How the number of immune cells recruited to sites of infection is determined and adjusted to differences in the cellular stoichiometry between host and pathogen is unknown. Here, we have uncovered a role for reactive oxygen species (ROS) as sensors of microbe size. By sensing the differential localization of ROS generated in response to microbes of different size, neutrophils tuned their interleukin (IL)-1β expression via the selective oxidation of NF-κB, in order to implement distinct inflammatory programs. Small microbes triggered ROS intracellularly, suppressing IL-1β expression to limit neutrophil recruitment as each phagocyte eliminated numerous pathogens. In contrast, large microbes triggered ROS extracellularly, amplifying IL-1β expression to recruit numerous neutrophils forming cooperative clusters. Defects in ROS-mediated microbe size sensing resulted in large neutrophil infiltrates and clusters in response to small microbes that contribute to inflammatory disease. These findings highlight the impact of ROS localization on signal transduction.
Inflammation recruits neutrophils to fight invading pathogens of different size. Warnatsch et al. show that reactive oxygen species localization tunes inflammation to compensate for differences in the number of neutrophils required to clear microbes of different size.