Differential expression and regulation of thyrotropin (TSH) in T cell lines

Neuroendocrinology of bone

The past decade has witnessed significant advances in our understanding of skeletal homeostasis and the mechanisms that mediate the loss of bone in primary and secondary osteoporosis. Recent breakthroughs have primarily emerged from identifying disease-causing mutations and phenocopying human bone disease in rodents. Notably, using genetically-modified rodent models, disrupting the reciprocal relationship with tropic pituitary hormone and effector hormones, we have learned that pituitary hormones have independent roles in skeletal physiology, beyond their effects exerted through target endocrine glands. The rise of follicle-stimulating hormone (FSH) in the late perimenopause may account, at least in part, for the rapid bone loss when estrogen is normal, while low thyroid-stimulating hormone (TSH) levels may contribute to the bone loss in thyrotoxicosis. Admittedly speculative, suppressed levels of adrenocorticotropic hormone (ACTH) may directly exacerbate bone loss in the setting of glucocorticoid-induced osteoporosis. Furthermore, beyond their established roles in reproduction and lactation, oxytocin and prolactin may affect intergenerational calcium transfer and therefore fetal skeletal mineralization, whereas elevated vasopressin levels in chronic hyponatremic states may increase the risk of bone loss.. Here, we discuss the interaction of each pituitary hormone in relation to its role in bone physiology and pathophysiology.

Casual associations of thyroid function with inflammatory bowel disease and the mediating role of cytokines

Background

Previous observational epidemiological studies have suggested a potential association between thyroid function and inflammatory bowel disease (IBD). However, the findings remain inconclusive, and whether this association is causal remains uncertain. The objective of this study is to investigate the causal association between thyroid function and IBD.

Methods

Genome-wide association studies (GWAS) involving seven indicators of thyroid function, IBD, and 41 cytokines were analyzed. Bidirectional two-sample Mendelian randomization (MR) and multivariable MR were conducted to examine the causal relationship between thyroid function and IBD and to explore the potential mechanisms underlying the associations.

Results

Genetically determined hypothyroidism significantly reduced the risk of CD (odds ratio [OR] = 0.761, 95% CI: 0.655-0.882, p < 0.001). Genetically determined reference-range TSH was found to have a suggestive causal effect on IBD (OR = 0.931, 95% CI: 0.888-0.976, p = 0.003), (Crohn disease) CD (OR = 0.915, 95% CI: 0.857-0.977, p = 0.008), and ulcerative colitis (UC) (OR =0.910, 95% CI: 0.830-0.997, p = 0.043). In reverse MR analysis, both IBD and CD appeared to have a suggestive causal effect on the fT3/fT4 ratio (OR = 1.002, p = 0.013 and OR = 1.001, p = 0.015, respectively). Among 41 cytokines, hypothyroidism had a significant impact on interferon-inducible protein-10 (IP-10) (OR = 1.465, 95% CI: 1.094-1.962, p = 0.010). The results of multivariable MR showed that IP-10 may mediate the causal effects of hypothyroidism with CD.

Conclusion

Our results suggest that an elevated TSH level reduces the risk of CD, with IP-10 potentially mediating this association. This highlights the pituitary-thyroid axis could serve as a potential therapeutic strategy for CD.

Pituitary crosstalk with bone, adipose tissue and brain

Traditional textbook physiology has ascribed unitary functions to hormones from the anterior and posterior pituitary gland, mainly in the regulation of effector hormone secretion from endocrine organs. However, the evolutionary biology of pituitary hormones and their receptors provides evidence for a broad range of functions in vertebrate physiology. Over the past decade, we and others have discovered that thyroid-stimulating hormone, follicle-stimulating hormone, adrenocorticotropic hormone, prolactin, oxytocin and arginine vasopressin act directly on somatic organs, including bone, adipose tissue and liver. New evidence also indicates that pituitary hormone receptors are expressed in brain regions, nuclei and subnuclei. These studies have prompted us to attribute the pathophysiology of certain human diseases, including osteoporosis, obesity and neurodegeneration, at least in part, to changes in pituitary hormone levels. This new information has identified actionable therapeutic targets for drug discovery.

Thyroid Hormones Interaction With Immune Response, Inflammation and Non-thyroidal Illness Syndrome

The interdependence between thyroid hormones (THs), namely, thyroxine and triiodothyronine, and immune system is nowadays well-recognized, although not yet fully explored. Synthesis, conversion to a bioactive form, and release of THs in the circulation are events tightly supervised by the hypothalamic-pituitary-thyroid (HPT) axis. Newly synthesized THs induce leukocyte proliferation, migration, release of cytokines, and antibody production, triggering an immune response against either sterile or microbial insults. However, chronic patho-physiological alterations of the immune system, such as infection and inflammation, affect HPT axis and, as a direct consequence, THs mechanism of action. Herein, we revise the bidirectional crosstalk between THs and immune cells, required for the proper immune system feedback response among diverse circumstances. Available circulating THs do traffic in two distinct ways depending on the metabolic condition. Mechanistically, internalized THs form a stable complex with their specific receptors, which, upon direct or indirect binding to DNA, triggers a genomic response by activating transcriptional factors, such as those belonging to the Wnt/β-catenin pathway. Alternatively, THs engage integrin αvβ3 receptor on cell membrane and trigger a non-genomic response, which can also signal to the nucleus. In addition, we highlight THs-dependent inflammasome complex modulation and describe new crucial pathways involved in microRNA regulation by THs, in physiological and patho-physiological conditions, which modify the HPT axis and THs performances. Finally, we focus on the non-thyroidal illness syndrome in which the HPT axis is altered and, in turn, affects circulating levels of active THs as reported in viral infections, particularly in immunocompromised patients infected with human immunodeficiency virus.

Thyroid stimulating hormone β-subunit splice variant is expressed in all fractional subsets of bone marrow hematopoietic cells and peripheral blood leukocytes and is modulated during bacterial infection

Thyroid stimulating hormone (TSH), a hormone produced in the anterior pituitary, is used to regulate thyroid hormone secretion. It has been known for over three decades that TSH is made by the cells of the immune system; however, the functional role of immune system TSH is unclear. We previously demonstrated that an alternatively-spliced isoform of TSHβ, referred to as the TSHβ splice variant (TSHβv), is the primary form of TSHβ made by hematopoietic cells in mice and humans. Most studies have linked TSHβv expression to myeloid cells of the immune system; however, it has recently been demonstrated that plasma cells in patients with Hashimoto's thyroiditis may be a source of immune system TSHβv. Here, we demonstrate that TSHβv is expressed in bone marrow precursors of lymphoid cells, monocytes, and granulocytes, as well as in mesenteric lymph node (MLN) cells. Plasma cells generated by in vitro culture with bacterial lipopolysaccharide (LPS), and MLN cells from mice infected with L. monocytogenes expressed TSHβv. There was an increase in the intensity of intracellular TSHβv expression in MLN cells following exposure to LPS, and in the proportion of TSHβv⁺ CD138⁺ MLN cells following L. monocytogenes infection. The number of TSHβv⁺ cells increased in MLN cells, particularly among CD138⁺ cells, following bacterial infection. This was confirmed by an increase in gene expression of BLIMP-1, the transcription factor for CD138, following infection. Levels of circulating thyroxine dropped significantly in mice 24 hrs post-infection. These findings suggest that immune system TSHβv may contribute to the host immune response during bacterial infection.

Novel Splicing of Immune System Thyroid Stimulating Hormone β-Subunit-Genetic Regulation and Biological Importance

Thyroid stimulating hormone (TSH), a glycoprotein hormone produced by the anterior pituitary, controls the production of thyroxine (T₄) and triiodothyronine (T₃) in the thyroid. TSH is also known to be produced by the cells of the immune system; however, the physiological importance of that to the organism is unclear. We identified an alternatively-spliced form of TSHβ that is present in both humans and mice. The TSHβ splice variant (TSHβv), although produced at low levels by the pituitary, is the primary form made by hematopoietic cells in the bone marrow, and by peripheral leukocytes. Recent studies have linked TSHβv functionally to a number of health-related conditions, including enhanced host responses to infection and protection against osteoporosis. However, TSHβv also has been associated with autoimmune thyroiditis in humans. Yet to be identified is the process by which the TSHβv isoform is produced. Here, a set of genetic steps is laid out through which human TSHβv is generated using splicing events that result in a novel transcript in which exon 2 is deleted, exon 3 is retained, and the 3' end of intron 2 codes for a signal peptide of the TSHβv polypeptide.

Actions of pituitary hormones beyond traditional targets

Studies over the past decade have challenged the long-held belief that pituitary hormones have singular functions in regulating specific target tissues, including master hormone secretion. Our discovery of the action of thyroid-stimulating hormone (TSH) on bone provided the first glimpse into the non-traditional functions of pituitary hormones. Here we discuss evolving experimental and clinical evidence that growth hormone (GH), follicle-stimulating hormone (FSH), adrenocorticotrophic hormone (ACTH), prolactin, oxytocin and arginine vasopressin (AVP) regulate bone and other target tissues, such as fat. Notably, genetic and pharmacologic FSH suppression increases bone mass and reduces body fat, laying the framework for targeting the FSH axis for treating obesity and osteoporosis simultaneously with a single agent. Certain 'pituitary' hormones, such as TSH and oxytocin, are also expressed in bone cells, providing local paracrine and autocrine networks for the regulation of bone mass. Overall, the continuing identification of new roles for pituitary hormones in biology provides an entirely new layer of physiologic circuitry, while unmasking new therapeutic targets.

Neuroendocrine-immune interaction: Evolutionarily conserved mechanisms that maintain allostasis in an ever-changing environment

It has now become accepted that the immune system and neuroendocrine system form an integrated part of our physiology. Immunological defense mechanisms act in concert with physiological processes like growth and reproduction, energy intake and metabolism, as well as neuronal development. Not only are psychological and environmental stressors communicated to the immune system, but also, vice versa, the immune response and adaptation to a current pathogen challenge are communicated to the entire body, including the brain, to evoke adaptive responses (e.g., fever, sickness behavior) that ensure allocation of energy to fight the pathogen. This phenomenon is evolutionarily conserved. Hence it is both interesting and important to consider the evolutionary history of this bi-directional neuroendocrine-immune communication to reveal phylogenetically ancient or relatively recently acquired mechanisms. Indeed, such considerations have already disclosed an extensive "common vocabulary" of information pathways as well as molecules and their receptors used by both the neuroendocrine and immune systems. This review focuses on the principal mechanisms of bi-directional communication and the evidence for evolutionary conservation of the important physiological pathways involved.

Beyond Reproduction: Pituitary Hormone Actions on Bone

The long-held belief that pituitary hormones act solely on master targets was first questioned when we documented G protein-coupled receptors for thyroid-stimulating hormone, follicle-stimulating hormone, adrenocorticotrophic hormone, oxytocin, and vasopressin on bone cells. These evolutionarily conserved hormones and their receptors are known to have primitive roles, and exist in invertebrate species as far down as coelenterates. It is not surprising therefore that each such hormone has multiple hitherto unrecognized functions in mammalian integrative physiology, and hence, becomes a potential target for therapeutic intervention. Here we discuss the skeletal actions of pituitary hormones.

MECHANISMS IN ENDOCRINOLOGY: Impact of isolated TSH levels in and out of normal range on different tissues

Routine treatment of thyroid cancer (TC) includes long-term suppression of TSH. The necessity of this treatment in low- and intermediate-risk patients as well as the extent of TSH suppression is currently under discussion. A literature search was performed to illustrate the role of TSH in extrathyroidal cells and to identify potential reasons for different effects of exogenously suppressed and endogenously low TSH levels. Although adverse effects of subnormal and supranormal TSH blood levels on heart and brain have not been consistently found, studies show a clear negative effect of suppressed TSH levels on bone mineral density. Experimental data also support an important role of TSH in the immune system. The ability of levothyroxine (l-T4) to regulate TSH levels and triiodothyronine levels in a physiological manner is limited. Reduction of circadian changes in TSH levels, decrease of thyroid hormone-binding proteins, prevention of potential compensatory increases of TSH levels (e.g., in old age), and unresponsiveness of TSH-producing cells to TRH on l-T4 treatment might cause adverse effects of suppressed TSH levels. In view of the adverse effects of aggressive TSH suppression, achieving the suggested levels of TSH between 0.9 and 1 mU/l in the treatment of low-to-intermediate risk TC patients appears justified.

Splicing Regulation of Pro-Inflammatory Cytokines and Chemokines: At the Interface of the Neuroendocrine and Immune Systems

Alternative splicing plays a key role in posttranscriptional regulation of gene expression, allowing a single gene to encode multiple protein isoforms. As such, alternative splicing amplifies the coding capacity of the genome enormously, generates protein diversity, and alters protein function. More than 90% of human genes undergo alternative splicing, and alternative splicing is especially prevalent in the nervous and immune systems, tissues where cells need to react swiftly and adapt to changes in the environment through carefully regulated mechanisms of cell differentiation, migration, targeting, and activation. Given its prevalence and complexity, this highly regulated mode of gene expression is prone to be affected by disease. In the following review, we look at how alternative splicing of signaling molecules—cytokines and their receptors—changes in different pathological conditions, from chronic inflammation to neurologic disorders, providing means of functional interaction between the immune and neuroendocrine systems. Switches in alternative splicing patterns can be very dynamic and can produce signaling molecules with distinct or antagonistic functions and localization to different subcellular compartments. This newly discovered link expands our understanding of the biology of immune and neuroendocrine cells, and has the potential to open new windows of opportunity for treatment of neurodegenerative disorders.

Hormones in the immune system and their possible role. A critical review

Immune cells synthesize, store and secrete hormones, which are identical with the hormones of the endocrine glands. These are: the POMC hormones (ACTH, endorphin), the thyroid system hormones (TRH, TSH, T3), growth hormone (GH), prolactin, melatonin, histamine, serotonin, catecholamines, GnRH, LHRH, hCG, renin, VIP, ANG II. This means that the immune cells contain all of the hormones, which were searched at all and they also have receptors for these hormones. From this point of view the immune cells are similar to the unicells (Tetrahymena), so it can be supposed that these cells retained the properties characteristic at a low level of phylogeny while other cells during the evolution accumulated to form endocrine glands. In contrast to the glandular endocrine cells, immune cells are polyproducers and polyreceivers. As they are mobile cells, they are able to transport the stored hormone to different places (packed transport) or attracted by local factors, accumulate in the neighborhood of the target, synthesizing and secreting hormones locally. This is taking place, e.g. in the case of endorphin, where the accumulating immune cells calms pain caused by the inflammation. The targeted packed transport is more economical than the hormone-pouring to the blood circulation of glandular endocrines and the targeting also cares the other receptor-bearing cells timely not needed the effect. Mostly the immune-effects of immune-cell derived hormones were studied (except endorphin), however, it is not exactly cleared, while the system could have scarcely studied important roles in other cases. The evolutionary aspects and the known as well, as possible roles of immune-endocrine system and their hormones are listed and discussed.

Biological Impact of the TSHβ Splice Variant in Health and Disease

Thyroid stimulating hormone (TSH), a glycoprotein hormone composed of α and β chains, is produced by thyrotrope cells of the anterior pituitary. Within the conventional endocrine loop, pituitary-derived TSH binds to receptors in the thyroid, resulting in the release of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃). T₄ and T₃ in turn regulate nearly every aspect of mammalian physiology, including basal metabolism, growth and development, and mood and cognition. Although TSHβ has been known for years to be produced by cells of the immune system, the significance of that has remained largely unclear. Recently, a splice variant of TSHβ (TSHβv), which consists of a truncated but biologically functional portion of the native form of TSHβ, was shown to be produced by bone marrow cells and peripheral blood leukocytes, particularly cells of the myeloid/monocyte lineage. In contrast, full-length native TSHβ is minimally produced by cells of the immune system. The present article will describe the discovery of the TSHβv and will discuss its potential role in immunity and autoimmunity, inflammation, and bone remodeling.

Hypothalamic neurohormones and immune responses

The aim of this review is to provide a comprehensive examination of the current literature describing the neural-immune interactions, with emphasis on the most recent findings of the effects of neurohormones on immune system. Particularly, the role of hypothalamic hormones such as Thyrotropin-releasing hormone (TRH), Corticotropin-releasing hormone (CRH) and Gonadotropin-releasing hormone (GnRH). In the past few years, interest has been raised in extrapituitary actions of these neurohormones due to their receptors have been found in many non-pituitary tissues. Also, the receptors are present in immune cells, suggesting an autocrine or paracrine role within the immune system. In general, these neurohormones have been reported to exert immunomodulatory effects on cell proliferation, immune mediators release and cell function. The implications of these findings in understanding the network of hypothalamic neuropeptides and immune system are discussed.

Ingested (oral) thyrotropin releasing factor (TRH) inhibits EAE

BACKGROUND

Ingested immunoactive proteins type I IFN, SIRS peptide 1-21, α-MSH, ACTH, SST inhibit clinical attacks and inflammation in acute EAE by decreasing Th1-like cytokines, increasing Th2-like cytokines or increasing T(reg) cell frequencies.

OBJECTIVE

We examined whether another protein, thyrotropin releasing factor (TRH), would have similar anti-inflammatory effects in EAE after oral administration.

DESIGN/METHODS

B6 mice were immunized with MOG peptide 35-55 and gavaged with control saline or TRH during ongoing disease. Splenocytes from mock fed or TRH fed mice were adoptively transferred into active MOG peptide 35-55 immunized recipient mice during ongoing disease.

RESULTS

Ingested (oral) TRH inhibited ongoing disease and decreased inflammation. Adoptively transferred cells from TRH fed donors protected against actively induced disease and decreased inflammation. In actively fed mice, oral TRH decreased IL-17 and TNF-α cytokines in both the spleen and the CNS. In recipients of donor cells from TRH fed mice there was a reduction of Th1 and Th17 and induction of Th2-like IL-13 cytokines in both the spleen and CNS. Oral TRH decreased clinical score and decreased inflammatory foci in both actively fed and recipients of actively fed mice. There was no significant increase in T(reg) cell frequencies in actively fed or recipients of TRH fed donor cells.

CONCLUSIONS

Ingested (orally administered) TRH can inhibit clinical disease, inhibit CNS inflammation by decreasing Th1-like, Th17 and TNF-α cytokines and increasing Th2-like cytokines (IL-13) in the CNS.

Recombinant human thyrotropin in veterinary medicine: current use and future perspectives

Recombinant human thyrotropin (rhTSH) was developed after bovine thyrotropin (bTSH) was no longer commercially available. It was approved by the Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) as an aid to diagnostic follow-up of differentiated thyroid carcinoma in humans and for thyroid remnant ablation with radioiodine. In addition, rhTSH is used in human medicine to evaluate thyroid reserve capacity and to enhance radioiodine uptake in patients with metastatic thyroid cancer and multinodular goiter. Likewise, rhTSH has been used in veterinary medicine over the last decade. The most important veterinary use of rhTSH is thyroidal functional reserve testing for the diagnosis of canine hypothyroidism. Recent pilot studies performed at Ghent University in Belgium have investigated the use of rhTSH to optimize radioiodine treatment of canine thyroid carcinoma and feline hyperthyroidism. Radioiodine treatment optimization may allow a decreased therapeutic dosage of radioiodine and thus may improve radioprotection. This review outlines the current uses of rhTSH in human and veterinary medicine, emphasizing research performed in dogs and cats, as well as potential future applications.

Skeletal receptors for steroid-family regulating glycoprotein hormones: A multilevel, integrated physiological control system

Pituitary glycoprotein hormone receptors, including ACTH-R, TSH-R, and FSH-R, occur in bone. Their skeletal expression reflects that central endocrine control is evolutionarily recent. ACTH receptors, in osteoblasts or the adrenal cortex, drive VEGF synthesis. VEGF is essential to maintain vasculature. In bone, ACTH suppression by glucocorticoids can cause osteonecrosis. TSH receptors occur on osteoblasts and osteoclasts, in both cases reducing activity. Thus, TSH directly reduces skeletal turnover, consistent with evolutionary adaptation to stress. FSH receptors accelerate bone resorption, whereas estrogen promotes bone formation, the forces usually balancing. With ovarian failure, low estrogen with high FSH causes rapid bone loss. The skeletal FSH effect in the menopause seems paradoxical, but it is a logical adaptation in lactation, where prolonged FSH elevation also occurs. In addition to receptors, there is some synthesis of pituitary glycoproteins at distributed sites; this is not well studied, but it may further modify the paradigm of central endocrine regulation.

Extrapituitary production of anterior pituitary hormones: an overview

Protein hormones from the anterior pituitary gland have well-established endocrine roles in their peripheral target glands. It is, however, now known that these proteins are also produced within many of their target tissues, in which they act as local autocrine or paracrine factors, with physiological and/or pathophysiological significance. This emerging concept is the focus of this brief review.

Immunological regulation of metabolism--a novel quintessential role for the immune system in health and disease

The hypothalamus-pituitary-thyroid (HPT) axis is an integrated hormone network that is essential for maintaining metabolic homeostasis. It has long been known that thyroid stimulating hormone (TSH), a central component of the HPT axis, can be made by cells of the immune system; however, the role of immune system TSH remains enigmatic and most studies have viewed it as a cytokine used to regulate immune function. Recent studies now indicate that immune system-derived TSH, in particular, a splice variant of TSHβ that is preferentially made by cells of the immune system, is produced by a subset of hematopoietic cells that traffic to the thyroid. On the basis of these and other findings, we propose the novel hypothesis that the immune system is an active participant in the regulation of basal metabolism. We further speculate that this process plays a critical role during acute and chronic infections and that it contributes to a wide range of chronic inflammatory conditions with links to thyroid dysregulation. This hypothesis, which is amenable to empirical analysis, defines a previously unknown role for the immune system in health and disease, and it provides a dynamic connection between immune-endocrine interactions at the organismic level.

Bone marrow cells produce a novel TSHbeta splice variant that is upregulated in the thyroid following systemic virus infection

Although cells of the immune system can produce thyroid-stimulating hormone (TSH), the significance of that remains unclear. Using 5' rapid amplification of cDNA ends (RACE), we show that mouse bone marrow (BM) cells produce a novel in-frame TSHbeta splice variant generated from a portion of intron 4 with all of the coding region of exon 5, but none of exon 4. The TSHbeta splice variant gene was expressed at low levels in the pituitary, but at high levels in the BM and the thyroid, and the protein was secreted from transfected Chinese hamster ovary (CHO) cells. Immunoprecipitation identified an 8 kDa product in lysates of CHO cells transfected with the novel TSHbeta construct, and a 17 kDa product in lysates of CHO cells transfected with the native TSHbeta construct. The splice variant TSHbeta protein elicited a cAMP response from FRTL-5 thyroid follicular cells and a mouse alveolar macrophage (AM) cell line. Expression of the TSHbeta splice variant, but not the native form of TSHbeta, was significantly upregulated in the thyroid during systemic virus infection. These studies characterize the first functional splice variant of TSHbeta, which may contribute to the metabolic regulation during immunological stress, and may offer a new perspective for understanding autoimmune thyroiditis.

Review on the occasion of a decade of recombinant human TSH: prospects and novel uses

The introduction of recombinant human thyroid-stimulating hormone (rhTSH) almost a decade ago represents a remarkable achievement in the history of clinical thyroidology. rhTSH now contributes substantially to the diagnostic approach to thyroid cancer, offering a reliable and safe alternative to thyroid hormone withdrawal by avoiding the morbidity of hypothyroidism. Several recent studies have also demonstrated the efficacy of radioiodine ablation of thyroid remnants after preparation with rhTSH. Moreover, the use of rhTSH in this context is associated with a lower whole body exposure to radiation compared to thyroid hormone withdrawal. Although not approved officially, rhTSH-assisted treatment of locoregional or distant metastatic disease may be the treatment of choice for patients in whom hypothyroidism may be relatively contraindicated, such as the very young and the aged, although additional efficacy studies are necessary. The compound has also been shown to be useful in the treatment of nontoxic multinodular goiter, especially when the radioiodine uptake is low. Finally, rhTSH may prove to be useful in studying the functional reserve of thyroid in the aging process, as well as the putative role of the TSH receptor in extrathyroidal tissue, such as lymphocytes, osteocytes, and adipocytes.

The immune system as a regulator of thyroid hormone activity

It has been known for decades that the neuroendocrine system can both directly and indirectly influence the developmental and functional activity of the immune system. In contrast, far less is known about the extent to which the immune system collaborates in the regulation of endocrine activity. This is particularly true for immune-endocrine interactions of the hypothalamus-pituitary-thyroid axis. Although thyroid-stimulating hormone (TSH) can be produced by many types of extra-pituitary cells--including T cells, B cells, splenic dendritic cells, bone marrow hematopoietic cells, intestinal epithelial cells, and lymphocytes--the functional significance of those TSH pathways remains elusive and historically has been largely ignored from a research perspective. There is now, however, evidence linking cells of the immune system to the regulation of thyroid hormone activity in normal physiological conditions as well as during times of immunological stress. Although the mechanisms behind this are poorly understood, they appear to reflect a process of local intrathyroidal synthesis of TSH mediated by a population of bone marrow cells that traffic to the thyroid. This hitherto undescribed cell population has the potential to microregulate thyroid hormone secretion leading to critical alterations in metabolic activity independent of pituitary TSH output, and it has expansive implications for understanding mechanisms by which the immune system may act to modulate neuroendocrine function during times of host stress. In this article, the basic underpinnings of the hematopoietic-thyroid connection are described, and a model is presented in which the immune system participates in the regulation of thyroid hormone activity during acute infection.

Neonatal exposure to propylthiouracil induces a shift in lymphoid cell sub-populations in the developing postnatal male rat spleen and thymus

Evidence of the connections between the immune system and the thyroid axis is increasingly strong; however, much of the data are focused on immune effects of altered thyroid status in adults or rodents with congenital defects of the pituitary/thyroid axis. The object of the present study was to determine the effects of PTU-induced hypothyroidism on the developing immune system of the rat by focussing on both the spleen and thymus gland. Male Sprague-Dawley rat pups were exposed to PTU through maternal milk by giving the mothers 0.02% PTU in their drinking water starting on the pups' day of birth until day 24 (d24), shortly before weaning on d28. Animals were sampled on days 14, 22, 30, and 91. The mean body weight was decreased in the PTU-treated animals on days 14, 22, and 30. The mean spleen and thymic weights and cellularity were all decreased in the PTU-treated animals on d22 and d30. PTU exposure increased the proportion of NK cells in the spleen on days 14, 22, and 30. The proportion of T-cells was increased on days 22 and 30 with a particular increase in the CD4+ T-cells, resulting in an increase in the ratio of helper T-cells to suppressor/cytotoxic T-cells at d22. PTU also decreased the proportion of splenic B-cells at days 14, 22, and 30 which could explain the increased proportion of both NK and T-cells during these sampling periods. PTU treatment decreased the lytic ability of NK cells at d22, but no functional differences were observed at days 14, 30, 91, despite the increased proportion of NK cells in PTU-exposed animals at days 14, 22, and 30. PTU exposure also increased the proportion of CD4+CD8- cells in the thymus on d22 and caused an increase in both the CD4+CD8- and CD4-CD8+ populations on d30. These data suggest that the effects of temporary, PTU-induced hypothyroidism on the cell populations in the spleen partially result from transient changes in thymic T-cell development, including a shift towards increased CD4+CD8- cells. The data also suggest that temporary hypothyroidism early in development decreases B-cell development in a transient fashion. Temporary hypothyroidism induced from birth to the latter stages of the weaning period induced transitory effects on the spleen, thymus, and immune cell sub-populations--all of which recovered to normal values when the animals matured.

Thyroid-stimulating hormone induces interleukin-18 gene expression in FRTL-5 cells: immunohistochemical detection of interleukin-18 in autoimmune thyroid disease

Interleukin (IL)-18 is a cloned cytokine that was identified originally as a factor having potent interferon (IFN)-gamma-inducing activity on Kupffer cells. First, we analyzed IL-18 gene expression by reverse transcription-polymerase chain reaction (RT-PCR) in rat thyroid FRTL-5 cells and human thyroid tissue samples. The expression of IL-18 mRNA in FRTL-5 cells was enhanced by thryoid-stimulating hormone (TSH) in a dose-dependent manner. 8-Bromo-cyclic adenosine monophosphate (cAMP) also increased in IL-18 mRNA levels. Furthermore, TGCT clones that exhibited an increase in intracellular cAMP accumulation showed an increased IL-18 mRNA signal when compared to controls. Taken together, these data suggested that the effect of TSH on IL-18 gene expression was mediated by activating protein kinase A. Treatment of FRTL-5 cells with the antithyroid drug, methimazole (MMI), suppressed this stimulatory action of TSH on IL-18 gene expression. Next, we examined IL-18 expression in human thyroid tissue derived from patients with autoimmune thyroid diseases (ATD). RT-PCR and immunohistology demonstrated that human thyroid follicular cells expressed IL-18. Especially in thyroid tissue from a patient with Hashimoto's thyroiditis, expression was more diffuse and extensive, generally observed in close relation to a lymphocytic infiltrate. Also, IL-18 protein was distributed in the same follicles that express Fas-L and HLA-DR. This study is the first to demonstrate the detection of IL-18 in the thyroid gland. The frequent expression of IL-18 in thyrocytes suggests that IL-18 itself might be a secreted immunomodulator in ATD.

Extrapituitary beta TSH and GH in early chick embryos

Somatotropes and thyrotropes are thought to be derived from the same cellular lineage and the expression of both growth hormone (GH) and thyrotropin (beta TSH) is thought to be dependent upon the same (Pit-1) transcription factor. The presence and comparative distribution of GH- and beta TSH-immunoreactivity in early chick embryos, was therefore investigated, especially as extrapituitary GH-immunoreactive cells are present in some peripheral tissues of early chick embryos prior to the ontogenic differentiation of the pituitary gland. At the end of the first trimester of incubation (embryonic day (ED) 7), GH-immunoreactivity was widespread in the head, particularly in neural tissue. Strong labeling was found in the diencephalon and mesencephalon and in neural ganglia and the trigeminal nerve. beta TSH-immunoreactivity was also present in these tissues, although restricted to the ependymal cells lining the diocoele and mesocoele and absent from mantle layers. It was also present in the cellular layer lining the otic vesicle, which was devoid of GH staining. In contrast, Rathke's pouch, the primordial pituitary gland was without GH- or beta TSH-staining. Control sections incubated with preabsorbed antisera or with pre-immune serum were completely devoid of staining. In the trunk, the epidermal cells were stained for beta TSH, but not for GH. Intense GH-immunoreactivity was present in the ventral and dorsal horns of the spinal cord and was particularly strong in the outer marginal layer. In contrast, beta TSH-immunoreactivity was again restricted to ependymal cells lining the spinal canal, which were devoid of GH-immunoreactivity. Strong GH staining was also present in the dorsal and ventral root ganglia, both of which lacked significant beta TSH staining. In non-neural tissues, both GH and beta TSH staining was present in the crop, although in topographically different cells. beta TSH-immunoreactivity was also present in the cells lining the bronchial ducts and the adluminal linings of the pleural and pericardial cavities. GH-immunoreactivity, in contrast, was absent from the lung but present in the surrounding intracostal muscles and in the Müllerian duct. Both GH- and beta TSH-immunoreactivity was present in liver hepatocytes. These results clearly show, for the first time, the presence of TSH-immunoreactivity in central and peripheral tissues of the ED7 chick embryo, prior to the differentiation of pituitary thyrotropes. They also show that beta TSH- and GH-immunoreactive cells are differentially located within embryonic tissues.

The thyrotropin (thyroid-stimulating hormone) receptor is expressed on murine dendritic cells and on a subset of CD45RBhigh lymph node T cells: functional role for thyroid-stimulating hormone during immune activation

Thyroid-stimulating hormone (TSH), a central neuroendocrine mediator of the hypothalamus-pituitary-thyroid axis, has been shown to affect various aspects of immunological development and function. To gain a better understanding of TSH involvement within the mammalian immune system, the expression and distribution of the TSH receptor (TSHr) has been studied by immunoprecipitation and by flow cytometric analyses. Using highly enriched populations of B cells, T cells, and dendritic cells, trace amounts of TSHr were precipitated from B cells and T cells, whereas high levels of TSHr were precipitated from the dendritic cell fraction. Flow cytometric analyses of TSHr expression on splenic and lymph node T cells revealed a major difference between those tissues in that only 2-3% of splenic T cells were TSHr+, whereas 10-20% of CD4+8- and CD4-8+ lymph node T cells expressed the TSHr, which was exclusively associated with CD45RB(high) cells and was not expressed during or after activation. The TSHr was not present on cells of the immune system during fetal or neonatal life. However, recombinant TSHbeta was found to significantly enhance the phagocytic activity of dendritic cells from adult animals and to selectively augment IL-1beta and IL-12 cytokine responses of dendritic cells following phagocytic activation. These findings identify a novel immune-endocrine bridge associated with professional APCs and naive T cells.

Cloning of thyrotropin-releasing hormone precursor and receptor in rat thymus, adrenal gland, and testis

TRH is a hypophysiotropic peptide that acts mainly via the hypothalamic-pituitary-thyroid axis, but TRH immunoreactivity is also detected in several peripheral tissues. PCR with two pairs of primers enabling amplification of three fragments of TRH complementary DNA (cDNA) was used to demonstrate local production of TRH. Products of the expected size were detected in the testis, adrenal gland, lymphoid organs, thymus, and spleen. The amplified cDNA fragments were cloned and sequenced to show that the TRH gene is expressed in the thymus, spleen, and adrenal gland. Competitive RT-PCR showed that the TRH messenger RNA content of the testis was about one third that of the hypothalamus, whereas the adrenal gland contained 2% and the thymus 6%. HPLC analysis of thymus and spleen extracts showed small amounts of TRH, with a particular processing pattern of pro-TRH in lymphoid organs. The expression of the TRH receptor gene in peripheral organs was investigated to determine whether TRH had an autocrine or a paracrine action. cDNA fragments that encompassed the coding region of the receptor were identified in the testis, adrenal gland and thymus. No signal was detected in the spleen. These findings indicate that TRH may have a biological activity in extrapituitary organs and may act locally in the testis, adrenal gland, and thymus.

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.

Immunoreactivity for the alpha-subunit of the pituitary glycoprotein hormones in pulmonary neuroendocrine cells of developing human lung and various perinatal diseases

Infant lung tissue, obtained at autopsy, was studied by immunohistochemistry for the presence of pituitary glycoprotein hormones (PGHs) in the lung. The infants, born at term or preterm, died of various causes. The results provide the first immunological evidence of the presence of the common a-subunit of the pituitary glycoprotein hormones (alphaPGH) in the lung. The immunoreactivity is located in the pulmonary neuroendocrine cells and neuroepithelial bodies. In addition, the cells labelled by alphaPGH antisera (alphaPGH cells) form a subpopulation of the neuroendocrine cells detected by anti-calcitonin immunohistochemistry (CT cells). Moreover, the number of alphaPGH cells appears to increase after neonatal pneumonia or when the number of CT cells is elevated following the development of disease. Also, the weak staining of one of the monoclonal antibodies against the specific b-subunit of thyrotropin (TSH) might, in combination with the increased detectability of a-subunits, indicate that TSH can be endogenously produced in the lung.

Local hormone networks and intestinal T cell homeostasis

Neuroendocrine hormones of the hypothalamus-pituitary-thyroid axis can exert positive or negative immunoregulatory effects on intestinal lymphocytes. Small intestine epithelial cells were found to express receptors for thyrotropin-releasing hormone (TRH) and to be a primary source of intestine-derived thyroid-stimulating hormone (TSH). The gene for the TSH receptor (TSH-R) was expressed in intestinal T cells but not in epithelial cells, which suggested a hormone-mediated link between lymphoid and nonhematopoietic components of the intestine. Because mice with congenitally mutant TSH-R (hyt/hyt mice) have a selectively impaired intestinal T cell repertoire, TSH may be a key immunoregulatory mediator in the intestine.

Immunomodulation of peripheral lymphocytes by hormones of the hypothalamus-pituitary-thyroid axis

The aim of this review is to provide a comprehensive examination of the current literature describing the immunoregulatory effects on the peripheral immune system by the hormones that comprise the hypothalamic-pituitary-thyroid (HPT) axis. This article discusses the effects of the HPT axis hormones on the peripheral lymphoid tissues and the immune responses mediated by the cells that comprise these lymphoid tissues. Neuroendocrine dysfunction in the HPT axis, either naturally or experimentally induced, and the resulting immune dysfunction are also discussed. Emphasis in this article is placed on the most recent study findings and those that provide a unique or novel way of evaluating HPT hormone effects on the immune system. Our knowledge of the immunoregulatory effects of the hormones that comprise the HPT axis has grown tremendously in the last 10 years. As can be seen in this review, the immunoregulatory effects of the HPT axis hormones are quite diverse and influence most, if not all, aspects of immune system physiology. The continued exploration of the bidirectional circuitry between the immune and neuroendocrine systems may allow for development of appropriate prophylactic procedures that prevent dysfunction in both systems.

TRH receptor on immune cells: in vitro and in vivo stimulation of human lymphocyte and rat splenocyte DNA synthesis by TRH

This work examined whether (1) immune cells express thyrotrophin releasing hormone (TRH) receptor mRNA and (2) TRH modulates lymphocyte activation. By Northern blot of RNA extracted from human peripheral blood mononuclear cells (PBMC) and rat splenocytes, a single TRH receptor mRNA band of about 3.8 kb (identical to that obtained from pituitary cells) was obtained, under both basal and stimulated conditions. A significant increase in DNA synthesis was observed in phytohemagglutinin-stimulated PBMC and concanavalin A (Con A) stimulated splenocytes when TRH (10(-6) M-10(-12) M) was added. After 5, 30, 60, 180 min and 24 h of TRH administration in vivo, a significant increase in the rat splenocyte proliferative response to Con A was observed. In vivo administration of anti-rat TSH antibody (1/1000) blocked the increase observed after 30 min of TRH administration on the Con A stimulated splenocyte response. TRH possess immunostimulatory functions directly via its receptor and indirectly via release of other immunostimulatory factors such as thyrotrophin.

Excess iodine induces the expression of thyroid solid cell nests in lymphocytic thyroiditis-prone BB/W rats

Previous epidemiological studies have suggested that lymphocytic thyroiditis and/or an increased iodine intake may be risk factors for the development of thyroid cancer. We previously reported that excess iodine accelerated the development of thyroid lymphocytic infiltration (LI) in the autoimmune BB/W rat model. We also found that excess iodine increased thyroid cell proliferation in a disordered manner. The present study was designed to further explore these observations and to address the question as to whether excess iodine under certain conditions predisposes the thyroid gland to neoplasia. To test this hypothesis, the lymphocytic thyroiditis-prone BB/W rat was exposed to excess iodine in drinking water. Ten BB/W rats at 4 weeks of age were given iodine water (NaI 0.05%) for 10 weeks, whilst another 10 BB/W rats were given tap water and served as controls. Eighteen normal Wistar rats were also divided into excess iodine and control groups, served as a comparison to the BB/W rats. We found that an excess iodine intake accelerated the development of LI in the BB/W rat. Severe LI was usually accompanied by prominent thyroid cell proliferation, evident as numerous microfollicles and cell masses, not forming normal thyroid follicles. Numerous lymphocytes and plasma cells often encroached on these areas of increased cellular proliferation. The surprising feature, and a possible indicator of activated thyroid cell proliferation, was the high incidence of thyroid solid cell nest-like lesions (SCN) in the iodine treated BB/W rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The evidence of thyroliberin/triiodothyronine control of TSH secretory response from human peripheral blood monocytes cultured in vitro

Immune system function has been shown to be under the influence of various neuromodulators and endocrine system peptides. This in vitro study describes the stimulatory effect of thyrotropin releasing hormone (thyroliberin, TRH) on thyrotropin (TSH) release from cultured human peripheral blood monocytes. The stimulatory effect of TRH on TSH release from monocytes is totally blocked by triiodothyronine (T3) administrations. These results indicate that TSH release from human monocytes is under the control of TRH/T3 mechanisms, similar to hypothalamic-pituitary-thyroid axis.

TSH beta subunit gene expression in human lymphocytes

Production of neuroendocrine peptides by human lymphocytes is thought to facilitate control of the immune response. The presence of neuroendocrine peptide gene expression, specifically the TSH beta subunit gene, was studied in human lymphocytes using Northern blot analysis and polymerase chain reaction (PCR) techniques. Northern blot analysis of human lymphocyte RNA probed with a TSH beta cDNA probe failed to demonstrate TSH beta subunit steady state message levels. PCR amplification of lymphocyte-derived cDNA using TSH beta subunit complementary primers resulted in amplification of a .38 Kb DNA fragment, confirming expression and initial exonic splicing of TSH beta subunit gene exons 2 and 3 in human lymphocytes. Sequence analysis of this .38 Kb DNA fragment demonstrated conservation of exon borders after splicing (exons 2 and 3) and predicted an amino acid translation product similar, if not identical, to human TSH beta peptide sequence. Hybridization with a TSH beta subunit cDNA probe of PCR-amplified reverse-transcribed lymphocyte RNA suggested that: (1) the abundance of TSH beta subunit gene transcripts in human lymphocytes is less than the relative abundance in T3-treated pituitary; and (2) this messenger RNA may be modulated by the presence of certain thyromimetic compounds (T2, T3, TRIAC).

Immunoreactive growth hormone production by human lymphocyte cell lines

1. Two human lymphocyte cell lines, a T-cell line and a B-cell line, were shown to produce and secrete immunoreactive growth hormone (irGH). The irGH molecules secreted by the two cell lines appeared to be de novo synthesized and their molecular size was similar to that of pituitary GH as well as irGH secreted by peripheral blood lymphocytes. 2. Affinity-purified irGH molecules had human growth hormone (hGH)-like mitogenic activity on Nb2 cells. These findings indicate that the irGH molecules produced by H9 and IM9 were similar to hGH in structure. 3. However, the irGH messages could not be amplified by polymerase chain reaction (PCR) primers which had been demonstrated to be able to amplify reverse-transcribed hGH messenger RNA successfully, suggesting that the lymphocyte-derived irGH and pituitary hGH are not exactly identical molecules. 4. We conclude that the H9 and IM9 cells produce a growth hormone-related molecule whose structure is different from that in the anterior pituitary.

Inhibition of immunoreactive growth hormone secretion from lymphoid cell lines by dexamethasone

The regulation of irGH secretion by the immune system was examined using lymphoid cell lines, H9 and IM9. Using a highly sensitive immunoassay, irGH secretion by H9 was negatively regulated by dexamethasone, whereas many other regulators of hGH secretion, including hormones, monoamines, and second messenger, had no measurable effect on irGH secretion. Treatment of H9 cells with dexamethasone for 48 hours could cause as high as 70% reduction in irGH secretion without affecting either cell numbers or viability. Using IM9, neither growth hormone releasing hormone nor thyrotropin releasing hormone had significant effect on either irGH steady-state level transcripts or irGH secretion. These findings suggest that irGH secretion by lymphocytes was regulated in a different manner from that by pituitary cells.