Bidirectional communication between the brain and the immune system.

There is now a substantial body of data available indicating that the brain, the nervous system, and the immune system are functionally connected. Consequently, environmental conditions of a psychosocial or physical nature may influence the body's defence. The magnitude of the change in immune reactivity is partly determined by the individual's evaluation of the psychological or physical stimulus. This is illustrated by pharmacological modification of perception resulting in more pronounced stress-induced immunomodulation. In man, it has been demonstrated that recently experienced life stress, particularly daily hassles, can codetermine the effect of an experimental stressor applied for a short period of time on the immune system. An intriguing finding relates to the synthesis and secretion of hormones and neuropeptides by immune cells. These chemical messengers act as autocrine or paracrine immunoregulatory molecules on the one hand, and as messengers for communication with the brain and peripheral nervous system on the other. Animal research indicates that this dialogue is of biological significance.