Two-way communication pathways between the brain and the immune system

Individual survival is achieved through a balance between mind and body. A dense network of soluble neuroendocrine and immune mediators exists to ensure close interactions. These hormones, cytokines, neurotransmitters all interact through positive and negative feed-forward and feed-back loops. The mediators, once considered specific to the central nervous system (CNS) or the immune system (IS), do in fact act in and can be recognized by both systems. Thus the brain, endocrine and immune systems share a number of ligands and receptors that use a common chemical language for communication within and between the CNS and the IS. These two systems can be regarded as sense organs. The IS responds to non-cognitive stimuli such as viruses, bacteria, tumors and carries the information concerning their presence to the CNS. The CNS, which reacts to and is modified by cognitive stimuli, transmits the relative information to the IS so it in turn can adapt as necessary. The present review focusses mainly on cytokines as examples of two-way regulators of neuroimmune communication.