EDITORIAL COMMENT Psychoneuroimmunology and Immunotoxicology: Implications for Carcinogenesis

A number of researchers have documented an association between depression and immunological dysregulation (1, 2). Extending this line of work, Jung and Irwin (3) reported a provocative and potentially important finding: Major depression interacted with cigarette smoking to promote lower natural killer (NK) cell activity. Among 245 men, NK cell activity was similar in nondepressed smokers and nonsmokers; however, smokers who met diagnostic criteria for major depression had lower NK cell activity than depressed nonsmokers. Thus, immune changes could not be attributed to the simple effects of smoking. These data are notable for several reasons. First and foremost, they address the question of depression as a risk factor for cancer, and suggest new avenues for exploration (3). However, they also have broader implications for the burgeoning field of immunotoxicology—they highlight the importance of assessing psychological variables such as depression or stress as cofactors in investigations of hazard identification and risk assessment (4). We consider each of these issues in turn.