Quebec Respiratory Health Network

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Asthma

Respiratory illnesses such as asthma and chronic obstructive pulmonary diseases are characterized by inflammation and remodelling of the bronchial mucosa and sub-mucosa. These mechanisms are important in the apparition and chronicity of the physiological characteristics particular to these pathologies and eventually lead to their clinical manifestations (symptoms).

Bronchial inflammation involves the participation of every structural and immunological cells of the bronchial tree, particularly mast cells, eosinophils and lymphocytes. These immune cells are recruited from the blood circulation and into the inflammatory site by cytokines, chemiokines and adherence molecules secreted by the affected tissue. These mediators activate the cells of the immune system and decrease their apoptosis, which helps them persist at the inflammation site where they release numerous mediators (leukotrienes, histamine, tumor necrosis factors) and pro-inflammatory cytokines (interleukins).

When the inflammation response becomes chronic and the respiratory function diminishes, remodelling takes place. These changes in tissue architecture have negative effects on respiratory function and can become irreversible. Indeed, respiratory airway remodelling leads to alterations responsible for the progressive decline of respiratory functions and the apparition of irreversible chronic obstruction which is resistant to classic therapies.

Bronchial remodelling is characterized by epithelial desquamation, hypertrophia and hyperplasia of smooth muscle, hypertrophia of glandular cells associated with hypersecretion of mucus and fragmentation of the elastin fibers of the conjonctive tissue. A thickening of the basal membrane along with sub-epithelial fibrosis characterized by a deposit of collagen and increase in myofibroblasts are also important elements in airway remodelling.