Staphylococcus aureus membrane and diacylated lipopeptide induce thymic stromal lymphopoietin in keratinocytes through the Toll-like receptor 2–Toll-like receptor 6 pathway

Background Staphylococcus aureus heavily colonizes the lesions of patients with atopic dermatitis (AD) and is known to trigger a worsening of AD. However, the exact mechanism by which S aureus promotes AD is unknown. Thymic stromal lymphopoietin (TSLP), which is highly expressed by keratinocytes in skin lesions of patients with AD and bronchial epithelial cells in asthmatic patients, represents a critical factor linking responses at interfaces between the body and the environment to allergic type 2 immune responses. Objectives We sought to examine the ability of synthetic lipopeptides and S aureus to induce TSLP expression in human keratinocytes and identify the pathway of induction. Methods We stimulated primary human keratinocytes with lipopeptides and S aureus –derived materials. The release and gene expression of TSLP were measured by means of ELISA and quantitative PCR, respectively. Results Diacylated lipopeptide upregulated the expression of TSLP and other proinflammatory molecules. Heat-killed S aureus and the subcellular fractions of S aureus induced TSLP's release, with the membranous fraction having the greatest activity. Small interfering RNA–mediated knockdown of either Toll-like receptor (TLR) 2 or TLR6 inhibited the diacylated lipopeptide– and S aureus membrane–induced TSLP gene expression. S aureus membrane– and diacylated lipopeptide–induced release of TSLP was enhanced by T H 2/TNF-α cytokines and partially suppressed by IFN-γ and TGF-β. Conclusions The results suggest that ligands for the TLR2-TLR6 heterodimer in S aureus membranes, including diacylated lipoproteins, could promote T H 2-type inflammation through TSLP production in keratinocytes, providing an overall picture of the vicious cycles between colonization by S aureus and AD in the T H 2-skewed sensitization process, exacerbation of the disease, or both.