Aspects of airway defence mechanisms

Abstract

This review deals with recent findings in the airways and lung defence. It is well known that the respiratory tract forms the largest part of the human body surface which is directly exposed to the influence of inspired air. This can differ with regard to temperature, humidity, capacity of harmful gases, vapors, pollutants, and living and non-living particles. Therefore the airways and lungs have very effective defence processes consisting of reflex and non-reflex mechanisms. The reflex reactions include coughing, sneezing, aspiration and apnoeic reflexes, laryngo- and bronchospasms and mucociliary transport which has been considered to be a non-reflex reaction. The electrostatic filter of the tonsilar ring, immunological and antimicrobial defence, oxidant-antioxidant and protease-antiprotease systems and the architecture of the airways belong to the non-reflex group. Considerable progress has been made in understanding molecular mechanisms over the last decade. From this viewpoint the defence complex of activated pulmonary epithelial and inflammatory cells together with their mediators is very important. This complex has not previously been identified in the airways defence system. Both reflex and non-reflex mechanisms are independent units, but they normally interact. It is paradoxical that an original physiological defence activity can change its character into a pathological one if it is inadequate, survives the cause of its activation or triggers some secondary pathological process. In spite of intensive study of the respiratory tract defence systems in the last few years there are many links in structure and function which need further elucidation. Thus these large complexes of defence mechanisms require further study.