The role of the immunoendocrine interaction via the hypothalamo-pituitary-adrenal axis in autoimmune disease Emphasis on the obese strain chicken model

Effect of migratory cycle and 17beta-estradiol on splenic leukocyte functions in female black-headed gulls

The immune function of wild birds is practically unknown. We have studied several functions of splenic leukocytes from the gull Larus ridibundus. Considering that avian physiology is strikingly affected by the seasonal migratory cycle, those functions were analyzed throughout the seasonal cycle. The functions assayed were: adherence to substrate, chemotaxis and lymphoproliferative response to mitogens. Estrogens have been reported to modulate the immune response in mammals; therefore serum levels of 17beta-estradiol were measured in order to find a putative effect of this hormone on the immune response of female gulls. According to our results, gull splenic leukocytes showed a response similar to that reported in mammals and poultry. In regard to the effect of the seasonal migratory cycle, when the gulls arrived from the migratory flight they showed an immunosuppression as we have obtained in chemotaxis and proliferations assays. The immune response increased during the resting period and especially in the premigratory period. We have found a lack of a direct effect of the age of the animals or even the serum estrogen levels in the immune response of the migratory gulls. These results suggest the existence of other hormones and releasing factors, which would modulate the immune response in gulls, or a unique major effect due to the long flight effort.

Seasonal changes in peripheral blood leukocyte functions of the turtle Mauremys caspica and their relationship with corticosterone, 17-beta-estradiol and testosterone serum levels

We have studied the most representative functions of lymphocytes such as adherence to substrate, mobility directed to a chemoattractant gradient (chemotaxis), proliferative response to mitogens and antibody-dependent cellular cytotoxicity (ADCC), as well as natural killer (NK) activity in peripheral blood cells from the turtle Mauremys caspica, and the seasonal changes of these functions in both female and male animals. The plasma levels of steroid hormones were determined to study their relationship with the immune functions. Our results show high chemotaxis, lymphoproliferative response and ADCC as well as NK activity in winter when the levels of corticosterone, testosterone and 17-beta-estradiol were depleted. Proliferative responses to phytohaemagglutinin (PHA), concanavalin A (Con A) and pokeweed mitogen (PWM) were increased in spring correlating with low levels of corticosterone and testosterone in middle and late spring. In summer, the proliferative response was decreased but adherence, chemotaxis, ADCC and NK activity were increased, although steroid hormones showed high plasma levels. In autumn, a depletion of both the hormone levels and the immune response were found except for adherence to substrate. The immune functions studied were strikingly influenced by the seasonal cycle, which induced a different pattern of response depending on the function analyzed. Moreover, these immune cells showed a different degree of dependence on steroids in relation to the function and the season considered, suggesting the existence of other factors that modulate the immune response studied.

How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions

The secretion of glucocorticoids (GCs) is a classic endocrine response to stress. Despite that, it remains controversial as to what purpose GCs serve at such times. One view, stretching back to the time of Hans Selye, posits that GCs help mediate the ongoing or pending stress response, either via basal levels of GCs permitting other facets of the stress response to emerge efficaciously, and/or by stress levels of GCs actively stimulating the stress response. In contrast, a revisionist viewpoint posits that GCs suppress the stress response, preventing it from being pathologically overactivated. In this review, we consider recent findings regarding GC action and, based on them, generate criteria for determining whether a particular GC action permits, stimulates, or suppresses an ongoing stress-response or, as an additional category, is preparative for a subsequent stressor. We apply these GC actions to the realms of cardiovascular function, fluid volume and hemorrhage, immunity and inflammation, metabolism, neurobiology, and reproductive physiology. We find that GC actions fall into markedly different categories, depending on the physiological endpoint in question, with evidence for mediating effects in some cases, and suppressive or preparative in others. We then attempt to assimilate these heterogeneous GC actions into a physiological whole.

The aging immune system: primary and secondary alterations of immune reactivity in the elderly

The function of the immune system is known to decline in the elderly. The present communication will show that, similar to the situation in children, it is necessary to distinguish between primary and secondary alterations of the immune reactivity in the elderly. The primary immunological change in the elderly is the age-dependent intrinsic decline of immune responsiveness that is also observed in healthy persons, i.e., those selected according to the criteria of the SENIEUR Protocol of EURAGE (European Community Concerted Action on Aging). Secondary immunological changes are due to underlying diseases and various environmental factors, including diet, drug intake, physical activity, etc. While primary immunodeficiencies of the elderly are not, or only to a very minor extent, presently influenced by therapeutic measures, secondary alterations of the immune function offer further possibilities for corrective measures. Clinically, the consequences of impaired immune function in the elderly include increased susceptibility to infectious disease, the emergence of tumors, and increased autoimmune reactions, the latter albeit often without concomitant autoimmune disease. In fact, autoimmune diseases in generally begin to develop at younger ages, but their consequences are major factors affecting the quality of life of the elderly. Investigations of basic molecular and cellular aspects of the aging immune system are, therefore, of theoretical, clinical and socioeconomic interest.

IL-1 is expressed in human adrenal gland in vivo. Possible role in a local immune-adrenal axis

IL-1 is an important mediator in the dialogue between the immune system and the hypothalamo-pituitary-adrenal axis. A direct influence of IL-1 upon adrenal steroidogenesis has been demonstrated in experimental animals. We therefore designed a study to see if IL-1 is expressed within the normal human adrenal gland. The combination of in situ hybridization and specific immunostaining to IL-1 beta was eminently suited to demonstrate both mRNA and protein production. The specific immunostaining of the different cells combined with in situ hybridization (IL-1) allowed us to identify the exact cellular source of IL-1. IL-1 mRNA occurred in the zona reticularis in 17 alpha-hydroxylase positive steroid cells surrounding the adrenomedullary cells. Some CD68+ macrophages in this zona showed a positive signal. A weak signal was seen to IL-1 mRNA in few chromaffin cells, while IL-1-like immunoreactivity was more frequent. We conclude that in the normal situation in man IL-1 is mainly expressed in specialized cortical cells. The occurrence of the major glucocorticoid inducing factor in the normal human adrenal gland itself provides evidence for an autocrine or paracrine reaction under physiological conditions.

Neuroendocrine-immune interactions in homeostasis and autoimmunity

Recent experimental evidence confirms the interrelationships between the central nervous, neuroendocrine and immune systems. Indeed, extensive duality exists in the use of neurotransmitters, hormones and receptors each system displays. In the present annotation, the effect of cytokines, soluble mediators of immune function, on the CNS and neuroendocrine systems is addressed and conversely, we discuss the modification of the immune compartment by the sympathetic nervous and neuroendocrine systems, with particular reference to the role of noradrenaline and corticosterone. Dysfunction between the systems is considered in the context of autoimmune conditions, with emphasis on experimental allergic encephalomyelitis and the contribution of corticosterone-driven T-cell apoptosis to recovery from the disease. Finally, we speculate on the relevance of neuroimmune interactions in the pathogenesis of multiple sclerosis.

Immunology discovers physiology

Not so long ago, it was believed that the brain is totally devoid of immunologic reactions, that cytokines derived from activated leukocytes serve only as communication molecules between leukocytes and that the immune system is regulated solely by intrinsic mechanisms. One by one, these old-time, traditional views have fallen by the wayside as neuroscientists, endocrinologists and pharmacologists have begun to explore immunology. The old view was that the immune system is autonomous because it neither affects nor is it affected by other physiologic systems. The new view is that cells of the immune system are inextricably linked with other physiological systems, including the neuroendocrine, cardiovascular, reproductive and central nervous systems (CNS). Changes in one system evoke changes in the other, and it is likely that communication loops have evolved between cells of the immune system and those of other tissues to coordinate and regulate functional activities aimed at preserving homeostasis during inflammation. The integrated view of immunophysiologists that cells of the immune system interact with the entire body, rather than existing as a separate physiologic system that operates autonomously, should help to unravel a number of mysteries in immunoregulation, such as the well-recognized redundant and pleiotropic properties of cytokines. Unfortunately, very few of these ideas have been incorporated into studying immunity of domestic animals. A complete understanding of immunobiology will be achieved only after this new field of immunophysiology is integrated into current immunological thinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-release inhibitory factor Evidence for dual stimulatory and inhibitory hypothalamic regulation over adrenocorticotropin secretion and biosynthesis

The hypothalamus is currently thought to stimulate the synthesis and secretion of ACTH uniquely by secreting neuropeptides into the hypophysial-portal circulation, of which the most important are CRH and arginine vasopressin. However, analysis of the effects of pituitary isolation on the pituitary-adrenal axis in a variety of species suggests that the hypothalamus exerts both stimulatory and inhibitory regulation over ACTH secretion and POMC biosynthesis, and that the inhibitory control is dominant. Because none of the currently known inhibitory factors in the hypophysial-portal circulation consistently decreases basal ACTH secretion and POMC mRNA levels in normal anterior pituitary cells, it is suggested that this inhibition is mediated by a currently unidentified hypothalamic substance, presumably a neuropeptide, which we have termed corticotropin-release inhibitory factor (CRIF). The possible roles in clinical medicine of agonists and antagonists of this putative CRIF are discussed.

Interleukin-1 receptor deficiency in brains from NZB and (NZB/NZW)F1 autoimmune mice

Interleukin-1 receptors (IL-1R) are expressed in the brain and the anterior pituitary of normal mice (C3H/He, Swiss), and appear to be involved in the neuroendocrine control of the immune response. Here we have studied the IL-1R density in the brain and the pituitary from several strains of autoimmune mice (NZB, (NZB/NZW)F1, MRL/MP-lpr), using quantitative autoradiography with recombinant human [125I]IL-1 alpha as a ligand. IL-1R was similar in the brain of C3H/He, Swiss and NZW (controls) and MRL/MP-lpr mice. In NZB mice a profound deficit (10% of control mice) in IL-1R was observed exclusively in the dentate gyrus. In (NZB/NZW)F1 the deficit was about 50%. These observations were independent of sex and age. Pituitary receptors were not affected in all the strains except NZW (30% increase). Competition experiments demonstrated that the affinity of IL-1R was not modified in dentate gyrus of (NZB/NZW)F1 and NZW mice. Thus, the number of IL-1R was the only parameter affected. This deficit was not reversed by corticosterone treatment (0.2 mg/20 g body weight, i.p.) and was poorly modified by lipopolysaccharide treatment (0.1 mg/20 g body weight, i.p.) compared to C3H/He mice. In conclusion, this central IL-1R deficit is unlikely to be the consequence of occupancy by abnormal synthesis of brain IL-1. This abnormality is tissue-specific with hereditary autosomal transmission. The role of central IL-1R in neuroimmunoendocrine interactions and in autoimmunity remains to be clarified.