to identify the importance of bacterial factors involved in the cellular infection process.

The major beneficiaries of this research will be academics in the biological, physical and mathematical sciences. The work will be of particular interest to immunologists and microbiologists. The research will be published in international open access journals to ensure wide access to the data generated by this work. In the long term novel technologies may arise from the physical analysis of Salmonella-macrophage interactions and this will be of benefit to scientists wishing to apply our technologies to other research questions. Should novel technologies arise then they will be developed by Cambridge Enterprise, the University of Cambridge office responsible for commercializing our scientific work. The generation of a macrophage signaling network in response to Salmonella infection may identify novel targets for drug development to prevent salmonellosis which will be on interest to the pharmaceutical industry. Any intellectual property arising from this work will again be developed by Cambridge Enterprise. Our work will generate a number of movies which may be useful teaching material particularly to children explaining how bacteria interact with cells. This material will be used in presentations of the research at the Cambridge Science fair and through the BBSRC media office. I will attend the BBSRC media course in order to develop my communication skills and I plan to run a website where the movies will be available to download.