The nervous system as a critical regulator of immune responses underlying allergy.

The nervous and immune systems collaborate in the control of homeostasis and host defence. All divisions of the nervous system, sympathetic, parasympathetic and sensory, act to regulate immune cell function. Processes under neuronal control include antigen processing and presentation, Th1/Th2 balance, immunoglobulin production and antigen specific responses, while involvement of the central nervous system allows for behavioral changes leading to avoidance of antigen or noxious stimuli. It therefore follows that dysregulation of these complex bidirectional neuroimmune signaling systems may contribute to the aetiology and pathophysiology of immune disorders including atopic disease. A greater understanding on how the brain perceives, processes and responds to immune challenges and how multiple neurotransmitters interact to maintain or skew the balance between tolerance and immunity will undoubtedly provide opportunities for the development of novel therapeutics. Furthermore, the implications for atopic disease of relatively recent developments such as the cholinergic anti-inflammatory pathway and the potential direct antigen-specific activation of the nervous system require further exploration.