Delayed effects of stress and immune activation

Stress responses play a crucial adaptive role but impose potentially subver sive demands on the organism. The same holds for the symptoms of illness as seen after immune activation by pathogens or tissue damage. The responses to immune stimuli and stressors show remarkable similarities and rely on si milar control mechanisms in the brain: i.e. they involve neuropeptides of t he corticotropin releasing factor (CRF) family. Immune and non-immune chall enges lead to responses that normally show a temporal relationship with the duration and intensity of the stimulus and the (re)activity of the stress- responsive systems return to their pre-challenged state within hours or day s. However, exposure of animals or man to specific stimuli can induce delay ed and long-lasting (weeks, months) alterations in stress responsive system s, resulting in a prolonged period of increased stress vulnerability. Immun e stimuli are particularly powerful in eliciting such a stress vulnerable s tate. Various adaptive changes in the (neuro)biological substrate as seen d uring this stress vulnerable state also occur in depression, and may be cau sally related to the depressive symptoms that are often associated with inf ectious and inflammatory diseases.