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To the Editor: Seidl et al1Seidl B. Kalali B. Gerhard M. Ring J. Ollert M. Mempel M. Thymic stromal lymphopoietin induction by polyinosinic:polycytidylic acid in human keratinocytes is preferentially mediated through protein kinase R and retinoid-inducible gene I and not Toll-like receptor 3.J Allergy Clin Immunol. 2009; 124: 862-864Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar have addressed identification of double-stranded RNA (dsRNA) sensors responsible for induction of thymic stromal lymphopoietin (TSLP) in dsRNA-stimulated human keratinocytes, which we recently demonstrated.2Kinoshita H. Takai T. Le T.A. Kamijo S. Wang X.L. Ushio H. et al.Cytokine milieu modulates release of thymic stromal lymphopoietin from human keratinocytes stimulated with double-stranded RNA.J Allergy Clin Immunol. 2009; 123: 179-186Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar By means of quantitative PCR and the use of small interfering RNA (siRNA) and pharmacologic inhibitors, they suggested that, unlike in bronchial epithelial cells, dsRNA-induced TSLP transcription in keratinocytes is dependent on protein kinase R and retinoid-inducible gene I, but not Toll-like receptor (TLR) 3, in their experimental conditions. Interestingly, 2 pharmacologic inhibitors, 2-amino-purin and SU6668, almost completely shut down the dsRNA-induced TSLP transcription, whereas TLR3-specific siRNA and bafilomycin A1 did not significantly inhibit it. The patterns of the inhibition of the TSLP transcription by the siRNA and pharmacologic inhibitors1Seidl B. Kalali B. Gerhard M. Ring J. Ollert M. Mempel M. Thymic stromal lymphopoietin induction by polyinosinic:polycytidylic acid in human keratinocytes is preferentially mediated through protein kinase R and retinoid-inducible gene I and not Toll-like receptor 3.J Allergy Clin Immunol. 2009; 124: 862-864Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar resemble those in transcription and release of IFN-β associated with interferon-regulatory factor 3 (IRF-3) activation but not IL-8 associated with nuclear factor κB (NF-κB) activation,3Kalali B.N. Kollisch G. Mages J. Muller T. Bauer S. Wagner H. et al.Double-stranded RNA induces an antiviral defense status in epidermal keratinocytes through TLR3-, PKR-, and MDA5/RIG-I-mediated differential signaling.J Immunol. 2008; 181: 2694-2704PubMed Google Scholar suggesting the contribution of IRF-3 in the dsRNA-induced TSLP transcription in keratinocytes. We would like to suggest 3 major concerns on the correspondence by Seidl et al,1Seidl B. Kalali B. Gerhard M. Ring J. Ollert M. Mempel M. Thymic stromal lymphopoietin induction by polyinosinic:polycytidylic acid in human keratinocytes is preferentially mediated through protein kinase R and retinoid-inducible gene I and not Toll-like receptor 3.J Allergy Clin Immunol. 2009; 124: 862-864Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar which should be addressed for confirmation of their conclusions. First, TSLP protein release would be measured. They previously analyzed the expression of IL-8 and IFN-β at both the protein and mRNA levels3Kalali B.N. Kollisch G. Mages J. Muller T. Bauer S. Wagner H. et al.Double-stranded RNA induces an antiviral defense status in epidermal keratinocytes through TLR3-, PKR-, and MDA5/RIG-I-mediated differential signaling.J Immunol. 2008; 181: 2694-2704PubMed Google Scholar; however, they have analyzed the TSLP expression only at the mRNA level.1Seidl B. Kalali B. Gerhard M. Ring J. Ollert M. Mempel M. Thymic stromal lymphopoietin induction by polyinosinic:polycytidylic acid in human keratinocytes is preferentially mediated through protein kinase R and retinoid-inducible gene I and not Toll-like receptor 3.J Allergy Clin Immunol. 2009; 124: 862-864Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar Second, negative control experiments to confirm that the pharmacologic inhibitors are specific for the function or downstream pathway of the dsRNA sensors would be performed; that is, another stimulation with no relation to the dsRNA sensors should not be inhibited by these inhibitors. Our third concern, although not directly on their data, is the possibility that TLR3 contributes to the dsRNA-induced TSLP in keratinocytes in other experimental conditions. In spite of the major concerns mentioned above, the issue Seidl et al1Seidl B. Kalali B. Gerhard M. Ring J. Ollert M. Mempel M. Thymic stromal lymphopoietin induction by polyinosinic:polycytidylic acid in human keratinocytes is preferentially mediated through protein kinase R and retinoid-inducible gene I and not Toll-like receptor 3.J Allergy Clin Immunol. 2009; 124: 862-864Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar have addressed is important because elucidation of the molecular mechanism of induction of TSLP, which is considered the “master switch” for TH2 responses, in each cell type of the TSLP producers could lead to identification of molecules to be drug targets to control allergic diseases. Blocking of pathways downstream of TSLP, such as the TSLP-TSLP receptor interaction4He R. Oyoshi M.K. Garibyan L. Kumar L. Ziegler S.F. Geha R.S. TSLP acts on infiltrating effector T cells to drive allergic skin inflammation.Proc Natl Acad Sci U S A. 2008; 105: 11875-11880Crossref PubMed Scopus (194) Google Scholar and OX40 ligand–OX40 interaction,5Seshasayee D. Lee W.P. Zhou M. Shu J. Suto E. Zhang J. et al.In vivo blockade of OX40 ligand inhibits thymic stromal lymphopoietin driven atopic inflammation.J Clin Invest. 2007; 117: 3868-3878Crossref PubMed Scopus (175) Google Scholar has been suggested as a promising strategy for treatment of allergic diseases. Switching off the master switch (ie, shutting down the release of TSLP at the lesion of atopic dermatitis or in the epithelia in patients with asthma and other allergic diseases) is another straightforward strategy, which could be similarly or more effective than targeting pathways downstream of TSLP. The ways to shut down the TSLP release are as follows: (1) avoidance, elimination, or neutralization of the environmental or endogenous factors that trigger the TSLP release; (2) blockade of recognition of the TSLP triggering factors by targeting sensors for them; (3) interception of signaling pathways downstream of the sensors; and (4) inhibition of the TSLP transcription by targeting the transcription factors. Exogenous and endogenous factors, including components derived from virus and microbes and proteases, have been suggested as TSLP triggers, and cytokines could modulate the TSLP induction.2Kinoshita H. Takai T. Le T.A. Kamijo S. Wang X.L. Ushio H. et al.Cytokine milieu modulates release of thymic stromal lymphopoietin from human keratinocytes stimulated with double-stranded RNA.J Allergy Clin Immunol. 2009; 123: 179-186Abstract Full Text Full Text PDF PubMed Scopus (98) Google Scholar, 6Kato A. Favoreto Jr., S. Avila P.C. Schleimer R.P. TLR3- and Th2 cytokine-dependent production of thymic stromal lymphopoietin in human airway epithelial cells.J Immunol. 2007; 179: 1080-1087PubMed Google Scholar, 7Briot A. Deraison C. Lacroix M. Bonnart C. Robin A. Besson C. et al.Kallikrein 5 induces atopic dermatitis-like lesions through PAR2-mediated thymic stromal lymphopoietin expression in Netherton syndrome.J Exp Med. 2009; 206: 1135-1147Crossref PubMed Scopus (380) Google Scholar, 8Kouzaki H. O'Grady S.M. Lawrence C.B. Kita H. Proteases induce production of thymic stromal lymphopoietin by airway epithelial cells through protease-activated receptor-2.J Immunol. 2009; 183: 1427-1434Crossref PubMed Scopus (270) Google Scholar Sensors for the TSLP triggers could include TLRs, protein kinase R, retinoid-inducible gene I–like receptors, protease-activated receptor 2, and unknown receptors.1Seidl B. Kalali B. Gerhard M. Ring J. Ollert M. Mempel M. Thymic stromal lymphopoietin induction by polyinosinic:polycytidylic acid in human keratinocytes is preferentially mediated through protein kinase R and retinoid-inducible gene I and not Toll-like receptor 3.J Allergy Clin Immunol. 2009; 124: 862-864Abstract Full Text Full Text PDF PubMed Scopus (6) Google Scholar, 6Kato A. Favoreto Jr., S. Avila P.C. Schleimer R.P. TLR3- and Th2 cytokine-dependent production of thymic stromal lymphopoietin in human airway epithelial cells.J Immunol. 2007; 179: 1080-1087PubMed Google Scholar, 7Briot A. Deraison C. Lacroix M. Bonnart C. Robin A. Besson C. et al.Kallikrein 5 induces atopic dermatitis-like lesions through PAR2-mediated thymic stromal lymphopoietin expression in Netherton syndrome.J Exp Med. 2009; 206: 1135-1147Crossref PubMed Scopus (380) Google Scholar, 8Kouzaki H. O'Grady S.M. Lawrence C.B. Kita H. Proteases induce production of thymic stromal lymphopoietin by airway epithelial cells through protease-activated receptor-2.J Immunol. 2009; 183: 1427-1434Crossref PubMed Scopus (270) Google Scholar Four transcription factors, NF-κB,6Kato A. Favoreto Jr., S. Avila P.C. Schleimer R.P. TLR3- and Th2 cytokine-dependent production of thymic stromal lymphopoietin in human airway epithelial cells.J Immunol. 2007; 179: 1080-1087PubMed Google Scholar activator protein 1,9Harada M. Hirota T. Jodo A.I. Doi S. Kameda M. Fujita K. et al.Functional analysis of the thymic stromal lymphopoietin variants in human bronchial epithelial cells.Am J Respir Cell Mol Biol. 2009; 40: 368-374Crossref PubMed Scopus (125) Google Scholar IRF-3,6Kato A. Favoreto Jr., S. Avila P.C. Schleimer R.P. TLR3- and Th2 cytokine-dependent production of thymic stromal lymphopoietin in human airway epithelial cells.J Immunol. 2007; 179: 1080-1087PubMed Google Scholar and signal transducer and activator of transcription (STAT) 6,6Kato A. Favoreto Jr., S. Avila P.C. Schleimer R.P. TLR3- and Th2 cytokine-dependent production of thymic stromal lymphopoietin in human airway epithelial cells.J Immunol. 2007; 179: 1080-1087PubMed Google Scholar have been suggested to contribute to the gene expression of TSLP. Pathways dependent on NF-κB, activator protein 1, and IRF-3 can be inhibited by glucocorticoids. Actually, glucocorticoids inhibits the dsRNA-induced TSLP protein release in keratinocytes10Le T.A. Takai T. Kinoshita H. Suto H. Ikeda S. Okumura K. et al.Inhibition of double-stranded RNA-induced TSLP in human keratinocytes by glucocorticoids.Allergy. 2009; 64: 1231-1232Crossref PubMed Scopus (17) Google Scholar and bronchial epithelial cells.6Kato A. Favoreto Jr., S. Avila P.C. Schleimer R.P. TLR3- and Th2 cytokine-dependent production of thymic stromal lymphopoietin in human airway epithelial cells.J Immunol. 2007; 179: 1080-1087PubMed Google Scholar Thus elucidation of the molecular mechanism of the TSLP induction could lead to novel approaches for treatment of allergic diseases. Furthermore, investigation of the environmental and endogenous factors that trigger or modulate the TSLP induction will provide us with the knowledge essential for understanding the role of the gene-environment interaction relevant in the initiation of TH2 sensitization and the exacerbation in allergic diseases. Thymic stromal lymphopoietin induction by polyinosinic:polycytidylic acid in human keratinocytes is preferentially mediated through protein kinase R and retinoid-inducible gene I and not Toll-like receptor 3Journal of Allergy and Clinical ImmunologyVol. 124Issue 4PreviewTo the Editor: Full-Text PDF