Live imaging of gut-associated innate immune cell motion

Immune responses involve complex dynamics at multiple scales. Even in the absence of pathogens, the immune system recognizes and actively regulates commensal microbes, including the large populations resident in the gut whose presence contributes to the host health. This recognition is typically assessed in terms of the number or activation state of immune cells, but in vitro studies imply that cellular motility and morphology should also be altered by microbial cues. How these physical behaviors are manifested inside a living host remains unclear. We therefore examined innate immune cells – neutrophils and macrophages – in larval zebrafish, a model vertebrate. Using light sheet fluorescence microscopy to obtain three-dimensional images, we tracked the positions of gut-associated neutrophils and macrophages over few hour durations. We compare dynamics in germ-free fish to those in fish inoculated with native gut bacteria, characterizing average speeds, measures of random-walk motion, and cellular morphology, illuminating search strategies employed by these immune cells in response to bacterial colonization.