The non-neuronal cholinergic system in the airways: an unappreciated regulatory role in pulmonary inflammation?

The parasympathetic neurotransmitter acetylcholine is also synthesised and secreted by non-neuronal cells and modifies their behaviour. This is termed the "non-neuronal cholinergic system" and is present in airway inflammatory cells. Acetylcholine is predominantly pro-inflammatory for lymphocytes and epithelial cells, anti-inflammatory for mast cells and macrophages, both pro- and anti-inflammatory for monocytes, and variable in neutrophils and eosinophils. Expression and function of components of the non-neuronal cholinergic system, for example cholinoceptors, can be modified by nicotine in cigarette smoke, the inflammation of asthma and chronic obstructive pulmonary disease (COPD), and the drugs used in clinical management of these diseases. The non-neuronal cholinergic system of airway inflammatory cells represents a previously unappreciated regulatory pathway, with immunomodulatory effects that potentially influence the inflammation of asthma and COPD.