Innate immune recognition of Debaryomyces hansenii requires Dectin-1-Card9 signaling

Abstract: Innate immune signaling plays a key role in host response to infection, yet the pattern recognition receptors (PRRs) that detect non-model gut-associated yeasts remain poorly defined. Here, we investigated macrophage sensing of Debaryomyces hansenii, a food-derived yeast that we found to be enriched within intestinal ulcers of Crohn’s Disease (CD) patients. Using a cell surface receptor antibody screen of bone marrow derived macrophages infected with a CD-patient isolate of D. hansenii, we showed that D. hansenii induced macrophage activation characterized by increased expression of costimulatory molecules, MHC-II, and pattern recognition receptors including the C-Type Lectin Receptor (CLR) Dectin-1. Antibody blockade experiments showed both Dectin-1 and complement receptor 3 subunit CD11b were required for phagocytosis of D. hansenii, while Dectin-1 was uniquely required for production of the pro-inflammatory cytokine Tnf. CRISPR-Cas9-mediated deletion of Dectin-1 phenocopied antibody neutralization effects on phagocytosis. Furthermore, deletion of Dectin-1 or its downstream signaling adaptor molecule Card9 resulted in reduced Tnf secretion in response to D. hansenii. Dectin-1-mediated uptake of D. hansenii was observed in primary bone marrow derived macrophage and dendritic cells, as well as across the spectrum of macrophage polarization states. Together, these findings define the role of Dectin-1-Card9 signaling axis in innate immune cell sensing of D. hansenii. These findings support the emerging relevance of innate immune recognition of a yeast in Crohn’s Disease pathogenesis.