Flagellin induces the expression of thymic stromal lymphopoietin in human keratinocytes via toll-like receptor 5.
BACKGROUND
Thymic stromal lymphopoietin (TSLP), highly expressed by keratinocytes in skin lesions of atopic dermatitis patients and bronchial epithelial cells in asthma, plays a key role in allergic diseases. Information on triggers for the release of TSLP in keratinocytes is still limited. Keratinocytes express Toll-like receptor (TLR) 5, the ligand for which is flagellin, the major structural protein of the flagella of Gram-negative bacteria. IL-4, IL-13 and TNF-α (Th2/TNF) are associated with allergic diseases. TGF-α, one of the ligands for the epidermal growth factor receptor, is overexpressed in keratinocytes in atopic dermatitis. We investigated the induction of TSLP expression in keratinocytes stimulated with flagellin and its modulation by the Th2/TNF cytokines and TGF-α.


METHODS
Primary human keratinocytes were stimulated with flagellin with or without cytokines. The TSLP released was measured by ELISA. Gene expression was analyzed by quantitative real-time PCR.


RESULTS
Stimulation of keratinocytes with flagellin induced the release of TSLP protein and upregulation of the gene expression of TSLP and other pro-inflammatory molecules. The flagellin-induced release of TSLP was enhanced by the Th2/TNF cytokines or TGF-α. Small interfering RNA-mediated knockdown of TLR5 expression suppressed the flagellin-induced TSLP gene expression.


CONCLUSIONS
Flagellin induces TSLP expression in keratinocytes via TLR5 and the expression can be upregulated by a cytokine milieu with Th2/TNF or TGF-α, suggesting that exposure of barrier-defective skin to Gram-negative bacteria or environmental flagellin contributes to the initiation and/or amplification of Th2-type skin inflammation including atopic dermatitis through the induction of TSLP expression in keratinocytes.
Atopy Research Center, Juntendo University Graduate School of Medicine, Tokyo, Japan.
Tuan Anh
TA
Le
Toshiro
T
Takai
Anh Tuan
AT
Vu
Hirokazu
H
Kinoshita
Xue
X
Chen
Shigaku
S
Ikeda
Hideoki
H
Ogawa
Ko
K
Okumura
D002478:Cells, Cultured; D018925:Chemokines / Q000235:genetics; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004357:Drug Synergism; D005408:Flagellin / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects / Q000235:genetics; D055785:Gene Knockdown Techniques; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000235:genetics; D018793:Interleukin-13 / Q000494:pharmacology; D015847:Interleukin-4 / Q000494:pharmacology; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D051198:Toll-Like Receptor 5 / Q000235:genetics / Q000378:metabolism*; D016211:Transforming Growth Factor alpha / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D015854:Up-Regulation / Q000235:genetics; D000094632:Thymic Stromal Lymphopoietin
D018925:Chemokines; D016207:Cytokines; D018793:Interleukin-13; D016209:Interleukin-8; D034741:RNA, Small Interfering; C495346:TLR5 protein, human; D051198:Toll-Like Receptor 5; D016211:Transforming Growth Factor alpha; D014409:Tumor Necrosis Factor-alpha; D018799:Intercellular Adhesion Molecule-1; D005408:Flagellin; D015847:Interleukin-4; D000094632:Thymic Stromal Lymphopoietin