Vagus nerve participates in regulation of the airways: inflammatory response and hyperreactivity induced by...

An initial recognition of occupational asthmogens present in dust, fume or aerosol particles is carried out by a specialized subset of immune cells, dendritic cells and macrophages, present in the airway tissues. When activated by asthmogens these cells release proinflammatory molecular signals and not only send them to other cells of the innate immunological system, but also activate sensory pathways that relay information to the central nervous system (CNS). The precise mechanisms by which the peripheral immune system can signal to the CNS the airway injury has been the subject of much debate. Recently, a new pathway of the CNS-mediated regulation of the peripheral immune response has been found. The efferent vagus nerve was proposed as an immune-to-brain pathway and it was suggested that acetycholine, the principal vagal neurotransmitter, may directly modulate the airway immune response to pathogenic invasion or to injury by irritant asthmogens. Sensory innervation of the airways by ascending fibres traveling in the vagus nerve as well as by pain sensory pathways, provides an important input about the status of injurious challenges in the inflammation zone of the airway compartments. These neural inflammation-sensing pathways can function at low thresholds of detection and can activate responses even when inflammatory agents are present in the airway tissues in quantities that are not high enough to reach the brain through the bloodstream. The cholinergic vagus nerves participate not only in the regulation of the airways inflammatory response. The airways function in response to spastic stimuli such as irritants, allergens, and inflammatory mediators is also controlled, in a larger part, by efferent vagal endings present in the airway smooth muscles. Cholinergic mechanisms represent the predominat constrictor neural pathway in human airways. Differences in expression of muscarinic acetylcholine receptors in asthma suggest that cholinergic system may participate in the molecular framework influencing the airway functions in occupational asthma.