Psychoimmunology before its time

CNS–immune system interactions: Conditioning phenomena

Converging data from different disciplines indicate that central nervous system processes are capable of influencing immune responses. This paper concentrates on recent studies documenting behaviorally conditioned suppression and enhancement of immunity. Exposing rats or mice to a conditioned stimulus previously paired with an immunomodulating agent results in alterations in humoral and cell-mediated immune responses to antigenic stimuli, and unreinforced reexposures to the conditioned stimuli result in extinction of the conditioned response. Although the magnitude of such conditioning effects has not been large, the phenomenon has been independently verified under a variety of experimental conditions. The biological impact of conditioned alterations in immune function is illustrated by studies in which conditioning operations were applied in the pharmacotherapy of autoimmune disease in New Zealand mice. In conditioned animals, substituting conditioned stimuli for active drugs delays the onset of autoimmune disease relative to nonconditioned animals using a dose of immunosuppressive drug that, by itself, is ineffective in modifying the progression of disease. The hypothesis that such conditioning effects are mediated by elevations in adrenocortical steroid levels receives no support from available data. Despite its capacity for self-regulation, it appears that the immune system is integrated with other psychophysiological processes and subject to modulation by the brain.

Exercise as a Time-conditioning Effector in Chronic Disease: a Complementary Treatment Strategy

Exercise has been widely believed to be a preventive and therapeutic aid in the treatment of various pathophysiological conditions such as cardiovascular disease and cancer. A common problem associated with such pathologies is cachexia, characterized by progressive weight loss and depletion of lean and fat body mass, and is linked to poor prognosis. As this syndrome comprises changes in many physiological systems, it is tempting to assume that the modulation of the psychoneuroimmunoendocrine axis could attenuate or even prevent cachexia progression in cancer patients. Cancer cachexia is characterized by a disruption in the rhythmic secretion of melatonin, an important time-conditioning effector. This hormone, secreted by the pineal gland, transmits circadian and seasonal information to all organs and cells of the body, synchronizing the organism with the photoperiod. Considering that exercise modulates the immune response through at least two different mechanisms-metabolic and neuroendocrine-we propose that the adoption of a regular exercise program as a complementary strategy in the treatment of cancer patients, with the exercise bouts regularly performed at the same time of the day, will ameliorate cachexia symptoms and increase survival and quality of life.

On the development of psychoneuroimmunology

Psychoneuroimmunology, the study of interactions among behavioral, neural and endocrine, and immune processes, coalesced as an interdisciplinary field of study in the late 1970s. Some of the early research that was critical in establishing neuroanatomical, neurochemical and neuroendocrine pathways and functional relationships between the brain and the immune system is outlined here. These and subsequent studies have led to the general acknowledgment that the nervous and immune systems are components of an integrated system of adaptive processes, and that immunoregulatory processes can no longer be studied as the independent activity of an autonomous immune system. This paradigm shift in the study of immunoregulatory processes and the elaboration of the mechanisms underlying behaviorally induced alterations of immune function promise a better understanding and a new appreciation of the multi-determined etiology of pathophysiological states.

Effect of thyrotropin-releasing hormone on immune functions of peripheral blood mononuclear cells

The tripeptide thyrotropin-releasing hormone (TRH) works as a hypothalamic hormone, but is found also outside the brain in intrinsic nerve fibers of the gastrointestinal tract. There is evidence that TRH modulates the activity of immunocompetent cells, although there are only very few data on TRH-mediated immune effector functions. Since we could recently show that TRH inhibits monocyte activities we were also interested in other possible TRH modulated immune functions. Peripheral blood mononuclear cells (PBMC) from ten healthy subjects were cultured for 7 days and pulsed with 0.125 and 0.250 microgram/ml Pokeweed mitogen (PWM). 10(-12) to 10(-6) M TRH was added simultaneously with PWM. Lymphocyte proliferation [(3H]thymidine incorporation), interferon-gamma (IFN-gamma) activity (RIA) and immunoglobulin activities (IgG, IgM, IgA; ELISA) were determined in the supernatants. We could demonstrate a TRH-dependent decrease in PWM-pulsed IgG activity with significant (alpha = 0.05) values at 10(-8) and 10(-10) M (-29 +/- 6%/-16 +/- 3% for PWM 0.125 microgram/ml and -17 +/- 9%/-11 +/- 9% for PWM 0.250 microgram/ml). This inhibitory effect could be abolished by an anti-TRH antiserum. There was no TRH effect on IgM and IgA activities, IFN-gamma activity and lymphocyte proliferation compared with the PWM stimulated values alone. The described TRH effect on the polyclonal IgG response by PBMC gives further evidence for a functional link between the immune system and the endocrine system, although its underlying mechanism is not yet clear.

Effect of chronic stress on ENU-induced tumors

The relation of stress to cancer is the subject of considerable controversy. We studied the possible influence of chronic stress on the time of development and frequency of tumors induced in rats after a single exposure to ethylnitrosourea during prenatal life. Time of development, localization, incidence, type, and size of tumors were similar in stressed rats and in controls. Our results in this paradigm do not support the hypothesis that chronic stress exerts a potentiating effect on carcinogenesis.

Beginnings and main directions of psychoneuroimmunology

The present paper offers a survey of advances in the domain of psychoneuroimmunology. Major topics covered are the role of the nervous system in regulation of the immune system functions, neuromediator and neuroendocrine mechanisms for regulation of the lymphoid cell activity and hypothalamic involvement in modulation of the activity of bone marrow as a source of stem cells. Emphasis has been on the neurophysiological correlates of the organism's reaction to antigen. Attention has been given to the work of A.D. Speransky and discussion of the psychoneuroimmunologic research based on literature data and findings from our own studies is presented in the historical context.

Corticotropin releasing factor induction of leukocyte-derived immunoreactive ACTH and endorphins

Human peripheral leukocytes infected by virus or treated with endotoxin will, like unstimulated mouse spleen macrophages, synthesize immunoreactive corticotrophin (ir-ACTH) and endorphins. The ir-ACTH produced appears to be identical with authentic ACTH, while enough of the material has been produced in hypophysectomized mice infected with virus to demonstrate a steroidogenic response. Because the production of ACTH by in vivo pituitary cells and by leukocytes is suppressed by dexamethasone both in vitro and in vitro, suggesting that the production of ACTH and endorphins by leukocytes is indeed controlled, we have investigated the effects of corticotropin releasing-factor (CRF), which is known to regulate the pituitary production of both ACTH and beta-endorphin. We now report that the production of ACTH and endorphins by leukocytes is indeed induced by synthetic CRF and, in turn, suppressed by dexamethasone, suggesting that, as in pituitary cells, the proopiomelanocortin (POMC) gene may be expressed and similarly controlled in leukocytes.

Endocrine regulation of the immune system

Immunoregulation, the major process of self-defence, appears to be more complex than has been previously thought, involving the central nervous and endocrine systems. This review demonstrates growing evidence for the hypothesis that endocrine factors from the pituitary and hypothalamus directly influence the development and function of the immune system. Both pituitary and hypothalamic hormones interfere with lymphocyte proliferation and function. Proliferation of T-lymphocytes as well as production of immunoglobulins by plasma cells seem to be hormone dependent. Clinical observations suggest that hematological, oncological, and immunological disorders known for their immune pathogenesis are associated with alterations of the endocrine homeostasis. Recently, human peripheral mononuclear cells have been shown to possess specific receptors for pituitary hormones. It is hypothesized that proteohormones act directly on lymphocytes via specific membrane receptors. Thus, the endocrine system, closely related to cortical and subcortical centers in the central nervous system, is one of the body's instruments to regulate and modulate its immune response. This hypothesized immunoregulatory pathway via the central nervous system and endocrine glands may well be of importance for the body's defence against infectious and malignant diseases. In addition, a new picture of the complex immunoregulatory mechanisms emerges for a better understanding of the function of the immune system. However, there is no single hormone which has yet been identified as being crucial for development and/or function of the immune system. It appears from the literature that a number of various proteohormones rather than a single hormone acts on immunocompetent cells.