Staphylococcus aureus is a major cause of skin and soft tissue infections and aggravator of the inflammatory skin disease atopic dermatitis (AD [eczema]). Epicutaneous exposure to S. aureus induces Th17 responses through skin Langerhans cells (LCs), which paradoxically contribute to host defense but also to AD pathogenesis. The molecular mechanisms underlying the interaction between S. aureus and LCs are poorly understood. Here we demonstrate that human LCs directly interact with S. aureus through the pattern recognition receptor langerin (CD207). Human, but not mouse, langerin interacts with S. aureus through the conserved β-N-acetylglucosamine (GlcNAc) modifications on wall teichoic acid (WTA), thereby discriminating S. aureus from other staphylococcal species. Importantly, the specific S. aureus WTA glycoprofile strongly influences the level of proinflammatory cytokines that are produced by in vitro-generated LCs. Finally, in a murine epicutaneous infection model, S. aureus strongly upregulated transcripts of Cxcl1, Il6, and Il17, which required the presence of both human langerin and WTA β-GlcNAc. Our findings provide molecular insight into the unique proinflammatory capacities of S. aureus in relation to skin inflammation. IMPORTANCE The bacterium Staphylococcus aureus is an important cause of skin infections and is also associated with the occurrence and severity of eczema. Langerhans cells (LCs), a specific subset of skin immune cells, participate in the immune response to S. aureus, but it is yet unclear how LCs recognize S. aureus. Therefore, we investigated the molecular mechanism underlying the interaction between LCs and S. aureus. We identified that wall teichoic acid, an abundant polymer on the S. aureus surface, is recognized by langerin, a receptor unique to LCs. This interaction allows LCs to discriminate S. aureus from other related staphylococcal species and initiates a proinflammatory response similar to that observed in patients with eczema. Our data therefore provide important new insights into the relationship between S. aureus, LCs, and eczema.

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Signal inhibitory receptor on leukocytes-1 (SIRL-1) is an inhibitory receptor with a hitherto unknown ligand, and is expressed on human monocytes and neutrophils. SIRL-1 inhibits myeloid effector functions such as reactive oxygen species (ROS) production. In this study, we identify S100 proteins as SIRL-1 ligands. S100 proteins are composed of two calcium-binding domains. Various S100 proteins are damage-associated molecular patterns (DAMPs) released from damaged cells, after which they initiate inflammation by ligating activating receptors on immune cells. We now show that the inhibitory SIRL-1 recognizes individual calcium-binding domains of all tested S100 proteins. Blocking SIRL-1 on human neutrophils enhanced S100 protein S100A6-induced ROS production, showing that S100A6 suppresses neutrophil ROS production via SIRL-1. Taken together, SIRL-1 is an inhibitory receptor recognizing the S100 protein family of DAMPs. This may help limit tissue damage induced by activated neutrophils.