Mitochondria sense bacterial lactate and drive release of neutrophil extracellular traps.

Neutrophils induce oxidative stress, creating a harsh phagosomal environment. However, Staphylococcus aureus can survive these conditions, requiring neutrophils to deploy mechanisms that sense bacterial persistence. We find that staphylococcal lactate is a metabolic danger signal that triggers neutrophil extracellular trap release (NETosis). Neutrophils coordinate mitochondria in proximity to S. aureus-containing phagosomes, allowing transfer of staphylococcal lactate to mitochondria where it is rapidly converted into pyruvate and causes mitochondrial reactive oxygen species, a precursor to NETosis. Similar results were observed in response to phylogenetically distinct bacteria, implicating lactate accumulation as a broad signal triggering NETosis. Furthermore, patients with systemic lupus erythematosus (SLE) are more susceptible to bacterial infections. We find that SLE neutrophils cannot sense bacterial lactate impairing their capacity to undergo NETosis upon S. aureus infection but initiate aberrant NETosis triggered by apoptotic debris. Thus, neutrophils adapt mitochondria as sensory organelles that detect bacterial metabolic activity and dictate downstream antibacterial processes.