How Does the Interplay of PI3-kinases at the Phagosomal Membrane Co-ordinate Pathogen Killing? (360G-Wellcome-211411_Z_18_Z)

Animals (including humans) are protected from bacterial infection by patrolling innate immune cells. Neutrophils (the most abundant phagocytes) engulf their prey into membrane-bound phagosomes, enabling targeted, segregated and highly concentrated microbicidal activity. Phosphoinositide 3-hydroxykinase (PI3K) signalling regulates many aspects of neutrophil function and PI3K-derived phospholipid mediators accumulate at the phagosomal membrane to facilitate killing. However, the identity of the PI3K isoform(s) involved, the mode of delivery to the phagosome, and the extent to which pathogens subvert this process have not been determined. Our novel preliminary data show that the lipid messenger PIP3 (a product of PI3K activity) waxes and wanes at the phagosomal membrane, reflecting ‘quantal’ delivery from an unidentified cellular organelle, with subsequent changes in phagosomal pH. I will undertake a detailed exploration of this critical process using the genetically tractable zebrafish, which allows high resolution in vivo imaging of neutrophils in relevant infection models. I will determine the dynamics of PI3K signalling in response to a range of pathogens,quantifying PI3K-derived phospholipids at the phagosomal membrane. My results will inform our knowledge of PI3K signalling in neutrophil bactericidal activity, and may suggest how these processes might be manipulated to enhance pathogen killing.