Persistence of physiological self antigen is required for the regulation of self tolerance

The knowns and unknowns of cardiac autoimmunity in viral myocarditis

Myocarditis can result from various infectious and non-infectious causes that can lead to dilated cardiomyopathy (DCM) and heart failure. Among the infectious causes, viruses are commonly suspected. But the challenge is our inability to demonstrate infectious viral particles during clinical presentations, partly because by that point, the viruses would have damaged the tissues and be cleared by the immune system. Therefore, viral signatures such as viral nucleic acids and virus-reactive antibodies may be the only readouts pointing to viruses as potential primary triggers of DCM. Thus, it becomes hard to explain persistent inflammatory infiltrates that might occur in individuals affected with chronic myocarditis/DCM manifesting myocardial dysfunctions. In these circumstances, autoimmunity is suspected, and antibodies to various autoantigens have been demonstrated, suggesting that immune therapies to suppress the autoimmune responses may be necessary. From this perspective, we endeavoured to determine whether or not the known viral causes are associated with development of autoimmune responses to cardiac antigens that include both cardiotropic and non-cardiotropic viruses. If so, what their nature and significance are in developing chronic myocarditis resulting from viruses as primary triggers.

Testicular Immunity and Its Connection with the Microbiota. Physiological and Clinical Implications in the Light of Personalized Medicine

Reproduction is a complex process, which is based on the cooperation between the endocrine-immune system and the microbiota. Testicular immunity is characterized by the so-called immune privilege, a mechanism that avoids autoimmune attacks against proteins expressed by spermatozoa. Testicular microbiota is connected with the gut microbiota, the most prevalent site of commensals inthe body. Both microbiotas take part inthe development of the immune system and protection againstpathogen invasion. Dysbiosis is caused by concurrent pathologies, such as obesity, diabetes, infections and trauma. The substitution of beneficial bacteria with pathogens may lead to destruction of spermatozoa directly or indirectly and, ultimately, to male infertility. Novel therapeutic interventions, i.e., nutritional interventions and supplementation of natural products, such as, probiotics, prebiotics, antioxidants and polyphenols, may lead to the restoration of the otherwise-impaired male reproductive potential, even if experimental and clinical results are not always concordant. In this review, the structure and immune function of the testis will be described with special reference to the blood-testisbarrier. The regulatory role of both the gut and testicular microbiota will be illustrated in health and disease, also emphasizing therapeutic attempts with natural products for the correction of male infertility, in the era of personalized medicine.

Double Negative T Regulatory Cells: An Emerging Paradigm Shift in Reproductive Immune Tolerance?

Immune regulation of female reproductive function plays a crucial role in fertility, as alterations in the relationship between immune and reproductive processes result in autoimmune subfertility or infertility. The breakdown of immune tolerance leads to ovulation dysfunction, implantation failure, and pregnancy loss. In this regard, immune cells with regulatory activities are essential to restore self-tolerance. Apart from regulatory T cells, double negative T regulatory cells (DNTregs) characterized by TCRαβ+/γδ+CD3+CD4–CD8– (and negative for natural killer cell markers) are emerging as effector cells capable of mediating immune tolerance in the female reproductive system. DNTregs are present in the female reproductive tract of humans and murine models. However, their full potential as immune regulators is evolving, and studies so far indicate that DNTregs exhibit features that can also maintain tolerance in the female reproductive microenvironment. This review describes recent progress on the presence, role and mechanisms of DNTregs in the female reproductive system immune regulation and tolerance. In addition, we address how DNTregs can potentially provide a paradigm shift from the known roles of conventional regulatory T cells and immune tolerance by maintaining and restoring balance in the reproductive microenvironment of female fertility.

Exposed and Sequestered Antigens in Testes and Their Protection by Regulatory T Cell-Dependent Systemic Tolerance

Continuous exposure of tissue antigen (Ag) to the autoantigen-specific regulatory T cells (Treg) is required to maintain Treg-dependent systemic tolerance. Thus, testis autoantigens, previously considered as sequestered, may not be protected by systemic tolerance. We now document that the complete testis antigen sequestration is not valid. The haploid sperm Ag lactate dehydrogenase 3 (LDH3) is continuously exposed and not sequestered. It enters the residual body (RB) to egress from the seminiferous tubules and interact with circulating antibody (Ab). Some LDH3 also remains inside the sperm cytoplasmic droplets (CD). Treg-depletion in the DEREG mice that express diphtheria toxin receptor on the Foxp3 promoter results in spontaneous experimental autoimmune orchitis (EAO) and Ab to LDH3. Unlike the wild-type male mice, mice deficient in LDH3 (wild-type female or LDH3 NULL males) respond vigorously to LDH3 immunization. However, partial Treg depletion elevated the wild-type male LDH3 responses to the level of normal females. In contrast to LDH3, zonadhesin (ZAN) in the sperm acrosome displays properties of a sequestered Ag. However, when ZAN and other sperm Ag are exposed by vasectomy, they rapidly induce testis Ag-specific tolerance, which is terminated by partial Treg-depletion, leading to bilateral EAO and ZAN Ab response. We conclude that some testis/sperm Ag are normally exposed because of the unique testicular anatomy and physiology. The exposed Ag: 1) maintain normal Treg-dependent systemic tolerance, and 2) are pathogenic and serve as target Ag to initiate EAO. Unexpectedly, the sequestered Ags, normally non-tolerogenic, can orchestrate de novo Treg-dependent, systemic tolerance when exposed in vasectomy.

T Lymphocytes and Testicular Immunity: A New Insight into Immune Regulation in Testes

The immune privilege of the testes is necessary to prevent immune attacks to gamete-specific antigens and paternal major histocompatibility complex (MHC) antigens, allowing for normal spermatogenesis. However, infection and inflammation of the male genital tract can break the immune tolerance and represent a significant cause of male infertility. Different T cell subsets have been identified in mammalian testes, which may be involved in the maintenance of immune tolerance and pathogenic immune responses in testicular infection and inflammation. We reviewed the evidence in the published literature on different T subtypes (regulatory T cells, helper T cells, cytotoxic T cells, γδ T cells, and natural killer T cells) in human and animal testes that support their regulatory roles in infertility and the orchitis pathology. While many in vitro studies have indicated the regulation potential of functional T cell subsets and their possible interaction with Sertoli cells, Leydig cells, and spermatogenesis, both under physiological and pathological processes, there have been no in situ studies to date. Nevertheless, the normal distribution and function of T cell subsets are essential for the immune privilege of the testes and intact spermatogenesis, and T cell-mediated immune response drives testicular inflammation. The distinct function of different T cell subsets in testicular homeostasis and the orchitis pathology suggests a considerable potential of targeting specific T cell subsets for therapies targeting chronic orchitis and immune infertility.

The application of naked DNA plasmid (DrZP3) and recombinant adenovirus (Ad-rZP3) in rat animal model to determine comparative efficacy of ZP3-Immunocontraceptive vaccines

The common physical and chemical methods for controlling rat pest are less than satisfactory and inhumane. Immunocontraception approach has been considered more humane and it can be accomplished by inducing the relevant host immune response that block further development of reproductive gametes. ZP3 proteins are known to play very important role during sperm-ovum fertilization. It is a self-antigen and only localized in female ovaries. Therefore, an immunization with ZP3 protein elsewhere will induce a generalize host immune response against ZP3 protein. This study employed rat ZP3 (rZP3) gene prepared from its cDNA of Rattus rattus diardii. It was delivered and expressed in vivo by naked plamid DNA (DrZP3) or recombinant ZP3-Adenovirus (Ad-rZP3). Expression studies in vitro with DrZP3 or Ad-ZP3 showed rZP3 proteins were successfully expressed in Vero cells. Hyperimmune serum against rZP3 that were prepared by immunizing several rats with purified rZP3-pichia yeast fusion protein showed it blocked sperms from binding DrZP3-transfected Vero cells. Female Sprague Dawley rats immunized with DrZP3 demonstrated a long-term effect for significant reduction of fertility up to 92.6%. Ovaries from rats immunized with DrZP3 were severely atrophied with disappearance of primordial follicles from ovarian cortex with an increased in the amount of oocyte-free cell clusters. Female rats immunized with Ad-rZP3 demonstrated 27% reduction of fertility. The infertility induced by Ad-rZP3 is comparatively low and ineffective. This could be due to a strong host immune response that suppresses the recombinant virus itself resulted in minimum rZP3 protein presentation to the host immune system. As a result, low antibody titers produced against rZP3 is insufficient to block oocytes from maturity and fertilization. Therefore, immunization with DrZP3 for immunocontraception is more effective than Ad-rZP3 recombinant adenovirus. It is proposed to explore further on the use of adenovirus or other alternative viruses to deliver ZP3 protein and for the development of enhanced expression of rZP3 in target host.

Exploiting PLGA-Based Biocompatible Nanoparticles for Next-Generation Tolerogenic Vaccines against Autoimmune Disease

Tolerogenic vaccines are aimed at inhibiting antigen-specific immune responses. Antigen-loaded nanoparticles (NPs) have been recently emerged as ideal tools for tolerogenic vaccination because their composition, size, and capability of loading immunomodulatory molecules can be readily exploited to induce peripheral tolerance. Among polymeric NPs, poly(lactic-co-glycolic acid) (PLGA) NPs have the advantage of currently holding approval for several applications in drug delivery, diagnostics, and other clinical uses by the Food and Drug Administration (FDA). PLGA-NPs are non-toxic and display excellent biocompatibility and biodegradability properties. Moreover, surface functionalization may improve their interaction with biological materials, thereby optimizing targeting and performance. PLGA-NPs are the most extensively studied in pre-clinical model in the field of tolerogenic vaccination. Thus, this review describes their potential applications in the treatment of autoimmune diseases.

Egress of sperm autoantigen from seminiferous tubules maintains systemic tolerance

Autoimmune responses to meiotic germ cell antigens (MGCA) that are expressed on sperm and testis occur in human infertility and after vasectomy. Many MGCA are also expressed as cancer/testis antigens (CTA) in human cancers, but the tolerance status of MGCA has not been investigated. MGCA are considered to be uniformly immunogenic and nontolerogenic, and the prevailing view posits that MGCA are sequestered behind the Sertoli cell barrier in seminiferous tubules. Here, we have shown that only some murine MGCA are sequestered. Nonsequestered MCGA (NS-MGCA) egressed from normal tubules, as evidenced by their ability to interact with systemically injected antibodies and form localized immune complexes outside the Sertoli cell barrier. NS-MGCA derived from cell fragments that were discarded by spermatids during spermiation. They egressed as cargo in residual bodies and maintained Treg-dependent physiological tolerance. In contrast, sequestered MGCA (S-MGCA) were undetectable in residual bodies and were nontolerogenic. Unlike postvasectomy autoantibodies, which have been shown to mainly target S-MGCA, autoantibodies produced by normal mice with transient Treg depletion that developed autoimmune orchitis exclusively targeted NS-MGCA. We conclude that spermiation, a physiological checkpoint in spermatogenesis, determines the egress and tolerogenicity of MGCA. Our findings will affect target antigen selection in testis and sperm autoimmunity and the immune responses to CTA in male cancer patients.

Bidirectional Estrogen-Like Effects of Genistein on Murine Experimental Autoimmune Ovarian Disease

This study was to investigate the bidirectional estrogen-like effects of genistein on murine experimental autoimmune ovarian disease (AOD). Female BALB/c mice were induced by immunization with a peptide from murine zona pellucida. The changes of estrous cycle, ovarian histomorphology were measured, and the levels of serum sex hormone were analyzed using radioimmunoassay. Proliferative responses of the ovary were also determined by immunohistochemistry. Administration of 25 or 45 mg/kg body weight genistein enhanced ovary development with changes in serum sex hormone levels and proliferative responses. Meanwhile, the proportions of growing and mature follicles increased and the incidence of autoimmune oophoritis decreased, which exhibited normal ovarian morphology in administration of 25 or 45 mg/kg body weight genistein, while a lower dose (5 mg/kg body weight genistein) produced the opposite effect. These findings suggest that genistein exerts bidirectional estrogen-like effects on murine experimental AOD, while a high dose (45 mg/kg body weight) of genistein may suppress AOD.

Augmentation of transgene-encoded protein after neonatal injection of adeno-associated virus improves hepatic copy number without immune responses

BACKGROUND

Achieving persistent expression is a prerequisite for genetic therapies for inherited metabolic enzymopathies. Such disorders potentially could be treated with gene therapy shortly after birth to prevent pathology. However, rapid cell turnover leads to hepatic episomal vector loss, which diminishes effectiveness. The current studies assessed whether tolerance to transgene proteins expressed in the neonatal period is durable and if the expression may be augmented with subsequent adeno-associated virus (AAV) administration.

METHODS

AAV was administered to mice on day 2 with reinjection at 14 or at 14 and 42 d with examination of changes in hepatic copies and B and T cell-mediated immune responses.

RESULTS

Immune responses to the transgene protein and AAV were absent after neonatal administration. Reinjection at 14 or at 14 and 42 d resulted in augmented expression with greater hepatic genome copies. Unlike controls, immune responses to transgene proteins were not detected in animals injected as neonates and subsequently. However, while no immune response developed after neonatal administration, anticapsid immune responses developed with further injections suggesting immunological ignorance was the initial mechanism of unresponsiveness.

CONCLUSIONS

Persistence of transgene protein allows for tolerance induction permitting readministration of AAV to re-establish protein levels that decline with growth.

Development of operational immunologic tolerance with neonatal gene transfer in nonhuman primates: preliminary studies

Achieving persistent expression is a prerequisite for effective genetic therapies for inherited disorders. These proof-of-concept studies focused on adeno-associated virus (AAV) administration to newborn monkeys. Serotype rh10 AAV expressing ovalbumin and green fluorescent protein (GFP) was administered intravenously at birth and compared with vehicle controls. At 4 months postnatal age, a second injection was administered intramuscularly, followed by vaccination at 1 year of age with ovalbumin and GFP. Ovalbumin was highest 2 weeks post administration in the treated monkey, which declined but remained detectable thereafter; controls demonstrated no expression. Long-term AAV genome copies were present in myocytes. At 4 weeks, neutralizing antibodies to rh10 were present in the experimental animal only. With AAV9 administration at 4 months, controls showed transient ovalbumin expression that disappeared with the development of strong anti-ovalbumin and anti-GFP antibodies. In contrast, increased and maintained ovalbumin expression was noted in the monkey administered AAV at birth, without antibody development. After vaccination, the experimental monkey maintained levels of ovalbumin without antibodies, whereas controls demonstrated high levels of antibodies. These preliminary studies suggest that newborn AAV administration expressing secreted and intracellular xenogenic proteins may result in persistent expression in muscle, and subsequent vector administration can result in augmented expression without humoral immune responses.

Mouse Sertoli cells sustain de novo generation of regulatory T cells by triggering the notch pathway through soluble JAGGED1

FOXP3(+) regulatory T cells (Tregs) are central to the maintenance of immunological homeostasis and tolerance. It has long been known that Sertoli cells are endowed with immune suppressive properties; however, the underlying mechanisms as well as the effective nature and role of soluble factors secreted by Sertoli cells have not been fully elucidated as yet. We hypothesized that conditioned medium from primary mouse Sertoli cells (SCCM) may be able and sufficient to induce Tregs. By culturing CD4(+)CD25(-)EGFP(-) T splenocytes purified from FOXP3-EGFP knock-in mice in SCCM, here we show, by flow cytometry and suppression assay, the conversion of peripheral CD4(+)FOXP3(-) T cells into functional CD4(+)FOXP3(+) Tregs. We also demonstrate that the Notch/Jagged1 axis is involved in regulating the de novo generation of Tregs although this process is transforming growth factor-beta1 (TGF-B) dependent. In particular, we identified by Western blot analysis a soluble form of JAGGED1 (JAG1) in SCCM that significantly influences the induction of Tregs, as demonstrated by performing the conversion assay in presence of a JAG1-specific neutralizing antibody. In addition, we show that SCCM modulates the Notch pathway in converted Tregs by triggering the recruitment of the Notch-specific transcription factor CSL/RBP-Jk to the Foxp3 promoter and by inducing the Notch target gene Hey1, as shown by chromatin immunoprecipitation assay and by real time-RT-PCR experiments, respectively. Overall, these results contribute to a better understanding of the molecular mechanisms involved in Sertoli cell-mediated immune tolerance and provide a novel approach to generate ex vivo functional Tregs for therapeutic purpose.

Regulatory T cells and vasectomy

CD4+ CD25+ regulatory T cells (Tregs) strongly influence the early and late autoimmune responses to meiotic germ cell antigens (MGCA) and the gonadal immunopathology in vasectomized mice. This is supported by the published and recently acquired information presented here. Within 24h of unilateral vasectomy (uni-vx) the ipsilateral epididymis undergoes epithelial cell apoptosis followed by necrosis, severe inflammation, and granuloma formation. Unexpectedly, vasectomy alone induced MGCA-specific tolerance. In contrast, uni-vx plus simultaneous Treg depletion resulted in MGCA-specific autoimmune response and bilateral autoimmune orchitis. Both tolerance and autoimmunity were strictly linked to the early epididymal injury. We now discovered that testicular autoimmunity in uni-vx mice did not occur when Treg depletion was delayed by one week. Remarkably, this delayed Treg depletion also prevented tolerance induction. Therefore, tolerance depends on a rapid de novo Treg response to MGCA exposed after vasectomy. Moreover, tolerance was blunted in mice genetically deficient in PD-1 ligand, suggesting the involvement of induced Treg. We conclude that pre-existing natural Treg prevents post-vasectomy autoimmunity, whereas vasectomy-induced Treg maintains post-vasectomy tolerance. We further discovered that vasectomized mice were still resistant to autoimmune orchitis induction for at least 12-16 months; thus, tolerance is long-lasting. Although significant sperm autoantibodies of low titers became detectable in uni-vx mice at 7 months, the antibody titers fluctuated over time, suggesting a dynamic "balance" between the autoimmune and tolerance states. Finally, we observed severe epididymal fibrosis and hypo-spermatogenesis at 12 months after uni-vx: findings of highly critical clinical significance.

Role of antigen-specific regulatory CD4+CD25+ T cells in tolerance induction after neonatal IP administration of AAV-hF.IX

Neonatal AAV8-mediated Factor IX (F.IX) gene delivery was applied as a model for exploring mechanisms of tolerance induction during immune ontogeny. Intraperitoneal delivery of AAV8/ Factor IX (hF.IX) during weeks 1–4 of life, over a 20-fold dose range, directed stable hF.IX expression, correction of coagulopathy in F.IX-null hemophilia B mice, and induction of tolerance to hF.IX; however, only primary injection at 1–2 days of life enabled increasing AAV8-mediated hF.IX expression after re-administration, due to the absence of anti-viral capsid antibodies. Adoptive splenocyte transfer from tolerized mice demonstrated induction of CD4⁺CD25⁺ T regulatory (T_reg) populations that specifically suppressed anti-hF.IX antibody responses, but not responses to third party antigen. Induction of hF.IX antibodies was only observed in tolerized mice after in vivo CD4⁺CD25⁺ cell depletion and hF.IX challenge. Thus, primary injection of AAV during a critical period in the first week of life does not elicit antiviral responses, enabling re-administration of AAV and augmentation of hF.IX levels. Expansion of hF.IX-specific CD4⁺CD25⁺ T_regs has a major role in tolerance induction early in immune ontogeny. Neonatal gene transfer provides a useful approach for defining the ontogeny of immune responses and may suggest approaches for inducing tolerance in the context of genetic therapies.

Regulatory T cells in the corpus luteum--new players in fertility control?

The discovery of dynamic populations of regulatory T cells in the corpus luteum opens new possibilities for immune regulation of early pregnancy.

Autoimmune oophoritis with multiple molecular targets mitigated by transgenic expression of mater

Primary ovarian insufficiency (POI) resulting from ovarian autoimmunity is a poorly understood clinical condition lacking in effective treatments. Understanding the targets of the autoimmune response and induction of ovarian-specific tolerance would allow development of focused therapies to preserve fertility in an at-risk population. MATER (maternal antigen that embryos require) is a known ovarian autoantigen targeted in autoimmune syndromes of POI. We attempt to induce ovarian-specific tolerance via transgenic expression of the MATER antigen on potentially tolerogenic antigen-presenting cells (APC), which typically present antigen via the major histocompatibility complex (MHC) class II molecule. We hypothesize that expression of MATER in a MHC class II-dependent manner on APC can mediate induction of ovarian tolerance. We utilized a well-characterized murine model of ovarian autoimmunity, whereby oophoritis develops after d 3 neonatal thymectomy (NTx). Wild-type and transgenic mice, carrying an MHC Class II-driven Mater gene (IE-Mater), were subjected to NTx and assessed for evidence of autoimmune oophoritis. After disease induction by NTx, female mice carrying the IE-Mater transgene had significant reductions in histological oophoritis (56%) and circulating ovarian autoantibodies (28%) compared with wild-type females (94% and 82%, respectively). Incidence of other autoimmunity was unaffected as assessed by antinuclear autoantibodies. Transgenic expression of MATER in APC can induce antigen-specific tolerance with a significant reduction in ovarian autoimmunity. Lack of complete disease protection suggests that other antigens may also play a role in autoimmune oophoritis. As a known autoantigen in the human APS1 (autoimmune polyglandular syndrome type 1), which is associated with POI, MATER may represent a relevant target for future diagnostic and therapeutic clinical interventions.

Neonatal helper-dependent adenoviral vector gene therapy mediates correction of hemophilia A and tolerance to human factor VIII

Neonatal gene therapy is a promising strategy for treating a number of congenital diseases diagnosed shortly after birth as expression of therapeutic proteins during postnatal life may limit the pathologic consequences and result in a potential "cure." Hemophilia A is often complicated by the development of antibodies to recombinant protein resulting in treatment failure. Neonatal administration of vectors may avoid inhibitory antibody formation to factor VIII (FVIII) by taking advantage of immune immaturity. A helper-dependent adenoviral vector expressing human factor VIII was administered i.v. to neonatal hemophilia A knockout mice. Three days later, mice produced high levels of FVIII. Levels declined rapidly with animal growth to 5 wk of age with stable factor VIII expression thereafter to >1 y of age. Decline in factor VIII expression was not related to cell-mediated or humoral responses with lack of development of antibodies to capsid or human factor VIII proteins. Subsequent readministration and augmentation of expression was possible as operational tolerance was established to factor VIII without development of inhibitors; however, protective immunity to adenovirus remained.

Thymic and peripheral differentiation of regulatory T cells

The development of regulatory T (Treg) cells is essential for the maintenance of immune tolerance and homeostasis. Here, we review recent studies that have advanced our understanding of Treg cell differentiation. In the thymus, TCR specificity to self-antigen appears to be a primary determinant for Treg cell lineage commitment, with c-Rel being an important factor that links T cell receptor (TCR) engagement and Foxp3 expression, along with cytokines and costimulatory molecules. It is also clear that postthymic events shape the peripheral Treg cell population. This includes preferential maintenance of Treg cells specific to self-antigens presented in the periphery, as well as the de novo generation of Treg cells from conventional Foxp3(-) T cells. The process of peripheral Treg cell differentiation shares some features with thymic Treg cell development, but there are notable differences. Together, thymic and peripheral Treg cell differentiation appear to generate an "imprint" of both self- and foreign antigens in the peripheral Treg cell population to provide dominant tolerance.

Plant-made pharmaceuticals for the prevention and treatment of autoimmune diseases: where are we?

Molecular farming in plants or plant cell cultures represents a viable alternative technology that holds great promise for the low-cost and large-scale production of recombinant proteins. The particular case of plant-based vaccines for the prevention of autoimmune diseases is addressed here, presenting a comprehensive overview of the different molecules and expression technologies that have been investigated so far in both academia and industry. The potential of plants not only as bioreactors but also as delivery systems for pharmaceuticals is discussed, and the advantages of oral delivery of autoantigens for the induction of immune tolerance are highlighted.

Regulatory T-cells and immune tolerance in pregnancy: a new target for infertility treatment?

BACKGROUND

Adaptation of the maternal immune response to accommodate the semi-allogeneic fetus is necessary for pregnancy success, and disturbances in maternal tolerance are implicated in infertility and reproductive pathologies. T regulatory (Treg) cells are a recently discovered subset of T-lymphocytes with potent suppressive activity and pivotal roles in curtailing destructive immune responses and preventing autoimmune disease.

METHODS

A systematic review was undertaken of the published literature on Treg cells in the ovary, testes, uterus and gestational tissues in pregnancy, and their link with infertility, miscarriage and pathologies of pregnancy. An overview of current knowledge on the generation, activation and modes of action of Treg cells in controlling immune responses is provided, and strategies for manipulating regulatory T-cells for potential applications in reproductive medicine are discussed.

RESULTS

Studies in mouse models show that Treg cells are essential for maternal tolerance of the conceptus, and that expansion of the Treg cell pool through antigen-specific and antigen non-specific pathways allows their suppressive actions to be exerted in the critical peri-implantation phase of pregnancy. In women, Treg cells accumulate in the decidua and are elevated in maternal blood from early in the first trimester. Inadequate numbers of Treg cells or their functional deficiency are linked with infertility, miscarriage and pre-eclampsia.

CONCLUSIONS

The potency and wide-ranging involvement of Treg cells in immune homeostasis and disease pathology indicates the considerable potential of these cells as therapeutic agents, raising the prospect of their utility in novel treatments for reproductive pathologies.

Contribution of antibody and T cell-specific responses to the progression of 139A-scrapie in C57BL/6 mice immunized with prion protein peptides

Prion diseases are associated with the conversion of the normal host cellular prion protein to an abnormal protease-resistant (PrPres) associated with infectivity. No specific immune response against prions develops during infection due to the strong tolerance to cellular prion protein. We examined the protective potential on prion diseases of immune responses elicited in C57BL/6 mice with PrP peptides 98-127 (P5) or 158-187 (P9) with CpG. After immunization, P5-treated mice developed high titer and long-lasting Abs, and P9-treated mice developed transient IFN-gamma secreting T cells and poor and variable Ab responses. Both treatments impaired early accumulation of PrPres in the spleen and prolonged survival of mice infected with 139A scrapie. Additional P9 boosts after 139A infection sustained the T cell response and partially inhibited PrPres early accumulation but did not improve the survival. Surprisingly, when P9 injections were started 1 mo after infection and repeated subsequently, specific T cell and Ab responses were impaired and no beneficial effect on prion disease was observed. After a single injection of P9, the number of IFN-gamma secreting CD4+ T cells was also reduced in mice 8- to 10-wk postinfection compared with healthy mice. In vivo and in vitro removal of CD4+CD25+ T cells restored the T cell response to P9 in infected mice. In conclusion, CD4+ T cells as well as Abs might participate to the protection against scrapie. Of importance, the peripheral accumulation of PrPres during infection negatively interferes with the development of T and B cell responses to PrP and regulatory T cells might contribute to this phenomenon.

A population dynamics analysis of the interaction between adaptive regulatory T cells and antigen presenting cells

Background

Regulatory T cells are central actors in the maintenance of tolerance of self-antigens or allergens and in the regulation of the intensity of the immune response during infections by pathogens. An understanding of the network of the interaction between regulatory T cells, antigen presenting cells and effector T cells is starting to emerge. Dynamical systems analysis can help to understand the dynamical properties of an interaction network and can shed light on the different tasks that can be accomplished by a network.

Methodology and Principal Findings

We used a mathematical model to describe a interaction network of adaptive regulatory T cells, in which mature precursor T cells may differentiate into either adaptive regulatory T cells or effector T cells, depending on the activation state of the cell by which the antigen was presented. Using an equilibrium analysis of the mathematical model we show that, for some parameters, the network has two stable equilibrium states: one in which effector T cells are strongly regulated by regulatory T cells and another in which effector T cells are not regulated because the regulatory T cell population is vanishingly small. We then simulate different types of perturbations, such as the introduction of an antigen into a virgin system, and look at the state into which the system falls. We find that whether or not the interaction network switches from the regulated (tolerant) state to the unregulated state depends on the strength of the antigenic stimulus and the state from which the network has been perturbed.

Conclusion/Significance

Our findings suggest that the interaction network studied in this paper plays an essential part in generating and maintaining tolerance against allergens and self-antigens.

ZP3 peptides administered orally suppress murine experimental autoimmune ovarian disease

Experimental autoimmune ovarian disease (AOD) is a T cell-mediated chronic inflammatory disease that may lead to premature ovarian failure. Autoimmune disease can be suppressed by oral administration of autoantigens leading to tolerance. One of the major mechanisms of oral tolerance is induction of regulatory CD4+ T cells that can mediate active suppression by producing immunomodulatory cytokines. However, the role of oral tolerance as a treatment for experimental AOD has received little attention. Therefore, the purpose of this study was to examine the conditions necessary to produce oral tolerance in experimental AOD in B6AF1 female mice. In this study, mice received different doses of peptides of the mouse zona pellucida 3 (pZP3) via gastric intubation for 7 times. After 4 times of oral administration, AOD was induced by immunization with pZP3. The optimal tolerating regimen for oral administration of pZP3 in mice was 10 microg, which decreased morbidity of oophoritis compared to the control group. In this moderate-dose therapeutic group (MD), alterations in the estrous cycle were normalized and CD4+ T cells that were CD25+ increased while those that were CD25- decreased. The severity of autoimmune oophoritis and the titer of ZP autoantibodies were also significantly reduced. These findings suggest that oral administration of pZP3 may be successfully used as an oral tolerance strategy for suppression of AOD.

Genetic vaccination with Flt3-L and GM-CSF as adjuvants: Enhancement of cellular and humoral immune responses that results in protective immunity in a murine model of hepatitis C virus infection

AIM: To investigate whether transfection of plasmid DNA encoding these cytokines enhances both humoral and cellular immune responses to hepatitis C virus (HCV) in a murine model.

METHODS: We established a tumor model of HCV infection using syngenic mouse myeloma cells stably transfected with NS5. Co-vaccination of DNA encoding granulocyte macrophage colony-stimulating factor (GM-CSF) and Flt-3 ligand together with a plasmid encoding for the HCV NS5 protein was carried out. Mice were sacrificed 14 d after the last immunization event with collection of spleen cells and serum to determine humoral and cellular immune responses.

RESULTS: Co-vaccination of DNA encoding GM-CSF and Flt-3 ligand together with a plasmid encoding for the HCV NS5 protein induced increased antibody responses and CD4+ T cell proliferation to this protein. Vaccination with DNA encoding GM-CSF and Flt-3L promoted protection against tumor formation and/or reduction in mice co-immunized with cytokine-encoding DNA constructs. This suggests this strategy is capable of generating cytotoxic T lymphocyte activity in vivo. Following inoculation with plasmid DNA encoding Flt-3L, no increase in spleen size or in dendritic cell (DC) and natural killer cell numbers was observed. This was in contrast to a dramatic increase of both cell types after administration of recombinant Flt3-L in vivo. This suggests that vaccination with plasmid DNA encoding cytokines that regulate DC generation and mobilization may not promote unwanted side effects, such as autoimmunity, splenic fibrosis or hematopoietic malignancies that may occur with administration of recombinant forms of these proteins.

CONCLUSION: Our data support the view that plasmid DNA vaccination is a promising approach for HCV immunization, and may provide a general adjuvant vaccination strategy against malignancies and other pathogens.

The role of physiological self-antigen in the acquisition and maintenance of regulatory T-cell function

The CD4+ CD25+ regulatory T cells (Tregs) are efficient regulators of autoimmunity, but the mechanism remains elusive. We summarize recent data for the conclusion that disease-specific Tregs respond to tissue antigens to maintain physiological tolerance and prevent autoimmunity. First, polyclonal Tregs from antigen-positive donors suppress autoimmune ovarian disease (AOD) or experimental autoimmune prostatitis in day 3 thymectomized (d3tx) mice more efficiently than Tregs from antigen-negative donors. Second, Tregs of antigen-negative adult mice respond to cognate antigen in vivo and rapidly gain disease-specific Treg function. Third, in d3tx female recipients devoid of neonatal ovarian antigens, only female Tregs suppressed AOD; the male Tregs gain AOD-suppressing function by responding to the ovarian antigen in the recipients and mask the supremacy of female Tregs in AOD suppression. Fourth, when Tregs completely suppress AOD, the ovary-draining lymph node is the only location with evidence of profound and persistent (but reversible) host T-cell suppression. Fifth, from these nodes, highly potent AOD-suppressing Tregs are retrievable. We conclude that self-tolerance involves the continuous priming of Tregs by autoantigens, and in autoimmune disease suppression, the effector T-cell response is continuously negated by potent disease-specific Tregs that accumulate at the site of autoantigen presentation.

Diversified serum IgG response involving non-myelin CNS proteins during experimental autoimmune encephalomyelitis

We sequentially analyzed the serum IgG response against normal mouse brain during experimental autoimmune encephalomyelitis in SJL/J mice injected with CFA, Bordetella pertussis toxin (BPT) and proteolipid protein 139-151 peptide, compared with mice that received CFA and BPT or were uninjected. Dynamic changes were observed from day 0 to day 28 in the 3 groups. Six highly discriminant antigenic bands (kappa=0.974) were identified. Three non-myelin proteins were characterized (mitochondrial aconitase hydratase 2, phosphoglycerate mutase 1, brain specific pyruvate deshydrogenase). The IgG response against two of them was less frequent in EAE whereas it was associated with multiple sclerosis in our previous work.

Large-scale expansion of rat CD4+ CD25+ T(reg) cells in the absence of T-cell receptor stimulation

T-cell receptor (TCR) stimulation is both central to homeostatic maintenance of CD4(+) CD25(+) regulatory T cells (T(reg) cells) in vivo and a prerequisite for the initiation of suppression by T(reg) cells, both in vivo and in vitro. However, TCR-independent stimulation of T(reg) cells, e.g. with superagonistic CD28-specific monoclonal antibodies (CD28-SA), not only expands these cells in vivo but, as we show here, also mediates large-scale expansion of rat T(reg) cells in vitro. Interestingly, CD28-SA stimulation plus interleukin (IL)-2 was even superior to conventional costimulation plus IL-2 in promoting T(reg) cell growth in vitro. Despite their highly activated phenotype suppression by T(reg) cells expanded in the absence of TCR stimulation remained fully dependent on TCR-triggering for initiation and cell contact was required to exert suppression. With regard to the regulation of suppression by CD28 stimulation we observed that neither the presence of a conventional anti-CD28 monoclonal antibody nor a CD28-SA generally rendered conventional T cells resistant to suppression by preactivated T(reg) cells. Taken together, we provide a novel protocol for long-term propagation of T(reg) cells in vitro and our data are the first to reveal a difference in the signals required for activation and expansion of T(reg) cells and those, involving the TCR, necessary for the initiation of suppression.

The Unveiling of Hidden T-Cell Determinants of a Native Antigen by Defined Mediators of Inflammation: Implications for the Pathogenesis of Autoimmunity

A major hypothesis for the induction of autoimmunity invokes the enhanced display of previously hidden (cryptic) epitopes under inflammatory conditions leading to the activation of self-reactive T cells. However, there is meager data that directly validate the influence of specific immune mediators on the upregulation of the presentation of cryptic determinants in vivo. We tested the effect on well-defined cryptic epitopes of hen eggwhite lysozyme (HEL) of the availability locally of a cytokine (IL-2, IL-4, IL-6, IL-10, TNF-alpha or granulocyte-macrophage colony-stimulating factor) at the antigen delivery site, or of the pretreatment of the immunogen with a cathepsin (Cat B, D, L or S) prior to use in vivo. Each of the three mouse strains (H-2(b/d/k)) tested revealed a unique profile of T-cell reactivity to different cryptic epitopes of HEL in response to a particular cytokine or cathepsin. These results provide proof of principle for the reversal of crypticity of self-epitopes by immune mediators in the local milieu. Moreover, co-immunization with an antigen and a cytokine offers a simple and reliable tool for studying the role of cryptic epitopes in autoimmunity. Our results also strengthen the rationale for the use of inhibitors of cytokine/cathepsin activity in the treatment of autoimmune diseases.

Deletion is neither sufficient nor necessary for the induction of peripheral tolerance in mature CD8+ T cells

Previous reports have demonstrated clonal deletion of CD8(+) T cells during peripheral tolerance induction to tissue antigens. However, direct evidence demonstrating a causal connection between deletion and tolerance has not been reported because of model limitations in which the tissue antigens were expressed in vital organs. Thus, studies were initiated in a mouse model where expression of a membrane-bound ovalbumin fusion protein (mOVA) was driven by a prostate specific androgen regulated probasin promotor, providing restricted expression in a non-vital organ where antigen levels can be abrogated through androgen deprivation. Adoptive transfer of mOVA specific CD8(+) T cells (OT-I) was used to assess the development of peripheral tolerance. Proliferation of OT-I cells was observed, as was partial deletion of transferred OT-I cells. Although deletion occurred, the long-term persistence of a stable level of OT-I cells was observed. Importantly, the persistent OT-I cells lost antigen responsiveness within 3 weeks of transfer. Castration resulted in loss of high-level prostate mOVA expression, with a resultant abrogation of tolerance induction, but surprisingly did not affect the deletion rate of OT-I cells. In contrast, abrogation of deletion through the adoptive transfer of OT-I cells from third generation CD95-deficient mice had no effect on tolerance induction. These data demonstrate the necessity for continued expression of tissue antigen throughout the establishment of peripheral tolerance. Furthermore, these findings demonstrate that deletion is neither sufficient nor required for CD8(+) T-cell tolerance to tissue antigens, suggesting that regulatory events independent of deletion are necessary for peripheral tolerance induction to prostate antigens.

The interactions of dendritic cells with antigen-specific, regulatory T cells that suppress autoimmunity

Dendritic cells (DCs) are important for several aspects of the development and function of CD4(+) CD25(+) regulatory T cells (Tregs), which are critical for maintaining peripheral tolerance and preventing autoimmunity. In cultures from human thymus, dendritic cells (DCs) conditioned with thymic stromal lymphopoietin (TSLP) mediate the production of Tregs from CD4(+) CD25(-) thymocytes. In cultures from mouse lymphoid organs, CD86-rich DCs induce the proliferation and improved suppressive function of antigen-specific Tregs. DC-expanded, antigen-specific Tregs show greatly enhanced efficacy relative to polyclonal populations in blocking experimental autoimmunity. In several animal models including NOD diabetes, Tregs directed to one autoantigen are able to block autoimmunity induced by multiple antigens from the target organ. Distinct states of DC differentiation or maturation are likely to be important for the emerging roles of DCs in the biology of Tregs, particularly the control of autoimmunity in an antigen-dependent manner.

CD4+CD25+ Regulatory T Cells Inhibit the Antigen-Dependent Expansion of Self-Reactive T Cells In Vivo

A deficiency of CD4+CD25+ regulatory T cells (CD25+ Tregs) in lymphopenic mice can result in the onset of autoimmune gastritis. The gastric H/K ATPase alpha (H/Kalpha) and beta (H/Kbeta) subunits are the immunodominant autoantigens recognized by effector CD4+ T cells in autoimmune gastritis. The mechanism by which CD25+ Tregs suppress autoimmune gastritis in lymphopenic mice is poorly understood. To investigate the antigenic requirements for the genesis and survival of gastritis-protecting CD25+ Tregs, we analyzed mice deficient in H/Kbeta and H/Kalpha, as well as a transgenic mouse line (H/Kbeta-tsA58 Tg line 224) that lacks differentiated gastric epithelial cells. By adoptive transfer of purified T cell populations to athymic mice, we show that the CD25+ Treg population from mice deficient in either one or both of H/Kalpha and H/Kbeta, or from the H/Kbeta-tsA58 Tg line 224 mice, is equally effective in suppressing the ability of polyclonal populations of effector CD4+ T cells to induce autoimmune gastritis. Furthermore, CD25+ Tregs, from either wild-type or H/Kalpha-deficient mice, dramatically reduced the expansion of pathogenic H/Kalpha-specific TCR transgenic T cells and the induction of autoimmune gastritis in athymic recipient mice. Proliferation of H/Kalpha-specific T cells in lymphopenic hosts occurs predominantly in the paragastric lymph node and was dependent on the presence of the cognate H/Kalpha Ag. Collectively, these studies demonstrate that the gastritis-protecting CD25+ Tregs do not depend on the major gastric Ags for their thymic development or their survival in the periphery, and that CD25+ Tregs inhibit the Ag-specific expansion of pathogenic T cells in vivo.

Autoimmune ovarian disease in day 3-thymectomized mice: the neonatal time window, antigen specificity of disease suppression, and genetic control

Discovery of the CD4+CD25+ T cells has stemmed from investigation of the AOD in the d3tx mice. Besides CD4+CD25+ T cell depletion, d3tx disease induction requires effector T cell activation prompted by lymphopenia. This is supported by other neonatal AOD models in which T cell-mediated injury has been found to be triggered by immune complex or Ag immunization. In addition, there is growing evidence that support a state of neonatal propensity to autoimmunity, which depends on concomitant endogenous antigenic stimulation, concomitant nematode infection, resistance to CD4+CD25+ T cell regulation, and participation of the neonatal innate system. The suppression of d3tx disease by polyclonal CD4+CD25+ T cells appears to be dependent on endogenous Ag and the persistence of regulatory T cells. Thus, suppression of AOD occurs in the ovarian LN, and AOD emerges upon ablation of the input regulatory T cells; and in AIP, the hormone-induced expression of prostate Ag in the CD4+CD25+ T cell donors rapidly enhances the capacity to suppress disease over Ag negative donors. Finally, genetic analysis of AOD and its component phenotypes has uncovered seven Aod loci. As the general themes that emerged, significant epistatic interactions among the loci play a role in controlling disease susceptibility, the majority of the Aod loci are linked to susceptibility loci of other autoimmune diseases, and the genetic intervals encompass candidate genes that are differentially expressed between CD4+CD25+ T cells and other T cells. The candidate genes include Pdcd1, TNFR superfamily genes, H2, Il2, Tgfb, Nalp5 or Mater, an oocyte autoAg that reacts with autoantibody in sera of d3tx mice.

Continuous control of autoimmune disease by antigen-dependent polyclonal CD4+CD25+ regulatory T cells in the regional lymph node

This study investigated the unresolved issue of antigen-dependency and antigen-specificity of autoimmune disease suppression by CD4⁺CD25⁺ T cells (T regs). Based on autoimmune ovarian disease (AOD) in day 3 thymectomized (d3tx) mice and polyclonal T regs expressing the Thy1.1 marker, we determined: (a) the location of recipient T cell suppression, (b) the distribution of AOD-suppressing T regs, and (c) the relative efficacy of male versus female T regs. Expansion of recipient CD4⁺ T cells, activation/memory marker expression, and IFN-γ production were inhibited persistently in the ovary-draining LNs but not elsewhere. The cellular changes were reversed upon Thy1.1⁺ T reg depletion, with emergence of potent pathogenic T cells and severe AOD. Similar changes were detected in the regional LNs during autoimmune dacryoadenitis and autoimmune prostatitis suppression. Although the infused Thy1.1⁺ T regs proliferated and were disseminated in peripheral lymphoid organs, only those retrieved from ovary-draining LNs adoptively suppressed AOD at a suboptimal cell dose. By depriving d3tx recipients of ovarian antigens, we unmasked the supremacy of ovarian antigen-exposed female over male T regs in AOD suppression. Thus, disease suppression by polyclonal T regs depends on endogenous antigen stimulation; this occurs in a location where potent antigen-specific T regs accumulate and continuously negate pathogenic T cell response.

Neonatal autoimmune disease: influence of CD4+ CD25+ regulatory T cells

Although previous studies have emphasized the tolerogenic property of murine neonatal immune system, recent studies indicate that neonatal mice are prone to autoimmune disease. This chapter will summarize the evidence for neonatal propensity to autoimmune ovarian disease (AOD) and describe the new finding that autoantibody can trigger a T cell-dependent autoimmune disease in neonatal but not adult mice. Based on depletion or addition of the CD4+ CD25+ T cells, disease resistance of older mice is explicable by the emergence of CD4+ CD25+ regulatory T-cell function after day 5, whereas disease susceptibility is associated with resistance to regulation by CD4+ CD25+ T cells.

The role of self-peptides in the development of CD4+ CD25+ regulatory T cells

The thymus produces a unique lineage of cells known as CD4+ CD25+ regulatory T cells, and the exact processes leading to their development continue to be defined. Highly specific interactions between developing thymocytes and cognate self-antigens expressed by radioresistant elements in the thymus have been shown to drive CD4+ CD25+ regulatory-T-cell development. The self-peptide(s) that mediate thymic selection of CD4+ CD25+ regulatory T cells can also promote their expansion in the periphery, and self-peptides might also play a role in the conversion of CD4+ CD25- T cells into CD25+ regulatory T cells.

CD4+CD25+ T Regulatory Cells, Immunotherapy of Cancer, and Interleukin-2

CD4+CD25+ T regulatory (Treg) cells control immunologic tolerance to self-antigens and play a role in suppressing antitumor immune responses, but the mechanism of suppression in vivo remains uncertain. Recently, signaling through the high-affinity interleukin-2 (IL-2) receptor has been shown to be critical for Treg cell differentiation and survival in vivo. Mice deficient in IL-2 or its receptor (CD25 or CD122) or deficient in downstream signaling molecules, including JAK-3 and STAT-5, do not develop a stable population of Treg cells and subsequently acquire lymphoproliferative disease and autoimmunity. in vitro, IL-2 is required to expand Treg cells and to induce their suppressive characteristics. Conversely, IL-2-based regimens can activate cellular antitumor immunity and are the mainstay of immunotherapies directed against melanoma and kidney cancers. Given the seemingly disparate effects of IL-2, the authors discuss the possibility that IL-2 may not be the optimal T-cell growth factor in vivo, but rather an inducer of self-tolerance. The authors propose that other gamma c-signaling cytokines, including IL-15, may be alternative choices for the immunotherapy of cancer.

Mouse lysozyme-M knockout mice reveal how the self-determinant hierarchy shapes the T cell repertoire against this circulating self antigen in wild-type mice

We have studied T cell tolerance to defined determinants within ML-M using wild-type (WT; ML-M(+/+)) and LysMcre (ML-M(-/-)) C3H (H-2(k)) mice to determine the relative contribution of ML-M-derived epitopes vs those from other self Ags in selection of the ML-M-specific T cell repertoire. ML-M was totally nonimmunogenic in WT mice, but was rendered immunogenic in LysMcre mice. Most of the response to ML-M in LysMcre mice was directed to the immunodominant determinant region 105-119. This determinant is spontaneously displayed (without adding exogenous ML-M) by macrophages of WT, but not LysMcre, mice and is stimulatory for peptide 105-119 (p105-119)-primed T cells. Moreover, neonatal tolerization of LysMcre mice with p105-119 or ML-M abrogated the T cell response to subsequent challenge with ML-M or p105-119. Furthermore, p95-109 and p110-125 of ML-M were immunogenic in LysMcre mice, but not in WT mice, thereby representing subdominant, tolerance-inducing epitopes of ML-M. As expected, the T cell repertoire to cryptic ML determinants in WT mice was also intact in LysMcre mice. Furthermore, the pattern of response to the related homologue of ML-M, hen eggwhite lysozyme, was similar in these two groups of mice. Thus, several codominant T cell determinants within ML-M contribute significantly to tolerance induction, and the anti-cryptic T cell repertoire to ML-M was positively selected on non-ML-M self ligands. These results reveal that the induction of self tolerance to a multideterminant protein follows the quantitative hierarchy of self-determinant expression and are of relevance in understanding the pathogenesis of autoimmunity.

CD4+ CD25+ Regulatory T Cell Repertoire Formation in Response to Varying Expression of a neo-Self-Antigen

We have examined the development of self-peptide-specific CD4+ CD25+ regulatory T cells in lineages of transgenic mice that express the influenza virus PR8 hemagglutinin (HA) under the control of several different promoters (HA transgenic mice). By mating these lineages with TS1-transgenic mice expressing a TCR that recognizes the major I-E(d)-restricted determinant from HA (site 1 (S1)), we show that S1-specific T cells undergo selection to become CD4+ CD25+ regulatory T cells in each of the lineages, although in varying numbers. In some lineages, S1-specific CD4+ CD25+ regulatory T cells are highly abundant; indeed, TS1xHA-transgenic mice can contain as many S1-specific CD4+ T cells as are present in TS1 mice, which do not express the neo-self HA. In another lineage, however, S1-specific thymocytes are subjected to more extensive deletion and far fewer S1-specific CD4+ CD25+ regulatory T cells accumulate in the periphery. We show that radioresistant stromal cells can direct both deletion and CD4+ CD25+ regulatory T cell selection of S1-specific thymocytes. Interestingly, even though their numbers can vary, the S1-specific CD4+ CD25+ regulatory T cells in all cases coexist with clonally related CD4+ CD25- T cells that lack regulatory function. These findings show that the formation of the CD4+ CD25+ regulatory T cell repertoire is sensitive to variations in the expression of self-peptides.

Tolerance and immunity in a mathematical model of T-cell mediated suppression

Regulatory CD4+CD25+ T cells play a major role in natural tolerance to body components and therefore are relevant to understand the self-non-self discrimination by the immune system. The most pressing theoretical question, regarding the fact that these regulatory cells perform their function through linked recognition of the APCs, is how this "non-specific" mechanism permits a proper balance between tolerance and immunity that is compatible with an effective self-non-self discrimination. To tackle this issue, we develop a numerical simulation, which extends a previous mathematical model of T-cell-mediated suppression to include the thymic generation and the peripheral dynamics of many T cell clones. This simulation can mimic the capacity of the immune system to establish natural tolerance to self-antigens and reliably mount immune responses to foreign antigens. Natural tolerance is based on ubiquitous and constitutive self-antigens, which select and sustain clones of specific regulatory cells. Immune responses to foreign antigens are only achieved if they displace the self-antigens from the APCs, leading to a loss of the regulatory cells, and/or if the foreign antigen introduction entails a sharp increase in the total number of APCs. Meaningful behavior is obtained even if differentiation of regulatory cells in the thymus is antigen non-specific, but requires that a minimum number of new T cells enter the periphery per unit of time, and that the repertoire is selected so that anti-self-affinities are within a proper interval. We conclude that positive selection is required to generate a sufficiently high frequency of self-antigen specific regulatory cells that reliably mediate natural tolerance. Negative selection is required to avoid the emergence at the periphery of very high affinity anti-self-regulatory cells that will make the tolerant state so robust that it could no be broken by the introduction of a foreign antigen. This result highlights the importance of repertoire selection in dominant tolerance proposing a novel role for the processes of positive and negative selection within this framework.

Continuous activation of autoreactive CD4+ CD25+ regulatory T cells in the steady state

Despite a growing interest in CD4+ CD25+ regulatory T cells (Treg) that play a major role in self-tolerance and immunoregulation, fundamental parameters of the biology and homeostasis of these cells are poorly known. Here, we show that this population is composed of two Treg subsets that have distinct phenotypes and homeostasis in normal unmanipulated mice. In the steady state, some Treg remain quiescent and have a long lifespan, in the order of months, whereas the other Treg are dividing extensively and express multiple activation markers. After adoptive transfer, tissue-specific Treg rapidly divide and expand preferentially in lymph nodes draining their target self-antigens. These results reveal the existence of a cycling Treg subset composed of autoreactive Treg that are continuously activated by tissue self-antigens.

Break of neonatal Th1 tolerance and exacerbation of experimental allergic encephalomyelitis by interference with B7 costimulation

Ig-PLP1 is an Ig chimera expressing proteolipid protein-1 (PLP1) peptide corresponding to aa residues 139-151 of PLP. Newborn mice given Ig-PLP1 in saline on the day of birth and challenged 7 wk later with PLP1 peptide in CFA develop an organ-specific neonatal immunity that confers resistance against experimental allergic encephalomyelitis. The T cell responses in these animals comprise Th2 cells in the lymph node and anergic Th1 lymphocytes in the spleen. Intriguingly, the anergic splenic T cells, although nonproliferative and unable to produce IFN-gamma or IL-4, secrete significant amounts of IL-2. In this work, studies were performed to determine whether costimulation through B7 molecules plays any role in the unusual form of splenic Th1 anergy. The results show that engagement of either B7.1 or B7.2 with anti-B7 Abs during induction of EAE in adult mice that were neonatally tolerized with Ig-PLP1 restores and exacerbates disease severity. At the cellular level, the anergic splenic T cells regain the ability to proliferate and produce IFN-gamma when stimulated with Ag in the presence of either anti-B7.1 or anti-B7.2 Ab. However, such restoration was abolished when both B7.1 and B7.2 molecules were engaged simultaneously, indicating that costimulation is necessary for reactivation. Surprisingly, both anti-B7.1 and anti-B7.2 Abs triggered splenic dendritic cells to produce IL-12, a key cytokine required for restoration of the anergic T cells. Thus, recovery from neonatally induced T cell anergy requires B7 molecules to serve double functions, namely, costimulation and induction of cytokine production by APCs.

Post-hematopoietic cell transplantation control of graft-versus-host disease by donor CD425 T cells to allow an effective graft-versus-leukemia response

After allogeneic hematopoietic cell transplantation (HCT), the high inverse correlation between graft-versus-host disease (GVHD) and leukemic relapse requires that calculated measures be taken to reduce GVHD pathology while retaining the graft-versus-leukemia (GVL) effect. We sought to determine whether donor CD4(+)CD25(+) regulatory T cells could control ongoing GVHD, thereby providing an initial window of time in which the alloreactive anti-host response is permitted to begin, with the intent of most effectively eliminating residual leukemia cells. Prevention of lethal GVHD by infusion of donor CD4(+)CD25(+) cells early after HCT (day 2) was achieved across a major histocompatibility complex barrier in the haploidentical C3H-->(B6xC3H)F(1) model. However, in vitro expansion of donor CD4(+)CD25(+) T cells, stimulated by recipient cells in the presence of high-dose interleukin-2, was required for successful regulation. In contrast, in the major histocompatibility complex-matched, minor histocompatibility antigen-disparate, CD8-mediated B10.BR-->CBA GVHD model, lethal disease could be completely prevented by a single infusion of freshly isolated donor CD4(+)CD25(+) cells administered as late as 10 days after HCT. Of importance, this late regulatory effect required only a 3:1 ratio of effector CD8:CD4(+)CD25(+) T cells, indicating a strong potential for the delayed infusion of CD4(+)CD25(+) cells to control GVHD across minor histocompatibility antigen barriers. Furthermore, this regulation did not interfere with complete and lasting donor engraftment of the hematopoietic compartment. Of most significance, the day 10 infusion of donor CD4(+)CD25(+) cells into CBA HCT recipients that had been challenged with the MMCBA6 myeloid leukemia cell line did not block an effective GVL response, despite reducing lethal GVHD. These results suggest that donor CD4(+)CD25(+) T cells infused soon after transplantation can ameliorate the development of GVHD without sacrificing a sufficient GVL effect.

Stem cell therapy in scleroderma

Scleroderma has a high mortality rate, especially in patients with early diffuse disease and poor prognostic features (such as high skin scores and internal organ involvement). In addition, there is no proven therapy for this disease. Finally, scleroderma has an autoimmune-related pathogenesis, particularly in early illness. In this setting, stem cell therapy is a reasonable potential choice. The rationale behind high-dose immunosuppressive therapy and stem cell transplantation in scleroderma, the regimens used, and the recent data from pilot studies are reviewed. The encouraging data, proper patient selection criteria, and appropriate therapy regimen make controlled studies appropriate, and such studies are currently under way in Europe and are soon to begin in the United States.

Evidence for a limited contribution of immune regulation to cardiac allograft acceptance

We have used donor-reactive DTH responses to study the immune regulation that is displayed by C57BL/6 mice after they accept DBA/2 cardiac or renal allografts. This regulation is expressed by splenocytes from the allograft acceptors, and involves their alloantigen-induced production of the anti-inflammatory cytokines transforming growth factor beta (TGFbeta) and/or interleukin-10 (IL-10) at DTH challenge sites, and presumably within accepted allografts. In cardiac allograft acceptors the production of these cytokines depends on a population of CD25(+) splenocytes. During these studies, we have encountered several situations in which allograft acceptance does not correlate with DTH-detectable immune regulation: (1) splenocytes from cardiac or kidney allograft acceptors lose TGFbeta-mediated inhibition of donor-reactive DTH responses by 150 days post-transplant, although they retain ongoing allograft function; (2) cardiac allograft acceptors rapidly reject donor-matched skin allografts, retain good cardiac allograft function, but lose DTH-detectable immune regulation; (3) Balb/c mice accept C57BL/6 cardiac allografts when treated with anti-CD40L mAb (MR1), but fail to express DTH-detectable immune regulation; and (4) infusion of C57BL/6 mice with peritoneal exudate cells (PEC) that were educated ex vivo to DBA/2 alloantigens in the presence of IL-10 and TGFbeta, causes them to exhibit DTH-detectable immune regulation mediated by both TGFbeta and IL-10, but they fail to accept DBA/2 cardiac allografts. These observations suggest that the process of allograft acceptance, as it is studied in murine transplant models, is metastable, and does not necessarily reflect the achievement of allograft tolerance. Further, the development of allograft tolerance probably requires more than regulatory T cells, representing a coordinated evolution of multiple immune processes over a prolonged period of time.

Delayed anti-kappa response in kappa-deficient mice after neonatal, oral immunization with kappa-containing IgG

Antibody responses to kappa (kappa)-light (L) chain are absent in normal (Ckappa+/+) animals because of tolerance due to the abundance of kappa-L chains expressed on more than 95% of all B cells and serum Ig.When heterozygous kappa-sufficient (Ckappa+/-) females are bred with homozygous kappa-deficient (Ckappa-/-) males, half of their offspring will become kappa-deficient but have received kappa-L chain containing maternal Ig, mainly IgG and IgA, through placental and intestinal transmission. The kappa-containing maternal Ig persists for more than 2 months in the circulation of the offspring. Starting from weeks 15 to 20 of age, a spontaneous antibody response towards the maternal kappa-L chains can be recorded. The time of onset, as well as the magnitude of the responses differ among individuals of the same litter. Invariably, once a response has been initiated, it transits into an IgG-type of response, which upon injection with kappa-containing protein shows the features of a secondary type of immune response.

Ovarian autoimmune disease and ovarian autoantibodies

Detection of specific autoantibodies remains the most practical clinical and research marker of autoimmune disease. The lack of consensus on ovary specific antibodies as a marker for ovarian autoimmunity has clinical and research consequences. The objective of this review is to summarize the evidence for ovarian autoimmunity and the detection of ovary specific autoantibodies in humans. Evidence favors the presence of an autoimmune disease of the ovary. Ovarian autoantibodies are associated primarily with premature ovarian failure (POF) and unexplained infertility. Variations in detection of ovarian autoantibodies are likely to be due to study design elements such as antibody test format, antigen preparation, and criteria for study and comparison groups. In addition, multiple targets appear to be involved in ovarian autoimmunity including ovarian cellular elements and oocyte related antigens. Many studies only assess one target antigen, leaving individuals with ovarian autoimmunity unidentified. The next most significant advance in characterizing ovarian autoimmunity will be definitive identification of the specific antigens and development of standardized tests based on use of specific antigens.

Induction of tolerance in autoimmune diseases by hematopoietic stem cell transplantation: getting closer to a cure?

Hematopoietic stem cells (HSCs) are the earliest cells of the immune system, giving rise to B and T lymphocytes, monocytes, tissue macrophages, and dendritic cells. In animal models, adoptive transfer of HSCs, depending on circumstances, may cause, prevent, or cure autoimmune diseases. Clinical trials have reported early remission of otherwise refractory autoimmune disorders after either autologous or allogeneic hematopoietic stem cell transplantation (HSCT). By percentage of transplantations performed, autoimmune diseases are the most rapidly expanding indication for stem cell transplantation. Although numerous editorials or commentaries have been previously published, no prior review has focused on the immunology of transplantation tolerance or development of phase 3 autoimmune HSCT trials. Results from current trials suggest that mobilization of HSCs, conditioning regimen, eligibility and exclusion criteria, toxicity, outcome, source of stem cells, and posttransplantation follow-up need to be disease specific. HSCT-induced remission of an autoimmune disease allows for a prospective analysis of events involved in immune tolerance not available in cross-sectional studies.