Asthma and lower airway disease
Accumulation of intraepithelial mast cells with a unique protease phenotype in TH2-high asthma

https://doi.org/10.1016/j.jaci.2010.03.003Get rights and content

Background

Previously, we found that mast cell tryptases and carboxypeptidase A3 (CPA3) are differentially expressed in the airway epithelium in asthmatic subjects. We also found that asthmatic subjects can be divided into 2 subgroups (“TH2 high” and “TH2 low” asthma) based on epithelial cell gene signatures for the activity of TH2 cytokines.

Objectives

We sought to characterize intraepithelial mast cells (IEMCs) in asthma.

Methods

We performed gene expression profiling in epithelial brushings and stereology-based quantification of mast cell numbers in endobronchial biopsy specimens from healthy control and asthmatic subjects before and after treatment with inhaled corticosteroids (ICSs). We also performed gene expression and protein quantification studies in cultured airway epithelial cells and mast cells.

Results

By means of unsupervised clustering, mast cell gene expression in the airway epithelium related closely to the expression of IL-13 signature genes. The levels of expression of mast cell genes correlate positively with lung function improvements with ICSs. IEMC density was 2-fold higher than normal in subjects with TH2-high asthma compared with that seen in subjects with TH2-low asthma or healthy control subjects (P = .015 for both comparisons), and these cells were characterized by expression of tryptases and CPA3 but not chymase. IL-13 induced expression of stem cell factor in cultured airway epithelial cells, and mast cells exposed to conditioned media from IL-13–activated epithelial cells showed downregulation of chymase but no change in tryptase or CPA3 expression.

Conclusion

IEMC numbers are increased in subjects with TH2-high asthma, have an unusual protease phenotype (tryptase and CPA3 high and chymase low), and predict responsiveness to ICSs. IL-13–stimulated production of stem cell factor by epithelial cells potentially explains mast cell accumulation in TH2-high asthmatic epithelium.

Section snippets

Airway Tissue Bank at the University of California, San Francisco

We studied biological samples from the Airway Tissue Bank at the University of California, San Francisco (UCSF). These samples had been collected during research bronchoscopy in healthy and asthmatic volunteers. Bronchoscopy included collection of epithelial brushings and bronchial biopsy specimens by using methods previously described.6, 12, 13, 14 For this study, we reviewed mast cell gene expression data from our previously generated epithelial microarray and quantitative RT-PCR (qPCR) data6

Gene expression for mast cell proteases is increased in asthmatic epithelium, especially in the TH2-high subgroup of asthma, and predicts responsiveness to ICSs

We previously provided summary data for gene expression for tryptase and CPA3 in epithelial brushings from 42 steroid-naive subjects with asthma and 28 healthy control subjects.6 These summary data showed that tryptase and CPA3 expression was higher than normal in asthmatic subjects. Here we show that each of these 2 genes is overexpressed in some, but not all, of the 42 asthmatic subjects (Fig 1). Interestingly, using microarray- or qPCR-based gene expression profiling, we found no difference

Discussion

We found that the numbers of mast cells in the airway epithelium were increased in some, but not all, of the 26 asthmatic subjects we studied. By classifying the asthmatic subjects as having TH2-high or TH2-low asthma based on expression of IL-13–responsive genes in their epithelial brushings, we discovered that IEMC numbers in the TH2-high subgroup were significantly higher than those in the TH2-low subgroup. In fact, the numbers of IEMCs in the TH2-low subgroup were similar to those in the

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    Supported by the National Institutes of Health National Research Service AwardF32HL093999-01 (R.H.D.), A1077439-025 and R01 HL080414 (J.V.F.), R01 HL095372 (P.G.W.), and P01 HL024136 (G.H.C.).

    Disclosure of potential conflict of interest: G. H. Caughey receives research support from the National Institutes of Health (NIH)/National Heart, Lung, and Blood Institute. P. G. Woodruff receives research support from Genentech. J. V. Fahy has consultant arrangements with Amira, Cytokinetics, Abbott, and GlaxoSmithKline and receives research support from Genentech and the NIH. The rest of the authors have declared that they have no conflict of interest.

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