Stress and infections

Neurotransmitters and neuroendocrine hormones can modify the functioning of immune cells and conversely cytokines produced by immune cells can alter brain homeostasis. This connection is further manifested by experimental studies showing a relationship between stress and resistance to infection. Human subjects with a high stress index were shown to be more susceptible to infection with common cold viruses. Furthermore, a diversity of experimental animal paradigms show that laboratory stressors such as forced exercise, avoidance learning, restraint, isolation, and cold exposure make animals more susceptible to primary infection with a variety of viruses and bacteria. The cellular and molecular basis for the observed modulation of host resistance is not fully understood but involves altered functioning of both T lymphocytes and cells of the hypothalamic-pituitary adrenal axis. Also involved is the altered production of cytokines and hormones produced by the immune system and brain.