Neuroimmune interactions in the lung

The nervous system and the immune system serve a vital role in protecting the airspace from inhaled irritants and pathogens. The mechanisms by which these disparate systems defend the airways are dissimilar. Activating the nervous system leads to changes in breathing patterns, coughing, increases in airway mucus secretion and bronchospasm. The immune system defends the host against inhaled pathogens by the cellular responses involved in innate and adaptive immunity. We review here the many ways in which mediators released as a consequence of immune cell activation can lead to changes in of neuronal reflex physiology, and conversely, how neurotransmitters released from airway nerves can modulate immune cell function. The lack of redundancy in defence mechanisms between the two system makes it likely that nerve-immune interactions in the airways increase the efficacy of host defence against inhaled ambient air. On the other hand, in those cases where immune stimulation is detrimental to the host, as in allergic asthma, the interactions between the immune and nervous system may contribute to disease. A better understanding of the molecular processes involved in nerve-immune interactions in the lungs would therefore increase our understanding of host defense mechanisms as well as the pathophysiology of certain airway diseases.