doi: 10.1111/cea.12330 Clinical & Experimental Allergy, 44, 953–964 ORIGINAL ARTICLE Basic Mechanisms in Allergic Disease © 2014 John Wiley & Sons Ltd T cell-mediated induction of thymic stromal lymphopoietin in differentiated human primary bronchial epithelial cells C. C. K. Hui 1 , D. M. Murphy 2 , H. Neighbour 3 , M. Al-Sayegh 1 , S. O’Byrne 1 , B. Thong 1 , J. A. Denburg 1 and M. Larch e 1,3 1 Division of Allergy & Clinical Immunology, Department of Medicine, McMaster University, Hamilton, ON, Canada, 2 Department of Respiratory Medicine, Cork University Hospital, Cork, Ireland and 3 Division of Respirology, Department of Medicine, Firestone Institute for Respiratory Health, St. Joseph’s Healthcare, Hamilton, ON, Canada Clinical & Experimental Allergy Correspondence: Mark Larch e, Divisions of Clinical Immunology & Allergy and Respirology, Department of Medicine, Firestone Institute for Respiratory Health, McMaster University, T2131-1, 2nd Floor, Juravinski Tower, St. Joseph’s Hospital Healthcare, 50 Charlton Avenue East, Hamilton, ON, L8N 4A6 Canada. E-mail: larche@mcmaster.ca Cite this as: C. C. K. Hui, D. M. Murphy, H. Neighbour, M. Al-Sayegh, S. O’Byrne, B. Thong, J. A. Denburg and M. Larch e, Clinical & Experimental Allergy, 2014 (44) 953– 964. Summary Background Inhaled peptide challenge has been shown to induce T cell-mediated, isolated late asthmatic reaction (LAR), characterized by recruitment of CD4 + T cells and increased levels of thymus and activation-regulated chemokine (TARC; CCL17). Epithelial-derived thymic stromal lymphopoietin (TSLP) has been shown to modulate dendritic cell function to promote T H 2 responses via CCL17 production. Objectives To elucidate the mechanisms involved in allergen-specific T cell-induced LAR and recruitment of CD4 + T cells by examining the effects of T cell-derived factors on the induction of TSLP in primary bronchial epithelial cells (PBEC). Methods PBEC grown at air–liquid interface from healthy individuals and patients with asthma were stimulated with double-stranded RNA (dsRNA) or supernatants from acti- vated allergen-specific T cells. TSLP was measured in PBEC culture supernatants. Neutral- izing antibodies and signalling inhibitors were used to examine the mechanisms responsible for the induction of epithelial-derived TSLP. The functional activity of PBEC- derived TSLP was measured using a bioassay involving the induction of CCL17 production from monocyte-derived dendritic cells (moDC). Results Both dsRNA and allergen-specific T cells induced enhanced TSLP secretion from asthmatic PBEC compared to healthy PBEC. Activated PBEC culture supernatant induced TSLP-dependent CCL17 production from moDC in a manner related to clinical asthmatic status. IL-1b, IL-6, and CXCL8, rather than T H 2 cytokines (IL-4/5/13), appeared to be the principle mediators of allergen-specific T cell-dependent induction of epithelial-derived TSLP, which was regulated by the MEK, MAPK, and NFjB pathways. Conclusion and Clinical Relevance Our data reveal a novel effect of allergen-specific T cells as a positive regulator of TSLP production by epithelial cells, suggesting T cell–air- way epithelium interactions that may lead to maintenance and amplification of allergic inflammation. TSLP is currently a candidate for therapeutic intervention in asthma, but the factors that drive TSLP expression (T cell-derived factors) may be equally relevant in the treatment of allergic inflammation. Keywords airway epithelial cells, allergens, asthma, CCL17, dendritic cells, T cells, TSLP Submitted 26 July 2013; revised 14 April 2014; accepted 14 April 2014 Introduction In recent years, there has been a world-wide increase in the prevalence of allergic asthma [1]. An important immunopathological hallmark of allergic asthma is the infiltration of T helper type 2 (T H 2) cells into the air- ways [2], a phenomenon promoted by the epithelial- cell-derived interleukin (IL)-7-like cytokine [3] thymic stromal lymphopoietin (TSLP). TSLP is known to acti- vate CD11c + dendritic cells (DC) [4]. TSLP-activated DC express thymus and activation-regulated chemokine (TARC; CCL17), resulting in the recruitment of CD4 + T H 2 cells expressing the chemokine receptor CCR4 [4, 5]. TSLP-activated DC also prime T H 2 cell differentia- tion through expression of OX40L [4, 6], thus initiating and perpetuating the inflammatory cascade.