The suppression of delayed-type hypersensitivity by CD8+ regulatory T cells requires interferon-gamma

A Fresh Glimpse into Cartilage Immune Privilege

The increasing prevalence of degenerative cartilage disorders in young patients is a growing public concern worldwide. Cartilage's poor innate regenerative capacity has inspired the exploration and development of cartilage replacement treatments such as tissue-engineered cartilages and osteochondral implants as potential solutions to cartilage loss. The clinical application of tissue-engineered implants is hindered by the lack of long-term follow-up demonstrating efficacy, biocompatibility, and bio-integration. The historically reported immunological privilege of cartilage tissue was based on histomorphological observations pointing out the lack of vascularity and the presence of a tight extracellular matrix. However, clinical studies in humans and animals do not unequivocally support the immune-privilege theory. More in-depth studies on cartilage immunology are needed to make clinical advances such as tissue engineering more applicable. This review analyzes the literature that supports and opposes the concept that cartilage is an immune-privileged tissue and provides insight into mechanisms conferring various degrees of immune privilege to other, more in-depth studied tissues such as testis, eyes, brain, and cancer.

The Proinflammatory Cytokines IL-18, IL-21, and IFN-γ Differentially Regulate Liver Inflammation and Anti-Mitochondrial Antibody Level in a Murine Model of Primary Biliary Cholangitis

Primary biliary cholangitis (PBC) is a cholestatic liver disease primarily featured by autoimmune-mediated damage of intrahepatic small- and medium-sized bile ducts. Elevated serum proinflammatory cytokines, serum anti-mitochondrial antibodies (AMAs), liver inflammation, and fibrosis are also hallmarks of PBC disease. However, whether the elevated proinflammatory cytokines play a role in autoimmune cholangitis remains unknown. Herein, we utilized the p40-/-IL-2Rα-/- PBC mouse model to investigate the roles of proinflammatory cytokines IL-18, IL-21, and IFN-γ in the onset and progression of PBC. IL-18-/-, IFN-γ-/-, and IL-21-/- mice were crossed with p40-/-IL-2Ra+/- mice, respectively, to produce corresponding cytokine-deficient PBC models. Autoantibody level, liver inflammation, and bile duct injury were analyzed. We found that livers from p40-/-IL-2Rα-/- mice exhibit similar transcriptomic characters of PBC patients. In p40-/-IL-2Rα-/- mice, deletion of IL-18 has no remarkable effect on disease progression, while deletion of IL-21 indicates that it is necessary for AMA production but independent of liver inflammation and cholangitis. IFN-γ is responsible for both AMA production and liver inflammation in our model. Our results demonstrate that different proinflammatory cytokines can regulate different effector functions in PBC pathogenesis and need to be considered in PBC treatment.

Unleashing the immune response to NY-ESO-1 cancer testis antigen as a potential target for cancer immunotherapy

INTRODUCTION

Cancer Immunotherapy has recently emerged as a promising and effective modality to treat different malignancies. Antigenic profiling of cancer tissues and determination of any pre-existing immune responses to cancer antigens may help predict responses to immune intervention in cancer. NY-ESO-1, a cancer testis antigen is the most immunogenic antigen to date. The promise of NY-ESO-1 as a candidate for specific immune recognition of cancer comes from its restricted expression in normal adult tissue but frequent occurrence in multiple tumors including melanoma and carcinomas of lung, esophageal, liver, gastric, prostrate, ovarian, and bladder.

MAIN BODY

This review summarizes current knowledge of NY-ESO-1 as efficient biomarker and target of immunotherapy. It also addresses limitations and challenges preventing a robust immune response to NY-ESO-1 expressing cancers, and describes pre-clinical and clinical observations relevant to NY-ESO-1 immunity, holding potential therapeutic relevance for cancer treatment.

CONCLUSION

NY-ESO-1 induces strong immune responses in cancer patients but has limited objective clinical responses to NY-ESO-1 expressing tumors due to effect of competitive negative signaling from immune-checkpoints and immune-suppressive tumor microenvironment. We propose that combination therapy to increase the efficacy of NY-ESO-1 specific immunotherapeutic interventions should be explored to unleash the immune response against NY-ESO-1 expressing tumors.

Alloimmunity and Tolerance in Corneal Transplantation

Corneal transplantation is one of the most prevalent and successful forms of solid tissue transplantation. Despite favorable outcomes, immune-mediated graft rejection remains the major cause of corneal allograft failure. Although low-risk graft recipients with uninflamed graft beds enjoy a success rate ∼90%, the rejection rates in inflamed graft beds or high-risk recipients often exceed 50%, despite maximal immune suppression. In this review, we discuss the critical facets of corneal alloimmunity, including immune and angiogenic privilege, mechanisms of allosensitization, cellular and molecular mediators of graft rejection, and allotolerance induction.

Interferon-γ derived from cytotoxic lymphocytes directly enhances their motility and cytotoxicity

Interferon gamma (IFNγ) is a key moderator of cell-mediated immunity with diverse, mainly pro-inflammatory actions on immunocytes and target tissue. Recent studies have shown it may enhance anti-tumor and antiviral effects of CD8 T cells. Here we investigate the mechanisms by which IFNγ mediates CD8 T-cell cytotoxic function. We show that in vivo, antigen-specific CD8 T cells that produce INFγ are necessary to effect rejection of skin grafts expressing OVA as a transgene in keratinocytes. The ability of CD8 T cells to produce IFNγ enhanced their ability to migrate to the site of antigen-presenting skin cells. By in vivo imaging, we show that CTL motility, particularly speed, during graft rejection was enhanced by locally available IFNγ. We then used a reductionist two-cell model of CTL effectors and keratinocyte targets to investigate the effects of locally available (paracrine) and CTL-producing (autocrine) IFNγ on the motility behavior and killing ability of the CTL. Using live-cell imaging by prolonged time-lapse microscopy of primary effector CD8 T cells and antigen-expressing primary keratinocyte targets, we show that CD8 T-cell cytotoxic function and motility is enhanced by locally available IFNγ. Conversely, deprivation of either autocrine or paracrine IFNγ, or blockade of IFNγ signaling to CTL markedly reduced their cytotoxic function, their kinematics, and effector cell survival. We conclude that in vitro and in vivo, autocrine production of IFNγ by CTL enhances their motility and promotes killing of primary target keratinocytes. The absolute need for local IFNγ to enable cytotoxic CD8 T-cell function is of significance for immunotherapy for chronic viral infection and for cancer.

Advances on Non-CD4 + Foxp3+ T Regulatory Cells: CD8+, Type 1, and Double Negative T Regulatory Cells in Organ Transplantation

The overwhelming body of research on T regulatory cells (Treg) has focused on CD4 + CD25 + Foxp3+ T cells. However, recent years have witnessed a resurgence in interest in CD4 - CD8+, CD4 - CD8- (double negative [DN]), and CD4 + Foxp3- type 1 Treg (Tr1) Treg and their role in controlling autoimmune diseases and in promoting the survival of organ allografts and xenografts. CD8+ and DN Treg can arise spontaneously (natural Treg) or can be induced in situ. Both CD8+ and DN Treg have been shown to enhance the survival of organ allografts and xenografts. Additionally, both can suppress alloimmune responses by contact-dependent mechanisms by either inducing apoptosis or mediating direct cytolysis of effector T cells. CD8+, DN, and Tr1 Treg can also act in a contact-independent manner by elaborating soluble immunosuppressive factors, such as TGF-β and IL-10. Applying CD8+, DN, and Tr1 Treg for enhancing the survival of organ allografts and xenografts is still in its infancy but holds significant potential. Furthermore, there is a need for a more comprehensive understanding of how current immunosuppressive therapies applied to organ transplantations affect the wide array of Treg populations.

Corneal transplantation and immune privilege

Corneal transplants have been successfully performed in human subjects for over 100 years and enjoy an immune privilege that is unrivaled in the field of transplantation. Immune privilege is defined as the reduced incidence and tempo in the immune rejection of corneal allografts compared to other categories of organ allografts performed under the same conditions. Skin allografts transplanted across various MHC or minor histocompatibility barriers undergo rejection in approximately 100% of the hosts. By contrast, orthotopic corneal allografts experience long-term survival in 50% to >90% of the hosts, depending on the histocompatibility barriers that confront the host. The capacity of corneal allografts to evade immune rejection is attributable to multiple anatomical, physiological and immunoregulatory conditions that conspire to prevent the induction and expression of alloimmunity.

Low-level laser reduces the production of TNF-α, IFN-γ, and IL-10 induced by OVA

Delayed, or type IV, hypersensitivity reactions are a useful model to study the effects of new substances on the immune system. In this study, the experimental model of the delayed type hypersensitivity (DTH) reaction to ovalbumin (OVA) was used to evaluate the immunomodulating effects of low-level laser therapy (LLLT), which is used as an adjuvant therapy in medicine, dentistry, and physical therapy because of its potential anti-inflammatory and analgesic effects observed in several studies. The effects of LLLT (λ 780 nm, 0.06 W/cm(2) of radiation, and fluency of 3.8 J/cm(2)) in reaction to ovalbumin in Balb/C mice were examined after the induction phase of the hypersensitivity reaction. The animals treated with azathioprine (AZA), the animals that received a vehicle instead of ovalbumin, and those not immunized served as controls (n = 6 for each group). Footpad thickness measurements and hematoxylin-eosin histopathological exams were performed. Proliferation tests were also performed (spontaneous, in the presence of concanavalin A and ovalbumin) to determine the production in mononuclear cells cultures of tumor necrosis factor-alpha (TNF-α), INF-γ, and IL-10. In the group of animals irradiated with lasers and in the group treated with AZA, footpad thickness measurements were significantly reduced in comparison to the control group (p < 0.05). This reduction was accompanied by a very significant reduction in the density of the inflammatory infiltrate and by a significant reduction in the levels of TNF-α, INF-γ, and IL-10. LLLT radiation was shown to have an immunomodulating effect on DTH to OVA in Balb/C mice.

The in vitro-Induction of Type II Collagen-Specific Immune Tolerance in BALB/C Mice

Type II collagen (CII) protein is the main component of hyaline cartilage. The clinical importance of CII in arthritis, aging, and osteoarthritis is significant, but its ability to induce specific immune tolerance has not been extensively studied previously. We have recently proven that CII is capable of inducing Anterior Chamber Associated Immune Deviation (ACAID) when injected into the eye. Here, we hypothesized that ACAID-mediated tolerance could be induced in Balb/c mice that receive an intravenous administration of CII-induced in vitro-generated ocular-like antigen-presenting cells (APCs) or T regulatory cells (Tregs). Delayed hypersensitivity (DTH) assays were used to examine this hypothesis. In mice injected with CII-specific ACAID APCs, the specific regulatory activities resided in the spleen cells, splenic T cells, and ACAID CD8+ T cells, as proven by local adoptive transfer (LAT) assays. Conversely, there was a lack of regulatory activity in the CD4+ CD25+ T cell compartment of the recipient mice. Thus, ACAID CD8+ Tregs generated in vitro could be directly responsible for the expression of CII-driven ACAID-mediated tolerance and could be used as potential therapeutic tools in the treatment of CH-associated autoimmune diseases.

Influence of CD8+ T regulatory cells on intraocular tumor development

The interior of the eye, or uvea, is a site of immune privilege where certain immune responses are attenuated or completely excluded to protect non-regenerating tissues essential for vision. One consequence of this immunoregulation is compromised immune mediated elimination of intraocular tumors. For example, certain murine tumor cell lines which are rejected by host immune responses when transplanted in the skin grow progressively when placed in the anterior chamber (a.c.) of the eye. Progressive ocular tumor growth occurs despite induction of tumor-specific CD8+ T cell responses capable of eliminating a subsequent tumor challenge in the skin or opposite eye. Why these CD8+ T effectors fail to eliminate established ocular tumors is not known. It is well appreciated that growth of tumors in the a.c. induces the generation of immunosuppressive CD8+ T regulatory (Treg) cells. However, the contribution of CD8+ Treg in ocular tumor progression remains unclear. Several studies indicate that these CD8+ Treg target responding CD4+ T cells to inhibit their induction of macrophage-dependent delayed type hypersensitivity (DTH) responses to tumor antigens (Ags). However, induction of tumor-specific CD4+ T cell responses does not assure intraocular tumor elimination. This review is focused on how CD8+ Treg could influence the tumoricidal activity of ocular tumor-specific CD8+ T effector cells.

Role of IFN-γ in the establishment of anterior chamber-associated immune deviation (ACAID)-induced CD8+ T regulatory cells

Introduction of alloantigens into the AC induces a form of immune tolerance known as ACAID, which induces antigen-specific CD8+ Tregs, contributing to ocular immune privilege by down-regulating immune responses. Recent evidence suggests IFN-γ is needed for the suppressive function of CD8+ ACAID Tregs. This study tested the hypothesis that IFN-γ is needed for alloantigen-specific ACAID CD8+ Tregs to execute their suppressive function but is not required for the establishment of ACAID CD8+ Tregs. To address this hypothesis, ACAID was induced by injecting BALB/c spleen cells into the AC of WT C57BL/6 mice, IFN-γ(-/-) C57BL/6 mice, or anti-IFN-γ-treated WT C57BL/6 mice. LAT assays using C57BL/6 APCs as stimulators, CD4+ T cells from C57BL/6 mice previously immunized toward BALB/c alloantigens as effector cells, and IFN-γ-competent, IFN-γ(-/-), or IFN-γR(-/-) CD8+ Tregs were used to evaluate the suppressive function of CD8+ ACAID Tregs in response to IFN-γ. IFN-γ(-/-) mice or mice treated with anti-IFN-γ antibody prior to AC injection of alloantigen failed to develop ACAID. The suppressive function of IFN-γ(-/-) ACAID CD8+ Tregs was restored through the administration of exogenous IFN-γ. This suppressive responsiveness toward IFN-γ was CD8+ Treg-intrinsic, as CD8+ Tregs from IFN-γR(-/-) mice, which were primed in the AC with alloantigens, were not able to suppress alloantigen-specific DTH responses. These results indicate that IFN-γ is not needed for the induction of CD8+ ACAID Tregs but is required for ACAID Tregs to exert the suppression of allospecific DTH responses.

Immune amplification of murine CD8 suppressor T cells induced via an immune-privileged site: quantifying suppressor T cells functionally

Background

CD8⁺ suppressor T cells exert antigen-specific suppression of the expression of hypersensitivity by activated T cells. Therefore, CD8⁺ suppressor T cells serve a major regulatory role for the control of active immunity. Accordingly, the number and/or activity of CD8⁺ suppressor T cells should be influenced by an immune response to the antigen. To test this hypothesis we used an adoptive transfer assay that measures the suppression of the expression of delayed-type hypersensitivity (DTH) by CD8⁺ suppressor T cells to quantify the antigen-specific suppression of DTH by these suppressor T cells.

Methods

Suppressor T cells were induced in the spleens of mice by the injection of antigen into the anterior chamber of an eye. Following this injection, the mice were immunized by the same antigen injected into the anterior chamber. Spleen cells recovered from these mice (AC-SPL cells) were titrated in an adoptive transfer assay to determine the number of AC-SPL cells required to effect a 50% reduction of antigen-induced swelling (Sw50) in the footpad of immunized mice challenged by antigen.

Results

Suppression of the expression of DTH is proportional to the number of AC-SPL cells injected into the site challenged by antigen. The number of AC-SPL cells required for a 50% reduction in DTH-induced swelling is reduced by injecting a cell population enriched for CD8⁺ AC-SPL cells. Immunizing the mice receiving intracameral antigen to the same antigen decreases the RSw50 of AC-SPL cells required to inhibit the expression of DTH.

Conclusions

The results provide the first quantitative demonstration that the numbers of antigen-specific splenic CD8⁺ suppressor T cells are specifically amplified by antigen during an immune response.

Tumor-derived exosomes confer antigen-specific immunosuppression in a murine delayed-type hypersensitivity model

Exosomes are endosome-derived small membrane vesicles that are secreted by most cell types including tumor cells. Tumor-derived exosomes usually contain tumor antigens and have been used as a source of tumor antigens to stimulate anti-tumor immune responses. However, many reports also suggest that tumor-derived exosomes can facilitate tumor immune evasion through different mechanisms, most of which are antigen-independent. In the present study we used a mouse model of delayed-type hypersensitivity (DTH) and demonstrated that local administration of tumor-derived exosomes carrying the model antigen chicken ovalbumin (OVA) resulted in the suppression of DTH response in an antigen-specific manner. Analysis of exosome trafficking demonstrated that following local injection, tumor-derived exosomes were internalized by CD11c+ cells and transported to the draining LN. Exosome-mediated DTH suppression is associated with increased mRNA levels of TGF-β1 and IL-4 in the draining LN. The tumor-derived exosomes examined were also found to inhibit DC maturation. Taken together, our results suggest a role for tumor-derived exosomes in inducing tumor antigen-specific immunosuppression, possibly by modulating the function of APCs.

IL-17A-dependent CD4+CD25+ regulatory T cells promote immune privilege of corneal allografts

IL-17A is a proinflammatory cytokine that has received attention for its role in the pathogenesis of several autoimmune diseases. IL-17A has also been implicated in cardiac and renal allograft rejection. Accordingly, we hypothesized that depletion of IL-17A would enhance corneal allograft survival. Instead, our results demonstrate that blocking IL-17A in a mouse model of keratoplasty accelerated the tempo and increased the incidence of allograft rejection from 50 to 90%. We describe a novel mechanism by which CD4(+)CD25(+) regulatory T cells (Tregs) respond to IL-17A and enhance corneal allograft survival. Our findings suggest the following: 1) IL-17A is necessary for ocular immune privilege; 2) IL-17A is not required for the induction of anterior chamber-associated immune deviation; 3) Tregs require IL-17A to mediate a contact-dependent suppression; 4) corneal allograft Tregs suppress the efferent arm of the immune response and are Ag specific; 5) Tregs are not required for corneal allograft survival beyond day 30; and 6) corneal allograft-induced Treg-mediated suppression is transient. Our findings identify IL-17A as a cytokine essential for the maintenance of corneal immune privilege and establish a new paradigm whereby interplay between IL-17A and CD4(+)CD25(+) Tregs is necessary for survival of corneal allografts.

α-Galactosylceramide ameliorates autoimmune diabetes in non-obese diabetic mice through a suppressive effect mediated by CD8+ T cells

Type 1 diabetes is an autoimmune disorder resulting from lymphocyte-mediated destruction of insulin-producing β cells in pancreas. Natural killer T cells are regulatory immune components controlling autoreactivity and immune homeostasis. Although early studies supported that amelioration of autoimmune diabetes by natural killer T cells was associated with Th1/2 shift, other Th2-independent regulatory mechanisms were also suggested. Since natural killer T cells are critical for the generation of CD8(+) regulatory T cells controlling anterior chamber-associated immune deviation and CD8(+) regulatory T cells also participate in suppression of immune responses like experimental autoimmune encephalomyelitis, we investigate whether the similar suppressive effects are involved in α-galactosylceramide-induced immune tolerance in non-obese diabetic mice. We demonstrate that repeated exposure of α-galactosylceramide reveals a hyporesponsiveness of total or antigen-presenting cells-depleted splenocytes upon anti-CD3/28 antibodies stimulation. The dispensability of dendritic cells in the hyporesponsiveness is consistent with the comparable expression of costimulatory molecules on CD11c(+) subsets between α-galactosylceramide- and vehicle-treated mice. α-Galactosylceramide treatment not only affects the effector T cell subsets and their cytokine production but also increases the secretion of transforming growth factor-β by splenocytes, implying the suppressive regulation. The adoptive transfer experiments demonstrate the suppressive effect of T cells from α-galactosylceramide-treated non-obese diabetic mice when co-transferred with vehicle-treated littermates. Finally, it reveals that CD8(+) subset among antigen-presenting cells-depleted splenocytes tends to confer the suppression since the protective ability vanishes upon withdrawal of CD8(+) subset. These results suggest that repeated exposure of α-galactosylceramide ameliorates autoimmune diabetes in non-obese diabetic mice mediated by CD8(+) T cell-associated suppression.

Antigen-specific splenic CD4+ and CD8+ regulatory T cells generated via the eye, suppress experimental autoimmune encephalomyelitis either at the priming or at the effector phase

The injection of antigen into the ocular anterior chamber (AC) induces the generation of splenic CD4(+) and CD8(+) regulatory T (Treg) cells, specific for the antigen injected into the AC. These Treg cells inhibit the induction (CD4(+)) and also the expression (CD8(+)) of a delayed-type hypersensitivity response. The ability of AC-induced self-antigen-specific Treg cells in modulating autoimmunity is not well defined. Here we show that an injection of encephalitogenic myelin oligodendrocyte glycoprotein (MOG(35-55)) peptide into the anterior chamber of the eye (AC-MOG), before the induction of or during established experimental autoimmune encephalomyelitis (EAE) induced by MOG(35-55), suppresses the induction or progression of EAE, respectively. CD4(+) or CD8(+) splenic Treg cells induced by an injection of AC-MOG prevent EAE either at the inductive (priming) or at the progressive (effector) phase, respectively. This suppression of EAE by an AC-MOG injection or by intravenous transfer of splenic regulatory cells induced by an AC-MOG injection is specific for the antigen injected into the AC. Additionally, our data suggest that splenic CD8(+) Treg cells that suppress active EAE may use a transforming growth factor (TGF)-β-dependent suppression mechanism while the suppression of the induction of EAE by the AC-induced CD4(+) Treg cells is independent of TGF-β. Thus, we show for the first time that regulation of EAE at the priming or the chronic phase requires different phenotypes of Treg cells. Hence, it is important to consider the phenotype of Treg cells while designing effective cell-based therapies against autoimmune disorders.

Two different regulatory T cell populations that promote corneal allograft survival

PURPOSE

To compare and contrast the T regulatory cells (Tregs) induced by anterior chamber (AC) injection of antigen with those induced by orthotopic corneal allografts.

METHODS

Anterior chamber-associated immune deviation (ACAID) Tregs were induced by injecting C57BL/6 spleen cells into the AC of BALB/c mice. Delayed-type hypersensitivity responses to C57BL/6 alloantigens were evaluated by a conventional ear swelling assay. Corneal allograft Tregs were induced by applying orthotopic C57BL/6 corneal allografts onto BALB/c hosts. The effects of anti-CD25, anti-CD8, anti-interferon-γ (IFN-γ), anti-IL-17A, or cyclophosphamide treatments on corneal allograft survival and ACAID were evaluated.

RESULTS

Administration of either anti-CD25 or anti-IFN-γ antibodies prevented the expression of ACAID and abolished the immune privilege of corneal allografts. By contrast, in vivo treatment with anti-CD8 antibody abrogated ACAID but had no effect on corneal allograft survival. Further discordance between ACAID and corneal allograft survival emerged in experiments in which the induction of allergic conjunctivitis or the administration of anti-IL-17A abolished the immune privilege of corneal allografts but had no effect on the induction or expression of ACAID.

CONCLUSIONS

Although orthotopic corneal allografts are strategically located for the induction of ACAID by the sloughing of corneal cells into the AC, the results reported here indicate that the Tregs induced by orthotopic corneal allografts are remarkably different from the Tregs that are induced by AC injection of alloantigen. Although both of these Treg populations promote corneal allograft survival, they display distinctly different phenotypes.

Mechanism and localization of CD8 regulatory T cells in a heart transplant model of tolerance

Despite accumulating evidence for the importance of allospecific CD8(+) regulatory T cells (Tregs) in tolerant rodents and free immunosuppression transplant recipients, mechanisms underlying CD8(+) Treg-mediated tolerance remain unclear. By using a model of transplantation tolerance mediated by CD8(+) Tregs following CD40Ig treatment in rats, in this study, we show that the accumulation of tolerogenic CD8(+) Tregs and plasmacytoid dendritic cells (pDCs) in allograft and spleen but not lymph nodes was associated with tolerance induction in vascularized allograft recipients. pDCs preferentially induced tolerogenic CD8(+) Tregs to suppress CD4(+) effector cells responses to first-donor Ags in vitro. When tolerogenic CD8(+) Tregs were not in contact with CD4(+) effector cells, suppression was mediated by IDO. Contact with CD4(+) effector cells resulted in alternative suppressive mechanisms implicating IFN-gamma and fibroleukin-2. In vivo, both IDO and IFN-gamma were involved in tolerance induction, suggesting that contact with CD4(+) effector cells is crucial to modulate CD8(+) Tregs function in vivo. In conclusion, CD8(+) Tregs and pDCs interactions were necessary for suppression of CD4(+) T cells and involved different mechanisms modulated by the presence of cell contact between CD8(+) Tregs, pDCs, and CD4(+) effector cells.

Gender specificity of altered human immune cytokine profiles in aging

Cytokine generation by T cells and monocytes was determined for 50 subjects aged 65 yr or older and concurrently studied young subjects individually matched to each old subject for sex, race, and national origin. Highly significant differences between cytokine levels of old and young subjects all were gender specific. For T cells stimulated with anti-CD3 plus anti-CD28 antibodies, mean ratios of IFN-gamma generation for healthy old to young subjects were 0.22 for men (P<0.001; n=15) and 3.35 for women (P<0.001; n=13), and those of IL-17 were 0.30 for men (P<0.001) and no difference for women. CD8 T cells were the source of high IFN-gamma in healthy old women. For old men with an inflammatory or immune disease (n=10), mean old to young ratios of T-cell-generated IFN-gamma and IL-17 increased with disease severity up to 5.78 and 2.97 (both P<0.01), respectively, without changes for old women with similar diseases (n=12). For differentiated LPS-stimulated monocytes, old to young ratios of TNF-alpha and IL-6 generation were high only in women with immune or inflammatory disease (2.38, P<0.05 and 1.62, P<0.01, respectively), whereas ratios of IFN-gamma-evoked IP-10 chemokine were low in all groups. Alterations in immune cytokine profiles with aging show significant gender specificity.

T cell sensitivity to TGF-beta is required for the effector function but not the generation of splenic CD8+ regulatory T cells induced via the injection of antigen into the anterior chamber

The introduction of antigen into the anterior chamber (AC) of the eye induces the production of antigen-specific splenic CD8⁺ regulatory T cells (AC-SPL cells) that suppress a delayed-type hypersensitivity (DTH) reaction in immunized mice. Because the generation of these regulatory T cells is also induced by exposure to transforming growth factor (TGF)-β and antigen or F4/80⁺ cells exposed to TGF-β and antigen in vitro, we investigated (i) whether these cells are produced in dominant negative receptor for transforming growth factor β receptor type II (dnTGFβRII) or Cbl-b^−/− mice whose T cells are resistant to TGF-β, (ii) whether DTH is suppressed by wild type (WT) CD8⁺ AC-SPL cells in Cbl-b^−/− and dnTGFβRII mice and (iii) the effect of antibodies to TGF-β on the suppression of DTH by CD8⁺ AC-SPL cells. DnTGFβRII immunized and Cbl-b^−/− mice produced splenic CD8⁺ regulatory cells after the intracameral injection of antigen and immunization. The suppression of a DTH reaction by CD8⁺ AC-SPL cells in WT mice was blocked by the local inclusion of antibodies to TGF-β when WT splenic CD8⁺ AC-SPL cells were injected into the DTH reaction site. Moreover, the DTH reaction in immunized dnTGFβRII and Cbl-b^−/− mice was not suppressed by the transfer of WT CD8⁺ AC-SPL cells to the site challenged with antigen. In aggregate, these observations suggest that T cell sensitivity to TGF-β is not an obligate requirement for the in vivo induction of CD8⁺ AC-SPL T cells but the suppression of an in vivo DTH reaction by CD8⁺ AC-SPL cells is dependent on TGF-β.

The suppression of hypersensitivity by ocular-induced CD8(+) T cells requires compatibility in the Qa-1 haplotype

The injection of antigen into the anterior chamber (AC, intracameral injection)2 of a murine eye induces the generation of splenic CD8⁺ regulatory T cells (AC-SPL cells) that effect the antigen-specific suppression of a Delayed-Type Hypersensitivity (DTH) reaction. Here we show (i) for the first time that the local antigen-specific suppression of DTH-induced swelling in immunized mice by either an intracameral injection of antigen or by the direct injection of CD8⁺ AC-SPL cells into an antigen-challenged site is associated with an absence of infiltrated mononuclear cells, (ii) the local antigen-specific suppression of the DTH reaction by CD8⁺ AC-SPL cells requires compatibility between the Qa-1 but not H2 antigen haplotype of the immunized recipient and the injected AC-SPL regulatory T cells, (iii) The suppression of the DTH reaction by CD8⁺ AC-SPL cells requires the expression of Qa-1 but not H2 antigens and is not due to bystander suppression.

Cytokines, chemokine receptors, CD4+CD25HIGH+ T-cells and clinical forms of human schistosomiasis

Previous studies have demonstrated that distinct immune response profiles can be correlated with the development/maintenance of different clinical forms of human schistosomiasis. We have previously shown that individuals with the more severe clinical forms of the disease such as those presenting different levels of fibrosis or with the hepatosplenic (HS) clinical form of the disease show significantly different immune response when compared with those with the intestinal clinical form (INT). To better understand the immune mechanisms associated with the clinical form of the schistosomiasis, in this study, we present the results of the evaluation, at a single cell level, of the cytokine patterns as well as the chemokine receptors expression by T-cell subsets after in vitro short-term stimulation with soluble egg antigens as well as the ex vivo frequency analysis of putative regulatory CD4+CD25HIGH+ T-cell subset in the peripheral blood mononuclear cells. We observed an increase on IL-4+, IL-5+ and IL-10+ cells both in the CD4+ and CD8+ lymphocytes in INT and a significant decrease on the number of IL-4+, IL-5+ and IL-10+ T-lymphocytes for HS. However, patients with detectable fibrosis presented decrease on IL-10+ (both CD4+ and CD8+ lymphocytes) and basal levels of IL-4 and IL-5. These data suggested that although INT group is under the influence of an effective immunoregulated immune response, mainly due to the high percentage of IL-10+ cells, it presents a mixed type (Type1/Type-2) immune profile. Moreover, the chemokine receptors expression demonstrated that CXCR3 and CXCR4 by CD4+ T-cells in INT may dictate the selective profile of IL-10 associated with the immunomodulatory events in human schistosomiasis. Additionally, the ex vivo analysis also suggests that higher levels of CD4+CD25HIGH+ T-cells may play a role in controlling morbidity in chronic human schistosomiasis. Taken together, these data suggest a major role of IL-10-producing CXCR4+ CD4+ T-cell subset for the asymptomatic outcome of the disease.

Upregulation of CD94 on CD8+T cells in anterior chamber-associated immune deviation

BACKGROUND

CD8+ regulatory T cells (Treg) have been considered to be involved in a model of ocular-induced tolerance, known as anterior chamber-associated immune deviation (ACAID). The phenotype and characteristics of CD8+Treg in ACAID remain only poorly understood. Recent studies have reported that the CD94-Qa-1 system is implicated in the induction of ACAID CD8+Treg, but the functions and characteristics of CD8+CD94+T cells remain unclear.

RESULTS

Both mRNA and protein of CD94 and NKG2A were markedly up-regulated on splenic CD8+T cells of ACAID mice compared with controls. Flow cytometric analysis showed that very few CD8+CD94+T cells express granzyme B, perforin and Foxp3. CD8+CD94+T cells, but not CD8+CD94-T cells, magnetically isolated from the spleens of ACAID mice, produced large amounts of TGF-beta1 and exhibited suppressive activity in vitro. Neutralization of TGF-beta1 caused reversal of suppression mediated by CD8+CD94+T cells.

CONCLUSION

CD8+CD94+T cells from ACAID mice exhibited suppressive activity in association with enhanced expression of TGF-beta1, suggesting that CD8+Treg are mainly distributed in CD94+T cell subpopulations.

Murine CD8+ regulatory T lymphocytes: the new era

Regulatory T lymphocytes unequivocally play a major role in the maintenance of immunologic homeostasis. The first descriptions of regulatory T lymphocytes concerned CD8(+) cells, but this field was brought into discredit when some of its central tenets turned out to be erroneous. CD4(+) regulatory T cells took over and, with the help of newly developed molecular tools, rapidly were phenotypically and functionally characterized. We now know that these cells control a large variety of immune responses. However some observations of in vitro or in vivo immune regulation could not be explained with CD4(+) regulatory T cell activity and depended on the action of a variety of CD8(+) T cell populations. In recent years, substantial progress has been made in the phenotypic and functional characterization of CD8(+) regulatory T cells. These cells play a role in the control of intestinal immunity, immunopathology, and autoimmunity, as well as in immune privilege of the eye, in oral tolerance, and in prevention of graft-versus-host disease and graft-rejection. The suppressor effector mechanisms used by these cells are in part shared with CD4(+) regulatory T cells and in part unique to this population. We here review the current literature on naturally occurring and experimentally induced murine CD8(+) regulatory T-cell populations.

Splenic CD8+ T cells secrete TGF-beta1 to exert suppression in mice with anterior chamber-associated immune deviation

Background CD8+ regulatory T cells (Treg) have been considered to be involved in a model of ocular-induced tolerance, known as anterior chamber-associated immune deviation (ACAID). The mechanisms of suppression by CD8+ T cells in ACAID remain only poorly understood. TGF-beta1 is considered as an inhibitory cytokine for immunosuppression in some models. The production of TGF-beta1 by CD8+ T cells in ACAID, and whether CD8+ T cells exert suppression through TGF-beta1, is unknown. Methods The suppressive effect of CD8+ T cells in ACAID mice was determined by a local adoptive transfer (LAT) assay. The production of TGF-beta1 by CD8+ T cells was measured by enzyme-linked immunosorbent assay (ELISA). Anti-TGF-beta1 antibodies were used in the LAT assay to test if they could block the inhibitory effect of CD8+ T cells. Results CD8+ T cells from ACAID mice were shown to block the delayed-type hypersensitivity (DTH) response in an antigen-specific manner in a LAT assay. These CD8+ T cells secreted TGF-beta1, and their suppression could partially be blocked by anti-TGF-beta1 antibodies. Conclusions Our study confirms that CD8+ T cells from ACAID mice possess inhibitory properties. This population exerts part of its suppressive function via the production of TGF-beta1.

Emerging concepts in CD8(+) T regulatory cells

CD8(+) T regulatory cells (T regs) are elicited by unique antigen presenting cells during viral infections, by manipulation of co-stimulatory molecules, or in the development of tumors. CD8(+) T regs display antigen-specificity, which is most exquisitely manifested by the HLA-E-restricted cytolytic CD8(+) T regs in MS. There is evidence that some CD8(+) T regs also express organ specificity. In many cases, IFN-gamma is required for either the induction or expression of CD8(+) T regs. CD8(+) T regs can produce suppression directly by killing immune cells or indirectly by co-opting other cells to elaborate end-stage suppressive molecules such as TGF-beta, IL-10, and indoleamine dioxygenase (IDO).

Endogenous cytotoxic T-cell response contributes to the long-term antiretroviral protection induced by a short period of antibody-based immunotherapy of neonatally infected mice

Neutralizing monoclonal antibodies (MAbs) are increasingly being considered for blunting human viral infections. However, whether they can also exert indirect effects on endogenous antiviral immune responses has been essentially overlooked. We have recently shown that a short (several-day) period of immunotherapy with the neutralizing 667 MAb of mouse neonates shortly after infection with the lethal FrCas(E) retrovirus not only has an immediate effect on the viral load but also permits an endogenous antiviral immunity to emerge. Even though passive immunotherapy was administered during the particular period of immunocompetence acquisition, the endogenous response eventually arising was protective and persisted long (>1 year) after the MAb has disappeared. As very high levels of anti-FrCas(E) antibodies, predominantly of the immunoglobulin G2a (IgG2a) isotype and showing strong neutralization activity, were found in the sera of MAb-treated mice, it was necessary to address whether this humoral immunity was sufficient on its own to confer full protection against FrCas(E) or whether a cytotoxic T-lymphocyte (CTL) response was also necessary. Using a variety of in vivo assays in young and adult animals previously infected by FrCas(E) and treated by 667, we show here that transient 667 immunotherapy is associated with the emergence of a CTL response against virus-infected cells. This cytotoxic activity is indispensable for long-term antiviral protective immunity, as high neutralizing antibody titers, even enhanced in in vivo CD8(+) cell depletion experiments, cannot prevent the FrCas(E)-induced death of infected/treated mice. Our work may have important therapeutic consequences, as it indicates that a short period of MAb-based immunotherapy conducted at a stage where the immune system is still developing can be associated with the mounting of a functional Th1-type immune response characterized by both CTL and IgG2a-type humoral contributions, the cooperation of which is known to be essential for the containment of chronic infections by a variety of viruses.