Scientists generally like work in carefully defined areas. For example, immunologists study the physiological functioning of the immune system while neuroscientists focus on the biology of neurons and their circuits. Each are highly complex fields in their own right and it is not surprising that many like to study their chosen discipline in splendid isolation.
However, in reality the major adaptive systems of the body (nervous, endocrine and immune) do not operate in isolation, these systems are in constant communication, collaborating and co-ordinating their actions to maintain optimal physiological functions and defence against external threats. In this context the divisions between nervous, immune and endocrine systems are artificial and in effect they form a neuro-immuno-endocrine super-system.
Disruption of any component of this super-system can result in sub-optimal adaptive responses and diminished defences, leading to disease. Hence immune disorders may have origins in disrupted neuroendocrine control and neurological symptoms may result from dysregulated immunity. By the same token, potential therapeutic approaches to immune conditions may include modulation of neural and endocrine responses.
We now recognize that commensal microbes are integrated into the neuro-immuno-endocrine super-system, influencing adaptive responses and regulating multiple physiological systems (See the holobiont). For example microbes in the intestine can influence neural and endocrine components of gut brain communication (the vagus nerve and HPA axis) that in turn play key roles in modulating immune responses. Furthermore, gut bacteria can act on common mediators, receptors and cells, such as the mast cell, that facilitate cross-talk between nervous, immune and endocrine systems. While this adds to the complexity of an already intricate communication system it also opens the possibility that changes in neuroendocrine environment may have an important role in mediating effects of gut bacteria on systemic immunity.