Plasma exudation in tracheobronchial and nasal airways: a mucosal defence mechanism becomes pathogenic in asthma and rhinitis.

Plasma exudation into airway tissue and lumen is a defence and inflammatory reaction. If exaggerated it may become pathogenic as in asthma and rhinitis. Exuded plasma contains an abundance of mediators (kinins, complement fragments, fibrinolysis- and coagulation-peptides etc.) which have direct inflammatory and obstructive actions and which can attract, prime, and activate inflammatory cells. The plasma exudate may cause airway hyperresponsiveness by increasing mucosal thickness. In the lumen the exuded plasma is added to irritant and viscous secretions and plugs. Antiasthma and antirhinitic drugs, including glucocorticoids, disodium cromoglycate, beta-adrenoceptor agonists and xanthines, have anti-exudative actions that may include a direct reduction of vascular permeability and other anti-inflammatory effects. Recent data with nasal and tracheobronchial airways in guinea-pigs and humans suggest that plasma can pass into the airway lumen without disturbing the integrity of the epithelial lining as a barrier to inhaled molecules. Potent proteins from circulating plasma can, thus, promptly appear on the surface of a normal mucosa to neutralize offending materials. It is proposed that plasma exudation must be considered a first line mucosal defence system along with mucociliary transport in the airways.