J Neurol (2007) 254 [Suppl 2]: II/8–II/11 DOI 10.1007/s00415-007-2003-8 Tjalf Ziemssen Simone Kern Psychoneuroimmunology – Cross-talk between the immune and nervous systems Introduction Psychoneuroimmunology (PNI) is the scientific field of study investigating the link between bidirectional com- munications among the nervous system, the endocrine and immune system as well as the implications of these linkages for physical and mental health, thereby fo- cussing on the measurable interaction between psycho- logical and physiological processes. The CNS and the immune system are the two major adaptive entities of the body. Although the immune system has often been regarded as autonomous, the last two to three decades have provided strong evidence that the CNS receives messages from the immune system [10].Vice versa there is substantial evidence for a brain-derived information outflow to the immune system [3, 18]. Thus, the brain and the immune system are involved in functionally relevant cross-talk,with homeostasis be- ing the main function. These two systems communicate through intricate chemical messengers that are able to breach their independent and often sequestered anatom- ical locations. The CNS is without ‘classical’ lymphatic drainage, meaning that in some ways it is devoid of the immune surveillance that is available for the rest of the body. In health there are mechanisms to exclude poten- JON 2003 ■ Abstract Psychoneuroimmunol- ogy is a relatively new field of study that investigates interactions be- tween behaviour and the immune system, mediated by the endocrine and nervous systems. The immune and central nervous system (CNS) Dr. T. Ziemssen () · S. Kern MS Center Dresden, Neuroimmunological laboratory Neurological Clinic, University Clinic Carl- Gustav Carus Dresden Fetscherstr. 74 01307 Dresden, Germany Tel.: +49-351/458-3859 Fax: +49-351/458-5873 E-Mail: Ziemssen@web.de maintain extensive communica- tion. On the one hand, the brain modulates the immune system by hardwiring sympathetic and parasympathetic nerves (auto- nomic nervous system) to lym- phoid organs. On the other hand, neuroendocrine hormones such as corticotrophin-releasing hormone or substance P regulate cytokine balance.Vice versa, the immune system modulates brain activity in- cluding sleep and body tempera- ture. Based on a close functional and anatomical link, the immune and nervous systems act in a highly reciprocal manner. From fever to stress, the influence of one system on the other has evolved in an in- tricate manner to help sense dan- ger and to mount an appropriate adaptive response. Over recent decades, reasonable evidence has emerged that these brain-to-im- mune interactions are highly mod- ulated by psychological factors which influence immunity and im- mune system-mediated disease. ■ Key words psychoneuroim- munology · autonomic nervous system · neuroendocrinology · stress · behavioural intervention Fig. 1 Reciprocal relationship between the CNS and immune system cytokines NPs NPs Hormones Neurotransmitters Immune system Central nervous system