Engineering and Physical Sciences Research Council Featured PhD Programmes
Peter MacCallum Cancer Centre Featured PhD Programmes

About the Project

Andrew Parnell (Physics) and Jason King (Biomedical Science)

To effectively prevent infections, phagocytic cells of the immune system need to efficiently engulf microbes of widely varying size, shape and biomechanical properties.

How phagocytic cup formation is spatially organized, and adapts to engulfing particles of different geometries and stiffness is however poorly understood. We will directly address this, providing insight into both fundamental mechanisms of phagocytosis and immune cell function.

1) Analyze the mechanisms and forces used for phagocytosis of particles with differing biophysical properties
2) Understand the role of surface ligands in facilitating engulfment
3) Identify the cytoskeletal regulators that enable phagocytosis of complex shapes and differing stiffness

To achieve this, we will integrate several interdisciplinary approaches. Although microbes are diverse in shape, and biophysical properties, most phagocytosis studies only use spherical spherical particles such as very stiff latex beads. Using soft matter and polymer biophysical approaches, we will stretch these to produce complex shapes more akin to the natural diversity of pathogens. We will also use hydrogel particles of defined sizes and stiffness allowing us to modify multiple physical parameters.

We will combine these with using Dictyostelium amoeba as a model phagocyte. This provides an excellent and well-characterised system in which the phagocytic cells can be genetically manipulated to ablate specific cytoskeletal regulators, and express various molecular reporters. This combination gives us a level of control over both the physical properties of the particles and genetics of the phagocyte not possible in any other system.

Recent advances in light microscopy means that now we can now study phagocytosis in 3D at high spatiotemporal resolution. We will generate particles of varying shape and stiffness, and measure them using AFM. Phagocytosis by Dictyostelium cells expressing various GFP-reporters will then be observed live in 3D and super resolution using an Airyscan microscope. Quantitative image analysis will then measure and integrate multiple phagocytic events, defining the important physical parameters and differential phagocyte responses. Importantly, by measuring the deformation of soft particles we will also be able to quantify and model the forces exerted by the cell. Manipulating the particle surface ligands, combined with using mutants in receptor activation and cytoskeletal regulation will then allow an understanding of how the forces are applied, and an understanding of how this relates to engulfment.

Capturing diverse microbes is a fundamental property of immune cells that remains poorly understood. This project will provide a detailed understanding of both how cells cope with the challenges of engulfing particles with diverse biophysical properties, as well as the underlying molecular mechanisms that underpin this.

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