Caging giants: Characterizing the molecular mechanisms of neutrophil swarming against Candida albicans hyphae

Neutrophils utilize many mechanisms to restrict fungal growth. When phagocytosis occurs, neutrophils can create many toxic antimicrobials including reactive oxygen species and the products of myeloperoxidase. If a pathogen is too large to phagocytose, neutrophils can also resort to the release of neutrophil extracellular traps or it can engage in the behavior of "swarming," in which the recruitment and antimicrobial action of many neutrophils are coordinated against a single target. Here we optimized an assay to study the behavior of swarming directly against live Candida albicans hyphae. We find that hyphae are highly potent targets for inducing swarming behavior and that swarming is very effective at restricting hyphal growth. We provide insight into the initial interactions between the pioneer neutrophil and the hyphae, including information on how fast signaling is initiated following neutrophil binding, how far neutrophils stretch before signaling occurs, and how the calcium signaling waves are unique in response to hyphal targets. We also find distinct and important roles for myeloperoxidase, spleen tyrosine kinase, Bruton's tyrosine Kinase, and CD18 in an effective neutrophil swarming response.