Continuous Exposure to House Dust Mite Elicits Chronic Airway Inflammation and Structural Remodeling

TLDR

Asthma is a chronic disease driven by intermittent or continuous aeroallergen exposure that leads to airway inflammation. The study aimed to investigate the effects of continuous antigen exposure in mice. Mice were intranasally exposed to house dust mite extract or ovalbumin for five consecutive days, followed by two days of rest, repeated for up to seven weeks. Continuous HDM exposure, unlike ovalbumin, induced severe persistent eosinophilic airway inflammation, accumulation of activated CD4⁺ T cells and Th2 cells, sustained Th2 cytokine production, airway remodeling with goblet cell hyperplasia, collagen deposition, peribronchial contractile tissue, and severe airway hyperreactivity; after cessation, inflammation resolved but remodeling persisted and hyperreactivity only partially resolved.

Abstract

It is now fully appreciated that asthma is a disease of a chronic nature resulting from intermittent or continued aeroallergen exposure leading to airway inflammation. To investigate responses to continuous antigen exposure, mice were exposed to either house dust mite extract (HDM) or ovalbumin intranasally for five consecutive days, followed by 2 days of rest, for up to seven consecutive weeks. Continuous exposure to HDM, unlike ovalbumin, elicited severe and persistent eosinophilic airway inflammation. Flow cytometric analysis demonstrated an accumulation of CD4+ lymphocytes in the lung with elevated expression of inducible costimulator a marker of T cell activation, and of T1/ST2, a marker of helper T Type 2 effector cells. We also detected increased and sustained production of helper T cell Type 2-associated cytokines by splenocytes of HDM-exposed mice on in vitro HDM recall. Histologic analysis of the lung showed evidence of airway remodeling in mice exposed to HDM, with goblet cell hyperplasia, collagen deposition, and peribronchial accumulation of contractile tissue. In addition, HDM-exposed mice demonstrated severe airway hyperreactivity to methacholine. Finally, these responses were studied for up to 9 weeks after cessation of HDM exposure. We observed that whereas airway inflammation resolved fully, the remodeling changes did not resolve and airway hyperreactivity resolved only partly.