Leukocytes and other types of cells produce proteins or glycoproteins, termed cytokines, that serve as chemical communicators from one cell to another. Neuromediators are able to modulate functions of immune cells and other cells and the relationship between the central nervous system (CNS) and the endocrine system have been known for many years. Communication between nerves and immune and inflammatory cells plays a major role in the modulation of several dysfunctions including ion transport, mucosal permeability and cytokine production. Cytokines are involved in both injury and repair, and the conditions underlying these distinct outcomes are under intense investigation and debate. Evidence from medical studies implicates the immune system in a number of psychiatric disorders with known or suspected developmental origins, including schizophrenia, anxiety-depression, and cognitive dysfunction.