Fig. 2

Human neutrophils phagocytose and transport bacteria through microfluidic mazes. a) Diagram detailing the microfluidic device used to measure the migration of neutrophils laden with phagocytosed bacteria. Each device has three independent cell loading channels, and each channel has 24 migration mazes. Each maze (magnified view) fits in one field of view for faster imaging. b) Experimental protocol used. First, bacteria were loaded into the channel, then drawn into the mazes by placing the device under a vacuum. The loading channel was washed with media, leaving the bacteria only in the mazes and the devices submerged in media. Finally, neutrophils were added to the channel. The device was transferred to the microscope stage for time-lapse imaging. The interactions between the moving neutrophils and live bacteria were usually monitored for up to 8 hours. c) Micrographs from a representative time-lapse series showing a neutrophil entering the maze (48 mins), phagocytosing the bacteria, which is acidified (red pHrodo signal 54 mins), and transporting the bacteria around and out of the maze (88 mins). Green and red arrows point at free bacteria and phagocytosed bacteria, respectively. d) Graphs show the velocity of neutrophils migrating in mazes laden with S. mitis, Fnn, and Fnp. Neutrophils laden with Fnn exhibited significantly higher velocity than the other species. Statistics: One-way ANOVA with Tukey’s multiple comparisons test. Each point is the average velocity of one neutrophil track. Data are pooled from N = 3 experiments per condition, N = 50 or more neutrophils per condition. Red horizontal line represents the median and the dashed lines represent the first and third quartile.