Neutrophils on the hunt : Migratory strategies employed by neutrophils to fulfill their effector function

During my Ph.D. research, I managed a series of projects, each focused on the mechanisms underlying cell migration. My work involved an in-depth examination of the complex strategies employed by neutrophils, with a specific focus on their ability to synchronize spatial-temporal cues and optimize their gradient perception. However, it is essential to acknowledge that not all projects yielded successful results, as some ideas were discontinued and are archived for future reference within this thesis. My main project investigated how neutrophils decode spatial cues for precise navigation. Human neutrophils showcased distinct movement patterns based on source type – linear or point-like. By combining single-cell tracking in 3D environments with proxy dyes, this project linked cell behaviors to gradient changes, revealing a stronger response to semi-exponential gradients from point sources. In addition, neutrophils exhibited oscillating migration speeds, using speed minima to adjust trajectories toward sources. Experiencing continuous concentration changes, they accelerated over time and employed a "Run and Fumble" strategy, alternating between consistent runs and strategic "tumbles" for efficient navigation. The project extended to the possibility of cells amplifying perceived gradients by enclosing their immediate surroundings, pushing attractants forward for enrichment while depleting it at the cell rear. Microfluidic devices were employed, and various experimental parameters configurations were optimized. Although significant differences in migratory efficacy were detected across pore sizes and device heights, quantifying gradient manipulation effects proved challenging. The "Laser-Assisted Protein Adsorption by Photobleaching" (LAPAP) project was promising, as it allowed the printing of gradients. Initially successful with dendritic cells, we aimed to adapt it for neutrophils. Through extensive experimentation with multiple parameters, we attempted to trigger responses from neutrophils. Despite these efforts and collaboration, the project failed due to practical challenges and limitations. Facing a lack of neutrophil-like cells at IST, we initially established the SCF-HoxB8 primary murine cell line. Despite their existence, their migratory behavior was largely unexplored due to potential limitations. Through differentiation protocol refinements we enhanced their migratory capabilities, though their capacity still lagged behind human neutrophils. Despite this, the improved migration potential of these cells pointed toward their utility for in vitro murine neutrophil migration studies.