Molecular identification of two types of interleukin-1 receptors in the murine pituitary gland

Endotoxin-Induced Inflammation Suppresses the Effect of Melatonin on the Release of LH from the Ovine Pars Tuberalis Explants-Ex Vivo Study

The secretion of the hormone melatonin reliably reflects environmental light conditions. Among numerous actions, in seasonal breeders, melatonin may regulate the secretion of the gonadotropins acting via its corresponding receptors occurring in the Pars Tuberalis (PT). However, it was previously found that the secretory activity of the pituitary may be dependent on the immune status of the animal. Therefore, this study was designed to determine the role of melatonin in the modulation of luteinizing hormone (LH) secretion from the PT explants collected from saline- and endotoxin-treated ewes in the follicular phase of the oestrous cycle. Twelve Blackhead ewes were sacrificed 3 h after injection with lipopolysaccharide (LPS; 400 ng/kg) or saline, and the PTs were collected. Each PT was cut into 4 explants, which were then divided into 4 groups: I, incubated with 'pure' medium 199; II, treated with gonadotropin-releasing hormone (GnRH) (100 pg/mL); III, treated with melatonin (10 nmol/mL); and IV, incubated with GnRH and melatonin. Melatonin reduced (p < 0.05) GnRH-induced secretion of LH only in the PT from saline-treated ewes. Explants collected from LPS-treated ewes were characterized by lower (p < 0.05) GnRH-dependent response in LH release. It was also found that inflammation reduced the gene expression of the GnRH receptor and the MT1 melatonin receptors in the PT. Therefore, it was shown that inflammation affects the melatonin action on LH secretion from the PT, which may be one of the mechanisms via which immune/inflammatory challenges disturb reproduction processes in animals.

LPS-induced inflammation potentiates the IL-1β-mediated reduction of LH secretion from the anterior pituitary explants

Acting at the level of the brain, interleukin- (IL-)1 β is considered to be one of the most potent downregulators of reproduction processes during immune/inflammatory challenge. IL-1 β suppresses gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus resulting in the inhibition of the luteinizing hormone (LH) release from the anterior pituitary (AP). However, the presence of IL-1 β receptors in the AP suggests the possible direct action of this cytokine on LH secretion. The study was designed to determine the effect of IL-1 β on the LH secretion from the AP explants collected from saline and LPS-treated ewes in the follicular phase. It was found that IL-1 β suppressed (P ≤ 0.01) GnRH-stimulated LH release and LH β gene expression in AP explants in both groups. However, IL-1 β action was more potent in the explants collected from LPS-treated animals. Pituitaries from LPS-treated animals were characterized by increased (P ≤ 0.01) IL-1 type I receptor and decreased (P ≤ 0.01) GnRH receptor gene expression level compared to the saline-treated group. IL-1 β also affected the GnRH-R gene expression in explants collected from LPS-treated animals. Our results show that direct action of IL-1 β on the pituitary gonadotropes could be one of the reasons of the reproductive processes disorders accompanying an inflammatory state.

Alcoholism and inflammation: neuroimmunology of behavioral and mood disorders

Alcohol abuse changes behavior and can induce major mood disorders such as depression. Recent evidence in pre-clinical rodent models and humans now supports the conclusion that the innate immune system is an important physiological link between alcoholism and major depressive disorders. Deficiency of toll-like receptor 4 (TLR4), a protein that has been known to immunologists for 50 years, not only prevents lipopolysaccharide (LPS)-induced sickness behavior but recently has been demonstrated to induce resistance to chronic alcohol ingestion. Activation of the immune system by acute administration of LPS, a TLR4 agonist, as well as chronic infection with Bacille Calmette-Guérin (BCG), causes development of depressive-like behaviors in pre-clinical rodent models. Induction of an enzyme expressed primarily in macrophages and microglia, 2,3 indoleamine dioxygenase, shunts tryptophan catabolism to form kynurenine metabolites. This enzyme is both necessary and sufficient for expression of LPS and BCG-induced depressive-like behaviors in mice. New findings have extended these concepts to humans by showing that tryptophan catabolites of 2,3 indoleamine dioxygenase are elevated in the cerebrospinal fluid of hepatitis patients treated with the recombinant cytokine interferon-α. The remarkable conservation from mice to humans of the impact of inflammation on mood emphasizes the ever-expanding role for cross-talk among diverse physiological symptoms that are likely to be involved in the pathogenesis of alcohol abuse. These findings present new and challenging opportunities for scientists who are engaged in brain, behavior and immunity research.

Inflammatory cytokines regulate glycoprotein subunit beta5 of thyrostimulin through nuclear factor-kappaB

Thyrostimulin is a heterodimeric hormone comprised of two glycoprotein hormone subunits, namely glycoprotein hormone subunit alpha2 and glycoprotein hormone subunit beta5 (GPB5). Immunological studies have revealed that both subunits colocalize in human pituitary corticotroph cells. Although recombinant thyrostimulin protein selectively activates the TSH receptor and has thyrotropic activity in rats, its biological functions have not been clarified. To explore the physiological regulators for the GPB5, the 5'-flanking region of the GPB5 coding sequence up to 3-kb upstream was analyzed by luciferase reporter assays. We found that nuclear factor-kappaB (NF-kappaB) markedly activated GPB5 transcription. Disruption of the putative NF-kappaB-binding motifs in the GPB5 5'-flanking region silenced the GPB5 activation by p65. Chromatin immunoprecipitation assays revealed that recombinant p65 bound to the predicted NF-kappaB-binding sites. Because NF-kappaB is known to associate with acute phase inflammatory cytokines, we examined whether TNFalpha or IL-1beta could regulate GPB5. Both these cytokines activated GPB5 transcription by 2- to 3-fold, and their effects were abolished by the addition of MG132, a NF-kappaB inhibitor. Our results suggest that inflammatory cytokines positively regulate thyrostimulin through NF-kappaB activation.

Immune modulation of the hypothalamic-pituitary-adrenal (HPA) axis during viral infection

Compelling data has been amassed indicating that soluble factors, or cytokines, emanating from the immune system can have profound effects on the neuroendocrine system, in particular the hypothalamic- pituitary-adrenal (HPA) axis. HPA activation by cytokines (via the release of glucocorticoids), in turn, has been found to play a critical role in restraining and shaping immune responses. Thus, cytokine-HPA interactions represent a fundamental consideration regarding the maintenance of homeostasis and the development of disease during viral infection. Although reviews exist that focus on the bi-directional communication between the immune system and the HPA axis during viral infection (188,235), others have focused on the immunomodulatory effects of glucocorticoids during viral infection (14,225). This review, however, concentrates on the other side of the bi-directional loop of neuroendocrine-immune interactions, namely, the characterization of HPA axis activity during viral infection and the mechanisms employed by cytokines to stimulate glucocorticoid release.

Cytokine-induced sickness behaviour: a neuroimmune response to activation of innate immunity

Sickness refers to a coordinated set of subjective, behavioural and physiological changes that develop in sick individuals during the course of an infection. These changes are due to the effects of interleukin-1 (IL-1) and other proinflammatory cytokines on brain cellular targets. Sickness behaviour is mediated by proinflammatory cytokines that are temporarily expressed in the brain during infection. These centrally produced cytokines are the same as those expressed by innate immune cells and they act on brain receptors that are identical to those characterized on immune cells. Primary afferent nerves represent the main communication pathway between peripheral and central cytokines. Proinflammatory cytokines modulate learning and memory processes. The expression and action of proinflammatory cytokines in the brain in response to peripheral cytokines are regulated by various molecular intermediates including anti-inflammatory cytokines such as interleukin-10 (IL-10) and the IL-1 receptor antagonist (IL-1ra), growth factors such as insulin-like growth factor-1 (IGF-1), hormones such as glucocorticoids and neuropeptides such as vasopressin and alpha-melanotropin.

NF kappa B activation in mouse pituitary: comparison of response to interleukin-1 beta and lipopolysaccharide

The mouse anterior pituitary contains both types of interleukin (IL)-1 receptors, IL-1 receptor type I (IL-1RI) and IL-1 receptor type II (IL-1RII). These receptors are expressed mainly on somatotroph cells. In the present study, the ability of the mouse pituitary to respond in vivo to IL-1 or to lipopolysaccharide (LPS) was demonstrated by measuring, with an electrophoretic mobility shift assay, the presence of an active NF kappa B complex in cell nuclei from pituitaries of mice injected intraperitoneally with recombinant rat-IL-1 beta or LPS. Using immunohistochemistry with an antibody directed against the p65 NF kappa B subunit, a rapid and transient NF kappa B response to LPS was observed. This response was present predominantly in the nuclei of glial fibrillary acidic protein (GFAP)-positive cells and F4/80-labelled cells of the posterior and the anterior pituitary 15 min after stimulation and became faint after 2 h. In comparison, the early and strong NF kappa B response to IL-1 beta treatment was localized into somatotroph cells, GFAP positive cells and F4/80-labelled cells of the posterior and anterior pituitary. Activation of NF kappa B in response to IL-1 beta was no longer apparent in IL-1RI knockout mice, confirming that this receptor is essential for the transduction of IL-1 signal in the pituitary, but remained after LPS treatment. In addition, we investigated the effect of IL-1 on target genes by measuring the mRNA and proteins synthesis of growth hormone (GH), IL-6 and IL-1ra in the pituitary and the plasma. IL-1 beta was shown to induce a rapid and strong synthesis of IL-6 and IL-1ra in the pituitary but failed to regulate GH contents or release. These data suggest that the pituitary is able to respond to a systemic infection via cytokine-mediated responses transduced by IL-1.

Co-localization of interleukin-1 receptor type I and interleukin-1 receptor antagonist with vasopressin in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus

Interleukin-1 receptor type I and interleukin-1 receptor antagonist were found in magnocellular neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus by immunohistochemical detection. Double-labelling experiments revealed that both proteins occurred in vasopressin-containing neurons. A similar distribution pattern was observed in a group of vasopressin-positive accessory magnocellular neurons. Axons emanating from the interleukin-1 receptor type I- and interleukin-1 receptor antagonist-immunoreactive neuronal cell bodies could be seen within the hypothalamic nuclei, and varicosities expressing interleukin-1 receptor antagonist immunoreactivity were observed in the internal zone of the median eminence, as well as in the hypothalamo-pituitary projection. The co-localization of interleukin-1 receptor type I with vasopressin is in agreement with findings that interleukin-1 has a stimulatory effect on vasopressin synthesis and release. The hypothalamic neurons may serve as a source of interleukin-1 receptor antagonist to balance the effects of interleukin-1.

Cytokines in the neuroendocrine system

Cytokines are important partners in the bidirectional network interrelating the immune and the neuroendocrine systems. These substances and their specific receptors, initially thought to be exclusively present in the immune system, have recently been shown to be also expressed in the neuroendocrine system. Cytokines can modulate the responses of all endocrine axes by acting at both the central and the peripheral levels. To explain how systemic cytokines may gain access to the brain, several mechanisms have been proposed, including an active transport through the blood-brain barrier, a passage at the circumventricular organ level, as well as a neuronal pathway through the vagal nerve. The immune-neuroendocrine interactions are involved in numerous physiological and pathophysiological conditions and seem to play an important role to maintain homeostasis.

Expression and localization of p80 and p68 interleukin-1 receptor proteins in the brain of adult mice

The biological effects of interleukin-1 (IL-1) are mediated by two distinct receptors, the p80 type I IL-1 and p68 type II IL-1 receptor proteins (IL-1RI and IL-1RII, respectively), both of which have been recently co-localized to the growth hormone synthesizing cells of the adenohypophysis. Previous studies have shown that IL-1 can bind to specific structures in the central nervous system, but the distribution of IL-1RI and IL-1RII proteins in the adult mouse brain has not been reported. Here we have used immunohistochemistry to study the expression, distribution and cellular localization of both isoforms of the IL-1 receptor proteins in the adult mouse brain. Using a combination of processing techniques (AMeX fixation and cryosectioning), we have immunolabeled brain sections for each isoform of the IL-1R. Both isoforms are expressed in the CNS, particularly in neuronal soma of the granular layer of the dentate gyrus and pyramidal cells of fields CA1-CA4 of Ammon's horn of the hippocampus, in epithelial cells of the choroid plexus and ependymal layer, and in neuronal soma of Purkinje cells of the cerebellum. The IL-1RII isoform, but not IL-1RI, is expressed in specific neuronal soma and proximal cell processes of neurons of the paraventricular gray matter of the hypothalamus. These immunohistochemical data directly demonstrate the neuronal expression of both IL-1R proteins in situ. The distribution and cellular localization of IL-1R proteins in the CNS provide a molecular basis for understanding reciprocal interactions between the immune system and the brain.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

Pathophysiological role of the cytokine network in the anterior pituitary gland

Recent evidence has demonstrated that cytokines and other growth factors act in the anterior pituitary gland. Using the traditional criteria employed to determine autocrine or paracrine functions our review shows that, in addition to their role as lymphocyte messengers, certain cytokines are autocrine or paracrine regulators of anterior pituitary function and growth. The cytokines known to regulate and/or be expressed in the anterior pituitary include the inflammatory cytokine family (IL-1 and its endogenous antagonist, IL-1ra; TNF-alpha, and IL-6), the Th1-cytokines (IL-2 and IFN-gamma), and other cytokines such as LIF, MIF, and TGF-beta. This review examines at the cellular, molecular, and physiological levels whether: (1) each cytokine alters some aspect of pituitary physiology; (2) receptors for the cytokine are expressed in the gland; and (3) the cytokine is produced in the anterior pituitary. Should physiological stimuli regulate pituitary cytokine production, this would constitute additional proof of their autocrine/paracrine role. In this context, we analyze in this review the current literature on the actions of cytokines known to regulate anterior pituitary hormone secretion, selecting the in vivo studies that support the direct action of the cytokine in the anterior pituitary. Further support for direct regulatory action is provided by in vitro studies, in explant cultures or pituitary cell lines. The cytokine receptors that have been demonstrated in the pituitary of several species are also discussed. The endogenous production of the homologous cytokines and the regulation of this expression are analyzed. The evidence indicating that cytokines also regulate the growth and proliferation of pituitary cells is reviewed. This action is particularly important since it suggests that intrinsically produced cytokines may play a role in the pathogenesis of pituitary adenomas. The complex cell to cell communication involved in the action of these factors is discussed.

Immune-endocrine interactions in the mammalian adrenal gland: facts and hypotheses

Several cytokines, which are the major mediators of the inflammatory responses, are well-known to stimulate the hypothalamopituitary corticotropin-releasing hormone (CRH)/adrenocorticotropic hormone (ACTH) system, thereby evoking secretory responses by the adrenal cortex. Many of these cytokines, including interleukin-1 (IL-1), IL-2, IL-6, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (INF-gamma) are synthesized in the adrenal gland by both parenchymal cells and resident macrophages, and the release of some of them (e.g., IL-6 and TNF-alpha) is regulated by the main agonists of steroid hormone secretion (e.g., ACTH and angiotensin-II) and bacterial endotoxins. Adrenocortical and adrenomedullary cells are provided with specific receptors for IL-1, IL-2, and IL-6. IL-1 and TNF-alpha directly inhibit aldosterone secretion of zona glomerulosa cells, whereas IL-6 enhances it. IL-2, IL-3, IL-6, and INF-alpha are able to directly stimulate glucocorticoid production by zona fasciculata and zona reticularis cells, whereas IL-1 exerts an analogous effect through an indirect mechanism involving the stimulation of catecholamine release by chromaffin cells and/or the activation of the intramedullary CRH/ACTH system; again, TNF-alpha depresses glucocorticoid synthesis. IL-6 raises androgen secretion by inner adrenocortical layers. IL-1 enhances the proliferation of adrenocortical cells, and findings suggest that cytokines may control the apoptotic deletion of senescent zona reticularis cells. The relevance of the intraadrenal cytokine system in the fine-tuning of the secretion and growth of the adrenal cortex under normal conditions remains to be explored. However, indirect proof is available that local immune-endocrine interactions may play an important role in modulating adrenal responses to inflammatory and immune challenges and stresses.

Interleukin-1 beta enhances interleukin-1 receptor antagonist content in human somatotroph adenoma cell cultures

In addition to the well-known modulation of immune and inflammatory responses, the interleukin-1 (IL-1) system has been shown to be involved in the regulation of anterior pituitary hormone secretion and growth. We previously demonstrated that IL-1 receptor antagonist (IL-1ra) is expressed in human pituitary adenomas cultured in vitro. In the present study, we investigated the regulation of IL-1ra protein by IL-1 beta (1-100 U/mL) in human somatotroph adenomas (n = 9) cultured for 12-48 h. IL-1 beta significantly enhanced the concentration of IL-1ra dose dependently in the somatotroph adenoma cell lysates, whereas IL-1ra concentrations remained unchanged in the culture supernatants. Furthermore, basal IL-1ra concentrations were significantly higher in the cell lysates compared with the corresponding culture supernatants. The regulation of IL-1ra in somatotroph adenoma cells is different from human cultured monocytes, in which IL-1 beta significantly stimulated IL-1ra secretion into the culture supernatants, and no change of intracellular IL-1ra content was observed. Incubation of the somatotroph adenoma cells with 100 U/mL IL-1 beta did not result in a change of GH concentrations in the culture supernatants. Enhancement of intracellular IL-1ra protein by IL-1 beta may represent a mechanism intrinsic to somatotroph adenoma cells to counterregulate the response to IL-1 beta on hormone secretion or cellular growth.

Cytokine expression and molecular mechanisms of their auto/paracrine regulation of anterior pituitary function and growth

The pituitary gland expresses cytokines and their receptors. IL-2 receptor transcripts and protein products are co-localized in ACTH-, PRL-, and GH-producing cells (double immunofluorescence). IL-2 and IL-6 (1-1000 IU/ml) are involved in the autocrine/paracrine regulation of normal and tumor (GH3 mammosomatotroph cell line and adenoma cell cultures) anterior pituitary hormone-producing cell growth (cell number, DNA synthesis, c-fos mRNA expression and autoradiography combined with hormone staining). IL-1 regulates the growth of normal pituitary cells but does not act on GH3 cells. IL-1ra, which blocks this action, is expressed in tumoral pituitary (mainly GH- and ACTH-) cells. In ACTH- cells, IL-1 enhances glucocorticoid feedback, stimulating glucocorticoid response element transcriptional activity. Cytokines, through specific functional receptors, act as inter/auto-cellular factors that regulate not only the function but also the growth of anterior pituitary cells.

Tumor necrosis factor receptors in the pituitary cells

To clarify the site and mode of action of tumor necrosis factor (TNF) in the pituitary, we studied the effects, binding sites of TNF and its receptor mRNA in the two types of mouse pituitary-derived cell lines, AtT-20, ACTH-producing cells and TtT/GF, folliculo-stellate (FS)-like cells. First, we examined the expression of TNF receptor mRNA in these cells. Using Northern blot analyses with radiolabeled cDNA to murine TNF receptor p60 and p80 mRNAs as probes, we identified both types of mRNA in the poly(A)-containing RNA prepared from AtT-20 cells and p60 TNF receptor mRNA from TtT/GF. The identified mRNA were compatible in size with those detected in the immune-competent cells. Next, we studied the TNF-binding sites on these cells. Scatchard plot analysis of the significant binding of [125I]TNF revealed a single type of binding site with a Kd (dissociation constant) of 210 pM and 131 binding sites/cell on AtT-20. Similarly on TtT/GF, [125I]TNF showed 353 binding sites/cell with a Kd of 900 pM. [125I]TNF binding on both types of cells competed with TNF and lymphotoxin (TNF beta) in an equimolar fashion. Third, TNF stimulates ACTH synthesis in AtT-20 cells, while TNF increases immunoreactive interleukin (IL)-6 release from TtT/GF cells. These findings demonstrate that AtT-20 and TtT/GF cells are equipped with fully functional TNF receptor system, and suggest that ligand of the receptor, TNF alpha and/or TNF beta, can modulate ACTH synthesis and release as a direct hormonal effector on corticotrophs or indirect modulator through another paracrine mediator, such as IL-6 from FS cells.

Neurobehavioral alterations in autoimmune mice

Inbred MRL, NZB and BXSB strains of mice spontaneously develop a systemic, lupus-like autoimmune disease. The progress of autoimmunity is accompanied with a cascade of behavioral changes, most consistently observed in tasks reflective of emotional reactivity and the two-way avoidance learning task. Given the possibility that behavioral alterations may reflect a detrimental consequence of autoimmune-inflammatory processes and/or an adaptive response to chronic malaise, they are tentatively labeled as autoimmunity-associated behavioral syndrome (AABS). It is hypothesized that neuroactive immune factors (pro-inflammatory cytokines, brain-reactive antibodies) together with endocrine mediators (corticotropin-releasing factor, glucocorticoids) participate in the etiology of AABS. Since AABS develops natively, and has a considerable face and predictive validity, and since the principal pathway to autoimmunity is known, AABS may be a useful model for the study of CNS involvement in human autoimmune diseases and by extension, for testing autoimmune hypotheses of several mental disorders (major depression, schizophrenia, Alzheimer's disease, autism and AIDS-related dementia).

Pituitary cytokine and growth factor expression and action

The complex range of pituitary regulatory mechanisms reviewed here underlies the critical function of the pituitary in sustaining all higher life forms. Thus, the ultimate net secretion of pituitary hormones is determined by signal integration from all three tiers of pituitary control. It is clear from our current knowledge that the trophic hormone cells of the anterior pituitary are uniquely specialized to respond to these signals. Unravelling their diversity and complexity will shed light upon the normal function of the master gland. Understanding these control mechanisms will lead to novel diagnosis and therapy of disordered pituitary function (357).

Hormones, lymphohemopoietic cytokines and the neuroimmune axis

The classical distinction between hormones and cytokines has become increasingly obscure with the realization that homeostatic responses to infection involve coordinated changes in both the neuroendocrine and immune systems. The hypothesis that these systems communicate with one another is supported by the ever-accruing demonstrations of a shared molecular network of ligands and receptors. For instance, leukocytes express receptors for hormones and these receptors modulate diverse biological activities such as the growth, differentiation and effector functions. Leukocyte lineages also synthesize and secrete hormones, such as insulin-like growth factor-I (IGF-I), in response to both growth hormone (GH) and also to cytokines such as tumor necrosis factor-alpha (TNF-alpha). Since hormones share intracellular signaling substrates and biological activities with classical lymphohemopoietic cytokines, neuroendocrine and immune tissues share a common molecular language. The physiological significance of this shared molecular framework is that these homeostatic systems can intercommunicate. One important example of this interaction is the mechanism by which bacterial lipopolysaccharide, by eliciting a pro-inflammatory cytokine cascade from activated leukocytes, modulate pituitary GH secretion as well as other CNS-controlled behavioral and metabolic events. This article reviews the cellular and molecular basis for this communication system and proposes novel mechanisms by which neuroendocrine-immune interactions converge to modulate disease resistance, metabolism and growth.

Differential effects of IL-1ra on sickness behavior and weight loss induced by IL-1 in rats

Peripheral and central injections of recombinant human interleukin-1 beta (IL-1 beta) have been shown to decrease social exploration and to induce body weight loss in rats. To characterize the receptor mechanisms of these effects, we used as a tool a specific antagonist of the receptors of IL-1, IL-1ra. Intraperitoneal (i.p.) administration of IL-1ra (8 mg/kg) blocked the effect of i.p. injection of IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 micrograms/rat, i.c.v.) abrogated the effects of centrally administered IL-1 beta (30 ng/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 micrograms/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1 beta on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.

Interleukin-1 beta and tumour necrosis factor-alpha stimulate the mRNA expression of interleukin-1 receptors in mouse anterior pituitary AtT-20 cells

The RT-PCR technique was used to study IL-1 receptor mRNA levels in AtT-20 cells. IL-1 beta increased type I IL-1 receptor mRNA levels within 1 h, with elevated levels remaining after 24 h, whereas it induced a bell-shaped alteration of type II IL-1 receptor mRNA levels, with a peak after 6 h. Tumour necrosis factor-alpha (TNF alpha) similarly up-regulated type II IL-1 receptor mRNA levels, and type I IL-1 receptor mRNAs albeit to a lesser extent than IL-1 beta. Furthermore, IL-1 beta also induced increases in TNF alpha and c-fos mRNAs. The IL-1 receptor antagonist can fully block all the above effects of IL-1 beta. Up-regulation of type II IL-1R mRNA levels in AtT-20 cells could constitute an important way to modulate IL-1 actions, since type II IL-1R is believed to antagonize IL-1 effects.

Characterization of Interleukin-2 (IL-2) receptor expression and action of IL-2 and IL-6 on normal anterior pituitary cell growth

The pituitary gland is known to express cytokines and their receptors. Interleukin-2 (IL-2) and IL-2 receptor (IL-2R) transcripts and protein products in corticotrophic cells have been previously described. IL-2R were also observed in PRL and GH-producing cells. The synthesis of IL-1 and IL-6 and their receptors by pituitary cells has also been reported. We recently demonstrated that the cytokines in addition to their regulatory effects on anterior pituitary hormone secretion are involved in the autocrine or paracrine regulation of pituitary growth. In the present study we show in normal rat anterior pituitary cells: (a) expression of IL-2Rα chain mRNA, (b) the co-localization of IL-2Rα chain with TSH, FSH and LH-producing cells, (c) the percentage of co-localization of IL-2R with all types of anterior pituitary hormone producing cells: PRL> > > ACTH> > GH> TSH = FSH = LH. (d) that [(3)H]-thymidine is incorporated into the nucleus of all types of hormoneproducing cells without incorporation into other cell types, following IL-2 and IL-6 stimulation. Our results suggest that IL-2 acts on all types of anterior pituitary hormone-producing cells and, through specific functional receptors on the same or other cells, constitutes, as well as IL-6, an inter or intra-cellular factor involved in the coordinate regulation not only of hormone secretion but also of the proliferation of anterior pituitary hormone-producing cells.

Peripheral administration of lipopolysaccharide induces the expression of cytokine transcripts in the brain and pituitary of mice

The reverse transcription polymerase chain reaction (RT-PCR) was used to assess the induction of mRNA of the proinflammatory cytokines IL-1 beta, IL-6 and TNF alpha in the spleen, pituitary, hypothalamus and hippocampus of mice after an intraperitoneal injection of lipopolysaccharide (LPS, 10 micrograms/mouse). The kinetics of cytokine gene expression induced by peripheral LPS in the pituitary and brain structures were different from that observed in the spleen. For IL-1 beta the dose-response curve was also measured and also found to be different. These results support the idea that one pathway by which peripheral immune stimuli affect brain functions includes local synthesis of proinflammatory cytokines in certain brain structures.

The syntax of immune-neuroendocrine communication

There is now overwhelming evidence that cytokines, peptide hormones and neurotransmitters, as well as their receptors, are endogenous to the brain, endocrine and immune systems. Here, Edwin Blalock discusses how these shared ligands and receptors are used as a common chemical language for communication within and between the immune and neuroendocrine systems. Such communication suggests an immunoregulatory role for the brain and a sensory function for the immune system. A clearer understanding of this circuitry is dramatically altering our understanding of physiology and may profoundly affect the treatment of human disease.

Expression of type I and type II interleukin-1 receptors in mouse brain

Although binding sites for IL-1 have been identified in the mouse brain, it is still unknown whether these binding sites correspond to the type I or type II IL-1 receptor. Quantitative autoradiography was used to confirm the presence of specific binding sites for radiolabelled recombinant human IL-1 alpha (125I-HuIL-1 alpha) in the brain of DBA/2 mice. IL-1 binding was highest in the dentate gyrus, consisting of a single class of high affinity binding sites with a Kd of 0.1 nM and a Bmax of 57 fmol/mg protein. A similar Kd of 0.2 nM was obtained using isolated membranes from the whole hippocampus, although the number of binding sites was lower (2 fmol/mg protein). Affinity cross-linking of 125I-Hu-IL-1 alpha to hippocampal membranes revealed the existence of two types of IL-1 receptor proteins, consistent with the sizes of the type I (85 kD) and type II (60 kD) IL-1 receptor. Oligonucleotide probes were then synthesized and used in RT-PCR followed by Southern blotting to show that the whole brain expresses transcripts for both the type I and type II IL-1 receptors. The murine neuroblastoma cell line, C1300, expresses type I rather than type II IL-1 receptor mRNA. The type I receptor protein can be identified by flow cytometry on the membrane of the C1300 neuronal cell line using indirect immunofluorescence with a rat anti-mouse type I IL-1 receptor MoAb. These data show that mouse brain expresses both type I and type II IL-1 receptor mRNA and proteins and offer further support to the idea that type I IL-1 receptors are synthesized and expressed by neurons.

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)

Riboprobe expression cassettes for measuring IGF-I, beta-actin and glyceraldehyde 3-phosphate dehydrogenase transcripts

The development of riboprobe expression cassettes for phosphorimager-based quantitation of steady-state transcripts for three different genes using solution hybridization, RNase protection assays is described. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and beta-actin genes are widely used as reporter genes to estimate the amount and integrity of RNA as well as for comparing gene expression among different tissues. To directly compare expression of these two genes in lymphoid tissue and liver, cDNA fragments of beta-actin and GAPDH from both mice and rats were generated by RT-PCR and cloned together into pGEM1 under control of the T7 RNA polymerase promoter. Antisense transcripts from this fusion construct protected the appropriate-sized fragments of beta-actin (115 nt) and GAPDH (214 nt) in RNA isolated from rat spleen, thymus and liver. Expression of GAPDH transcripts was less variable across tissues because this mRNA was only two-fold lower in liver as compared to either thymus or spleen, whereas expression of beta-actin transcripts was eight-fold lower in liver than in these tissues. Two other riboprobe expression cassettes (IGF-I/actin) were constructed by ligating a cDNA fragment of mouse or rat beta-actin that would protect 115 nt to either a mouse or rat IGF-I genomic DNA fragment containing 182 bp of exon 4. These mouse and rat IGF-I/actin riboprobes were used to conclusively demonstrate that rat CSF-1-derived bone marrow macrophages, mouse elicited peritoneal macrophages and the murine PU5-1R macrophage cell line synthesize abundant transcripts for both IGF-I and beta-actin. However, the mouse M1 progenitor myeloid cell line does not express RNA for IGF-I, as demonstrated by the absence of protected transcripts for IGF-I in the presence of abundant protected transcripts for beta-actin. Phosphorimager scanning of the gels revealed that macrophages of both mice and rats express IGF-I transcripts at a level of 60-100% of those found in liver. These data show that a single riboprobe can be developed to generate multigene antisense RNAs that can then be used to quantitatively compare IGF-I transcripts in macrophages and other tissues to an internal standard, with GAPDH transcripts being less variable among tissues than those for beta-actin. This approach should be broadly applicable for measuring a variety of markers of cellular activation.