Recognition of Fungal β‐glucan by Human Neutrophil CR3 Results in Homotypic Aggregation and Neutrophil Extracellular Traps

Abstract

The armament of neutrophil‐mediated host defense against fungal and bacterial pathogens includes the formation of a lattice of DNA and microbicidal enzymes known as Neutrophil Extracellular Traps (NETs). The receptor mediated interactions and intracellular signaling events responsible for the elaboration of NETs in response to fungi are not known and were determined in this study. Recognition of the fungal cell wall component β‐glucan by human neutrophils resulted in rapid formation of cell aggregates and NET release. This response required fibronectin + β‐glucan demonstrating a role for CD11b/CD18. CD11b/CD18 blockade obviated this response which did not require production of oxidative metabolites. Downstream signaling events were determined using a global phosphoproteomic approach. Upon fibronectin + β‐glucan treatment, 46 phosphopeptides were upregulated and 15 were downregulated as compared to fibronectin alone. Validation revealed a functional role for ERK (Y204). NET formation to Candida albicans hyphae was also shown to be dependent on CD11b/CD18 recognition of hyphal β‐glucan, occur in the absence of reactive oxidant species, and depend on ERK. This study successfully identified a key receptor ligand interaction that induces NET formation and elucidates the global tyrosine phosphoproteome of human neutrophils to gain a better understanding of innate immune responses to fungal pathogens.NIH GM066194