The Neuroimmune System in Psychiatric Disorders

The term “neuroimmune system” emphasizes the fact that nervous and lymphoid tissues constitute a unified system that functions in the maintenance of homeostasis. The conventional division between the two systems has blurred, as well as the distinction between neuropeptides on the one hand, and immune cytokines on the other. Two lines of research have altered our perspective on neuroimmune interactions: (a) the identification of conventional neuropeptides and their receptors, especially those related to the hypothalamic–pituitary–adrenal (HPA) axis, in most lymphoid tissues and (b) the large body of evidence that cytokines, historically associated with immune system communication, play vital roles in nervous function. The role of the HPA axis in coordinating responses to stressors and the role of the immune system in mediating the “sickness” response underscore this reciprocal relationship between the central nervous system and the immune system. Despite this nascent state of knowledge, the evidence for hyper-reactivity of the HPA axis and the alterations in cytokine levels observed in several psychiatric disorders including major depressive disorder, posttraumatic stress disorder, stress and anxiety disorders, schizophrenia, and addiction now serves as a foundation for further research establishing a causative relationship between alterations in immune system function and these debilitating psychiatric disorders. Lastly, newer studies showing the ability to target cytokines and neuropeptides as a therapeutic for these disorders have yielded promising results and provides a promising avenue of effective treatment for individuals with such disorders.