Polymorphisms in the canine IL7R 3'UTR are associated with thymic output in Labrador retriever dogs and influence post-transcriptional regulation by microRNA 185

Interleukin-7 (IL-7) and its receptor (IL-7R) are essential for T cell development in the thymus, and changes in the IL-7/IL-7R pathway have been implicated in age-associated thymic involution which results in a reduction of naïve T cell output. The aim of this study was to investigate the relationship between IL7 and IL7R genetic variation and thymic output in dogs. No single nucleotide polymorphisms (SNPs) were identified in the canine IL7 gene, but a number were present in the canine IL7R gene. Polymorphisms in the IL7R exon 8 and 3'UTR were found to be associated with signal joint T cell receptor excision circle (sj-TREC) values (a biomarker of thymic output) in young and geriatric Labrador retrievers. Additionally, one of the SNPs in the IL7R 3'UTR (SNP 14 c.1371 + 446 A > C) was found to cause a change in the seed-binding site for microRNA 185 which, a luciferase reporter assay demonstrated, caused changes in post-transcriptional regulation, and therefore might be capable of influencing IL-7R expression. The research findings suggest a genetic link between IL7R genotype and thymic output in dogs, which might impact on immune function as these animals age and provide further evidence of the involvement of IL-7/IL-7R pathway in age-associated thymic involution.

Perturbation of the T cell receptor repertoire occurs with increasing age in dogs

Immunosenescence is the gradual deterioration in immune system function associated with ageing. This decline is partly due to involution of the thymus, which leads to a reduction in the output of naive T cells into the circulating lymphocyte pool. Expansion of existing naive and memory T cell populations, to compensate for the reduction in thymic output, can lead to reduced diversity in the T cell repertoire with increasing age, resulting in impairment of immune responses to novel antigenic challenges, such as during infection and vaccination. Since associations between T cell repertoire and age have only been examined in a limited number of species, to gain further insights into this relationship, we have investigated age-related changes in the canine T cell receptor (TCR) repertoire. Blood samples were obtained from Labrador retriever dogs of varying ages and variation in the complementary determining region 3 (CDR3) of the T cell receptor beta (TCRB) chain was investigated. CDR3 size spectratyping was employed to evaluate clonal expansion/deletion in the T cell repertoire, allowing identification of profiles within individual variable (V) region families that skewed away from a Gaussian distribution. Older dogs (10-13 years) were found to have an increased number of TCRB V gene spectratypes that demonstrated a skewed distribution, compared with young dogs (≤3 years). Additionally, there was a reduction in the number of clonal peaks present in the spectratypes of old dogs, compared with those of young dogs. The study findings suggest that there is an age-associated disturbance in the diversity of the T cell receptor repertoire in dogs.

An Age-Associated Decline in Thymic Output Differs in Dog Breeds According to Their Longevity

The age associated decline in immune function is preceded in mammals by a reduction in thymic output. Furthermore, there is increasing evidence of a link between immune competence and lifespan. One approach to determining thymic output is to quantify signal joint T cell receptor excision circles (sj-TRECs), a method which has been developed and used in several mammalian species. Life expectancy and the rate of aging vary in dogs depending upon their breed. In this study, we quantified sj-TRECs in blood samples from dogs of selected breeds to determine whether there was a relationship between longevity and thymic output. In Labrador retrievers, a breed with a median expected lifespan of 11 years, there was an age-associated decline in sj-TREC values, with the greatest decline occurring before 5 years of age, but with sj-TREC still detectable in some geriatric animals, over 13 years of age. In large short-lived breeds (Burnese mountain dogs, Great Danes and Dogue de Bordeaux), the decline in sj-TREC values began earlier in life, compared with small long-lived breeds (Jack Russell terriers and Yorkshire terriers), and the presence of animals with undetectable sj-TRECs occurred at a younger age in the short-lived breeds. The study findings suggest that age-associated changes in canine sj-TRECs are related to breed differences in longevity, and this research highlights the use of dogs as a potential model of immunosenescence.

Immune senescence: significance of the stromal microenvironment

The immune system undergoes age-associated changes known as immunosenescence, resulting in increased susceptibility to infections, cancers and autoimmunity in the aged. The basis of our understanding of immunosenescence has been derived primarily from studies examining intrinsic defects within many of the cells of the immune system. While these studies have provided insight into the mechanisms of immunosenescence, a picture is now emerging that the stromal microenvironment within lymphoid organs also contributes significantly to the age-associated decline of immune function. These extrinsic defects appear to impact the functional activity of immune cells and may offer a potential target to recover immune activity. Indeed, rejuvenation studies which have targeted the stromal niche have restored immune function in aged successfully, highlighting the impact of the microenvironment towards the aetiology of immunosenescence.

Disorganization of the splenic microanatomy in ageing mice

The precise mechanisms responsible for immunosenescence still remain to be determined, however, considering the evidence that disruption of the organization of primary and secondary lymphoid organs results in immunodeficiency, we propose that this could be involved in the decline of immune responses with age. Therefore, we investigated the integrity of the splenic microarchitecture in mice of increasing age and its reorganization following immune challenge in young and old mice. Several differences in the anatomy of the spleen with age in both the immune and stromal cells were observed. There is an age-related increase in the overall size of the white pulp, which occurs primarily within the T-cell zone and is mirrored by the enlargement of the T-cell stromal area, concurrent to the distinct boundary between T cells and B cells becoming less defined in older mice. In conjunction, there appears to be a loss of marginal zone macrophages, which is accompanied by an accumulation of fibroblasts in the spleens from older animals. Furthermore, whereas the reorganization of the white pulp is resolved after several days following antigenic challenge in young animals, it remains perturbed in older subjects. All these age-related changes within the spleen could potentially contribute to the age-dependent deficiencies in functional immunity.

The effect of age on thymic function

Age-related regression of the thymus is associated with a decline in naïve T cell output. This is thought to contribute to the reduction in T cell diversity seen in older individuals and linked with increased susceptibility to infection, autoimmune disease, and cancer. Thymic involution is one of the most dramatic and ubiquitous changes seen in the aging immune system, but the mechanisms which underlying this process are poorly understood. However, a picture is emerging, implicating the involvement of both extrinsic and intrinsic factors. In this review we assess the role of the thymic microenvironment as a potential target that regulates thymic involution, question whether thymocyte development in the aged thymus is functionally impaired, and explore the kinetics of thymic involution.

Immunosenescence: a product of the environment?

The major function of the immune system is to provide protection against pathogens, in order to prevent infections and potential death. However, with increasing age the immune system undergoes alterations culminating in a progressive deterioration in the ability to respond to infection and vaccination. The precise mechanisms associated with immunosenescence have not been fully elucidated although extensive analyses have suggested that intrinsic defects within immune cells are potentially involved. Despite the stromal niche playing a critical role in the development and activation of immune cells, the role of extrinsic factors within the microenvironment in immunosenescence is less well understood. Moreover, emerging evidence suggests that the aged microenvironment contributes significantly to the age-associated decline of immune function and additionally may offer a potential target for rejuvenating the immune system. Indeed, rejuvenation strategies which have targeted the thymic stromal microenvironment have proved to be successful in recovering thymic function in the aged.

Time-series transcriptional profiling yields new perspectives on susceptibility to murine osteoarthritis

OBJECTIVE

Chronological age is a powerful epidemiologic risk factor for osteoarthritis (OA), a multifactorial disease that is characterized by articular cartilage (AC) degradation. It is unclear from a molecular perspective how aging interacts with OA to produce this risk to AC integrity. To address this key question, we used in vivo time-course analysis of OA development and murine interstrain variability in natural susceptibility to OA to examine changes in non-OA-prone CBA mice versus OA-prone STR/Ort mice, which develop disease that bears significant histologic resemblance to human OA. Through global transcriptome profiling, we attempted to discover the molecular signature linked with both OA vulnerability and progression.

METHODS

Affymetrix Mouse Gene 1.0 ST Array profiles were generated from AC samples derived from CBA and STR/Ort mice at 3 different ages, corresponding to the stages prior to, at, and late after the natural onset of OA in the STR/Ort mice.

RESULTS

We found that the OA in STR/Ort mice exhibited a molecular phenotype resembling human OA, and we pinpointed a central role of NF-κB signaling and the emergence of an immune-related signature in OA cartilage over time. We discovered that, strikingly, young healthy AC has a highly expressed skeletal muscle gene expression program, which is switched off during maturation, but is intriguingly retained in AC during OA development in STR/Ort mice.

CONCLUSION

This study is the first to show that AC chondrocytes share a high-abundance gene-expression program with skeletal muscle. We show that failure to switch this program off, as well as the restoration of this program, is associated with inappropriate expression of NF-κB signaling pathways, skeletal muscle-related genes, and induction and/or progression of OA.

The origin and implication of thymic involution

Age-related regression of the thymus is associated with a decline in naïve T cell output which is thought to contribute to the reduction in T cell diversity in older individuals that is partially responsible for an increase in susceptibility and severity of infections, cancers and autoimmune diseases. Thymic involution is one of the most dramatic and ubiquitous changes in the ageing immune system, but the precise regulators remain anonymous. However, a picture is emerging, implicating extrinsic and intrinsic factors that may contribute towards age-associated thymic involution. In this review we assess the role of the thymic microenvironment as a possible target of thymic involution, question whether thymocyte development in the aged thymus is functional and explore why the thymus involutes.

Evidence of conserved neuroendocrine interactions in the thymus: intrathymic expression of neuropeptides in mammalian and non-mammalian vertebrates

The function of lymphoid organs and immune cells is often modulated by hormones, steroids and neuropeptides produced by the neuroendocrine and immune systems. The thymus intrinsically produces these factors and a comparative analysis of the expression of neuropeptides in the thymus of different species would highlight the evolutionary importance of neuroendocrine interaction in T cell development. In this review, we highlight the evidence which describes the intrathymic expression and function of various neuropeptides and their receptors, in particular somatostatin, substance P, vasointestinal polypeptide, calcitonin gene-related peptide and neuropeptide Y, in mammals (human, rodent) and non-mammals (avian, amphibian and teleost), and conclude that neuropeptides play a conserved role in vertebrate thymocyte development.

Variation of human natural killer cell phenotypes with age: identification of a unique KLRG1-negative subset

Human natural killer (NK) cells subsets are phenotypically characterized by their lack of CD3 and low/high expression of CD56. This study revealed an age-associated increase in the ratio of CD3(-)CD56(dim) to CD3(-)CD56(bright) NK cells, whereas distinct expression patterns of CD2, CD16, CD57, and the C-type lectin family members killer cell lectin-like receptor -D1 (CD94) and -G1 (KLRG1), were noted on both these NK and the CD3(+)CD56(+) T cell subsets; moreover, CD94 and KLRG1 expression were significantly reduced with age. Although the proportion of CD3(-)CD56(bright) NK cells vs CD3(-)CD56(dim) cells decreased with age, the percentage of CD3(-)CD56(bright) cells expressing IFN-gamma after activation significantly increased, potentially representing compensatory augmentation of cytokine production to maintain the important immunoregulatory role of these cells in older individuals. Collectively, these results highlight new evidence for a continuum of change during immunologic aging and present unique data for variation of NK cell subsets with human aging.

BTN1A1, the mammary gland butyrophilin, and BTN2A2 are both inhibitors of T cell activation

Butyrophilin (BTN) genes encode a set of related proteins. Studies in mice have shown that one of these, BTN1A1, is required for milk lipid secretion in lactation, whereas butyrophilin-like 2 is a coinhibitor of T cell activation. To understand these disparate roles of BTNs, we first compared the expression and functions of mouse Btn1a1 and Btn2a2. Btn1a1 transcripts were not restricted to lactating mammary tissue but were also found in virgin mammary tissue and, interestingly, spleen and thymus. In confirmation of this, BTN1A1 protein was detected in thymic epithelial cells. By contrast, Btn2a2 transcripts and protein were broadly expressed. Cell surface BTN2A2 protein, such as the B7 family molecule programmed death ligand 1, was upregulated upon activation of T cells. We next examined the potential of both BTN1A1 and BTN2A2 to interact with T cells. Recombinant Fc fusion proteins of murine BTN2A2 and, surprisingly BTN1A1, bound to activated T cells, suggesting the presence of one or more receptors on these cells. Immobilized BTN-Fc fusion proteins, but not MOG-Fc protein, inhibited the proliferation of CD4 and CD8 T cells activated by anti-CD3. BTN1A1 and BTN2A2 also inhibited T cell metabolism, IL-2, and IFN-gamma secretion. Inhibition of proliferation was not abrogated by exogenous IL-2 but could be overcome following costimulation with high levels of anti-CD28 Ab. These data are consistent with a coinhibitory role for mouse BTNs, including BTN1A1, the BTN expressed in the lactating mammary gland and on milk lipid droplets.

Early-life nutrition influences thymic growth in male mice that may be related to the regulation of longevity

Nutrition and growth rate during early life can influence later health and lifespan. We have demonstrated previously that low birthweight, resulting from maternal protein restriction during pregnancy followed by catch-up growth in rodents, was associated with shortened lifespan, whereas protein restriction and slow growth during lactation increased lifespan. The underlying mechanisms by which these differences arise are unknown. In the present study, we report that maternal protein restriction in mice influences thymic growth in early adult life. Offspring of dams fed a low-protein diet during lactation (PLP offspring) had significant thymic growth from 21 days to 12 weeks of age, whereas this was not observed in control mice or offspring of dams fed a low-protein diet during pregnancy (recuperated offspring). PCNA (proliferating-cell nuclear antigen) and SIRT1 (silent information regulator 1) protein levels at 21 days of age were significantly higher in the thymus from both PLP mice (P<0.001 and P<0.05 respectively) and recuperated mice (P<0.001 and P<0.01 respectively) compared with controls. At 12 weeks, PLP mice maintained a higher SIRT1 level, whereas PCNA was decreased in the thymus from recuperated offspring. This suggests that mitotic activity was initially enhanced in the thymus from both PLP and recuperated offspring, but remained sustained into adulthood only in PLP mice. The differential mitotic activity in the thymus from PLP and recuperated mice appeared to be influenced by changes in sex hormone concentrations and the expression of p53, p16, the androgen receptor, IL-7 (interleukin-7) and the IL-7 receptor. In conclusion, differential thymic growth may contribute to the regulation of longevity by maternal diet.

An evolutionary perspective on the mechanisms of immunosenescence

There is an accumulating body of evidence that a decline in immune function with age is common to most if not all vertebrates. For instance, age-associated thymic involution seems to occur in all species that possess a thymus, indicating that this process is evolutionary ancient and conserved. The precise mechanisms regulating immunosenescence remain to be resolved, but much of what we do know is consistent with modern evolutionary theory. In this review, we assess our current knowledge from an evolutionary perspective on the occurrence of immunosenescence, we show that life history trade-offs play a key role and we highlight the possible advantages of the age-related decline in thymic function.

Is thymocyte development functional in the aged?

T cells are an integral part of a functional immune system with the majority being produced in the thymus. Of all the changes related to immunosenescence, regression of the thymus is considered one of the most universally recognised alterations. Despite the reduction of thymic size, there is evidence to suggest that T cell output is still present into old age, albeit much diminished; leading to the assumption that thymocyte development is normal. However, current data suggests that recent thymic emigrant from the aged thymus are functionally less responsive, giving rise to the possibility that the generation of naïve T cell may be intrinsically impaired in the elderly. In light of these findings we discuss the evidence that suggest aged T cells may be flawed even before exiting to the periphery and could contribute to the age-associated decline in immune function.

Neuropeptides and thymic hormones in the Xenopus thymus

T-cell development is characterised by a complex series of events in the thymus, which results in the development of self-restricted immunocompetent lymphocytes. We have previously reported the expression of neuropeptides in the thymus of various species, highlighting the evolutionary importance of neuroendocrine interactions in thymocyte development. Despite the many physiological and functional similarities in their immune systems, no study has addressed the importance of neuropeptides and thymic hormones in T-cell development in Xenopus. Immunohistochemical analysis revealed that the neuropeptides substance P, neuropeptide Y, somatostatin, calcitonin gene related peptide, and vasoactive intestinal polypeptide and the thymic hormones thymosin alpha1, thymosin beta4, and thymopoietin are found in the Xenopus thymus. This was further corroborated by RT-PCR. Furthermore, double staining revealed that neuropeptides and thymic hormones are coexpressed within the epithelial cell component of the thymus. These results show that neuropeptides and thymic hormones are expressed in the thymus of Xenopus, and suggest that they are likely to play a role in T-cell development.

Architectural changes in the thymus of aging mice

Age-associated thymic involution is one of the most dramatic and ubiquitous changes in the immune system, although the precise mechanisms involved still remain obscured. Several hypotheses have been proposed incorporating extrinsic and intrinsic factors, however, changes in the thymic microenvironment itself is one of the least investigated. We therefore decided to undertake a detailed histological examination of the aging thymus in order to elucidate possible mechanisms of thymic atrophy. This investigation provides insight into the changes within the murine thymus with age, demonstrating a new approach to quantify protein expressional differences while preserving the thymic architecture. There is a decline in expression of thymic epithelial cell-specific makers and an increase in fibroblast content in the aging mouse thymus. This is concurrent with a disorganization of the thymic compartments, a morphological transformation within the epithelial cells and alterations of their archetypal staining patterns. Furthermore, this is linked to a rise in apoptotic cells and the novel finding of increased senescence in the thymus of older mice that appears to be colocalized in the epithelial compartment. These changes within the thymic epithelial cells may be in part accountable for thymic atrophy and responsible for the decline in T-cell output.

Functional analysis of neuropeptides in avian thymocyte development

The function of lymphoid organs and immune cells is often modulated by peptides and hormones produced by the neuroendocrine and immune systems. We have previously reported the intrathymic expression of neuropeptides in the thymus of different species and that neuropeptides can influence murine thymocyte development in vitro. To further explore the evolutionary nature of neuroendocrine interactions in the thymus, we identified the expression of calcitonin-gene-related peptide, neuropeptide Y, somatostatin (SOM), substance P and vasointestinal polypeptide, as well as their receptors on chicken thymic epithelial cells (TEC) and thymocytes by immunofluorescence and reverse transcription polymerase chain reaction (RT-PCR). All the studied neuropeptides and their receptors were found to be expressed in both TEC and thymocytes, suggesting that intrathymic neuroendocrine interactions may take place within the avian thymus. In order to elucidate whether such interactions play a role in avian thymocyte development, neuropeptides and their antagonists were added to embryonic thymus organ cultures and found to influence chicken thymopoiesis. In particular, an antagonist of SOM increased the proportion of double-positive thymocytes, while SOM itself appeared to inhibit the early stages of thymocyte development. Taken together, these data provide further evidence to suggest that neuropeptides play a conserved role in vertebrate thymocyte development.

Immunosenescence: emerging challenges for an ageing population

It is now becoming apparent that the immune system undergoes age-associated alterations, which accumulate to produce a progressive deterioration in the ability to respond to infections and to develop immunity after vaccination, both of which are associated with a higher mortality rate in the elderly. Immunosenescence, defined as the changes in the immune system associated with age, has been gathering interest in the scientific and health-care sectors alike. The rise in its recognition is both pertinent and timely given the increasing average age and the corresponding failure to increase healthy life expectancy. This review attempts to highlight the age-dependent defects in the innate and adaptive immune systems. While discussing the mechanisms that contribute to immunosenescence, with emphasis on the extrinsic factors, particular attention will be focused on thymic involution. Finally, we illuminate potential therapies that could be employed to help us live a longer, fuller and healthier life.

Evolutionary conservation of neuropeptide expression in the thymus of different species

Evidence suggests that the immune and neuroendocrine systems cross talk by sharing ligands and receptors. Hormones and neuropeptides produced by the neuroendocrine system often modulate the function of lymphoid organs and immune cells. We have previously reported the intrathymic expression of somatostatin (SOM) in the mouse and that several neuropeptides, most notably calcitonin-gene-related peptide (CGRP), neuropeptide Y (NPY), SOM and substance P (SP), can modulate thymocyte development. However, little is known about the intrathymic expression of these neuropeptides either in the mouse or in other species. Moreover, a comparative analysis of the expression of these molecules would highlight the evolutionary importance of intrathymic neuroendocrine interactions in T-cell development. We have studied the expression of different neuropeptides in the thymus of zebrafish, Xenopus, avians, rodent, porcine, equine and human by immunohistochemistry and reverse transcription-polymerase chain reaction. We found that CGRP, NPY, SOM, SP and vasointestinal polypeptide (VIP) are expressed in the thymus of all species investigated. The thymic location of many of these neuropeptides was conserved and appears to be within the stromal compartments. Interestingly, in the avian thymus the expression of CGRP, SOM and SP appears to change depending on the age of the tissue. These findings suggest that neuropeptides may play an important role in T-cell development and provide further evidence of cross talk between the immune and neuroendocrine systems.

Regulatory T cells in human disease and their potential for therapeutic manipulation

Regulatory T cells are proposed to play a central role in the maintenance of immunological tolerance in the periphery, and studies in many animal models demonstrate their capacity to inhibit inflammatory pathologies in vivo. At a recent meeting [Clinical Application of Regulatory T Cells, 7-8 April 2005, Horsham, UK, organized by the authors of this review, in collaboration with the British Society for Immunology and Novartis] evidence was discussed that certain human autoimmune, infectious and allergic diseases are associated with impaired regulatory T-cell function. In contrast, evidence from several human cancer studies and some infections indicates that regulatory T cells may impair the development of protective immunity. Importantly, certain therapies, both those that act non-specifically to reduce inflammation and antigen-specific immunotherapies, may induce or enhance regulatory T-cell function. The purpose of this review was to summarize current knowledge on regulatory T-cell function in human disease, and to assess critically how this can be tailored to suit the therapeutic manipulation of immunity.

Effects of T-lymphocyte depletion on muscle fibrosis in the mdx mouse

Duchenne muscular dystrophy was initially described as a myosclerosis because of the conspicuous progression of interstitial fibrosis. Using the mdx mouse homologue, we have shown previously that the accumulation of intramuscular collagen is profoundly influenced by the presence or absence of T lymphocytes. Here we have used thymectomy and antibody depletion to examine the effect of ablating CD4 or CD8 or both subsets of T lymphocytes on skeletal muscle fibrosis in mdx and C57BL10 (wild-type) mice. Depletion of either or both subsets at 4 weeks of age did not influence fibrosis in mdx mice, as determined by measuring hydroxyproline levels and collagen deposition in diaphragm. Additionally, expression of transforming growth factor-beta1, which is implicated in collagen deposition, either decreased (mdx mice) or increased (C57BL/10 mice) after double CD4/8 depletion. Our data suggest that depletion of lymphoid cells may affect the tight regulatory control of transforming growth factor-beta1, with possible pleiotropic effects, and more importantly, that the fibrotic process is self-sustaining from a very early stage.

A Fully Human Antitumor ImmunoRNase Selective for ErbB-2-Positive Carcinomas

We report the preparation and characterization of a novel, fully human antitumor immunoRNase (IR). The IR, a human RNase and fusion protein made up of a human single chain variable fragment (scFv), is directed to the ErbB-2 receptor and overexpressed in many carcinomas. The anti-ErbB-2 IR, named hERB-hRNase, retains the enzymatic activity of the wild-type enzyme (human pancreatic RNase) and specifically binds to ErbB-2-positive cells with the high affinity (K(d) = 4.5 nm) of the parental scFv. hERB-hRNase behaves as an immunoprotoxin and on internalization by target cells becomes selectively cytotoxic in a dose-dependent manner at nanomolar concentrations. Administered in five doses of 1.5 mg/kg to mice bearing an ErbB-2-positive tumor, hERB-hRNase induced a dramatic reduction in tumor volume. hERB-hRNase is the first fully human antitumor IR produced thus far, with a high potential as a poorly immunogenic human drug devoid of nonspecific toxicity, directed against ErbB-2-positive malignancies.

One for all and all for one: thymic epithelial stem cells and regeneration

It has long been believed that the thymic epithelial microenvironment originates from both the endodermal and ectodermal germ cell layers. However, a growing body of evidence indicates that such a dual origin is not the case, and that the diverse thymic epithelial populations all develop from a common epithelial stem cell. This article explores these data, investigates the identity of such cells and the signals that might control their expansion and differentiation, and considers the possibility of stem cell transplantation for thymic regeneration.

The developmentally regulated expression of Twisted gastrulation reveals a role for bone morphogenetic proteins in the control of T cell development

The evolutionarily conserved, secreted protein Twisted gastrulation (Tsg) modulates morphogenetic effects of decapentaplegic (dpp) and its orthologs, the bone morphogenetic proteins 2 and 4 (BMP2/4), in early Drosophila and vertebrate embryos. We have uncovered a role for Tsg at a much later stage of mammalian development, during T cell differentiation in the thymus. BMP4 is expressed by thymic stroma and inhibits the proliferation of CD4(-)CD8(-) double-negative (DN) thymocytes and their differentiation to the CD4(+)CD8(+) double-positive (DP) stage in vitro. Tsg is expressed by thymocytes and up-regulated after T cell receptor signaling at two developmental checkpoints, the transition from the DN to the DP and from the DP to the CD4(+) or CD8(+) single-positive stage. Tsg can synergize with the BMP inhibitor chordin to block the BMP4-mediated inhibition of thymocyte proliferation and differentiation. These data suggest that the developmentally regulated expression of Tsg may allow thymocytes to temporarily withdraw from inhibitory BMP signals.

A new human antitumor immunoreagent specific for ErbB2

PURPOSE

Our aim was to isolate a novel human mini-antibody(scFv) that specifically targets ErbB2-positive cancer cells. ErbB2, a tyrosinekinase receptor, is overexpressed in clinically significant tumors, such as breast, ovary, and lung carcinomas. In normal tissues, it is expressed only in certain epithelial cell types.

EXPERIMENTAL DESIGN

A large phagemid library (Griffin.1 library) of human scFv was used for the isolation of the ErbB2-specific scFv. A very effective strategy was developed for the isolation, consisting in a double subtractive selection, the use of two different combinations of "positive," i.e., ErbB2-bearing, and "negative" cell lines.

RESULTS

Here we report the isolation of the first human anti-ErbB2 mini-antibody endowed with antitumor action. Both in its soluble and phage format, it binds specifically to ErbB2, inhibits its autophosphorylation, is internalized by target cells, and exerts a strong and specific antiproliferative action on ErbB2-positive target cells. A correlation was found between the extent of this antiproliferative effect and the expression levels of ErbB2 on target cells, with a strong cytotoxicity for hyper-expressing cells, such as SKBR3, in which apoptosis was evidenced.

CONCLUSIONS

This scFv is a potentially effective immunoreagent for diagnostics and therapeutics of certain cancers, both as a readily diffused molecule in solid tumors and as an essential asset for the construction of fully human anticancer drugs.

Somatostatin is expressed in the murine thymus and enhances thymocyte development

A functional interaction between the immune and the nervous system has been suggested, with neuropeptides acting as immunomodulators. Somatostatin (SOM) is a neuropeptide, mainly produced in the brain, that binds to five different receptors (SSTR). It is believed that SOM along with one of its receptors, SSTR2, is expressed in the murine thymus, although their exact localization is unresolved. We found that SOM is highly expressed in both cortical and medullary epithelial cells whereas its receptor SSTR2 is expressed on thymocytes. In order to elucidate its role in thymopoiesis, SOM was added in fetal thymic organ culture (FTOC) and found to increase thymocyte numbers and enhance maturation. SOM increased the cellular proliferation of total splenocytes but inhibited proliferation of thymocytes and purified splenic T cells. Furthermore, SOM was able to induce the migration of thymocytes. We also investigated the effect of four other neuropeptides in FTOC and found that, vasoactive intestinal peptide had a marginal effect, whereas substance P increased thymic cellularity, at intermediate but not at low or high concentrations. In contrast, both neuropeptide Y and calcitonin gene-related peptide reduced thymocyte numbers. This study supports the hypothesis for a role of neuropeptides, particularly somatostatin, in immune regulation and development.

Truncation of the Mll gene in exon 5 by gene targeting leads to early preimplantation lethality of homozygous embryos

The mixed lineage leukemia gene (MLL) was originally identified through its involvement in reciprocal translocations in leukemias. MLL codes for a large multidomain protein and bears homology to the Drosophila developmental control gene trithorax in two small domains in the amino terminal region, the central zinc finger domain and the carboxy SET domain. Like the Drosophila trx, MLL has also been shown to be a positive regulator of Hox gene expression. We have targeted Mll (the murine homologue of MLL) in exon 5 causing expression of three truncated in-frame Mll transcripts. These transcripts retain all or some of the AT hook motifs and the DMT domain. This mutant allele causes early in vivo preimplantation lethality of homozygous embryos prior to the 2-cell stage. Embryos cultured in vitro progress to the 2-cell stage, but further development is arrested. The heterozygotes exhibit mild skeletal defects as well as defects in some neuroectodermal derivatives.

Intrathymic function of the human cortical epithelial cell surface antigen gp200-MR6: single-chain antibodies to evolutionarily conserved determinants disrupt mouse thymus development

The mouse monoclonal antibody MR6 recognizes a 200 000 MW protein (gp200-MR6), which is expressed highly on human thymic cortical epithelial cells. The antigen is also expressed on some epithelial tumours and we have previously shown that MR6 inhibits the proliferation of the colon carcinoma cell lines HT29. However, the role of this molecule in the thymus is not known. In order to generate reagents that could be used in murine thymic functional studies we isolated antibodies specific to human gp200-MR6, using a phage display library expressing single-chain (sFv) antibodies. Three independent clones were isolated by panning with purified protein and their specificity was confirmed by immunohistochemistry, Western blotting and flow cytometry. In addition to human thymus, these phage antibodies also recognized the homologous antigen in mouse, pig and other species. Expressed as soluble sFv one of these clones inhibited the proliferation of HT29 cells and a mouse thymic epithelial cell line, suggesting that this antibody exhibits similar functional activity to MR6. In fetal thymic organ culture, thymocytes recovered from thymic lobes cultured in the presence of this sFv, were reduced in number fivefold compared with the control and the majority remained at the double-negative stage of development. These data indicate that gp200-MR6 plays an important role in thymocyte development. In addition, this is the first report to demonstrate that specific sFv can be used to study, and alter, thymic development. This work also highlights the advantage of phage antibody technology in selecting such reagents for functional assays.

The human thymic microenvironment: new approaches to functional analysis

Although immunohistological techniques have revealed molecular niches within the human thymic microenvironment, functional analysis is limited by the assay systems available. However, our recent studies using antibody phage display have revealed a high degree of molecular conservation between the microenvironmental molecules of different species. We have therefore isolated single-chain antibodies specific for evolutionarily conserved epitopes, shared by human and mouse, and used these in murine thymic functional assays. The detection of such shared human/rodent molecules makes it possible to functionally 'walk' from mouse to man, providing us with an experimental approach to functional analysis of the human thymus.

The gp200-MR6 molecule which is functionally associated with the IL-4 receptor modulates B cell phenotype and is a novel member of the human macrophage mannose receptor family

The human gp200-MR6 molecule has previously been shown to have either an antagonistic or agonistic effect on IL-4 function, demonstrated by inhibition of IL-4-induced proliferation of T cells or mimicking of IL-4-induced maturation of epithelium, respectively. We now show that gp200-MR6 ligation can also mimic IL-4 and have an anti-proliferative pro-maturational influence within the immune system, causing up-regulation of co-stimulatory molecules on B lymphocytes. Biochemical analysis and cDNA cloning reveal that gp200-MR6 belongs to the human macrophage mannose receptor family of multidomain molecules. It comprises 1722 amino acids in toto (mature protein, 1695 amino acids; signal sequence, 27 amino acids) organized into 12 external domains (an N-terminal cysteine-rich domain, a fibronectin type II domain and 10 C-type carbohydrate recognition domains), a transmembrane region and a small cytoplasmic C terminus (31 amino acids) containing a single tyrosine residue (Y1679), but no obvious kinase domain. Strong amino acid sequence identity (77%) suggests that gp200-MR6 is the human homologue of the murine DEC-205, indicating that this molecule has much wider functional activity than its classical endocytic role. We also show that the gp200-MR6 molecule is closely associated with tyrosine kinase activity; the link between gp200-MR6 and the IL-4 receptor may therefore be via intracellular signaling pathways, with multifunctionality residing in its extracellular multidomain structure.

The gp200-MR6 molecule which is functionally associated with the IL-4 receptor modulates B cell phenotype and is a novel member of the human macrophage mannose receptor family

The human gp200-MR6 molecule has previously been shown to have either an antagonistic or agonistic effect on IL-4 function, demonstrated by inhibition of IL-4-induced proliferation of T cells or mimicking of IL-4-induced maturation of epithelium, respectively. We now show that gp200-MR6 ligation can also mimic IL-4 and have an anti-proliferative pro-maturational influence within the immune system, causing up-regulation of co-stimulatory molecules on B lymphocytes. Biochemical analysis and cDNA cloning reveal that gp200-MR6 belongs to the human macrophage mannose receptor family of multidomain molecules. It comprises 1722 amino acids in toto (mature protein, 1695 amino acids; signal sequence, 27 amino acids) organized into 12 external domains (an N-terminal cysteine-rich domain, a fibronectin type II domain and 10 C-type carbohydrate recognition domains), a transmembrane region and a small cytoplasmic C terminus (31 amino acids) containing a single tyrosine residue (Y1679), but no obvious kinase domain. Strong amino acid sequence identity (77%) suggests that gp200-MR6 is the human homologue of the murine DEC-205, indicating that this molecule has much wider functional activity than its classical endocytic role. We also show that the gp200-MR6 molecule is closely associated with tyrosine kinase activity; the link between gp200-MR6 and the IL-4 receptor may therefore be via intracellular signaling pathways, with multifunctionality residing in its extracellular multidomain structure.

Characterization of a recent retroposon insertion on mouse chromosome 2 and localization of the cognate parental gene to chromosome 11

The genomic sequence on mouse Chromosome (Chr) 2 corresponding to a previously identified novel cDNA has been characterized. The genomic organization of this locus, adjacent to the beta 2 microglobulin gene, has the properties of a processed gene or retroposon including the presence of a short flanking direct repeat, a polyadenylation signal/poly A tract, and the absence of introns. Analysis of inbred and wild-derived Mus DNAs reveals the retroposon to be a feature only of M. m. domesticus subspecies, suggesting that the insertion event is relatively recent. This notion is supported by the presence of an open reading frame and the lack of sequence divergence in the flanking direct repeats. The complex chromatin configuration characteristic of this region in mouse and human is not, therefore, related to this cDNA. The cognate parental gene encoding the cDNA was mapped to Chr 11. A further, more ancient retroposon present in many Mus species localizes to Chr 17.

Selection of antibodies to cell surface determinants on mouse thymic epithelial cells using a phage display library

The network of thymic epithelium contributes significantly to the thymic stromal cell environment, which plays a vital role in the generation and maturation of thymocytes. Monoclonal antibodies (mAb) have revealed considerable heterogeneity within this epithelial component of the mouse thymic microenvironment, but many of these antibodies recognize epitopes that are located inside the cell and so cannot be used in functional studies. As an alternative approach to isolate antibodies specific to thymic epithelium, we used a phage display library expressing single chain Fv antibodies. For selection, a thymic cell suspension was incubated with the phage display library, and major histocompatibility complex class II positive cells, the majority of which are epithelial, were then specifically selected. Phage bound to these cells were eluted and the selection procedure was repeated for a further five rounds. Immunohistochemical analysis revealed that these phage antibodies show differential staining of thymic epithelial subsets. Flow cytometric analysis of a thymic epithelial cell line using a panel of these antibodies demonstrated that they recognize epitopes on the cell surface. Furthermore, some of these antibodies also labelled human thymic epithelium, suggesting that the epitopes recognized by these antibodies are conserved between human and rodent thymus. Our approach therefore provides a rapid method to select antibodies specific for thymic epithelial cell surface determinants in their native configuration.

Analysis of T cell repertoire and function in mice transgenic for the human V beta 3 TCR

We have constructed mice containing the human V beta 3 TCR gene from the influenza virus haemagglutinin specific human CD4+ T cell clone HA1.7. Similar cell yields were obtained from transgenic and non-transgenic lymphoid tissue, with normal levels of T cells and with no unusual bias of the CD4 or CD8 subpopulations. Immunostaining and FACS analysis of transgenic thymocytes, spleen, and mesenteric lymph nodes revealed that the majority of T cells expressed the human V beta 3 TCR on the cell surface. Small numbers of cells expressing murine TCR beta chain were also detected. Polymerase chain reaction analysis revealed that an extensive V alpha TCR repertoire was used in the human V beta 3 transgenic mice. Lymphocytes from the spleen and mesenteric lymph nodes of transgenic mice were assessed for functional activity in vitro. Isolated cells were stimulated with mitogen or superantigen, as well as directly through the TCR-CD3 complex, and their ability to proliferate and secrete lymphokines analysed. Cells from transgenic mice responded well after stimulation with phytohaemagglutinin, concanavalin A, anti-CD3 antibody, anti-CD3 antibody with phorbol ester, and Staphylococcus aureus enterotoxin B, and also showed alloreactivity in a mixed lymphocyte reaction. Minimal levels of response were detected after stimulation with murine TCR beta antibody. Together, these data suggest that a human TCR beta chain is able to associate with a murine TCR alpha chain, to form a fully functional surface TCR-CD3 complex.

Is TCR beta expression an essential event in early thymocyte development?

The evolution of a T cell through the thymus is characterized by several distinct morphological changes. The underlying mechanisms allowing a double negative thymocyte to mature to a double positive one expressing both CD4 and CD8 are still hazy. Here, Donald Palmer, Adrian Hayday and Michael Owen discuss the latest development in the field and data that underscore the crucial role of TCR components in the transition of double negative to double positive thymocytes.

Expression of the alpha beta T-cell receptor is necessary for the generation of the thymic medulla

The architecture of the thymus of mice that congenitally fail to express the alpha beta T-cell receptor (TCR alpha beta) has been examined by immunohistology. In these mice, a defined mutation was introduced into the TCR alpha gene by homologous recombination. By using antibodies specific for cortical or medullary epithelium and for major histocompatibility complex antigens, the network of cortical epithelium in these mice was shown to be essentially unaltered in comparison with that of normal mice. In contrast, the thymic medulla was considerably reduced in size. This analysis shows that expression of the alpha beta TCR but not the gamma delta TCR is obligatory for establishing the thymic medulla and suggests that the growth of medullary epithelial cells may require contact with TCR alpha beta-expressing cells.

The chromatin structure of the mouse beta-2-microglobulin locus

Within the promoter regions of both major histocompatibility complex (MHC) class I genes and the beta 2-microglobulin (beta 2m) gene, there are a number of common regulatory elements suggesting co-ordinate control. However, there is also evidence to suggest that beta 2m and class I are differentially regulated, indicating that these genes may have distinct regulatory elements. We sought to explore this question by analysing DNase I hypersensitive (DH) sites flanking the beta 2m gene. Five DH sites have been found within the vicinity of the beta 2m gene. One of these sites (DH1) located within the promoter region, correlates with the transcriptional activity of beta 2m since it is weak in embryonal (beta 2m negative) cell lines. The remaining DH sites (2-5) are located downstream of the beta 2m gene. The most proximal downstream site, (DH2) located 5.5 kb from the last exon, was observed only in embryonal cell lines, indicating possible involvement in the downregulation of beta 2m. Furthermore, this site is markedly diminished in differentiated F9 cells. Possible roles for the remaining sites are discussed, in particular relationship to a second transcriptional unit identified in the vicinity. In addition, a similar analysis reveals a cluster of DH sites located downstream from the last exon of the human beta 2m gene.

Evidence that the intracellular effects of adenosine in the guinea-pig aorta are mediated by inosine

Previous studies have demonstrated that high concentrations of adenosine interact with both a cell surface receptor and with an intracellular site to evoke relaxation of the guinea-pig aorta. The intracellular action of adenosine was investigated in the present study. The purine sensitive 'P-site' did not appear to be involved since other P-site agonists did not consistently evoke relaxation. A major interaction with intracellular S-adenosylhomocysteine hydrolase also appeared unlikely since 1-homocysteine had only minor effects on adenosine-evoked responses. Inhibition of adenosine deaminase attenuated responses evoked by high concentrations of adenosine. The deaminated metabolite of adenosine, inosine, also evoked aortic relaxation. These responses were mediated solely via an intracellular site since they were blocked by an inhibitor of nucleoside-facilitated diffusion but were unaffected by an adenosine receptor antagonist. These results indicate that a major part of the intracellular effect of adenosine is mediated by its deaminated metabolite inosine.

Comparison of the potency of 8-phenyltheophylline as an antagonist at A1 and A2 adenosine receptors in atria and aorta from the guinea-pig

The potency of 8-phenyltheophylline as an antagonist at A1 adenosine receptors in guinea-pig atria and at A2 adenosine receptors in the guinea-pig aorta has been investigated. 8-Phenyltheophylline was an apparently competitive antagonist of the negative chronotropic effect of adenosine, 2-chloroadenosine, L-N6-phenyl-isopropyl adenosine (L-PIA) and 5'-N-ethylcarboxamide adenosine (NECA) on atria and of the relaxant effect of adenosine, 2-chloroadenosine and NECA on the aorta. The pA2 values for 8-phenyltheophylline ranged from 6.4 to 6.6 and were not significantly different, irrespective of the agonist or tissue used. These results indicate that 8-phenyltheophylline is a relatively potent antagonist at adenosine receptors but does not exhibit selectivity for either of the putative sub-types in isolated tissues.

Hyperphagocytosis and the effect of lipopolysaccharide injection in tumour-bearing mice

(AxT6)F1 hybrid mice received s.c. transplants from (AxT6)F1 mammary carcinomas. At 1, 2 or 4 weeks after tumour transplantation, the mice were bled to obtain plasma and then challenged with 25 micron E. coli lipopolysaccharide (LPS) endotoxin i.v. The mice were killed 24 hr later, further plasma was obtained and their liver ratios and spleen ratios were determined. A similar procedure was carried out on non-tumour-bearing mice. Progressive tumour growth was associated with an increase in the liver ratio. In parallel, mice with 4-week tumour transplant showed increased uptake of colloidal carbon particles and 51Cr-labelled sheep red blood cells in the liver. The plasma amino aspartate transaminase (AST) and the ornithine carbamoyl transferase (OCT) showed a constant rise in all groups of mice after LPS injection. However, at 24 hr after LPS injection, the AST level showed the greatest rise in mice with 4-week tumour transplants. By contrast, OCT, which is liberated only from hepatocytes, showed the greatest rise in non-tumour-bearing mice.