In vivo modulation of the distribution of thymocyte subsets: effects of estrogen on the expression of different T cell receptor V beta gene families in CD4-, CD8- thymocytes

Sex Hormones in Acquired Immunity and Autoimmune Disease

Women have stronger immune responses to infections and vaccination than men. Paradoxically, the stronger immune response comes at a steep price, which is the high incidence of autoimmune diseases in women. The reasons why women have stronger immunity and higher incidence of autoimmunity are not clear. Besides gender, sex hormones contribute to the development and activity of the immune system, accounting for differences in gender-related immune responses. Both innate and adaptive immune systems bear receptors for sex hormones and respond to hormonal cues. This review focuses on the role of sex hormones particularly estrogen, in the adaptive immune response, in health, and autoimmune disease with an emphasis on systemic lupus erythematosus.

Oestrogen, an evolutionary conserved regulator of T cell differentiation and immune tolerance in jawed vertebrates?

In teleosts, as in mammals, the immune system is tightly regulated by sexual steroid hormones, such as oestrogens. We investigated the effects of 17β-oestradiol on the expression of several genes related to T cell development and resulting T cell subpopulations in sea bass, Dicentrarchus labrax, for a primary lymphoid organ, the thymus, and two secondary lymphoid organs, the head-kidney and the spleen. In parallel, the oxidative burst capacity was assessed in leucocytes of the secondary lymphoid organs. Apoptosis- and proliferation-related genes, indicative of B and T cell clonal selection and lymphoid progenitor activity, were not affected by elevated oestrogen-levels. Sex-related oestrogen-responsiveness in T cell and antigen-presenting cell markers was observed, the expression of which was differentially induced by oestrogen-exposure in the three lymphoid organs. Remarkably, in the spleen, oestrogen increased regulatory T cell-related gene expression was associated with a decrease in oxidative burst capacity. To the best of our knowledge, this study indicates for the first time that physiological levels of oestrogen are likely to promote immune tolerance by modulating thymic function (i.e., T cell development and output) and peripheral T cells in teleosts, similar to previously reported oestrogenic effects in mammals.

Oestrogen receptor distribution related to functional thymus anatomy of the European sea bass, Dicentrarchus labrax

In jawed vertebrates, the crosstalk between immune and endocrine system as well as many fundamental mechanisms of T cell development are evolutionary conserved. Oestrogens affect mammalian thymic function and plasticity, but the mechanisms of action and the oestrogen receptors involved remain unclear. To corroborate the oestrogenic regulation of thymic function in teleosts and to identify the implicated oestrogen receptor subtypes, we examined the distribution of nuclear and membrane oestrogen receptors within the thymus of the European Sea bass, Dicentrarchus labrax, in relation to its morpho-functional organisation. Immunohistological analysis specified thymus histology and organisation in teleosts and described, for the first time, Hassall's corpuscle like structures in the medulla of sea bass. All oestrogen receptors were expressed at the transcript and protein level, both in T cells and in stromal cells belonging to specific functional areas. These observations suggest complex regulatory actions of oestrogen on thymic function, notably through the stromal microenvironment, comprising both, genomic and non-genomic pathways that are likely to affect T cell maturation and trafficking processes. Comparison with birds, rodents and humans supports the thymic localization of oestrogen receptors and suggests that oestrogens modulate T cell maturation in all gnathostomes.

Sex, the aging immune system, and chronic disease

The immune systems of men and women differ in significant ways, especially after puberty. In particular, females are generally more prone to autoimmunity, but experience lower rates of infections and chronic inflammatory disease. Sex hormones, genes encoded on the sex chromosomes, and gender-specific behaviors likely contribute to these differences. The aging process is associated with changes in the composition and function of the immune system and these changes may occur at an accelerated rate in men as compared to women. Moreover, after the age of menopause, the incidence of chronic inflammatory disease in women approaches or exceeds that observed in males. At the same time, the incidence of autoimmunity in post-menopausal women is decreased or equivalent to the rates observed in similarly-aged men. Additional studies addressing the influence of sex on the pathogenesis of chronic and autoimmune diseases in the aged are warranted.

Salivary glands - "an unisex organ'?

Usually no distinction is made between female and male salivary glands although cyclic changes of and ⁄ or differences in serum and salivary sex steroid concentrations characterize women and men. Moreover, sexual dimorphism is well recognized in salivary glands of rodents.Salivary glands contain estrogen and androgen receptors and are, according to modern high throughput technologies,subjected to gender differences not explainable by gene dose effects by the X chromosome alone. Because sex steroids are lipophilic, it is often thought that approximately 10% of them passively diffuse from plasma to saliva. Indeed, saliva can find use as sample material in sports medicine, pediatrics, veterinary medicine and behavioral sciences. Last but not least, humans and other primates are unique in that they have a reticular zone in their adrenal cortex, which produces dehydroepiandrosterone and androstendione pro-hormones. These are processed in peripheral tissues, not only in female breast and uterus and male prostate, but also in salivary glands by an intracrine enzymatic machinery to active 17b-estradiol,dihydrotestosterone and others, to satisfy and buffer against a constantly changing needs caused by circadian,menstrual, pregnancy and chronobiological hormonal changes in the systemic circulation. Female dominance of Sjögren's syndrome and certain forms of salivary gland cancer probably reflect these gender-based differences.

Can estrogens promote hypertension during systemic lupus erythematosus?

SLE is a chronic autoimmune inflammatory disorder that predominantly affects young women. Based on this observation, it has been speculated that sex steroids, particularly estrogens, contribute to SLE disease progression. Young women with SLE are at an increased risk for the development of hypertension yet the reasons for this are unclear. One potential mechanism for the increased risk of hypertension during SLE is the chronic inflammation caused by immune complex mediated tissue injury. Estrogens are known to have an immunomodulatory role that can lead to the production of characteristic autoantibodies important for immune complex formation. Therefore, it is conceivable that during SLE estrogens contribute to tissue injury, increased inflammation and hypertension. This brief review discusses the increased risk for hypertension during SLE, the role of estrogens in immune system function, evidence for estrogens in SLE, and a possible link between estrogens and SLE hypertension.

Role of ovarian hormones in age-associated thymic involution revisited

A commonly held view that ovarian hormones are causally involved in age-associated thymic involution has been recently challenged. In particular, their relevance in the progression of thymic involution has been disputed. To reassess this issue 10-month-old rats with well advanced thymic involutive changes were ovariectomized (Ovx), and after 1 month thymic cellularity, thymocyte development and levels of recent thymic emigrants (RTEs) were examined in peripheral blood and spleen. In addition, the distribution of major conventional and regulatory T-cell subsets was analyzed in the same peripheral lymphocyte compartments. Ovariectomy increased thymic weight and cellularity above the levels in both 10-month-old and age-matched controls indicating that ovarian hormone ablation not only prevented further progression of thymic involution, but also reversed it. The increased thymic cellularity was accompanied by altered thymocyte differentiation/maturation culminating in increased thymic output of naïve T cells as indicated by elevated levels of both CD4+ and CD8+ RTEs in peripheral blood and spleen. The changes in T-cell development produced: (i) a disproportional increase in cellularity across thymocyte subsets, so that relative proportions of cells at all maturational stages preceding the CD4+CD8+ T cell receptor (TCR)alphabeta(low) stage were reduced; the relative numbers of CD4+CD8+ TCRalphabeta(low) cells entering positive selection and their immediate CD4+CD8+ TCRalphabeta(high) descendents were increased, while those of the most mature CD4+CD8- and CD4-CD8+ TCRalphabeta(high) cells remained unaltered; (ii) enhanced cell proliferation across all thymocyte subsets and (iii) reduced apoptosis of cells within the CD4+CD8+ thymocyte subset. The augmented thymic output of naïve T cells in Ovx rats most likely reflected an early disinhibition of thymocyte development followed by increased positive/reduced negative selection, at least partly, due to raised thymocyte surface Thy-1 expression. The greater number of CD4+CD25+Foxp3+ cells in both thymus and peripheral blood suggested augmented thymic production of these cells. In addition, an increased CD4+/CD8+ cell ratio was found in the spleen of Ovx rats. Thus, ovarian hormone ablation led not only to increased diversity of the T-cell repertoire, but also to a new balance among distinct T-cell subsets in the periphery.

Oestradiol inhibition of vascular myointimal proliferation following immune, chemical and mechanical injury

The lower incidence of coronary artery disease in premenopausal women and in postmenopausal women treated with oestrogen supports the hypothesis that oestrogen protects the vasculature from injuries or from responding to injuries with arteriosclerosis. The mechanism remains unknown, although currently the most frequent suggestion is that oestrogen induces beneficial quantitative and qualitative changes in serum lipoprotein concentrations. We studied other mechanisms and in particular the direct effects of 17 beta-oestradiol on vascular smooth muscle and the endothelium. Our focus has been on the vascular response to injury by myointimal and medial thickening, leading to narrowing or occlusion of the vessel. This is frequently seen in coronary arteries within months following angioplasty and a few years following cardiac transplantation. We find that oestradiol treatment protects and reduces the vascular response to injury in three in vivo and one in vitro models: (1) in the rabbit cardiac allograft where oestrogen inhibits accelerated graft atherosclerosis; (2) in monocrotaline- or hypoxia-induced pulmonary hypotension in the rat, where oestrogen attenuates pulmonary artery pressure, right ventricular hypertrophy and medial thickening of the pulmonary artery; (3) oestrogen protects against balloon injury in rabbit aorta; and (4) it inhibits smooth muscle cell proliferation in the porcine left anterior descending coronary artery.

Estrogen and CD4+ T cells

PURPOSE OF REVIEW

Many autoimmune rheumatic autoimmune disorders predominantly affect women. Sex hormones, in particular estrogen, can influence CD4 T-helper development and function. We highlight recent studies that begin to provide insights into the mechanisms by which estrogen modulates CD4 T-cell development and function, and thus potentially contribute to disease pathogenesis.

RECENT FINDINGS

High levels of estrogen can lead to thymic atrophy. Recent studies showed that this phenomenon results from effects of estrogen at multiple stages in early T-cell development. Estrogen is also known to affect mature CD4 T-cell function, and, in particular, their ability to produce selected cytokine profiles. The mechanisms by which estrogen can exert these effects were also recently explored and shown to include effects on expression of critical molecules known to be involved in these processes.

SUMMARY

Dissecting the molecular pathways employed by estrogen to modulate CD4 T cells will be critical in elucidating the manner by which estrogen exerts its effects on this compartment. Given that cell type specific differences underlie the ability of many hormonal therapies to exert tissue-specific estrogenic or antiestrogenic activities, this knowledge will be crucial to further exploitation of hormonal therapies in rheumatic autoimmune diseases.

Estrogen-induced generation of reactive oxygen and nitrogen species, gene damage, and estrogen-dependent cancers

In addition to the direct effect of estrogen on mitochondria and the redox cycling of catechol estrogen, estrogen-induced proinflammatory cytokines, such as interleukin-1 beta (IL-1beta) and tumor necrosis factor alpha (TNF-alpha), also generate reactive oxygen and nitrogen species (RO/NS). Different cellular signaling pathways may operate in response to varying levels of estrogen-induced RO/NS, leading to genotoxic damage, cell apoptosis, or cell growth. At high levels of RO/NS, cells receiving genotoxic insults, if not repaired, may engage the apoptotic pathways. There is increasing evidence supporting that estrogen-induced alterations in the genome of cells is produced by oxidative attack. Furthermore, ROS generated by estrogen exposure and/or active metabolites of estrogen in combination with receptor-mediated proliferation of genetically damaged cells may be involved in tumor development. This view is supported by the findings of DNA modifications produced in vitro or in vivo by natural and synthetic estrogens in the target organs of cancer both in experimental models and in humans. Interaction of estrogen-induced oxidants and estrogen metabolites with DNA was shown to generate mutations in genes. Cotreatment with an inhibitor of IL-1beta and TNF-alpha synthesis, pentoxifylline, decreased stilbene estrogen-induced levels of myeloperoxidase (MPO), 8-hydroxydeoxyguanosine formation, and gene mutations, and prevented stilbene estrogen-induced lesions. Stable MCF-7 clones overexpressing IL-1beta resulted in a high level of IL-1beta peptide secretion undergoing cell apoptosis, and an elevated level of p53 protein in response to high oxidative stress when compared to nontransfected cells, whereas MCF-7 clones overexpressing IL-1beta that resulted in a moderate level of IL-1beta secretion stimulated the clonal expansion of MCF-7 and TM3 cells. Estrogen-induced MCF-7 cell growth and cyclin D1 expression were suppressed by antioxidants and mitochondrial blockers. These studies support that in addition to ovarian estrogen-mediated ER signaling, mitogenic signals may also come from estrogen-induced RO/NS. Further validation of this concept that the concentration of the RO/NS within the cellular microenvironment determines its stimulatory or inhibitory growth signals as well as its genotoxic effects regulating the growth of estrogen-dependent tumors may result in novel preventive strategies.

Gene Expression Profiling of 17β-Estradiol and Genistein Effects on Mouse Thymus

Estrogen regulates thymic development and involution and modulates immune function. Despite its critical role in thymus, as well as in autoimmune disorders, the mechanism by which estrogen affects the thymus is not well understood. We previously reported that the estrogenic soy isoflavone genistein, as well as 17beta-estradiol (E2), could induce thymic involution, but genistein effects were only partially mediated through estrogen receptors. To provide insights into mechanisms of estrogenic effects in the thymus, we investigated thymic gene expression changes induced by E2 (125 ng/day) and genistein (1500 ppm in feed) in weanling mice using high-density DNA arrays. We identified several E2-responsive genes involved in thymic development and thymocyte signaling during selection and maturation. Functional characterization indicated effects on genes involved in transcription, apoptosis, and the cell cycle. This study also identified changes in several E2-regulated transcripts essential to maintain immune self-tolerance. E2 upregulated more genes than genistein, while genistein downregulated more genes than E2. Though each treatment regulated several genes not altered by the other, there was considerable overlap in the genes regulated by E2 and genistein. Changes in transcription factors and cell cycle factors were consistent with decreases in cell proliferation induced by both genistein and E2. As indicated by the regulation of non-E2-responsive genes, genistein also induced unique effects through non-estrogenic mechanisms. The specific downregulation of the CD4 coreceptor transcript by genistein was consistent with the decline of CD4+ thymocytes in genistein-treated mice in our previous study. This is the first study identifying E2 and genistein target genes in the thymus. These findings provide new mechanistic insights toward explaining estrogen action on thymocyte development, selection, and maturation, as well as the effects of genistein on prenatal and neonatal thymic development and function.

Differential expression of immunoregulatory genes in male and female Norway rats following infection with Seoul virus

Males of many species are more susceptible than females to infections caused by parasites, bacteria, fungi, and viruses. Following inoculation with Seoul virus, male rats have more virus present in target organs and shed virus longer than females. The goal of this study was to test the hypothesis that variation in the expression of genes associated with immune function mediates sex differences in hantavirus infection. Using DNA microarrays, we examined changes in gene expression in lung tissue during the early (when animals are viremic and shedding virus; Day 15 post-inoculation (p.i.)) and late (animals have low levels of infectious virus, but high antibody titers; Day 40 p.i.) phases of infection in adult male and female rats. After normalizing the gene expression levels from infected animals to the gene expression levels from same-sex uninfected controls, our data revealed that 1,813 genes were differentially expressed between the sexes during infection. The expression of key transcriptional factors (e.g., eIF-2 alpha, NF-kappa B, IRF-1, NF-IL-6, and STAT6) and genes that encode for proinflammatory (e.g., TNF alpha R, IL-1R, and IL-1RAcP), antiviral (e.g., IFN gamma R and Mx proteins), T cell (e.g., CD3 and TCR), and Ig superfamily (e.g., IgM, IgG, and MHC class I and II) proteins was higher in females than males. Conversely, males had higher expression of heat shock protein genes (e.g., hsp70) suggesting that cellular stress is elevated in males. These data provide candidate genes and cellular pathways that may underlie sex differences in responses to Seoul virus and possibly other hemorrhagic fever viruses.

Neonatal androgenization affects the intrathymic T-cell maturation in rats

The thymus structure, expression of CD4/CD8/TCRalphabeta on thymocytes and thymocyte proliferative and apoptotic indexes were analyzed in sexually immature 30-day-old and in sexually mature 60-day-old female rats neonatally androgenized (NA) by subcutaneous injection of 500 microg testosterone propionate/day on days 1-3 and in their vehicle-administered counterparts. The treatment affected normal thymus development. Thus, at 30 days of age, there was a reduction in the thymus weight, reflecting a decrease in the main thymic compartments. However, at 60 days of age, thymus weight did not significantly differ from that in age-matched controls, since the cortical volume enlargement was followed by a proportional decrease in the medullary volume. In rats of both ages, the changes in thymic compartments most likely reflected alterations in the size of both lymphoid and nonlymphoid components. Furthermore, in NA rats, substantial changes in thymocyte phenotypic characteristics were registered, in spite of their age. In both groups of NA rats, a decrease in the relative proportion of the least mature CD4-8-TCRalphabeta- cells and in that of CD4+8- TCRalphabeta-/TCRalphabeta(low) cells followed by an increase in the percentage of their successor CD4+8+TCRalphabeta-/TCRalphabeta(low) cells was detected. In addition, in 30-day-old NA rats, the relative proportions of CD4+8+TCRalphabeta(high) cells (just positively selected) and that of mature single positive (CD4+8- and CD4-8+) and CD4-8- double negative TCRalphabeta(high) cells, were reduced, while in 60-day-old NA rats only the percentage of CD4+8+TCRalphabeta(high) thymocytes was decreased. Thus, the study showed that the changes in the development of the hypothalamo-pituitary-gonadal axis induced by neonatal androgenization may affect the thymus development and intrathymic T-cell maturation.

Influence of the Murine Oestrous Cycle on the Induction of Mucosal Immunity

PROBLEM

To determine if the stage of oestrous cycle, at the time of immunization, affects the magnitude of mucosal and systemic immunity.

METHOD OF STUDY

Female BALB/c mice were immunized with tetanus toxoid and cholera toxin by the oral, intranasal and transcutaneous routes. Groups of mice were immunized at proestrus, oestrus, postestrus and diestrus. Antibodies in serum and mucosal secretions were determined by ELISA and T cell responses by lymphocyte proliferation assay.

RESULTS

Oral immunization at the oestradiol dominant stage of cycle (oestrus and proestrus) significantly enhanced TT-specific IgG and IgA levels in female reproductive tract (FRT) secretions and TT-specific IgA levels in faecal extracts. Transcutaneous immunization at diestrus enhanced TT-specific IgG in faecal extracts. TT-specific T cell proliferation is greatest following intranasal immunization at proestrus and transcutaneous immunization at diestrus, particularly in the caudal and lumbar lymph nodes draining the FRT and colon.

CONCLUSIONS

Reproductive cycle-associated changes in the endogenous sex hormones oestradiol and progesterone influence the levels of vaccine-induced immunity in the FRT and distal colon following oral and transcutaneous immunization.

Is macrophage migration inhibitory factor a therapeutic target in systemic lupus erythematosus?

Systemic lupus erythematosus (SLE) is the prototype of a cluster of diseases that are characterized by a loss of self tolerance and chronic inflammation in organs including skin, kidney, brain and joints. Researchers have long debated the varying contributions of the components of the immune system to the pathogenesis of SLE, but the emigration of leucocytes from the microcirculation, and the subsequent tissue inflammation mediated by these inflammatory cells, are key features of chronic inflammation seen in SLE. Macrophage migration inhibitory factor (MIF) is a broad-spectrum pro-inflammatory cytokine. We hypothesize that MIF is an important inflammatory mediator in the perpetuation of immune activation in SLE, via its effects on activation of T and B cells, and endothelial and effector cells. As MIF exerts anti-apoptotic effects, it may also play a role in promoting abnormal survival of autoreactive lymphocytes, thus perpetuating autoimmune reactivity. In addition, MIF has a unique relationship with glucocorticoids, in that MIF can override the effects of glucocorticoids and may be important in steroid resistance. By virtue of its pluripotent functions, we propose that MIF may be a critical mediator of inflammation and damage in SLE, and that targeting of MIF may offer therapeutic benefits in this disease.

Gender-dependent immunosuppression following subacute exposure to fumonisin B1

The effects of fumonisin B1 (FB1), a mycotoxin produced by Fusarium lertcillioides, on the immune system are controversial; FB1 exposure causing immunosuppression in poultry, swine, bovine and rodents species and immunostimulation in rodent species. The current study was conducted to examine the effects of FB1 on the immune system of BALB/c mice and to determine if there is sex specificity. Female and male mice (five per group) received five daily subcutaneous (s.c.) injections of 2.25 mg/kg/day of FB1, on the following day tissues were collected for immunological examinations. FB1 treatment dramatically reduced relative spleen and thymus weights in females, whereas there was no effect on organ weights in males. Exposure to FB1 reduced splenic cellularity and the basal rate of lymphocyte proliferation in females only. In addition, phytohemagglutinin (PHA-P)-induced T-lymphocyte and LPS-induced B-lymphocyte proliferation were reduced in female mice. Splenocytes from female mice exposed to FB1 showed a reduced expression of interleukin-2 mRNA. These changes occurred in the absence of alterations in tumor necrosis factor alpha or interleukin-1beta mRNA expression. Phenotypic analysis indicated that FB treatment caused a relative increase in the T-lymphocyte population in the spleen of female mice only. In contrast, FB1 dramatically reduced the immature CD4+/CD8+ double positive cell population in the thymus of females. No changes were evident in the thymocyte populations of male mice treated with FB1. The results of this study indicate that FB1 is immunosuppressive in mice; the magnitude of FB1-induced immunosuppression is highly dependent on sex, females being more susceptible than males.

Androgens indirectly accelerate thymocyte apoptosis

Apoptotic processes, or the disturbance of the natural regulation of these processes, may be involved in the pathogenesis of autoimmune diseases (AID). Women are, in general, more susceptible than men to develop AID like rheumatoid arthritis. Androgens and glucocorticoids, in contrast to oestrogens, have favourable effects in AID models as well as in human AID. It is known that glucocorticoids (GC), used for treatment of AID, increase apoptosis in the thymus resulting in decreased numbers of CD4+ CD8+ thymocytes. It was asked whether androgens, in contrast to oestrogens, exert their favourable effects in the treatment of AID by a mechanism comparable to that described for GC by eliminating the apoptosis prone CD4+ CD8+ population in the thymus. Although both androgens and oestrogens proved thymolytic, a significantly decreased percentage of CD4+ CD8+ thymocytes was observed by flow cytometry after treatment of mice with the androgen methyltestosterone, but not with the oestrogen ethinylestradiol. To investigate whether the observed thymolytic effects were due to the presence of hormone receptors on thymocytes, cells were isolated from the thymus and incubated with androgens or oestrogens to measure apoptosis. Several techniques were used to determine thymocyte apoptosis in vitro, but no enhanced apoptotic signal was observed. Using the very sensitive TUNEL assay, no direct effect of androgens on thymocytes in vitro could be observed. This is in sharp contrast to the high signal observed with GC. Therefore, upon in vivo androgen treatment, other cells containing androgen receptors than thymocytes are probably involved in inducing the increase in thymic apoptosis. To study the role of the androgen receptor on thymocyte apoptosis, androgen receptor mutant (Tfm/Y) mice were treated with androgens. No alterations of thymocyte subpopulations were seen, suggesting that changes in the percentage of CD4+ CD8+ thymocytes after administration of androgens depend on the presence of functional androgen receptors. Thus, it is concluded that androgens indirectly accelerate thymocyte apoptosis in vivo.

Altered immune response in adult women exposed to diethylstilbestrol in utero

OBJECTIVE

Between 1940 and 1970, 1.5 million female fetuses were exposed to diethylstilbestrol in utero. Numerous deleterious effects on reproductive anatomic and physiologic characteristics have been documented in these women. However, the effects of this exposure on nonreproductive systems, which may have lifelong consequences as this cohort of women progresses beyond the childbearing years, have received little attention. On the basis of an earlier preliminary observation of altered immune reponse, we hypothesized that diethylstilbestrol-exposed women may show abnormalities in T-cell-mediated immune response.

STUDY DESIGN

Thirteen women exposed to diethylstilbestrol in utero were compared with 13 age- and menstrual cycle phase-matched control subjects with respect to the in vitro T-cell response to the mitogens phytohemagglutinin, concanavalin A, and interleukin 2.

RESULTS

As compared with controls, tritiated thymidine incorporation by T cells harvested from diethylstilbestrol-exposed women was increased 3-fold over a range of concentrations in response to concanavalin A (P <.001), increased by 50% over a range of concentrations in response to phytohemagglutinin (P <.001), and increased 2-fold in response to the endogenous mitogen interleukin 2 (P <.05).

CONCLUSIONS

In vitro evidence suggests that women exposed to diethylstilbestrol have alterations in T-cell-mediated immunity. These changes require further attention with regard to their characterization, their role in the pathogenesis of cancer and autoimmunity, and their presence in normal women exposed to diethylstilbestrol in utero.

In vivo modulation of the distribution of thymocyte subsets by female sex steroid hormones

This study examined the effects of the principal ovarian steroids, 17 beta-estradiol (E) and progesterone (P), on the thymic structure and on the intrathymic development of T-cells. Adult female rats were ovariectomized (OVX) and treated for 14 days with physiological doses of either E or P; controls received an equivalent volume of vehicle. Ovariectomy produced a marked increase (vs. sham-operated controls) in thymus weight, which was associated with an increase in the volume and cellularity of both the medulla and cortex. Treatment of OVX rats with E reduced the thymic weight to value, which was significantly lower than that of sham-operated controls decreasing the volume of cortex below level in sham-OVX rats, and reversing the effect of ovariectomy on the volume of medulla. P only prevented the increases in thymus weight and cortical volume induced by OVX. However, unlike E, it had no discernable effect on the medullary volume. E treatment reduced the cellularity of the cortex and medulla to values, which were lower than those of sham-OVX rats, while P only reversed the effects of OVX on the cellularity of both the compartments. Ovariectomy also had a profound effect on the thymocyte profile, increasing the proportion of CD4+8+TCR alpha beta- cells and producing a corresponding decrease in the relative proportions of all TCR alpha beta high cell subsets. The decrease in the latter was opposed by treatment with E or P. However, the sensitivity of the less mature cells (except CD4-8-TCR alpha beta-, the percentage of which was reduced by both hormones) to the two hormones differed. E reduced the relative proportion of CD4-8+TCR alpha beta-, CD4-8+TCR alpha beta low and CD4+8+TCR alpha beta- cells, while P increased the percentage of CD4-8+TCR alpha beta low cells. The results suggest that E and P affect both the lymphoid and nonlymphoid compartments of the thymus, and that while P increases the volume of the nonlymphoid component of the medulla, E has the opposite effect. The finding that ovariectomy decreased while E and P increased the relative proportion of the most mature thymocytes, which include CD4-8-TCR alpha beta high cells that are believed to harbour potentially autoreactive cell clones, is particularly interesting and may relate to the high propensity of autoimmune diseases in females.

Neuroendocrine control of thymus physiology

The thymus gland is a central lymphoid organ in which bone marrow-derived T cell precursors undergo differentiation, eventually leading to migration of positively selected thymocytes to the peripheral lymphoid organs. This differentiation occurs along with cell migration in the context of the thymic microenvironment, formed of epithelial cells, macrophages, dendritic cells, fibroblasts, and extracellular matrix components. Various interactions occurring between microenvironmental cells and differentiating thymocytes are under neuroendocrine control. In this review, we summarize data showing that thymus physiology is pleiotropically influenced by hormones and neuropeptides. These molecules modulate the expression of major histocompatibility complex gene products by microenvironmental cells and the extracellular matrix-mediated interactions, leading to enhanced thymocyte adhesion to thymic epithelial cells. Cytokine production and thymic endocrine function (herein exemplified by thymulin production) are also hormonally controlled, and, interestingly in this latter case, a bidirectional circuitry seems to exist since thymic-derived peptides also modulate hormonal production. In addition to their role in thymic cell proliferation and apoptosis, hormones and neuropeptides also modulate intrathymic T cell differentiation, influencing the generation of the T cell repertoire. Finally, neuroendocrine control of the thymus appears extremely complex, with possible influence of biological circuitry involving the intrathymic production of a variety of hormones and neuropeptides and the expression of their respective receptors by thymic cells.

The effects of hormones on sex differences in infection: from genes to behavior

Males of many species are more susceptible than females to infections caused by parasites, fungi, bacteria, and viruses. One proximate cause of sex differences in infection is differences in endocrine-immune interactions. Specifically, males may be more susceptible to infection than females because sex steroids, specifically androgens in males and estrogens in females, modulate several aspects of host immunity. It is, however, becoming increasingly more apparent that in addition to affecting host immunity, sex steroid hormones alter genes and behaviors that influence susceptibility and resistance to infection. Thus, males may be more susceptible to infection than females not only because androgens reduce immunocompetence, but because sex steroid hormones affect disease resistance genes and behaviors that make males more susceptible to infection. Consideration of the cumulative effects of sex steroid hormones on susceptibility to infection may serve to clarify current discrepancies in the literature and offer alternative hypotheses to the view that sex steroid hormones only alter susceptibility to infection via changes in host immune function.

Strain differences in binding properties of estrogen receptors in immature and adult BALB/c and MRL/MP-lpr/lpr mice, a model of systemic lupus erythematosus

The aim was to compare binding properties of estrogen receptors in brain, reproductive and immune tissues of immature and adult female BALB/c mice, and in the same tissues of MRL/MP-lpr/lpr mice. The latter strain spontaneously develops an autoimmune disease resembling human systemic lupus erythematosus (lupus; SLE). It is hypothesized that estradiol, through its receptors, mediates the progression of murine SLE. High-speed cytosols were prepared from hypothalamus, spleen, thymus and uterus of both strains, and incubated with the synthetic estrogen (3)H-moxestrol (NEN). Scatchard plots were derived from binding isotherms obtained after in vitro incubation. In addition, cervical lymph nodes from MRL mice could be used, but were too small in BALB/c mice. There was a significant increase in the affinity of the binding reaction i.e. a decrease in the apparent molar dissociation constant (Kd), in immune tissues and uterus with maturation in MRL but not BALB/c mice, whose tissues had, overall, a lower affinity for (3)H-moxestrol. Receptor concentrations were significantly higher in spleen and cervical lymph nodes of adult compared with immature MRL mice, but the opposite pattern was observed in BALB/c mouse spleen on maturation. These properties of estrogen receptors in MRL mice may underlie estrogen-mediated exacerbation of murine SLE.

Expression pattern of notch1, 2 and 3 and Jagged1 and 2 in lymphoid and stromal thymus components: distinct ligand-receptor interactions in intrathymic T cell development

The suggested role of Notch1 or its mutants in thymocyte differentiation and T cell tumorigenesis raises the question of how the different members of the Notch family influence distinct steps in T cell development and the role played by Notch ligands in the thymus. We report here that different Notch receptor-ligand partnerships may occur inside the thymus, as we observed differential expression of Notch1, 2 and 3 receptors, their ligands Jagged1 and 2, and downstream intracellular effectors hairy and Enhancer of Split homolog 1 (HES-1) and hairy and Enhancer of Split homolog 5 (HES-5), depending on ontogenetic stage and thymic cell populations. Indeed, while Jagged2 is expressed in both stromal cells and thymocytes, Jagged1 expression is restricted to stromal cells. Moreover, a differential distribution of Notch3, with respect to Notch1, was observed in distinct age-related thymocyte subsets. Finally, Notch3 was preferentially up-regulated in thymocytes, following the induction of their differentiation by interaction with thymic epithelial cells expressing the cognate Jagged1 and 2 ligands, suggesting that, besides Notch1, Notch3 may also be involved in distinct steps of thymocyte development. Our results suggest that the Notch signaling pathway is involved in a complex interplay of T cell developmental stages, as a consequence of the heterogeneity and specific expression of members of the Notch receptor family and their cognate ligands, in distinct thymic cell compartments.

Effects of stress on leukocyte trafficking and immune responses: implications for vaccination

Increased susceptibility of animals to infectious disease during the periparturient period results in suffering and economic losses. Stress appears to delay inflammation by reducing efficiency of CD62L-mediated immune surveillance by phagocytes. It is important to note that the effects of stress are not limited to alteration of leukocyte trafficking patterns since various stressors (e.g., transport, parturition, and castration) also decrease IFN-gamma secretion by lymphocytes, and may decrease antigen presentation efficiency by down-regulating class II molecule expression on antigen presenting cells, and delay or impair immune responses to vaccination. Documented immunosuppression in periparturient animals, particularly the bias toward Th2 immune responses, and also changes in general leukocyte trafficking patterns suggest that vaccination intending to elicit cell-mediated immunity may not be efficacious at this point of the production cycle. Based on findings of numerous periparturient studies on immunosuppression in cattle, waiting at least 30 days after parturition before administering routine vaccinations is recommended.

Overexpression of the anti-apoptotic oncogene, bcl-2, in the thymus does not prevent thymic atrophy induced by estradiol or 2,3,7, 8-tetrachlorodibenzo-p-dioxin

Dexamethasone (Dex), estradiol (E2), and 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) all affect the immune system, causing immunosuppression and thymic atrophy. It is still uncertain how and where these compounds act to induce thymic atrophy. However, it has been suggested that these compounds may have similar actions and targets, i.e., apoptosis of immature thymocytes for Dex and TCDD and preferential targeting of double-positive cells by Dex and E2. The lckpr-bcl-2 transgenic mouse has been shown to be protected against Dex-induced thymic atrophy. We used this murine model to determine if bcl-2 expression would also protect against E2- and TCDD-induced thymic atrophy. Our results indicate that, although the bcl-2 transgenic (TG+) mice were fully protected from atrophy induced by a single dose of Dex, atrophy was still induced in these mice following treatment with E2 or TCDD. Phenotypic analysis of thymocytes from TG- and TG+ mice also showed distinct consequences of atrophy induced by Dex, E2, and TCDD. Finally, since there are alternative pathways for apoptosis that are bcl-2 independent, both TG- and TG+ thymocytes were examined directly for indications of apoptosis using the TUNEL assay. After TCDD and E2 treatment there were no detectable signs of apoptosis in either TG- or TG+ mice even at early time points and at elevated dose levels. These results indicate that there are distinct mechanisms for the actions of Dex, E2, and TCDD in the thymus and that apoptosis is not a key mechanism of E2- and TCDD-induced thymic atrophy.

Neuroendocrine control of the thymus

Thymocytes undergo a complex process of differentiation, largely dependent on interactions with the thymic microenvironment, a tridimensional cellular network formed by epithelial cells, macrophages, dendritic cells, and fibroblasts. One key cellular interaction involves the TCR-CD3 complex expressed by thymocytes with MHC-peptide complexes present on microenvironmental cells. Additionally, thymic epithelial cells (TEC) interact with thymocytes via soluble polypeptides such as thymic hormones and interleukins, as well as through extracellular matrix (ECM) ligands and receptors. Such types of heterotypic interactions are under neuroendocrine control. For example, thymic endocrine function, represented by thymulin production, is up-regulated, both in vivo and in vitro, by thyroid and pituitary hormones, including prolactin and growth hormone. We also showed that these peptides enhance the expression of ECM ligands and receptors, as well as the degree of TEC-thymocyte adhesion. In addition, we studied the thymic nurse cell complex, used herein as an in vitro model for ECM-mediated intrathymic T-cell migration. We observed that T-cell migration is also hormonally regulated as ascertained by the thymocyte entrance into and exit from these lymphoepithelial complexes. Taken together these data clearly illustrate the concept that neuroendocrine circuits exert a pleiotropic control on thymus physiology. Lastly, the intrathymic production of classic hormones such as prolactin and growth hormone suggests that, in addition to endocrine circuits, paracrine and autocrine interactions mediated by these peptides and their respective receptors may exist in the thymus, thus influencing both lymphoid and microenvironmental compartments of the organ.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and diethylstilbestrol affect thymocytes at different stages of development in fetal thymus organ culture

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and estrogen induce thymic atrophy and alter thymocyte development. In the present study we investigate whether TCDD and the synthetic estrogen diethylstilbestrol (DES) alter intrathymic development by the same or different mechanisms. We compared the effects of TCDD and DES on thymocyte development in fetal thymus organ culture (FTOC) and found that both compounds caused a reduction in cell yield. TCDD- and DES-treated FTOCs yielded fewer CD4 + CD8+ double-positive cells. However TCDD treatment also led to a greater percentage of cells in the CD8+ single-positive compartment. At lower dioxin concentrations, our results demonstrated an actual increase in CD8+ cells, whereas DES-treated fetal thymocytes were mainly enriched in CD4-CD8- double-negative cells. More alpha beta-TCR+ positive cells were seen in TCDD- but not in DES-exposed cultures. Furthermore, in this study we found that TCDD and DES also alter intrathymic development at different stages in the CD4-CD8- double-negative compartment. TCDD induced a relative increase in c-kit + CD44 + CD25-HSA-thymocytes, while DES induced an relative increase in c-kit-CD44-CD25 + HSA+ cells. RT-PCR revealed that TCDD reduced RAG-1, RAG-2, and TdT gene expression in the CD4-CD8- double-negative thymocytes. Co-treatment by TCDD and DES in FTOC yielded a mixture of effects induced by each agent. Taken together, our results demonstrate that TCDD and DES affect thymocytes at different stages of development, suggesting distinct mechanisms for induction of thymic atrophy.

Estradiol down-regulates LPS-induced cytokine production and NFkB activation in murine macrophages

PROBLEM

In vivo and in vitro studies have indicated that estradiol can affect cytokine production in different cell types. This study examines whether estradiol affects inflammatory cytokine production by murine splenic macrophages.

METHODS

Mouse splenic macrophages were first treated with 17 beta-estradiol, followed by lipopolysaccharide (LPS) stimulation. The production of cytokines by macrophages with or without estradiol treatment was determined at both the protein and mRNA levels. The nuclear factor-kB (NFkB) activity of activated mouse splenic macrophages was also evaluated by electrophoretic mobility shift assay.

RESULT

Our results show that 17 beta-estradiol decreases LPS-induced IL-1 alpha, IL-6, and TNF-alpha production but not IL-10, IL-12, and macrophage inflammatory protein (MIP) production by splenic macrophages. Furthermore, inhibition of cytokine production by 17 beta-estradiol was associated with a decreased LPS-induced NFkB-binding activity.

CONCLUSION

Because cytokines are important mediators of immune function, the alteration of cytokine production by 17 beta-estradiol may thus have a profound effect on the outcome of immune response during inflammation.

Changes in the blood-thymus barrier of adult rats after estradiol-treatment

The accessibility of the thymus parenchyma for relatively large Mw (+/- 150 Kd) proteins has been studied by the intravenous injection of monoclonal antibodies (mAbs) specific either for all T cells (His-17) or MHC class II molecules (His-19) in control and estradiol benzoate (EB)-treated adult Wistar rats. In controls, the transcapsular route rather than cortical capillaries seems to be involved in the entry of molecules into the thymus. By contrast, a specific staining for either T cells (His-17) or MHC class II molecules (His-19 positive cells) disappears almost completely from the thymic cortex of EB-treated rats except in the immediate subcapsular epithelial cell layer. In these rats, T cells and epithelial cells intimately associated to blood vessels from both inner cortex and corticomedullary border showed additional staining with the respective mAbs confirmed by electron microscopy. The disappearance of the transcapsular route together with the increased vascular permeability of cortical blood vessels would be related to the reinforcement of the subcapsular epithelial cell layer and to direct effects of EB on vascular endothelia, respectively. These results are discussed in relationship to the cell migration into and out of adult thymus, as suggested by the changes in intrathymic T cell subsets evaluated by flow cytometry.

Immunoendocrine mechanisms in mammary tumor progression: direct prolactin modulation of peripheral and preneoplastic hyperplastic-alveolar-nodule- infiltrating lymphocytes

We have previously shown that the immunoregulatory function of prolactin may play a role in the progression of the mouse mammary preneoplastic hyperplastic alveolar nodule (HAN) line C4 to carcinoma. In this study we investigated the direct effect of prolactin on lymphocytes isolated from normal and C4-HAN-bearing mice. In addition, we tested the effect of ovariectomy on prolactin/lymphocyte interaction to see whether, as has been reported in rats [Mukherjee P., Hymer W. C. (1992) Prog Neuroendocrinol Immunol 5: 108; Viselli S. M. et al. (1991) Endocrinology 129: 983], removal of estrogen would enhance the response to prolactin in mice. Proliferation of splenocytes, lymph node cells and HAN-infiltrating lymphocytes was stimulated by prolactin in a dose-responsive fashion. Ovariectomy did not alter this effect consistently. Cell-cycle analysis based on simultaneous staining of DNA and RNA revealed that prolactin-stimulated lymphocytes progress through all phases of the cell cycle whereas anti-prolactin antiserum inhibits this stimulation. Two-color flow-cytometric analysis revealed the time-dependent induction of interleukin-2 (IL-2) receptor expression on both CD4+ and CD8+ cells by prolactin. Prolactin-treated lymphocytes also produced low yet detectable levels of bioactive IL-2 in a dose- and time-dependent fashion. Prolactin enhanced lymphocyte responsiveness to mitogens and showed a marked synergism at suboptimal concentrations. Pretreatment of splenocytes from HAN bearers with a high concentration of prolactin slightly enhanced natural killer (NK) activity; anti-prolactin antiserum reduced the NK lytic activity of poly(I).poly(C)-activated splenocytes from HAN-bearing mice. Our results provide direct experimental evidence for the stimulatory effect of prolactin on lymphocyte function and IL-2-mediated lymphocyte proliferation and suggest a mechanism linking the endocrine system to immunomediated enhancement of HAN progression.

Ultrastructural changes in the adult rat thymus after estradiol benzoate treatment

Although numerous authors have correlated high levels of circulating estrogens with thymic involution, a systematic analysis to date on the histological changes affecting the thymus gland in that situation is lacking. In the present study we report both histological and ultrastructural changes occurring in the thymus of adult Wistar rats which received a single dose either of 100 micrograms or 500 micrograms of estradiol benzoate. Both doses induced thymic involution which correlated well with histological changes observed in the lymphoid populations but also with profound modifications in the thymic epithelial component. Moreover, intrathymic erythro-and granulopoiesis, increased numbers of both macrophages and plasma cells, and important variations in the thymic vascular permeability occurred in estradiol benzoate treated rats. These results are discussed from the perspective that changes in both the non-lymphoid cell components of thymic microenvironments and vascular permeability are essential to understand the general effects of sex steroids on the immune system.

Suppression of B lymphopoiesis during normal pregnancy

We describe a dramatic reduction in numbers and activity of committed B lymphocyte precursors in the bone marrow of normal pregnant mice. Changes in cells responsive to IL-7 were evident as early as 6.5 d of pregnancy and values were < 10% of normal at parturition. B lineage precursors, identified by display of CD45R and absence of surface IgM, were also substantially depressed, and subpopulations representing different stages in the B lineage were assessed by three-color flow cytometry. Early pro-B cells are medium to large in size and have been previously characterized by low expression of the heat-stable antigen (HSA). This category of cells was not reduced, and in fact may have been slightly elevated, during pregnancy. In contrast, all subsequent populations of B lineage precursors, defined by patterns of expression of heat-stable and CD43 antigens, were substantially depressed. The immediate precursors of B cells (small pre-B cells) were identified by small size, expression of CD45R, absence of CD43, and lack of surface IgM. These were the most reduced of any phenotypically defined population in bone marrow. Numbers of newly formed B cells, characterized by the presence of sIgM, but not sIgD, were also diminished. However, B cells with a mature phenotype (sIgM+, sIgD+) were present in normal to somewhat elevated numbers. Mitogen-responsive B cells clonable in a semisolid agar assay were not significantly affected. A bromodeoxyuridine (BrdU) labeling technique was used to evaluate mitotic activity, which revealed an increased proportion of long-lived lymphocytes in the bone marrow of pregnant mice. These observations indicate that B lymphopoiesis is markedly downregulated during pregnancy and that all precursor populations beyond the early pro-B cell stage are affected. The pregnancy-related changes in bone marrow were selective for B lineage precursors, as cells expressing myeloid and erythroid markers were not reduced. In spleen, evidence was obtained for partial depletion of one subset of B cells. These cells, which have been reported to be recent immigrants from marrow, are characterized as having high levels of sIgM and HSA. Changes in other major B lymphocyte subsets in the spleen were less remarkable. When considered with results from the BrdU labeling procedure, the findings indicate that both production and export of lymphocytes from marrow may be substantially decreased. Numbers of B cell precursors were higher in postpartum animals whose litters were removed at birth, suggesting that lactation may prolong regeneration of lymphocyte production.(ABSTRACT TRUNCATED AT 400 WORDS)

Thymus changes in experimentally induced myasthenia gravis

Experimental myasthenia gravis (EMG) was elicited in female AO rats, 8-12 weeks of age, by injection of 100 micrograms/rat Torpedo marmorata acetylcholine receptor (AChR)-protein incorporated in CFA. Bordetella pertussis, 24 x 10(9) microorganisms, rat, was injected simultaneously as additional adjuvant. Rats were sacrificed on the day of appearance of the clinical signs of EMG, and thymuses were used for histological analysis using stereologic method, and thymocyte subsets were estimated by flow cytometry. Two and three colour fluorescence was applied to determine DN (CD4-CD8-), DP (CD4+CD8+), SP-CD4+ (CD4+CD8-) and SP-CD8+ (CD4-CD8+) subsets, as well as thymocytes expressing TCR alpha/beta. Rats immunized with BSA and rats injected with saline were used as controls. From 56 rats immunized with AChR-protein, 44 rats developed the disease, between day 7 and 11 after immunization. Severity of disease varied from + to + + +. Stereologic analysis of tissue sections revealed a highly significant reduction of thymic cortex and hypertrophy of medulla in EMG thymuses. Similar, but very slight changes were observed in thymuses of rats immunized with BSA. Percentages of DN, SP-CD4+, and SP-CD8+ subpopulations were significantly increased, while the percentage of DP population showed a marked decrease. These preliminary data suggest an alteration of thymocyte maturational events. Whether these changes could be responsible for the initiation of autoimmunity, or are occurring as a secondary phenomenon, after EMG was already established following the injection of cross reactive antigen, is a matter for discussion.

Oestrogen retards the development of spontaneous thymomas in BUF/Mna rats

BUF/Mna rats develop spontaneous thymomas with nearly 100% incidence in both sexes. While the thymomas in males develop from around 9 months of age, those in females start from 13-15 months of age. To clarify the mechanism of the delay of thymomagenesis in females, the effect of sex hormones on the development of thymomas was examined after either gonadectomy or oestrogen treatment. Prepubertal ovariectomy accelerated the thymoma development in females, whereas orchiectomy did not affect it. An intraperitoneal injection of oestriol (20 mg) into males at 2 months of age remarkably diminished the thymic weight to about one-tenth of age-matched controls at 16 months of age. These results suggest that oestrogen can actually retard the onset of thymoma in spite of genetic control of its incidence. However, oestrogen did not cause thymic involution when it was injected into rats over 9 months of age. Immunohistochemically, there seemed to be no distinct difference in distribution of oestrogen-receptor-bearing epithelial cells between thymomas and 2- to 3-month-old thymuses. The oestrogen sensitivity of the thymus might be destined to be lost, as the thymic epithelial cells start neoplastic changes with the impairment of oestrogen-receptor function.