Extrathymic pathways of T-cell differentiation and immunomodulation

The influence of 17β-oestradiol on lymphopoiesis and immune system ontogenesis in juvenile sea bass, Dicentrarchus labrax

The female sex steroid 17β-oestradiol (E2) is involved in the regulation of numerous physiological functions, including the immune system development and performance. The role of oestrogens during ontogenesis is, however, not well studied. In rodents and fish, thymus maturation appears to be oestrogen-dependent. Nevertheless, little is known about the function of oestrogen in immune system development. To further the understanding of the role of oestrogens in fish immune system ontogenesis, fingerlings of European sea bass (Dicentrarchus labrax) were exposed for 30 days to 20 ng E2·L^-1, at two ages tightly related to thymic maturation, i.e., 60 or 90 days post hatch (dph). The expression of nuclear and membrane oestrogen receptors was measured in the thymus and spleen, and the expression of several T cell-related gene markers was studied in both immune organs, as well as in the liver. Waterborne E2-exposure at 20.2 ± 2.1 (S.E.) ng·L^-1 was confirmed by radioimmunoassay, leading to significantly higher E2-contents in the liver of exposed fish. The majority of gene markers presented age-dependent dynamics in at least one of the organs, confirming thymus maturation, but also suggesting a critical ontogenetic window for the implementation of liver resident γδ and αβ T cells. The oestrogen receptors, however, remained unchanged over the age and treatment comparisons with the exception of esr2b, which was modulated by E2 in the younger cohort and increased its expression with age in the thymus of the older cohort, as did the membrane oestrogen receptor gpera. These results confirm that oestrogen-signalling is involved in thymus maturation in European sea bass, as it is in mammals. This suggests that esr2b and gpera play key roles during thymus ontogenesis, particularly during medulla maturation. In contrast, the spleen expressed low or non-detectable levels of oestrogen receptors. The E2-exposure decreased the expression of tcrγ in the liver in the cohort exposed from 93 to 122 dph, but not the expression of any other immune-related gene analysed. These results indicate that the proliferation/migration of these innate-like T cell populations is oestrogen-sensitive. In regard to the apparent prominent role of oestrogen-signalling in the late thymus maturation stage, the thymic differentiation of the corresponding subpopulations of T cells might be regulated by oestrogen. To the best of our knowledge, this is the first study investigating the dynamics of both nuclear and membrane oestrogen receptors in specific immune organs in a teleost fish at very early stages of immune system development as well as to examine thymic function in sea bass after an exposure to E2 during ontogenesis.

Effect of Estriol, Chorionic Gonadotropin, and Oncostatin M on the Expression of Recombinase RAG-1 in Regulatory T Lymphocyte Subpopulations

We studied the effect of estriol, chorionic gonadotropin, oncostatin M, and hormone-cytokine combinations on the expression of recombinase RAG-1 in T-regulatory (Treg) and T helper 17 (Th17) lymphocytes. It was found that estriol in a concentration corresponding to the first trimester of pregnancy increased the level of Treg (CD4⁺FoxP3⁺) cells and suppressed the formation of Th17 (CD4⁺RORC⁺) lymphocytes. This effect was nor observed after individual administration of chorionic gonadotropin and oncostatin M, but some combinations of the studied hormones with oncostatin M increased the percentage of CD4⁺FOXP3⁺ cells. In the presence of oncostatin M, the studied hormones enhanced the expression of RAG-1 in CD4⁺FoxP3⁺ cells, but not in CD4⁺RORC⁺ cells, thereby initiating of Treg T-cell receptor (TCR) revision. The mechanisms of hormone cytokine control of induction of the immune tolerance during pregnancy are discussed.

Fibrotic liver microenvironment promotes Dll4 and SDF-1-dependent T-cell lineage development

The reconstitution of the T-cell repertoire and quantity is a major challenge in the clinical management of HIV infection/AIDS, cancer, and aging-associated diseases. We previously showed that autologous bone marrow transfusion (BMT) via the hepatic portal vein could effectively restore CD4+ T-cell count in AIDS patients also suffering from decompensated liver cirrhosis. In the current study, we characterized T-cell reconstitution in a mouse model of liver fibrosis induced by CCl4 and found that T-cell reconstitution after BMT via hepatic portal vein was also greatly enhanced. The expression of Dll4 (Delta-like 4), which plays an important role in T-cell progenitor expansion, was elevated in hepatocytes of fibrotic livers when compared to normal livers. This upregulation of Dll4 expression was found to be induced by TNFα in an NFκB-dependent manner. Liver fibroblasts transfected with Dll4 (LF-Dll4) also gained the capacity to promote T-cell lineage development from hematopoietic stem cells (HSCs), resulting in the generation of DN2 (CD4 and CD8 DN 2) and DN3 T-cell progenitors in vitro, which underwent a normal maturation program when adoptively transferred into Rag-2 deficient hosts. We also demonstrated a pivotal role of SDF-1 produced by primary liver fibroblasts (primary LF) in T-lineage differentiation from HSCs. These results suggest that Dll4 and SDF-1 in fibrotic liver microenvironment could promote extrathymic T-cell lineage development. These results expand our knowledge of T-cell development and reconstitution under pathological conditions.

Effects of apoptosis on liver aging

As an irreversible and perennial process, aging is accompanied by functional and morphological declines in organs. Generally, aging liver exhibits a decline in volume and hepatic blood flow. Even with a preeminent regenerative capacity to restore its functions after liver cell loss, its biosynthesis and metabolism abilities decline, and these are difficult to restore to previous standards. Apoptosis is a programmed death process via intrinsic and extrinsic pathways, in which Bcl-2 family proteins and apoptosis-related genes, such as p21 and p53, are involved. Apoptosis inflicts both favorable and adverse influences on liver aging. Apoptosis eliminates transformed abnormal cells but promotes age-related liver diseases, such as nonalcoholic fatty liver disease, liver fibrosis, cirrhosis, and liver cancer. We summarize the roles of apoptosis in liver aging and age-related liver diseases.

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.

The significance of neonatal thymectomy for shaping the immune system in children with congenital heart defects

The thymus plays an important role in the development of the immune cell pool; it serves as the primary location for T-lymphocyte maturation. Early cardiac surgical interventions for congenital heart defects are necessarily associated with thymectomy, i.e. the partial or complete removal of the thymus. A newborn infant already has a functioning thymus and developed cells of the immune system. However, thymectomy eliminates the primary location where T cells differentiate and mature. This study summarizes the current knowledge of the cellular disturbances and potential clinical consequences associated with performing thymectomy in children treated surgically for congenital heart defects.

The production of alpha/beta and gamma/delta double negative (DN) T-cells and their role in the maintenance of pregnancy

The ability of the thymus gland to convert bone marrow-derived progenitor cells into single positive (SP) T-cells is well known. In this review we present evidence that the thymus, in addition to producing SP T-cells, also has a pathway for the production of double negative (DN) T-cells. The existence of this pathway was noted during our examination of relevant literature to determine the cause of sex steroid-induced thymocyte loss. In conducting this search our objective was to answer the question of whether thymocyte loss is the end product of a typical interaction between the reproductive and immune systems, or evidence that the two systems are incompatible. We can now report that "thymocyte loss" is a normal process that occurs during the production of DN T-cells. The DN T-cell pathway is unique in that it is mediated by thymic mast cells, and becomes functional following puberty. Sex steroids initiate the development of the pathway by binding to an estrogen receptor alpha located in the outer membrane of the mast cells, causing their activation. This results in their uptake of extracellular calcium, and the production and subsequent release of histamine and serotonin. Lymphatic vessels, located in the subcapsular region of the thymus, respond to the two vasodilators by undergoing a substantial and preferential uptake of gamma/delta and alpha/beta DN T- cells. These T- cells exit the thymus via efferent lymphatic vessels and enter the lymphatic system.The DN pathway is responsible for the production of three subsets of gamma/delta DN T-cells and one subset of alpha/beta DN T-cells. In postpubertal animals approximately 35 % of total thymocytes exit the thymus as DN T-cells, regardless of sex. In pregnant females, their levels undergo a dramatic increase. Gamma/delta DN T-cells produce cytokines that are essential for the maintenance of pregnancy.

Histologic Features of Postnatal Development of Immune System Organs in the Sprague-Dawley Rat

The immune system of the rat undergoes substantial functional and morphological development during the postnatal period. Some aspects of this development are genetically predetermined, while other aspects depend on environmental influences. Detailed information on postnatal development is important in the interpretation of histopathologic findings in juvenile toxicology and pubertal assay studies, as well as other studies conducted in juvenile rats. Studies were conducted to provide detailed characterization of histologic features of the major functional compartments of immune system organs in male and female Sprague-Dawley rats at weekly intervals from the day of birth through postnatal day (PND) 42. Maturation of the individual immune system organs occurred across a range of ages, with histologic maturation of T-cell-related compartments typically occurring prior to maturation of B-cell-related compartments. The sequence of histologic maturation was bone marrow and thymus on PND 14, mesenteric lymph node on PND 21, Peyer's patches and bronchus-associated lymphoid tissue on PND 28, mandibular lymph node, nasopharynx-associated lymphoid tissue, and diffuse mucosal mononuclear cell population of small intestine on PND 35, and spleen on PND 42. An estimation of functional maturation can be made based on the morphological indications of maturity of each compartment of immune system organs, but histologic indications of maturity do not confirm functional immunocompetence.

Routine thymectomy in congenital cardiac surgery changes adaptive immunity without clinical relevance

The actual importance of the thymus in both children and adults is largely unclear. In congenital cardiac surgery, a partial or total thymectomy is frequently performed to improve access to the heart and great vessels. We performed a literature search to evaluate the effect on the adaptive immune system of the removal of thymus tissue in patients with congenital heart disease. A PubMed search according to Dunning's standard provided 149 articles, of which 13 addressed our search question. Each study has been tabulated with author, cases, controls, follow-up, methods, results and limitations. A first group of articles repeatedly showed the effect on the T-cell compartment, including the impact on subgroups of this compartment. More recent studies, usually with a longer follow-up, confirm that the earlier changes in T-cell population appear to be permanent. Only one author found a normalization of T-cell population five years after thymectomy. In contrast to these clear changes in T-cell population, there is currently no clear clinical relevance. A literature search on thymectomy in congenital cardiac surgery revealed clear changes in T-cell-related immunity; however, there is a lack of clinical relevance. Further investigation of the adaptive immune system is required to explain this discrepancy.

Tissue biopsy monitoring of operational tolerance in liver allograft recipients

PURPOSE OF REVIEW

Highly selected, long-surviving, liver allograft recipients with normal/near normal liver injury tests can be weaned from immunosuppression. Baseline biopsies document changes before weaning and can help stratify risk of rejection or dysfunction after weaning; biopsies after weaning are used to study mechanisms of operational tolerance and to monitor for subclinical events.

RECENT FINDINGS

Clinicopathological features associated with successful weaning include a lack of sensitization [negative donor-specific antibodies (DSA) and lack of tissue C4d deposits]; 'inexperienced' recipient immune system with limited potential for cross-reactivity (less immunological memory; infant recipients); noninflamed allograft in those with nonviral, nonimmunological original diseases; upregulation of liver genes associated with iron metabolism; allograft colonization with 'immunosuppressive' cells (Treg and γδ-1>γδ-2); and longer time on immunosuppression, which might signal slow clonal deletion or silencing. The differential diagnosis of histopathological findings detected before and after weaning includes emerging infections, typical and atypical cellular rejection, indolent antibody-mediated rejection, 'autoimmunity', and other causes of progressive fibrosis.

SUMMARY

Operationally tolerant liver allograft recipients can be successfully managed with very low, and sometimes no immunosuppression, but challenges exist. Newer approaches to tissue pathology and tissue, serum, and cross-platform analytics are needed to predict successful weaning and to monitor for subclinical events.

A quantitative study of the mechanisms behind thymic atrophy in Gαi2-deficient mice during colitis development

Mice deficient for the G protein subunit Gαi2 spontaneously develop colitis, a chronic inflammatory disease associated with dysregulated T cell responses. We and others have previously demonstrated a thymic involution in these mice and an aberrant thymocyte dynamics. The Gαi2(-/-) mice have a dramatically reduced fraction of double positive thymocytes and an increased fraction of single positive (SP) thymocytes. In this study, we quantify a number of critical parameters in order to narrow down the underlying mechanisms that cause the dynamical changes of the thymocyte development in the Gαi2(-/-) mice. Our data suggest that the increased fraction of SP thymocytes results only from a decreased number of DP thymocytes, since the number of SP thymocytes in the Gαi2(-/-) mice is comparable to the control littermates. By measuring the frequency of T cell receptor excision circles (TRECs) in the thymocytes, we demonstrate that the number of cell divisions the Gαi2(-/-) SP thymocytes undergo is comparable to SP thymocytes from control littermates. In addition, our data show that the mature SP CD4(+) and CD8(+) thymocytes divide to the same extent before they egress from the thymus. By estimating the number of peripheral TREC(+) T lymphocytes and their death rate, we could calculate the daily egression of thymocytes. Gαi2(-/-) mice with no/mild and moderate colitis were found to have a slower export rate in comparison to the control littermates. The quantitative measurements in this study suggest a number of dynamical changes in the thymocyte development during the progression of colitis.

Thymectomy in early childhood: a model for premature T cell immunosenescence?

The thymus is the main source of recent thymic emigrants (RTE) and naïve T cells. The aging of the immune system (immunosenescence) is characterized by loss of thymic function, decreased numbers of RTE, peripheral proliferation of mature T cells, and oligoclonal expansions of specific T cell subpopulations. As shown in several studies, thymectomized patients demonstrate signs of premature immunosenescence reminiscent of aged people, such as decreased proportions of naïve T cells and RTE, a compensatory increase of mature T cell subpopulations with increased proliferation rates, restriction of the T cell receptor repertoire, and a delayed response to new antigens and vaccinations. This review demonstrates that, despite some limitations, childhood thymectomy may serve as an useful model for premature immunosenescence, mimicking changes expected after physiological thymus involution in the elderly. Thus, it may prove an insightful tool for obtaining better understanding of human naïve T cell development, thymic function, and maintenance of the naïve T cell pool.

The estrogen-injected female mouse: new insight into the etiology of PCOS

BACKGROUND

Female mice and rats injected with estrogen perinatally become anovulatory and develop follicular cysts. The current consensus is that this adverse response to estrogen involves the hypothalamus and occurs because of an estrogen-induced alteration in the GnRH delivery system. Whether or not this is true has yet to be firmly established. The present study examined an alternate possibility in which anovulation and cyst development occurs through an estrogen-induced disruption in the immune system, achieved through the intermediation of the thymus gland.

METHODS, RESULTS AND CONCLUSION

A putative role for the thymus in estrogen-induced anovulation and follicular cyst formation (a model of PCOS) was examined in female mice by removing the gland prior to estrogen injection. Whereas all intact, female mice injected with 20 microg estrogen at 5-7 days of age had ovaries with follicular cysts, no cysts were observed in animals in which thymectomy at 3 days of age preceded estrogen injection. In fact, after restoring immune function by thymocyte replacement, the majority of thymectomized, estrogen-injected mice had ovaries with corpora lutea. Thus, when estrogen is unable to act on the thymus, ovulation occurs and follicular cysts do not develop. This implicates the thymus in the cysts' genesis and discounts the role of the hypothalamus. Subsequent research established that the disease is transferable by lymphocyte infusion. Transfer took place between 100-day-old estrogen-injected and 15-day-old naïve mice only when recipients were thymectomized at 3 days of age. Thus, a prerequisite for cyst formation is the absence of regulatory T cells. Their absence in donor mice was judged to be the result of an estrogen-induced increase in the thymus' vascular permeability, causing de facto circumvention of the final stages of regulatory T cell development. The human thymus has a similar vulnerability to steroid action during the fetal stage. We propose that in utero exposure to excessive levels of steroids such as estrogen has a long-term effect on the ability of the thymus to produce regulatory T cells. In female offspring this can lead to PCOS.

Vbeta usage and T regulatory cells in children following partial or total thymectomy after open heart surgery in infancy

During open heart surgery in infants the thymus was usually removed, partly or completely. Our previous studies on 16 such children indicated reduced T-cell output later in life with signs of extrathymic maturation of the T cells, but no reduction in T regulatory cells (CD4+CD25+). The diversity of the T-cell repertoire in these children was examined to test if the extrathymic microenvironment could alter Vbeta usage. The expression of Foxp3 and CD127 in CD4+CD25(high) T cells was measured in order to determine whether the T regulatory cells had the phenotype of natural T regulatory cells. There was a wide distribution of Vbeta usage in both study and control groups. Significant variability was found in Vbeta usage for CD4+ and CD8+ T cells when the distribution of the percentage of T cells expressing each Vbeta family was analysed between individuals within each group (P < 0.001; Kruskal-Wallis). Significant difference was also found in average usage of Vbeta2, Vbeta5.1 and Vbeta14 chains within CD4+ T cells and Vbeta2, Vbeta8 and Vbeta21.3 chains within CD8+ cells between the groups (P < 0.05; Student's t-test). There was no difference between the two groups with regard to the proportion of CD4+CD25(high) T cells and no difference in the average expression of Foxp3 or CD127 within the CD4+CD25(high) population. Our data provide evidence that cardiothoracic surgery in infants and total or partial thymectomy alters Vbeta usage, suggesting more limited selection in such children than in the control group. The frequency of natural T regulatory cells seems to be unimpaired.

Thymectomy in early childhood: significant alterations of the CD4(+)CD45RA(+)CD62L(+) T cell compartment in later life

The study was aimed to assess indicators of immunosenescence, such as the total counts of peripheral blood CD4(+)CD45RA(+)CD62L(+) (naive) T cells, the numbers of T cell receptor excision circles (TRECs), and Ki67-expression as marker of peripheral replication in thymectomized patients (TP) (n=101) compared to age-matched healthy donors (HD) (n=81). In TP, there was an inverse correlation between naive T cells and chronological age (p<0.001) or time post thymectomy (p<0.001). TP demonstrated lower TREC numbers in naive T cells compared to HD (p<0.001). TREC numbers negatively correlated with time post thymectomy (p<0.001). Percentages of Ki67-expresssing naive T cells were higher in TP compared to HD (p<0.05). The findings of the presented long-term follow up cohort of thymectomized patients indicate that changes of the peripheral naive T cell subset in TP may resemble the findings of an aging immune system in elderly persons after thymic involution. Our data provide evidence that peripheral T cell homeostasis in TP is maintained at minimal levels mainly by extrathymic expansion of existing naive T cells in the periphery to compensate the diminished thymic output.

Normal mouse kidneys contain activated and CD3+CD4- CD8- double-negative T lymphocytes with a distinct TCR repertoire

Healthy liver, intestine, lung, and skin harbor resident lymphocytes with conventional and unconventional phenotypes. Lymphocytes also have been detected in healthy mice kidneys; however, these cells have not been well studied and have been largely overlooked. To better characterize the intra-renal lymphocytes, we extensively perfused C57BL/6J mice with PBS and then isolated mononuclear cells for flow cytometry analysis. We observed T cells, B cells, and NK cells in normal mice kidneys after extensive perfusion. Approximately 50% of kidney T lymphocytes expressed intermediate levels of CD3 (CD3int T cells). Similar to liver and lung, a high percentage of unconventional CD3+CD4(-)CD8(-) double-negative T cells was observed in normal mice kidneys, from which 11% expressed B220 antigen. Unlike the spleen and blood, the classic CD4+ and CD8+ T lymphocytes in the kidney had a high proportion of activated CD69+ and effector/memory CD44- CD62L ligand phenotypes. Also, a small percentage of CD4+CD25+forkhead box p3+ and NKT cells was observed in perfused and exanguinated kidneys. In addition, a distinct TCR repertoire was found on intra-renal conventional and unconventional T cells compared with those from the spleen. Finally, after 24 h of renal ischemia reperfusion injury (IRI), increased production of cytokines IFN-gamma and TNF-alpha by CD4+ and CD8+ T cells, isolated from perfused kidneys, was observed. These data suggest that some of these cells harbored in the kidney could be implicated in the immune response of the IRI pathogenic process.

Histochemical and molecular overview of the thymus as site for T-cells development

The thymus represents the primary site for T cell lymphopoiesis, providing a coordinated set for critical factors to induce and support lineage commitment, differentiation and survival of thymus-seeding cells. One irrefutable fact is that the presence of non-lymphoid cells through the thymic parenchyma serves to provide coordinated migration and differentiation of T lymphocytes. Moreover, the link between foetal development and normal anatomy has been stressed in this review. Regarding thymic embryology, its epithelium is derived from the embryonic endodermal layer, with possible contributions from the ectoderm. A series of differentiating steps is essential, each of which must be completed in order to provide the optimum environment for thymic development and function. The second part of this article is focused on thymic T-cell development and differentiation, which is a stepwise process, mediated by a variety of stromal cells in different regions of the organ. It depends strongly on the thymic microenvironment, a cellular network formed by epithelial cells, macrophages, dendritic cells and fibroblasts, that provide the combination of cellular interactions, cytokines and chemokines to induce thymocyte precursors for the generation of functional T cells. The mediators of this process are not well defined but it has been demonstrated that some interactions are under neuroendocrine control. Moreover, some studies pointed out that reciprocal signals from developing T cells also are essential for establishment and maintenance of the thymic microenvironment. Finally, we have also highlighted the heterogeneity of the lymphoid, non-lymphoid components and the multi-phasic steps of thymic differentiation. In conclusion, this review contributes to an understanding of the complex mechanisms in which the foetal and postnatal thymus is involved. This could be a prerequisite for developing new therapies specifically aimed to overcome immunological defects, linked or not-linked to aging.

Diminished response to tick-borne encephalitis vaccination in thymectomized children

In order to analyze the clinical impact of immunological alterations in thymectomized children after exposure to a new antigen (tick-borne encephalitis virus (TBEV) vaccine), 17 thymectomized children completed a three-dose immunization regimen. Thymectomized children showed significantly lower TBEV IgG antibody levels after the second vaccination when compared to healthy age-matched controls (n=30) (p=0.03), but a normal response after the third vaccination. Age at thymectomy correlated significantly with the TBEV IgG antibody levels (p=0.04). Thymectomized children also showed significantly lower total counts and percentages for naïve T cells correlating with time after thymectomy (p=0.02), than observed for controls. These changes in T cell subsets and the decreased ability to respond to new antigens in thymectomized children, as observed here, may precede more striking effects such as higher infection rates or autoimmune conditions as they age.

Severe defect in thymic development in an insertional mutant mouse model

Transgenic mice were generated expressing NK1.1, an NK cell-associated receptor, under control of the human CD2 promoter. Unexpectedly, one of the founder lines, Tg66, showed a marked defect in thymic development characterized by disorganized architecture and small size. Mapping of the transgene insertion by fluorescence in situ hybridization revealed integration in chromosome 2, band G. Already from postnatal day 3, the thymic architecture was disturbed with a preferential loss of cortical thymic epithelial cells, a feature that became more pronounced over time. Compared with wild-type mice, total thymic cell numbers decreased dramatically between 10 and 20 days of age. Thymocytes isolated from adult Tg66 mice were predominantly immature double-negative cells, indicating a block in thymic development at an early stage of differentiation. Consequently, Tg66 mice had reduced numbers of peripheral CD4(+) and CD8(+) T cells. Bone marrow from Tg66 mice readily reconstituted thymi of irradiated wild-type as well as RAG-deficient mice. This indicates that the primary defect in Tg66 mice resided in nonhemopoietic stromal cells of the thymus. The phenotype is observed in mice heterozygous for the insertion and does not resemble any known mutations affecting thymic development. Preliminary studies in mice homozygous for transgene insertion reveal a more accelerated and pronounced phenotype suggesting a semidominant effect. The Tg66 mice may serve as a useful model to identify genes regulating thymic epithelial cell differentiation, thymic development, and function.

Transplant Tolerance Associated With a Th1 Response and Not Broken by IL-4, IL-5, and TGF-β Blockade or Th1 Cytokine Administration

BACKGROUND

Specific transplant tolerance is mediated by CD4 T cells that die unless supported by T-cell derived cytokines and donor antigen. This study examined the role of Th1 and Th2 cytokines in the maintenance of tolerance.

METHODS

Tolerance to fully allogeneic PVG cardiac allografts in DA rats was induced by short-term anti-CD3 monoclonal antibody therapy. Responses of tolerant cells to donor and third party antigen were assessed in vivo by examination of the infiltrate in the heart and application of skin grafts, and in vitro in mixed lymphocyte culture. Cell subsets were stained, induction of cytokine mRNA assayed by reverse-transcriptase polymerase chain reaction and the role of cytokines determined by treating with blocking monoclonal antibody to cytokines or cytokine administration.

RESULTS

Tolerated grafts had a T cell and macrophage infiltrate with increased mRNA for Th1 cytokines, interleukin (IL)-2, and interferon (IFN)-gamma but not Th2 cytokines. Peripheral lymphocytes proliferated in mixed lymphocyte culture and expressed Th1 cytokine mRNA. Tolerant hosts accepted PVG and rejected Lewis skin allografts and the lymph nodes draining both these grafts had similar induction of Th1 and Th2 cytokine mRNA. Treatment of tolerant rats with Th1 cytokines IL-2, IFN-gamma, and IL-12p70 or monoclonal antibody that blocked IL-4, IL-5, and transforming growth factor-beta did not prevent acceptance of PVG skin grafts.

CONCLUSIONS

These studies in a model of tolerance regulated by CD4CD25 T cells demonstrated there was no defect in Th1 responses. Tolerance was due to regulation that was not solely dependent on IL-4, IL-5, or transforming growth factor-beta and was not inactivated or overwhelmed by administration of Th1 cytokines, IL-2, IFN-gamma or IL-12p70.

Cells with haematopoietic stem cell phenotype in adult human endometrium: relevance to infertility?

BACKGROUND

Uterine lymphoid cell repertoires are specialized in order to meet the twin demands of successful pregnancy and local immunosurveillance. The possibility that some of these populations might differentiate locally from progenitor cells has been proposed.

METHODS

Endometrial tissue from women with a history of infertility as well as fertile controls was examined for haematopoietic stem cells (HSCs) and lymphoid progenitors using three-colour flow cytometry.

RESULTS

Significant populations of phenotypic HSCs (CD34+ CD45+ ) were detected in all samples, a high proportion of which co-expressed the differentiation marker CD45RA (45.7%), indicating ongoing differentiation. Almost 30% of uterine HSCs co-expressed CD56 and 44% co-expressed CD7, suggesting the presence of lymphoid progenitors. Small proportions expressed CD127 and CD122, receptors for interleukin (IL)-7 and IL-15, respectively. HSC numbers were similar in the endometrial samples from fertile and infertile women. However, the proportion co-expressing the natural killer (NK) antigen CD56 was significantly increased compared with HSCs found in the endometrium of fertile controls (P = 0.002).

CONCLUSIONS

This is the first demonstration of cells with an HSC phenotype in the human endometrium, and increased proportions of NK progenitors in endometrium of women with infertility suggests a dysregulation of this pathway that may contribute to infertility.

Evidence for extrathymic T cell maturation after thymectomy in infancy

Our previous study showed that children who had been partially or completely thymectomized during heart surgery as infants had lower proportions and numbers of total lymphocytes and reduced proportions of T cells (CD3(+)), helper T cells (CD4(+)) and naive T cells (CD3(+) CD4(+) CD45RA(+)), but normal proportion of cytotoxic T cells (CD8(+)). In this study T lymphocytes from a selected group of eight of these children and age- and gender-matched controls were characterized further using flow cytometry to determine phenotypes of T cells and T cell subsets related to T cell regulation and phenotypes suggestive of extrathymic maturation. Immune function was assessed by measuring autoantibodies and antibodies against vaccines. The study group had significantly lower numbers of all the main subsets of T lymphocytes and the composition was different. Thus, the proportions of lymphocytes with the following phenotypes: CD3(+), CD2(+), CD7(+), CD4(+), CD62L(+), CD4(+) CD62L(+) and CD4(+) CD69(-) were significantly reduced in the study group compared with the control group, but significantly higher proportions were seen of lymphocytes expressing CD8alpha(+) CD8beta(-) and TCRgammadelta(+) CD8alpha(+) CD8beta(-). The absolute number and proportion of CD4(+) CD25(+) cells were reduced but the proportions of the subgroup of naive regulatory T cells (CD4(+) CD25(+) CD62L(+)) and non-activated regulatory T cells (CD4(+) CD25(+) CD69(-)) were not reduced in the thymectomized children. We conclude that the phenotypic characteristics of T lymphocytes of children who have lost their thymus in infancy are indicative of extrathymic maturation. T regulatory cells appear to be less affected than other subsets by the general reduction in T cell numbers.

Thymic output and functionality of the IL-7/IL-7 receptor system in centenarians: implications for the neolymphogenesis at the limit of human life

During aging, the thymus undergoes a marked involution that is responsible for profound changes in the T-cell compartment. To investigate the capacity of the thymus to produce new cells at the limit of human lifespan, we analyzed some basic mechanisms responsible for the renewal and maintenance of peripheral T lymphocytes in 44 centenarians. Thymic functionality was analyzed by the quantification of cells presenting the T-cell receptor rearrangement excision circles (TREC). A new method based upon real-time PCR was used, and we found that most centenarians (84%) had undetectable levels of TREC+ cells. Six-color cytofluorimetric analysis revealed that centenarians had an extremely low number of naïve T cells; central memory and effector memory T cells were greatly increased, while terminally differentiated cells were as numerous as in young (aged 20-45) or middle-aged (aged 58-62) donors. Interleukin (IL)-7 and IL-7 receptor alpha-chain (CD127) levels were the same at all ages, as shown by ELISA, flow cytometry and real-time PCR. However, IL-7 plasma levels were higher in centenarian females than males. The presence of TREC+ cells and of very few naïve T lymphocytes suggests that in centenarians such cells could either derive from residues of thymic lymphopoietic islets, or even represent long-living lymphocytes that have not yet encountered their antigen. IL-7 could be one of the components responsible, among others, for the higher probability of reaching extreme ages typical of females.

Prevention of toxic epidermal necrolysis by regulatory T cells

To analyze immunoregulation of autoreactive T cells specific for epidermal skin antigens, we crossed transgenic mice expressing ovalbumin selectively in keratinocytes under the keratin 5 promoter (K5-mOVA) with mice expressing a K(b)-restricted OVA-specific T cell receptor transgene (OT-I). In athymic double-transgenic mice, OT-I cells developed extrathymically and, at 8-12 weeks of age, initiated severe epidermal damage mimicking toxic epidermal necrolysis (TEN). In contrast, euthymic double-transgenic mice showed thymic deletion of OT-I cells, had few of these cells in the periphery, and never developed skin changes mimicking TEN. Adoptive transfer of OT-I cells isolated from euthymic double-transgenic mice induced TEN in athymic K5-mOVA single-transgenic mice. This spontaneous disease in athymic double-transgenic mice was prevented by transferring lymph node cells from euthymic mice, but was not prevented when CD4(+) or CD25(+) cells were depleted from this population. Although purified CD4(+)CD25(+) cells scarcely prevented the skin disease induced by adoptive transfer of OT-I cells, they efficiently prevented the disease when co-transferred with CD11c(+) dendritic cells. These results suggested that thymus-derived regulatory T cells cooperate with CD11c(+) dendritic cells to prevent life-threatening skin damage such as TEN.

BAT mAb induces lymphopoiesis in nude mice

The athymic nude mouse provides a powerful tool in the study of human tumors, as it enables growth of human tumors due to deficiencies in T cell functions. However, deficiencies in T cell functions might limit research on efficacy of immune modulators in cancer immunotherapy. BAT mAb mediates its anti-cancer activity through modulation of the immune system that involves both NK and T cells. We analyzed lymphocyte populations in blood 5 and 14 days following the injection of BAT antibody alone or following engraftment of human colon carcinoma cells. Our results demonstrate that BAT injection induced lymphopoiesis in the nude mouse. Percentage of CD3 cells increased up to 24%, CD4 cells up to 20% but no increase was found in CD8 T cells in BAT-injected nude mice. Injection of BAT 12 days post-tumor engraftment propagated CD3, CD4 and CD8 cells seen in the blood 5 days later but not seen in the blood 14 days post-BAT injection. It is possible that this decrease is associated with migration of the lymphocytes from the blood to the tumor sites in the livers. The percentage of CD56-positive NK cells increased (up to 18%) by BAT administration alone or post-tumor injection. The presence of tumors alone did not induce lymphopoiesis in the nude mice. Propagation and lymphopoiesis by BAT mAb might have future clinical implications.

Immunopotentiation of NKT cells by low-protein diet and the suppressive effect on tumor metastasis

Mice were fed with a 5% low-protein diet for two weeks, at which point tumor inoculation was conducted. Following this inoculation, the 5% low-protein diet was continued. On the other hand, control mice were fed with a normal diet (25% protein) and such diet was continued after tumor inoculation. In comparison with control mice, mice fed with the 5% low-protein diet showed a prominent prolongation of survival rate when injected with both EL4 and 3LL tumors. Interestingly, CD1d(-/-) mice, which primarily lack natural killer T (NKT) cells, did not show the prolongation of survival rate even when they received a 5% low-protein diet. The most striking phenomenon seen in tumor-bearing mice fed with the 5% low-protein diet was the suppression of tumor metastasis to the liver and lung. Such suppression was not seen in CD1d(-/-) mice who were fed with a 5% low-protein diet. Phenotypic study revealed that the proportion of NKT cells after tumor inoculation decreased in the mice fed with a normal diet. However, such decrease did not occur in mice fed with the 5% low-protein diet. Reflecting the activation of NKT cells by feeding, tumor cytotoxicity and cytokine production were also augmented by the 5% low-protein diet. These results suggest that a low-protein diet has the potential to augment the innate immunity against tumors, especially mediated by the activation of NKT cells.

Are zinc-bound metallothionein isoforms (I+II and III) involved in impaired thymulin production and thymic involution during ageing?

BACKGROUND: With advancing age, thymic efficiency shows progressive decline due to thymic involution allowing impaired cell-mediated immunity and the appearance of age-related diseases. The intrinsic cause of thymic involution is still undefined. Chronic inflammation and high glucocorticoids (GCs) may be involved. However, transgenic mice, with increased GC sensitivity and over expression of GC receptors, display delayed age-associated thymic involution. This fact suggests that other substances may affect thymic involution. Among them, both isoforms of metallothioneins (MTs) I+II and III are the major candidates because their increments leads to organ atrophy in constant stress and are induced by IL-6, which increases in ageing. Enhanced MTs in ageing allows constant sequester of zinc ions and no subsequent zinc release leading to low zinc ion bioavailability for thymic efficiency. This sequester is very limited in very old age. Thus, we have investigated the MTmRNA (I+II and III) in the thymus from young, old and very old mice. METHODS: MTmRNA and IL-6mRNA (RT-PCR) in the thymus from different donors were tested. Concomitantly, TECs proliferation, zinc ion bioavailability (ratio total thymulin/active thymulin), thymulin activity and corticosterone were tested from different donors. RESULTS: Both isoforms of MTmRNA and IL-6mRNA increase in old thymus coupled with low zinc ion bioavailability, reduced TECs proliferation, impaired thymulin activity and enhanced plasma corticosterone in comparison with young. Conversely, although the thymus is involuted in very old mice because of no changes in thymus weight in comparison to old mice, reduced MTmRNA, especially MT-I+II isoforms, and low IL6mRNA occur. Concomitantly, good zinc ion bioavailability, maintained TECs proliferation, satisfactory thymulin activity and reduced corticosterone are observed in very old mice. CONCLUSIONS: The concomitant increments by high IL-6 of both MT isoforms in the thymus from old mice may be involved in thymic involution because provoking low zinc ion bioavailability, which is relevant for thymic efficiency. By contrast, the limited increments of MTs by low IL-6 induce good zinc ion bioavailability and satisfactory thymic efficiency in very old mice. Therefore, abnormal increased MTs may provoke complete thymic involution during ageing and the possible appearance of age-related diseases. If their increments are instead limited by low inflammation, healthy ageing and longevity may be reached.

The variations during the circadian cycle of liver CD1d-unrestricted NK1.1+TCR gamma/delta+ cells lead to successful ageing. Role of metallothionein/IL-6/gp130/PARP-1 interplay in very old mice

NKT cells derive from the thymus and home to the liver. Liver NKT cells can be divided in two groups: 'classical' and 'non-classical'. The first is CD1d-restricted, the second is CD1d-unrestricted. NKT cells (classical and non-classical) co-express T-cell receptor (TCR) and NK-cell marker (NK1.1), display cytotoxicity and produce IFN-gamma under IL-12 stimulation affecting, thereby, Th1 response and innate immunity. NK1.1(+)TCR alpha/beta(+) cells belong to both groups. NK1.1(+)TCR gamma/delta(+) cells belong to the second group. Anyway, both NKT cell subtypes, via IFN-gamma production, protect against viruses and bacteria from early in life. Immune variations as well as zinc rhythmicity during the circadian cycle confer the immune plasticity, which is essential for successful ageing. Liver NK1.1(+)TCR gamma/delta(+) cells, rather than TCR alpha/beta(+), from young and very old mice display 'in vitro' (under IL-12 stimulation) nocturnal peaks in cytotoxicity and IFN-gamma production. The acrophase of liver NK1.1(+)TCR gamma/delta(+) cells is present in young and very old mice, not in old. The interplay among zinc-bound metallothionein (MT)/IL-6/gp130/poly(ADP-ribose) polymerase-1 (PARP-1) may be involved in conferring plasticity to liver NK1.1(+)TCR gamma/delta(+) cells. IL-6, via sub-unit receptor gp130, induces MTmRNA. At night, gene expressions of MT, IL-6, gp130 are lower in very old mice than old and young MT-I transgenic mice (MT-I*). In very old mice, this phenomenon allows limited sequester of intracellular zinc from MT leading to good free zinc ion bioavailability for immune efficiency and zinc-dependent PARP-1 activity. Indeed (1) in vitro, high IL-6 provokes strong accumulation of MT, impaired cytotoxicity and low zinc ion bioavailability in liver NK1.1(+)TCR gamma/delta(+) cells exclusively from old and MT-I* mice. (2) The ratio total/endogen PARP-1 activity is higher in very old than in old and MT-I* mice, suggesting a higher capacity of PARP-1 in base excision DNA-repair in very old age thanks to low zinc-bound MT. Cytotoxicity and IFN-gamma production from liver NK1.1(+)TCR gamma/delta(+) cells are thus preserved leading to successful ageing. In conclusion, MT/IL-6/gp130/PARP-1 interplay may confer plasticity to liver CD1d-unrestricted NK1.1(+)TCR gamma/delta(+) cells, where MT, IL-6, gp130 are the main upstream protagonists, and PARP-1 is the main downstream protagonist in immunosenescence.

Extrathymic T cells expand in nude mice following different allogeneic stimuli

We studied extrathymic lymphocyte populations expanded in nude mice after allogeneic stimuli. These were either cells from different tissues or Immunoglobulin (Ig). Although the cells transferred, obtained from Thy-1.1+ donors, were able to induce similar increase in the nude host Thy-1.2+ population, the expanded populations could be qualitatively distinguished from each other by their different expression of mature T cell molecules and by their functional profile. The extrathymic lymphocytes expanded in animals receiving allogeneic fetal thymocytes (FT) were preferentially CD4+ cells and could confer a functional immunocompetent system to the nude host, able to reject allogeneic skin grafts. In contrast, allogeneic adult red blood cells (RBC) led to the expansion of a CD8+ population and to an auto-reactive profile, resulting in the rejection of syngeneic skin grafts by most of the nude hosts. Neither of these profiles was achieved with the other stimuli. These findings support the view that different activation pathways and/or regulatory interactions may lead to the development of distinct extrathymic populations.

Age-related bias in function of natural killer T cells and granulocytes after stress: reciprocal association of steroid hormones and sympathetic nerves

Stress-associated immune responses were compared between young (8 weeks of age) and old (56 weeks) mice. Since stress suppresses the conventional immune system (i.e. T and B cells) but inversely activates the primordial immune system (i.e. extrathymic T cells, NKT cells, and granulocytes), these parameters were analysed after restraint stress for 24 h. The thymus became atrophic as a function of age, and an age-related increase in the number of lymphocytes was seen in the liver. Although the number of lymphocytes in both the thymus and liver decreased as the result of stress, the magnitude was much more prominent in the thymus. To determine stress-resistant lymphocyte subsets, two-colour immunofluorescence tests were conducted in the liver and spleen. NKT cells were found to be such cells in the liver of young mice. On the other hand, an infiltration of granulocytes due to stress was more prominent in the liver of old mice than in young mice. Liver injury as a result of stress was prominent in young mice. This age-related bias in the function of NKT cells and granulocytes seemed to be associated with a difference in the responses of catecholamines (high in old mice) and corticosterone (high in young mice) after stress. Indeed, an injection of adrenaline mainly induced the infiltration of granulocytes while that of cortisol activated NKT cells. The present results suggest the existence of age-related bias in the function of NKT cells and granulocytes after stress and that such bias might be produced by different responses of sympathetic nerves and steroid hormones between young and old mice.

Evolution of the thymus size in response to physiological and random events throughout life

During embryogenesis and in the early stages of life, the thymus is a crucial organ for the generation of the T cell repertoire. T cells are generated from hematopoietic stem cells already differentiated to precursor T cells in the bone marrow. These cells enter the thymus guided by chemotactic factors secreted by this organ. The complex maturation process takes place that ensures self-tolerance and homeostasis. Thymocytes that show autoreactivity do not leave the thymus, but rather die by apoptosis. The final percentage of mature T cells that survive to migrate from the thymus to the periphery is very low: at most 5%, under optimal conditions. The highest migration occurs in childhood and adulthood, at least in mice and humans; however, it declines throughout life and is minimal in the elderly. Under normal circumstances, the thymus commences involution soon after birth, and this involution correlates with the capacity to export mature T cells to the periphery. Hormones, cytokines, and neurotransmitters all play a role in this age-associated process, but the reasons for and mechanisms of this involution remain unknown. Apart from physiological conditions that change throughout life and govern age-related thymus evolution, random states and events provoked by intrinsic or extrinsic factors can induce either thymus involution, as in reversible transient thymic hypoplasias, or thymic hyperplasias. The age-associated involution, unlike transient involutions, follows a regular pattern for all individuals, though there are clear differences between the sexes. Nevertheless, even the age-associated involution seems to be reversible, raising the possibility of therapeutic strategies aimed at enhancing thymus function in the elderly.

Crossroads of extrathymic lymphocytes maturation pathways

The majority of T cells located in peripheral lymphoid organs are dependents on the thymus for regular differentiation and function. Only a minority of T lymphocytes are thymus-independent. These cells pass by extrathymic maturation processes and become mature T lymphocytes. Some data suggest that mechanism of extrathymic lymphocytes maturation (eTLM) includes migration, proliferation, differentiation and selection of lymphocytes as well as thymic pathway. With aging and progression of thymic involution or in accidental thymic involution, pathway of eTLM derives emphasis. T cells from extrathymic pathway probably can polarize action of thymic-dependent T cells or participate in immune reaction in antigen-destructive or antigen-protective manners. Consequently, extrathymic pathways can be a source of self-reactive T cells or cells which participate in mechanisms of trophoblast or tumor escape. Results of eTLM probably are not presets, already depend upon many factors and microenvironmental snapshots. Factors like cytokines, prostaglandine, microbes, MHC molecules, hormones, Fas ligand, heat shock proteins, phenotypes of dendritic cells and APCs, probably can be polarizing courses of eTLM pathway. Definitive to the course of extrathymic-derived cells action, presumably is resultant of microenvironmental relations and interactions of foregoing factors. Hypothesis that microbes, especially viruses, can be promoters of extrathymic (self)antigen-reactive lymphocytes maturation is real as well as hypothesis that extrathymic lymphocytes selection and products of selected lymphocytes can be included in mechanisms of tumor, trophoblast and transplant rejection or escape.

Augmentation of NKT and NK cell-mediated cytotoxicity by peptidoglycan monomer linked with zinc

BACKGROUND

Peptidoglycan monomer (PGM), which was originally prepared by biosynthesis from culture fluids of penicillin-treated Brevibacterium divaricatum, is an immunostimulator, the activities of which might be improved by addition of zinc (Zn) to the basic molecule.

METHODS

To test the possible cytotoxic effects of this new analogue, we analyzed the ability of PGM-Zn and PGM to change the phenotypic profile of hepatic and splenic mononuclear lymphatic cells and to affect the growth of malignant T-cell line YAC-1 and syngeneic thymocytes.

RESULTS

Pretreatment of C57BL/6 mice primarily with PGM-Zn over 6 days (10/mg/kg intraperitoneally) significantly enhanced the proportions of NK1.1high+, CD4-CD8-, CD69+, and CD3intermediate/NK1.1+/IL2R-beta+ (NKT) cells in the liver, and major histocompatibility complex class II+, CD69+, and CD8+ cells in the spleen. Both types of cells were highly cytotoxic against YAC-1 and syngeneic thymocytes, increasing the destruction of YAC-1 by 70% on addition of hepatic cells and by 30% on addition of splenic cells. Destruction of thymocytes increased by 10 and 50%, respectively.

CONCLUSION

The results point to PGM-Zn as a potent cytotoxicity-inducing agent, which also generates autoreactive NKT cells.