The control of the surface topography of neutrophils

• Main Author: Al-Jumaa, Maha Awadh
• Published: Cardiff University 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.742861

Neutrophils are characterised by undergoing rapid cell shape change, especially during cell spreading and phagocytosis. In both situations, the cell changes from a spherical to a non-spherical configuration. This must necessarily require additional cell surface membrane as a sphere is the minimum surface area to enclose a given volume. Although it has been proposed that this additional membrane may come from cell surface structures called wrinkles or micro-ridges, it has not been possible to directly test this hypothesis. In this thesis, a methodology was established that would permit such a test. By incorporating freely diffusible fluorescent molecules into the plasma membrane of neutrophils, a methodology was devised that allows the diffusion time into a subdomain within a photobleached area to be monitored. As the diffusion time depended on the diffusion pathlength, this gave a measure of the surface topography. In osmotically swollen cells, in the neutrophil tail and the phagocytic cup, it was found that the membrane was smooth. However, in the cell body, there was a significant delay in diffusion, consistent with the presence of surface wrinkles. These wrinkles were reduced by osmotic swelling, and as cells spread onto a substrate. The wrinkledness could be increased by osmotic shrinking. This was the first time that changes in cell surface topography could be monitored. In order to establish whether changes in cell surface topography were important for rapid cell shape change, cells were suddenly hyper-wrinkled (osmotically) during phagocytosis or chemotaxis. In both cases this procedure immediately arrested the cell behaviour. On restoration of normal surface topography (by return osmolality to normal), cells then continued to undergo shape change. In the hyper-wrinkled state an abnormal shape change could be induced by uncaging cytosolic IP3 and so force a Ca2+ signal. The data presented in this thesis therefore confirms that surface wrinkling changes during neutrophil shape change, and that this was a key factor in neutrophil shape change.