Psychoneuroimmunology: potential relevance to chronic orofacial pain.

Studies undertaken over the past ten years have demonstrated that stress and depression can induce immune alterations, including decreased numbers of immunocompetent cells and impaired lymphocyte and natural killer cell activity. Factors such as age and severity of symptomatology influence these effects. The substantial stress and depression associated with chronic pain syndromes and the evidence for opioid involvement in immunomodulation suggest that immune system changes may occur in some patients with chronic facial pain.