Stress-related modulation of immunity: a review of human studies.

The assumption that life changes and stressful events can alter host defense is based mainly on studies of changes in a variety of immune and inflammatory reactions. Whether those changes also confer an increased susceptibility to infectious agents and neoplasms, or modify the course of such diseases, is still less well substantiated. Nonetheless, psychological and neural modulation of immunity has recently been possible to approach from a mechanistic viewpoint. For instance, generation of a variety of lipid mediators from arachidonic acid may be under control of dietary and endocrine factors that can be affected by stress. Since these lipids, eg, lipoxygenase products, are potent regulators of leukocyte functional responses, their significance as one of several mechanisms is discussed. The role of various neuropeptides in leukocyte function has only recently been discovered. Since the release of, eg, substance P, enkephalins, and endorphins, which all have modulating effects on leukocyte functional responses, is under neural control and can occur in the vicinity of immunocompetent cells, they might constitute one of several links between the mind and the immune system.