| [ Summary ] |
During respiration, airborne dust and pathogens are inhaled into the lung. To prevent the injury induced by these organisms, respiratory host defences effectively remove or inactivate microorganisms in the conducting airways and alveoli, by immunologic and nonimmunologic mechanisms. These mechanisms operating in the naso-oro-pharynx and along the trachea and conducting airways clear the respiratory mucosa of excessive microorganisms that can be inhaled with ambient air or aspirated with oropharyngeal secretions. The air-exchange surface has had to develop additional mechanisms for auto-cleansing. These include immunoglobulins and cells, especially macrophages, Iymphocytes, and polymorphonuclear cells, which generate inflammatory reactions. Respiratory infections may occur when certain components of the defense system are absent, and examplified by IgG subclass deficiency, IgA inactivation, and impaired cell-mediated immunity. |