Anti-IL-5 treatment reduces deposition of ECM proteins in the bronchial subepithelial basement membrane of mild atopic asthmatics

Abstract

Eosinophil-derived TGF-beta has been implicated in remodeling events in asthma. We hypothesized that reduction of bronchial mucosal eosinophils with anti-IL-5 would reduce markers of airway remodeling. Bronchial biopsies were obtained before and after three infusions of a humanized, anti-IL-5 monoclonal antibody (mepolizumab) in 24 atopic asthmatics in a randomized, double-blind, placebo-controlled study. The thickness and density of tenascin, lumican, and procollagen III in the reticular basement membrane (RBM) were quantified immunohistochemically by confocal microscopy. Expression of TGF-beta1 mRNA by airway eosinophils was assessed by in situ hybridization, and TGF-beta1 protein was measured in bronchoalveolar lavage (BAL) fluid by ELISA. At baseline, airway eosinophil infiltration and ECM protein deposition was increased in the RBM of asthmatics compared with nonasthmatic controls. Treating asthmatics with anti-IL-5 antibody, which specifically decreased airway eosinophil numbers, significantly reduced the expression of tenascin, lumican, and procollagen III in the bronchial mucosal RBM when compared with placebo. In addition, anti-IL-5 treatment was associated with a significant reduction in the numbers and percentage of airway eosinophils expressing mRNA for TGF-beta1 and the concentration of TGF-beta1 in BAL fluid. Therefore eosinophils may contribute to tissue remodeling processes in asthma by regulating the deposition of ECM proteins.

Figure 1

(a) A comparison of tenascin, lumican, and procollagen III expression in the reticular basement membrane between normal controls (n = 10) and asthmatic individuals (n = 11) before and after anti–IL-5. N denotes normal subjects. The crossbars represent the median values. (b) A comparison of the number of MBP⁺ eosinophils in the bronchial mucosa of normal controls and asthmatic subjects at baseline. (c) The correlation between eosinophil numbers and thickness of tenascin in the reticular basement membrane at baseline.

Figure 2

The effect of anti–IL-5 on the total expression (thickness × density) of tenascin, lumican, and procollagen III in the bronchial subepithelial reticular basement membrane. The crossbars represent the median values.

Figure 3

Representative photomicrographs of tenascin immunoreactivity in the reticular basement membrane from a normal subject (a) and from an asthmatic subject pretreatment (b) and posttreatment (c) with anti–IL-5. Lumican immunoreactivity from a normal subject (d) and from pretreatment (e) and posttreatment (f) with anti–IL-5 is also shown. Examples of procollagen III immunoreactivity pretreatment (g) and posttreatment (h) with anti–IL-5 are presented, although the decrease shown was not typical of all subjects. i shows an example of isotype control immunoreactivity. Immunoreactivity of ECM proteins is shown in green. Sections were counterstained with DAPI (blue).

Figure 4

The effect of anti–IL-5 on (a) TGF-β1mRNA⁺ eosinophils in the bronchial mucosa, (b) the percentage of eosinophils expressing TGF-β1mRNA in the bronchial mucosa, and (c) the concentration of TGF-β1 in bronchoalveolar lavage fluid. The crossbars represent the median values.