The Immunology of Behavior—Exploring the Role of the Immune System in Brain Health and Illness

Advances in our understanding of immunology especially cellular immunology and cytokine biology have led to monumental changes in the practice of medicine. Indeed, elucidation of the pathways involved in T-cell regulation have led to a series of therapeutic agents referred to as ‘checkpoint inhibitors' that are revolutionizing the treatment of cancer. Similarly, the development of biological therapies that target cytokines and other mediators of the inflammatory response have changed the landscape of the treatment of autoimmune and inflammatory disorders. These developments have impacted millions of lives and represent some of the most important achievements of modern medicine. Not surprisingly, the revolution in immunology has made its way to the basic and clinical neurosciences with a growing appreciation of the role of the immune system in brain health and illness. From its participation in brain development to its contributions to adulthood disorders and neurodegeneration, the immune system as a major regulator of neuronal function throughout the life cycle has attracted significant attention, enough so to warrant its own special issue of Neuropsychopharmacology reviews. In this issue, we have attempted to give a sample of the important research being conducted in this area with an emphasis on (1) the fundamental mechanisms by which the immune system supports neuronal integrity, (2) the pathways by which the peripheral and central immune compartments become activated and communicate—especially in the context of stress, (3) the factors that represent risk and resilience for both immune dysregulation and behavioral change, (4) the impact of the immune system on neurotransmitter systems and neurocircuits that regulate behavior, and (5) the immunological contributions to developmental disorders and neurodegeneration. It should be noted, however, that throughout the issue it is emphasized that no mental disorder is fundamentally an immunological disorder, rather the point is repeatedly made that the immune system potentially participates in a subgroup of symptoms that cut across multiple psychiatric diseases. The therapeutic promise of targeting different facets of the immune system is also addressed in every review, and each review outlines the many gaps in our knowledge and what steps need to be taken to move the field forward