Directional Secretory Response of Double Stranded RNA-Induced Thymic Stromal Lymphopoetin (TSLP) and CCL11/Eotaxin-1 in Human Asthmatic Airways

Background Thymic stromal lymphoproetin (TSLP) is a cytokine secreted by the airway epithelium in response to respiratory viruses and it is known to promote allergic Th2 responses in asthma. This study investigated whether virally-induced secretion of TSLP is directional in nature (apical vs. basolateral) and/or if there are TSLP-mediated effects occurring at both sides of the bronchial epithelial barrier in the asthmatic state. Methods Primary human bronchial epithelial cells (HBEC) from control (n = 3) and asthmatic (n = 3) donors were differentiated into polarized respiratory tract epithelium under air-liquid interface (ALI) conditions and treated apically with dsRNA (viral surrogate) or TSLP. Sub-epithelial effects of TSLP were examined in human airway smooth muscle cells (HASMC) from normal (n = 3) and asthmatic (n = 3) donors. Clinical experiments examined nasal airway secretions obtained from asthmatic children during naturally occurring rhinovirus-induced exacerbations (n = 20) vs. non-asthmatic uninfected controls (n = 20). Protein levels of TSLP, CCL11/eotaxin-1, CCL17/TARC, CCL22/MDC, TNF-α and CXCL8 were determined with a multiplex magnetic bead assay. Results Our data demonstrate that: 1) Asthmatic HBEC exhibit an exaggerated apical, but not basal, secretion of TSLP after dsRNA exposure; 2) TSLP exposure induces unidirectional (apical) secretion of CCL11/eotaxin-1 in asthmatic HBEC and enhanced CCL11/eotaxin-1 secretion in asthmatic HASMC; 3) Rhinovirus-induced asthma exacerbations in children are associated with in vivo airway secretion of TSLP and CCL11/eotaxin-1. Conclusions There are virally-induced TSLP-driven secretory immune responses at both sides of the bronchial epithelial barrier characterized by enhanced CCL11/eotaxin-1 secretion in asthmatic airways. These results suggest a new model of TSLP-mediated eosinophilic responses in the asthmatic airway during viral-induced exacerbations

Bilateral TSLP-induced secretion of Th2-related chemokines and pro-inflammatory mediators in HBEC.

<p>CCL22/MDC (A),CCL17/TARC (B), TNF alpha (C) and CXCL8 (D) secreted by ALI-differentiated HBEC treated with TSLP (apical 10 ng/ml×48 h). Bars represent means ± SE of triplicate values from 3 experiments done with cells from 3 controls and 3 asthmatic donors. Results are expressed as fold increase from baseline relative to control values (medium alone). **P<0.01, *P<0.05.</p

Baseline characteristics for subjects.

<p>Baseline characteristics for subjects.</p

Linear correlation of TSLP and CCL11/Eotaxin-1 secretion during rhinovirus-induced asthma exacerbation.

<p>(A) Positive linear relationship of nasal airway protein levels of TSLP and CCL11/eotaxin-1 in subjects with rhinovirus-induced asthma exacerbation P<0.01 (r = Pearson correlation). (B) Multivariate linear analysis demonstrates that the link between TSLP and CCL11/eotaxin-1 in subjects with rhinovirus-induced asthma exacerbation (n = 20) is independent of age, gender and ethnicity. Values in boldface represent statistical significance (p<0.05).</p

TSLP and CCL11/Eotaxin-1 secretion during rhinovirus-induced asthma exacerbation.

<p>Nasal airway protein levels of TSLP (<b>A</b>), CCL11/eotaxin-1 (<b>B</b>) in asthmatic children with PCR-confirmed rhinovirus and clinical wheezing (asthma; n = 20) vs. age-matched non-asthmatic children without clinical wheezing or rhinovirus (control; n = 20).</p

Model of TSLP-induced eosinophilic responses in the asthmatic airways during viral-induced exacerbations.

<p>After activation of airway antiviral immunity the asthmatic bronchial epithelium exhibit prominent secretion of TSLP in the apical compartment, which may amplify Th2 luminal responses (apical secretion) via secretion of CCL11/eotaxin-1. Sub-epithelial Th2 responses maybe further augmented by the TSLP-induced secretion of CCL11/eotaxin-1 by the underlying airway smooth muscle.</p

Antiviral and TSLP-induced immune responses in human airway smooth muscle cells (HASMC).

<p>(A) Time response of TSLP secretion after administration of dsRNA (10 ug/ml) in HASMC. (B) CCL11/eotaxin-1 secreted by HASMC treated with TSLP (10 ng/ml×48 h). Data represent the means ± SE of triplicate values from 3 different asthmatic (n = 3) and control (n = 3) donors. Bars data expressed as fold increase from baseline relative to control values (medium alone). **P<0.01, *P<0.05.</p