Interleukin-2 induction of ACTH secretion: presence of an interleukin-2 receptor alpha-chain-like molecule on pituitary cells

Compatibility of porcine and human interleukin 2: implications for xenotransplantation

BACKGROUND

Xenotransplantation provides a possible solution to the severe shortage of allogeneic organ donors. The pig, which shares many physiological similarities with humans, makes it an optimal species for preclinical experimentation and clinical applications. Interleukin 2 (IL2) is a potent growth factor secreted primarily by T helper lymphocytes and it is vital to the cellular expansion required for a productive immune response and the development and peripheral expansion of CD4+CD25+ regulatory T cells. Therefore, it is essential to understand of the compatibility of IL2 between pigs and humans.

METHODS

We first compared the cDNA and protein sequences and the crystal structures of human and porcine IL2 and IL2 receptors, respectively. The effect of IL2 to induce T cell proliferation was determined by 3H-thymidine incorporation and cell cycle detection.

RESULTS

Porcine IL2 induced very limited proliferation of human lymphocytes while it functioned well on porcine lymphocytes. Human IL2 had remarkably reduced effects on porcine lymphocytes whereas it worked well on human lymphocytes.

CONCLUSION

Our present study showed that the interaction of IL2 and IL2R across species might have defects. Together with the wide physiological functions of IL2, our data indicated that physiological disorders could be caused by the poor function of xenogeneic donor IL2 on host cells in full hematopoietic chimera. Our data suggested an additional potential advantage for the mixed xenogeneic chimeras.

Plasticity of neuroendocrine-thymus interactions during ontogeny and ageing: role of zinc and arginine

Thymic re-growth and reactivation of thymic functions may be achieved in old animals by different endocrinological or nutritional manipulations such as, (a) treatment with melatonin, (b) implantation of a growth hormone (GH) secreting tumour cell line (GH3 cells) or treatment with exogenous GH, (c) castration or treatment with exogenous luteinizing hormone-releasing hormone (LHRH), (d) treatment with exogenous thyroxin or triiodothyronine, and (e) nutritional interventions such as arginine or zinc supplementation. These data strongly suggest that thymic involution is a phenomenon secondary to age-related alterations in neuroendocrine-thymus interactions and that it is the disruption of these interactions in old age that is responsible for age-associated immune-neuroendocrine dysfunctions. The targets involved in hormones-induced thymic reconstitution may directly or indirectly involve hormone receptors, cytokines, arginine, and a trace element such as zinc, which is pivotal for the efficiency of neuroendocrine-immune network during the whole life of an organism. The effect of GH, thyroid hormones, and LHRH may be due to specific hormone receptors on thymocytes and on thymic epithelial cells (TECs), which synthesize thymic peptides. Melatonin may also act through specific receptors on T-cells. In this context, the role of zinc, which turnover is reduced in old age, is pivotal because of its involvement through zinc fingers in the gene expression of hormone receptors. In addition, the effects of zinc are multifaceted: from the reactivation of zinc-dependent enzymes, to cell proliferation and apoptosis, to cytokines expression and to the reactivation of thymulin, which is a zinc-dependent thymic hormone required for intrathymic T-cell differentiation and maturation as well as for the homing of stem cells into the thymus. Zinc is also required for arginine action, via NO pathway. The role of zinc is therefore crucial in neuroendocrine-thymus interactions. According to data in animals and humans, the above reported endocrinological manipulations (GH, thyroid hormones, and melatonin) or arginine treatment may also act via zinc pool in restoring thymic activity in ageing allowing improvements on peripheral immune efficiency.

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.

Effects of interleukin-2 on the expression of corticotropin-releasing hormone in nerves and lymphoid cells in secondary lymphoid organs from the Fischer 344 rat

This study examined the influence of interleukin (IL)-2 on corticotropin releasing hormone (CRH) immunoreactivity in the Fischer 344 (F344) rat spleen. Rats were given either vehicle or 1, 10, 25, 50, 100, or 200 ng of human recombinant (hr)IL-2 by intraperitoneal (i.p.) injection, and were sacrificed 0.5, 1, 4, 12, or 24 h after treatment. Spleens and mesenteric lymph nodes were prepared for immunocytochemistry to localize CRH. In spleens from vehicle-treated animals, CRH immunoreactivity was present in several types of cells of the immune system, but CRH(+) nerves were not observed in either spleens or lymph nodes from vehicle-treated animals. Treatment with IL-2 induced CRH expression in nerves in the spleen in a dose- and time-dependent manner. CRH(+) nerves were not found in the mesenteric lymph nodes after IL-2 treatment, instead a dramatic time- and dose-dependent accumulation of CRH(+) cells (resembling small lymphocytes and large granular mononuclear cells) in the cortex and medulla. These findings indicate that IL-2 stimulates the synthesis of CRH in nerves that innervate the F344 rat spleen, and promote the appearance of CRH(+) immunocytes into draining mesenteric lymph nodes.

Increased serum-soluble interleukin-2 receptor in burn patients: characterization and effects on the immune system

The consequences of high serum concentrations of the interleukin (IL)-2 receptor alpha chain (sIL-2Ralpha) in several diseases are poorly understood. The objective of this study was to determine the form of sIL-2Ralpha in burn patients and its biological role. sIL-2Ralpha was measured in 18 severely burned individuals who received nutritional support with a normal or low fat content. sIL-2Ralpha was elevated throughout the study and it was notably lower in patients fed a low fat diet. Serum IL-6 and sIL-2Ralpha significantly correlated (r = 0.74, p < 0.05) in burn patients. The presence of sIL-2Ralpha was associated with a decrease in DR molecules in the CD2(-) and CD11b(+) cells of these patients. Western blot analysis of serum protein with N-terminal or C-terminal specific antibodies indicated that sIL-2Ralpha represents the extracellular domain of this molecule. Patient serum inhibited specifically murine, but not human IL-2-dependent T-cell proliferation. To determine the significance of sIL-2Ralpha, recombinant sIL-2Ralpha was used in different cellular model involving IL-2. sIL-2Ralpha inhibited natural killer cell activity by 50% in the presence of IL-2. The basal proliferation of peripheral blood mononuclear cells was inhibited by sIL-2Ralpha, but phytohemagglutinin-induced proliferation was unaffected by this form of receptor. Interferon (INF)-gamma production induced by OKT-3 on peripheral blood mononuclear cells was not altered by sIL-2Ralpha, but IL-2 induced increase in INF-gamma production was suppressed. The decreasing production of INF-gamma in the presence of IL-4 was significantly increased in the presence of sIL-2Ralpha in media. These results show that the large amount of sIL2-Ralpha circulating in burn patients is related to the inflammatory response. The amount of dietary fat modulates sIL2Ralpha concentration in burn patients, confirming the beneficial effect of low fat administration after burn trauma. Inhibition of T-cell activation in burn patients is not directly related to sIL-2Ralpha, although the presence of sIL-2Ralpha in serum can inhibit some IL-2 mediated response, such as the emergence of TH1 and TH2 cells.

Central monoamine activity following acute and repeated systemic interleukin-2 administration

Interleukin-2 (IL-2), together with other cytokines, may be involved in communication between the immune system and the CNS. Moreover, IL-2 alterations have been implicated in psychiatric disorders, and IL-2 immunotherapy may engender neuropsychiatric and cognitive disturbances. Given the presumed relationship between mood disturbances and monoamine activity, the present investigation was undertaken to determine the central monoamine alterations associated with acute and repeated systemic IL-2 administration in mice. Acute, systemic IL-2 (0.55-17.6 x 10(3) IU) did not influence plasma adrenocorticotropic hormone or corticosterone levels, but increased the utilization of norepinephrine (NE) within the paraventricular nucleus of the hypothalamus. In contrast to the effects of acute IL-2 administration, when administered repeatedly (for 7 days), IL-2 increased NE utilization within the median eminence plus arcuate nucleus and in the hippocampus, and to a lesser extent in the central amygdala and medial prefrontal cortex. These changes in utilization were accompanied by increased levels of NE within the median eminence plus arcuate nucleus and central amygdala, and reduced NE within the locus coeruleus. As well, serotonin (5-hydroxytryptamine; 5-HT) levels were altered within the hippocampus and prefrontal cortex, and dopamine turnover was reduced within the caudate and substantia nigra. The finding of altered central neurotransmitter activity needs to be considered in the context of the marked cognitive/memory impairments, as well as the neuropsychiatric symptoms, which are associated with IL-2 immunotherapy in humans.

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.

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.

Immunoneuroendocrine connectivity: the paradigm of the thymus-hypothalamus/pituitary axis

It is now largely established that the immune and neuroendocrine systems cross-talk by using similar ligands and receptors. In this context, the thymus-hypothalamus/pituitary axis can be regarded as a paradigm of connectivity in both normal and pathological conditions. For example, cytokines and thymic hormones modulate hypothalamic-pituitary functions: (a) interleukin (IL)-1 seems to upregulate the production of corticotropin-releasing factor and by adrenocorticotropin by hypothalamic neurons and pituitary cells, respectively; (b) thymulin enhances LH secretion. Conversely, a great deal of data strongly indicate that the hypothalamic-pituitary axis plays a role in the control of thymus physiology. Growth hormone (GH) for example, enhances thymulin secretion by thymic epithelial cells (TEC), both in vivo and in vitro, also increasing extracellular matrix-mediated TEC/thymocyte interactions. Additionally, gap junction-mediated cell coupling among TEC is upregulated by ACTH. In a second vein, it was shown that GH injections in aging mice increased total thymocyte numbers and the percentage of CD3-bearing cells, as well concanavalin-A mitogenic response and IL-6 production. In addition to mutual effects, thymus-pituitary similarities for cytokine and hormone production have been demonstrated. Cytokines such as IL-1, IL-2, IL-6, interferon-gamma, transforming growth factor-beta and others can be produced by hypothalamic and/or pituitary cells. Conversely, hormones including GH, PRL, LH, oxytocin, vasopressin and somatostatin can be produced intrathymically. Moreover, receptors for various cytokines and hormones are expressed in both the thymus and the hypothalamus/pituitary axis. Lastly, it is noteworthy that a thymus-pituitary connectivity can also be seen under pathological situations. In this regard, an altered HPA axis has been reported in AIDS, human falciparum malaria and murine rabies, that also show a severe thymic atrophy.

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.

The role of neuroendocrine immune interactions in the initiation of humoral immunity in chickens

The presence of neuroendocrine immune interaction in mammalian species has been studied extensively and has been established. However, such an interaction is not as well established in avian species. Furthermore, the role of such an interaction in the initiation of humoral immunity is not well understood. Therefore, the present studies were conducted to determine mechanisms involved in the initiation of humoral immunity in chickens. Cornell K-strain White Leghorn immature male chickens were used for all the experiments. Changes in hormonal and leukocyte profiles after antigen stimulation were studied. The ability of different leukocytes to produce ACTH was also investigated. It was concluded that the first step in the initiation of humoral immunity after antigen exposure is the release of interleukin-1 by macrophages, which in turn stimulates the production of CRF by hypothalamus and/or leukocytes. It is important to mention that CRF production could also be a direct effect of antigen stimulation. The CRF will then stimulate ACTH production by anterior pituitary and/or leukocytes. In addition, CRF will directly enhance lymphocyte activities in the spleen. Corticosteroid production will be stimulated by ACTH and will cause redistribution of lymphocytes from circulation to secondary lymphoid organs such as the spleen for antigen processing and eventual production of antibodies against the invading antigens. Finally, both ACTH and corticosteroids will later act in a negative feedback manner to regulate and control the process of antibody production by inhibiting lymphocyte activities and/or reducing the responsiveness to different stimuli.

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.

Cyclosporine A affects open field behavior in DA rats

Since the introduction of Cyclosporine A (CsA) for immunosuppression in solid-organ transplantation, the rate of allograft rejection has decreased substantially. However, treatment with CsA induces neuropsychological complications in patients, including affective disorders such as anxiety, disorientation, depression, aggression, paranoia, and apathy. These CsA-induced affective side effects cannot be extensively studied in humans. Therefore, this study investigates the effects of intraperitoneal CsA (20 mg/kg) injections on the open-field behavior of male Dark Agouti (DA) rats 1, 6, 12, and 23 h after drug administration on 3 consecutive days. CsA induced an increase in emotionality in DA rats 6 h after injection, reflected by decreased ambulatory activity in the open field and increased defecation. In addition, a decrease in rearing activity was observed 12 h after CsA administration. These behavioral alterations are discussed in the view of changes in cytokine profiles induced by CsA.

Molecular cloning of the cDNA coding sequence of IL-2 receptor-gamma (gammac) from human and murine forebrain: expression in the hippocampus in situ and by brain cells in vitro

IL-2 has been implicated in various neurobiological processes of the mammalian CNS. To understand how IL-2 acts in the brain, our lab has sought to determine the molecular pharmacological characteristics of brain IL-2 receptors (IL-2R). The lymphocyte IL-2Rgamma, an essential subunit for IL-2 signaling, is also a common subunit (gammac) for multiple immune cytokine receptors (e.g., IL-4R, IL-7R, IL-9R, IL-15R). Having previously cloned the alpha and beta subunits of the IL-2R heterotrimer complex from normal murine forebrain, we examined the hypothesis that the brain IL-2Rgamma is derived from the same or a closely related gene coding sequence as that expressed by lymphocytes. In this study, we cloned and sequenced the full-length IL-2Rgamma coding region from saline-perfused mouse forebrain and from a human hippocampal library. The cDNA sequences of IL-2Rgamma from human and murine brain were 100% homologous to their lymphocyte sequences. Northern blot analysis showed that the mRNA transcripts in murine brain were the expected size, but the predominant transcript expressed in the brain was different than in the spleen. Compared to the spleen, very low levels of IL-2Rgamma were expressed in the forebrain. In the murine hippocampus, a region where a number of neurobiological actions of IL-2 have been reported, IL-2Rgamma mRNA was detected over the dentate gyrus and CA1-CA4 by in situ hybridization histochemistry. IL-2Rgamma was found to be constitutively expressed by murine HN33.dw hippocampal neuronal cells, murine NB41A3 neuroblastoma cells, astrocyte-enriched mixed glial cell cultures, and in SCID mouse forebrain. The human cortical neuronal cell lines, HCN-1A and HCN-2, did not express the IL-2Rgamma gene. These data suggest the possibility that, in addition to being essential in IL-2 signaling in brain, IL-2Rgamma could be a common subunit (gammac) for multiple cytokine receptors which may be operative in the mammalian CNS.

Neurotoxic consequences of central long-term administration of interleukin-2 in rats

Interleukin-2 is an immunoregulatory cytokine with several recently established CNS activities. Central effects of interleukin-2 include growth promotion for neuronal and glial cells as well as modulatory influences on neurotransmission and hormone release. However, little is known about the consequences in the CNS of chronically elevated levels of interleukin-2. Alterations in the interleukin-2/interleukin-2 receptor system are not only associated with CNS trauma, inflammation and certain neuropathologies; elevated interleukin-2 concentrations are especially induced during the therapeutic use of interleukin-2 in cancer treatments. In the present study, intracerebroventricular (i.c.v.) interleukin-2 infusions (5 15 U/h) were performed in Sprague Dawley rats for up to 14 days. Interleukin-2-treated animals showed significantly increased plasma levels of corticosterone indicating an hyperfunctioning of the hypothalamic-pituitary-adrenocortical axis that lasted over the 14 day infusion period. Moreover, the performance of interleukin-2-treated animals in the Morris swim maze task was transiently impaired. Quantitative receptor autoradiographic analyses revealed changes in the binding levels of cholinergic M1 and M2 as well as dopaminergic D1 and D2 receptors in selected brain areas in which interleukin-2 was shown to modulate neurotransmission and which are enriched with interleukin-2 receptor expression. Decreased receptor binding levels were observed in the frontoparietal cortex (M2, D1, D2), hippocampal CA1 region (M1, M2) and the nucleus accumbens (D2). Histological and immunohistochemical examination of the brains of interleukin-2-treated animals revealed multiple alterations. Interleukin-2 treatment resulted in an intracranial accumulation of non-neural, MHC class II-positive cells as well as T and B lymphocytes within the infused brain hemisphere. Cellular infiltrates were associated with angiogenesis and the deposition of extracellular matrix material, such as fibronectin. Adjacent brain regions that were partly invaded and dislodged by the cellular masses were characterized by reactive astrogliosis, microglial activation, endothelial upregulation of adhesion molecules, myelin damage and neuronal loss. Together the data suggest that persistently elevated central levels of interleukin-2 can interfere with several CNS functions and may lead to nervous tissue injury. These findings could be relevant to CNS pathologies characterized by abnormal interleukin-2 production and to central responses to interleukin-2 treatments.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

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.

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.

Interleukin-2 and interleukin-2 receptor expression in human corticotrophic adenoma and murine pituitary cell cultures

The production of IL-1 and IL-6 by pituitary cells has recently been demonstrated. In this study we investigated the expression of IL-2 and its receptor (IL-2R) by pituitary cells of different species. In Northern blots, a single hybridizing band of 1 kb, identical to that in normal stimulated lymphocytes, was obtained with specific IL-2 probes. In the mouse AT-20 pituitary tumor cell line, IL-2 mRNA expression was detected after stimulation with corticotropin-releasing hormone or phorbol myristate acetate. In human corticotrophic adenoma cells, basal IL-2 mRNA expression as well as IL-2 secretion were further stimulated by phorbol myristate acetate. Both adenoma and AtT-20 cells showed detectable amounts of IL-2R mRNA and by immunofluorescence, IL-2R membrane expression. In addition, dual immunofluorescence studies in rat anterior pituitary cells demonstrated colocalization of IL-2R with ACTH-positive cells and other cell types expressing the receptor. In addition to the action of lymphocyte-produced IL-2, this cytokine may have a paracrine or autocrine regulatory role within the pituitary. It remains to be established whether IL-2 production occurs in the normal pituitary or is intrinsic to the process of tumor development of these cells. IL-2 may be involved in the growth control of pituitary cells.

Bellini, Carpaccio, and receptors in the central nervous system

With the convergence of science from the fields of neurobiology and immunology, many exciting and challenging surprises have emerged regarding cytokines, neuroendocrine hormones, neuropeptides, excitatory amino acids, and their receptors. For some time neurobiologists have known that subsets of neural cells had different receptors for the same ligand. Those subsets of cells could be as different as neurons and astrocytes and as closely related as astrocytes from different lineages or anatomical areas. The neurobiological puzzle has been to determine the functional meaning of these differences. Immunologists in contrast have long understood the clear cut differences between T and B lymphocytes or T helper/inducer and T cytotoxic/suppressor cells and their response to cytokines. However, it is only very recently that they have discovered preferential use by these cells of different receptors for an identical cytokine ligand. Indeed, identical cytokines in the central nervous system and immune response may induce their pleiotropic responses by utilizing different receptors in these two systems. Immunologic paradigms may help neurobiologists predict the existence of subsets of neural cells and their function. Likewise, neurobiology may enable immunologists to predict roles for receptors in gene families as well as the existence of as yet unidentified receptors.

Immunoregulators in the nervous system

The nervous system, through the production of neuroregulators (neurotransmitters, neuromodulators and neuropeptides) can regulate specific immune system functions, while the immune system, through the production of immunoregulators (immunomodulators and immunopeptides) can regulate specific nervous system functions. This indicates a reciprocal communication between the nervous and immune systems. The presence of immunoregulators in the brain and cerebrospinal fluid is the result of local synthesis--by intrinsic and blood-derived macrophages, activated T-lymphocytes that cross the blood-brain barrier, endothelial cells of the cerebrovasculature, microglia, astrocytes, and neuronal components--and/or uptake from the peripheral blood through the blood-brain barrier (in specific cases) and circumventricular organs. Acute and chronic pathological processes (infection, inflammation, immunological reactions, malignancy, necrosis) stimulate the synthesis and release of immunoregulators in various cell systems. These immunoregulators have pivotal roles in the coordination of the host defense mechanisms and repair, and induce a series of immunological, endocrinological, metabolical and neurological responses. This review summarizes studies concerning immunoregulators--such as interleukins, tumor necrosis factor, interferons, transforming growth factors, thymic peptides, tuftsin, platelet activating factor, neuro-immunoregulators--in the nervous system. It also describes the monitoring of immunoregulators by the central nervous system (CNS) as part of the regulatory factors that induce neurological manifestations (e.g., fever, somnolence, appetite suppression, neuroendocrine alterations) frequently accompanying acute and chronic pathological processes.

Neurohormonal immunoregulation

The immune system may be divided into primary lymphoid organs (bone marrow, bursa of Fabricius, and thymus), which produce mature leukocytes and secondary organs (spleen, lymph nodes, tonsils, Peyer's patches, etc.), which are concerned with specific immune responses. In the primary organs, stem cells proliferate and differentiate into various subsets of polymorphonuclear and mononuclear cells. Evidence is increasing that cell proliferation in the primary lymphoid organs is dependent on pituitary growth hormone (GH) and prolactin (PRL), which control the expression of growth regulatory genes (protooncogenes) such as c-myc and also induce essential growth factors (insulinlike growth factor, thymic and bursal hormones, etc.) and, possibly, their receptors. The adrenocorticotropic hormone-adrenal axis serves as an inhibitory pathway, antagonizing the action of PRL and GH on primary lymphoid tissue. The effect of glucocorticoids is especially forceful on thymocytes through the activation of the genetically programmed suicide pathway. Sex hormones also regulate the primary lymphoid organs, but their mechanism of action remains to be clarified. Thymus-derived feedback signals toward the pituitary gland have already been described. The pituitary gland exerts a similar regulatory influence on mature lymphocytes during their antigen-driven differentiation. PRL or GH is required for primary immune reactions; however, the secondary immune response may be less dependent on these hormones. Once the immune system is primed, antigen itself becomes a primary regulator. Exposure of memory cells to antigen leads to the production of growth factors (interleukins) and to the expression of their receptors. Therefore, antigen appears to fulfill, at this stage, a role that is originally played by GH or PRL in the primary lymphoid organs and, to some extent, also during antigen-driven differentiation. During immune reactions, interleukin-1 and tumor necrosis factor activate the adrenocorticotropic hormoneadrenal axis, which plays an important role in setting upper limits to and terminating responses. Lymphocytes have receptors for and react to numerous hormones, neurotransmitters, and mediators derived from a number of organs and tissues. Therefore, ultimately the reaction of a lymphocyte will be the vector of all positive and negative signals received. A hierarchy and sequential system of signals exists. Primary regulatory signals (competence signals) represent the most powerful regulators (e.g., PRL, GH or antigen) of lymphoid cells. The delivery of a competence signal is the prerequisite for subsequent lymphoproliferation, which is regulated by growth factors that are specific for a certain developmental stage of the lymphoid cell and act sequentially. Hormonal factors that promote growth and differentiation deliver the second regulatory signals. Competence factors and growth and differentiation hormones regulate gene expression in lymphocytes. The third class of signals modulate the function of mature effector cells (e.g., locomotion, secretion, phagocytosis, cytotoxicity). Neuro-transmitters appear to function as secondary signal modulators and tertiary functional regulators.

Cytokine modulation of pituitary hormone secretion

A rapidly expanding body of evidence indicates that cytokines do indeed regulate pituitary hormone secretion. Recent studies with cytokines in vivo and in vitro support the idea that cytokines are the principal mediators of the neuroendocrine responses previously observed in infectious and inflammatory states. The dominant route of this modulation appears to be via the brain and hypothalamus, although a role for direct effects on the pituitary has not been excluded. These effects may be mediated by circulating cytokines, endogenously produced cytokines, or both. A number of receptor systems and second messengers may be involved, and a role for arachidonate metabolite pathways appears particularly likely. A final question: Of what use to the organism is the ability of immune activation to control pituitary hormone secretion? For some pituitary secretions there is a reasonable basis for speculation. Glucocorticoids serve to limit the severity of immune responses and recent studies argue that defects in this pathway permit the expression of autoimmune disease. Inhibition of thyroid function may limit the catabolic side effects of infectious illness. Stimulation of growth hormone could have the same effect, and growth hormone and prolactin may serve to enhance some immune responses.

Interleukins, signal transduction, and the immune system-mediated stress response

Overwhelming evidence indicates that the administration of cytokines such as IL-1 alpha and beta, IL-6, and TNF-1 alpha stimulates one or more components of the HPA axis. The hypothesis driving this research is that host infection and tissue injury trigger the synthesis and release of several cytokines that act locally at sites of trauma and distally upon entering the circulation. Available evidence suggests that the primary source of HPA axis-acting or circulating cytokines is activated monocytes or macrophages; therefore, a direct relationship should exist between the appearance of monokines in plasma and the subsequent appearance of pituitary-adrenocortical hormones in plasma as well. Clarification of the physiological role of monokines as mediators of the host stress response will come from in vivo studies in which the type, sequence of appearance, duration of elevation, and quantification of each monokine is monitored along with ACTH and glucocorticoids, following an appropriate immune challenge. In several recent reports, investigators have administered bacterial-derived endotoxin or LPS to stimulate the physiological events associated with infection or injury and chronicled plasma levels of IL-1, IL-6, and TNF-alpha (37,56,57). In human subjects, endotoxin challenge enhanced plasma TNF-alpha levels by 1 hour, which returned to basal levels by 4 hours (37), whereas, IL-6 plasma activity increased at 2 hours post-challenge and returned to baseline by 6 hours (56). Thus, both of these monokines are implicated as possible acute activators of the HPA axis. In perhaps the most revealing study to date, LPS challenge of mice indicated both a differential appearance and disappearance rate in serum for TNF-alpha and IL-1 and a differential regulation of these monokines by glucocorticoid feedback (57). Serum TNF was detected 45 minutes post-LPS, peaked by 1 hour, and returned to control levels by 3 hours. Serum corticosterone concentrations rose rapidly over a time course similar to that of TNF. Even after serum TNF concentration had returned to basal conditions, corticosterone levels remained maximally elevated, and serum corticosterone was still significantly above basal levels 24-hour post-LPS. The rapid return of circulating TNF to pre-LPS challenge levels appeared to be regulated by negative glucocorticoid feedback, because TNF remained maximally elevated for at least 6 hours in adrenalectomized or hypophysectomized mice. LPS-induced levels of IL-1 were delayed as compared to serum TNF, peaked at 4 hours, and remained elevated even at 24 hours.(ABSTRACT TRUNCATED AT 400 WORDS)

The cholinergic neuronal differentiation factor from heart cells is identical to leukemia inhibitory factor

A protein secreted by cultured rat heart cells can direct the choice of neurotransmitter phenotype made by cultured rat sympathetic neurons. Structural analysis and biological assays demonstrated that this protein is identical to a protein that regulates the growth and differentiation of embryonic stem cells and myeloid cells, and that stimulates bone remodeling and acute-phase protein synthesis in hepatocytes. This protein has been termed D factor, DIA, DIF, DRF, HSFIII, and LIF. Thus, this cytokine, like IL-6 and TGF beta, regulates growth and differentiation in the embryo and in the adult in many tissues, now including the nervous system.