Neutrophil polarisation

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Neutrophils are the primary cells of the immune system responsible for detecting and preventing bacterial infections, as well as driving inflammation. Neutrophils circulate freely in the bloodstream, and when passing through an inflamed region attach the blood vessel wall, traverse the endothelium (transendothelial migration), and migrate through the connective tissue to the site of infection (chemotaxis). Prior to chemoattractant exposure, neutrophils are spherical and their actin cytoskeleton, the main regulator of cell shape, forms a peripheral shell. Upon stimulation, they become elongated with an F-actin rich lamellipodium that extends in the direction of the chemical gradient and start moving. The signalling cascade involved in the detection and transduction of chemoattractive signals is becoming progressively better understood; however, surprisingly little is known about actin dynamics or cortex mechanics during polarisation and migration. Studies of neutrophil locomotion to date have concentrated on movement on 2-D substrates. Physiologically, neutrophils spend most of their useful lifetime migrating in confined environments. Phenomenological descriptions of locomotion in 3-D suggest that it operates via different mechanisms than movement on flat surfaces. Despite its physiological importance, locomotion in 3-D has been largely ignored due to greater technical difficulties in examining it experimentally. We propose to examine neutrophil polarisation and locomotion in 3-D environments from a biophysical perspective focusing on the dynamics of the cytoskeleton and the mechanical forces at play. Understanding these phenomena will advance our knowledge of cell migration in confined environments, an area of particular relevance to antibacterial and inflammatory processes. To answer these questions, we will build a multidisciplinary team of scientists that will use a combination of microfluidic, microscopy, micromanipulation, and molecular cell biology techniques.