Optimising Innate Host Defence to Combat Antimicrobial Resistance

The treatment of bacterial infection is complicated by antibiotic resistance. The body's defence against bacteria relies on the immune system and requires blood cells, called macrophages and neutrophils that eat and kill bacteria. Despite being frequently exposed to bacteria that cause serious infections most people rarely become ill due to these bacteria. We can learn from how the immune system protects most people and develop medicines to re-engage this system if it fails. This approach is currently limited by incomplete understanding of the precise mechanisms that kill bacteria in immune cells but our consortium has made great strides to address this. We now wish to refine our understanding of mechanisms that we have already identified and supplement this with further experiments to identify the best approaches with which to modulate these responses in patients. In the body macrophages are the first line of defence against bacteria. We will use techniques that manipulate all the macrophage's genes individually and identify which are most important in regulating bacterial killing. We have also identified that when macrophages commit cell-suicide it helps clear bacteria and we will look for genes that regulate this process. When macrophages are overwhelmed by bacteria neutrophils are important to remove bacteria. For neutrophils we cannot manipulate the cell's genes but we will use an approach that uses antibodies to target all the proteins in the cell and will perform a similar screen to identify factors influencing bacterial killing. We also have some candidates we have already identified which regulate this process. We will then study how important the mechanisms we find are in models of infection where immune cells interact with other cell types. In particular we want to ensure we not only enhance bacterial killing but also minimize the capacity of neutrophil-derived immune factors to cause bystander damage to the body's tissues. Next we will screen panels of chemical structures to enhance the selected mechanisms of bacteria killing. We will work with industry partners to adapt these structures for medical use. In particular we will test how well these target the specific location in the cell where the killing factors are produced using new approaches, termed super-resolution microscopy (SRM), that allow us to measure their production and location in the cell with great precision. We will modify the chemical structures to ensure our medicines target the right mechanism and location in the macrophage or neutrophil. These compounds will then be tested in our models of bacterial infection, including models of bacteria resistant to multiple antibiotics. We will also test how the bacteria respond to attempts by the immune system to kill them. This will also inform understanding of how bacteria escape immune responses and spread between species to establish reservoirs of infection in animals that contribute to human disease with antibiotic resistant bacteria. To confirm our findings are relevant to patients and to test potential medicines that we develop we will study macrophages and neutrophils from healthy volunteers or patients at risk of bacterial infection. Our approach will be significantly enhanced by our ability to image the interaction of bacteria with macrophages and neutrophils, and specifically the factors that regulate or mediate bacterial killing, in the lung of patients. This involves new developments with unique chemical probes and fibre optical imaging. We can potentially translate our findings rapidly to patients because many of the agents we will use to manipulate the innate response are drugs licensed for other medical indications. Our approach will reduce reliance on antibiotics and provide an alternative approach based on modifying the body's immune response that will be active against a range of bacteria, irrespective of their sensitivity to antibiotics.