Staphylococcus aureus from atopic dermatitis skin accumulates in the lysosomes of keratinocytes with induction of IL‐1α secretion via TLR9

Abstract Background Staphylococcus aureus ( S. aureus ) is frequently detected in the skin of patients with atopic dermatitis (AD), and involved in the flare of AD. There are some evidence‐specific strains of S. aureus affect the severity of AD. However, the mechanism of predominant colonization and the aggravation of dermatitis by certain strains of S. aureus in the patients with AD are still unknown. Objective To reveal the characteristics of S. aureus from patients with AD ( S. aureus ‐AD), we analyzed the interaction of S. aureus ‐AD and keratinocytes in comparison with those of S. aureus laboratory strains ( S. aureus ‐stand.). Methods We stimulated HaCaT cells, keratinocyte cell line, and human epidermal keratinocytes by heat‐killed S. aureus strains, then evaluated immune response of keratinocytes by ELISA, immunofluorescence staining, and flow cytometry. Results Upon incubation with keratinocytes, three out of four strains of heat‐killed S. aureus ‐AD were strongly agglutinated inside the cytoplasm. In the cells, they are located in lysosomes and promoted the secretion of interleukin‐1α (IL‐1α). These reactions were not observed by any of four strains of S. aureus ‐stand. and S. epidermidis and were abolished by the treatment of S. aureus with proteinase K. Moreover, the IL‐1α secretion was diminished by the inhibition of Toll‐like receptor 9 (TLR9). Conclusion S. aureus ‐AD accumulates in lysosome of keratinocytes by means of bacterial cell wall proteins and induces IL‐1α via TLR9.