Interactions between the nervous and immune systems.

Substantial morphologic and functional evidence exists that supports the reciprocal interactions that occur between the nervous and immune systems. The nervous and immune systems have been increasingly found to use a common chemical language in the form of neuropeptides, cytokines, and hormones. Sophisticated immunologic techniques such as the identification and detection of immune cell surface markers enable researchers to determine the origin and activity of diverse cells in the blood and central nervous system. These techniques have elucidated the activity of immune cells in the central nervous system (CNS) that was previously thought to be privileged from immune surveillance in the presence of an intact blood brain barrier. Immune cells in the CNS play a central role in several degenerative diseases such as Alzheimer's disease, Huntington's disease, Multiple sclerosis, AIDS dementia complex, and nerve destruction associated with trauma. Immune cells also play a role in demyelinating peripheral nerve disorders. Cytokines and neuropeptides secreted by peripheral immune cells have profound effects on behavior that is mediated by the CNS. The close integration between immune and nervous system responses is being increasingly recognized in physiologic and pathologic conditions.