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

Innate immune signaling plays a key role in host response to infection, yet the pattern recognition receptors 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 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 co-stimulatory molecules, MHC-II, and pattern recognition receptors, including the C-type lectin receptor 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 tumor necrosis factor (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 disease pathogenesis.