Neutrophil-Leishmania infantum Interaction Induces Neutrophil Extracellular Traps, DAMPs, and Inflammatory Molecule Release

Neutrophils, the first cells to arrive at infection sites, release neutrophil extracellular traps (NETs) comprising nuclear and/or mitochondrial DNA webs decorated with proteins. Similar to other parasites, Leishmania infantum induces NET extrusion. However, our understanding of NET formation and neutrophil fate after NET release in a Leishmania infection context is limited. Our study aimed to determine the DNA origin of the NET scaffolds released by human neutrophils in response to chemical or L. infantum stimulation. Neutrophils were incubated with PMA, PHA, LPS, or L. infantum, followed by DNA and elastase activity quantification; additionally, we evaluated the source of DNA that composes NETs. Neutrophil viability was evaluated by annexin-V/7AAd labeling. Expression of IL6, TNFA, IL10, CXCL1, CXCL8, and FPR1 in response to the L. infantum interaction was assessed. Neutrophils incubated with chemicals or L. infantum released NETs. However, neutrophils stimulated by the chemicals showed lower viability after 1 h in comparison to neutrophils incubated with parasites. NETs from chemically stimulated neutrophils were mainly composed of nuclear DNA. Conversely, the NET induced by the parasites was of mitochondrial DNA origin and had no leishmanicidal activity. After 4 h of parasite stimulation, neutrophils peak the expression of genes such as IL6, TNFA, CXCL1, CXCL8, and FPR1. Our study demonstrates that neutrophils produce NETs after chemical or L. infantum exposure. Although they are not toxic to the parasite, NETs are released as danger signals. These findings support the role of neutrophils in releasing signaling molecules, which influence the inflammatory environment in which the infectious process occurs.