Showing papers on "Immune tolerance published in 1999"

Mature T lymphocyte apoptosis--immune regulation in a dynamic and unpredictable antigenic environment.

Abstract: Apoptosis of mature T lymphocytes preserves peripheral homeostasis and tolerance by countering the profound changes in the number and types of T cells stimulated by diverse antigens. T cell apoptosis occurs in at least two major forms: antigen-driven and lymphokine withdrawal. These forms of death are controlled in response to local levels of IL-2 and antigen in a feedback mechanism termed propriocidal regulation. Active antigen-driven death is mediated by the expression of death cytokines such as FasL and TNF. These death cytokines engage specific receptors that assemble caspase-activating protein complexes. These signaling complexes tightly regulate cell death but are vulnerable to inherited defects. Passive lymphokine withdrawal death may result from the cytoplasmic activation of caspases that is regulated by mitochondria and the Bcl-2 protein. The human disease, Autoimmune Lymphoproliferative Syndrome (ALPS) is due to dominant-interfering mutations in the Fas/APO-1/CD95 receptor and other components of the death pathway. The study of ALPS patients reveals the necessity of apoptosis for preventing autoimmunity and allows the genetic investigation of apoptosis in humans. Immunological, cellular, and molecular evidence indicates that throughout the life of a T cell, apoptosis may be evoked in excessive, harmful, or useless clonotypes to preserve a healthy and balanced immune system.

CD8alpha+ and CD8alpha- subclasses of dendritic cells direct the development of distinct T helper cells in vivo.

Abstract: Cells of the dendritic family display some unique properties that confer to them the capacity to sensitize naive T cells in vitro and in vivo. In the mouse, two subclasses of dendritic cells (DCs) have been described that differ by their CD8α expression and their localization in lymphoid organs. The physiologic function of both cell populations remains obscure. Studies conducted in vitro have suggested that CD8α+ DCs could play a role in the regulation of immune responses, whereas conventional CD8α− DCs would be more stimulatory. We report here that both subclasses of DCs efficiently prime antigen-specific T cells in vivo, and direct the development of distinct T helper (Th) populations. Antigen-pulsed CD8α+ and CD8α− DCs are separated after overnight culture in recombinant granulocyte/macrophage colony-stimulating factor and injected into the footpads of syngeneic mice. Administration of CD8α− DCs induces a Th2-type response, whereas injection of CD8α+ DCs leads to Th1 differentiation. We further show that interleukin 12 plays a critical role in Th1 development by CD8α+ DCs. These findings suggest that the nature of the DC that presents the antigen to naive T cells may dictate the class selection of the adaptative immune response.

Mobilizing Dendritic Cells for Tolerance, Priming, and Chronic Inflammation

Abstract: M igration of Dendritic Cells from Blood to Tissues. A fundamental aspect of dendritic cell (DC) function is their capacity to migrate. It allows them to exert a continuous surveillance for incoming antigens in almost all body tissues and a prompt report to T cells in secondary lymphoid organs.

Conversion of tumor-specific CD4+ T-cell tolerance to T-cell priming through in vivo ligation of CD40.

Abstract: Tumor antigen-specific T-cell tolerance limits the efficacy of therapeutic cancer vaccines. Antigen-presenting cells mediate the induction of T-cell tolerance to self-antigens. We therefore assessed the fate of tumor-specific CD4+ T cells in tumor-bearing recipients after in vivo activation of antigen-presenting cells with antibodies against CD40. Such treatment not only preserved the responsiveness of this population, but resulted in their endogenous activation. Established tumors regressed in vaccinated mice treated with antibody against CD40 at a time when no response was achieved with vaccination alone. These results indicate that modulation of antigen-presenting cells may be a useful strategy for enhancing responsiveness to immunization.

Generation of immunity to the HER-2/neu oncogenic protein in patients with breast and ovarian cancer using a peptide-based vaccine.

Abstract: HER-2/neu is a "self" tumor antigen that is overexpressed in 15-30% of human adenocarcinomas. Vaccine strategies directed against HER-2/neu and other self tumor antigens require development of methods to overcome immune tolerance to self-proteins. In rats, rat neu peptide vaccines have been shown to be an effective way of circumventing tolerance to rat neu protein and generating rat neu-specific immunity. The present report validates that a similar peptide-based vaccine formulation is effective for inducing T-cell immunity to HER-2/neu protein in humans with breast and ovarian cancer. The vaccine formulation included groups of peptides derived from the HER-2/neu extracellular domain (ECD) or intracellular domain (ICD) mixed with granulocyte macrophage colony stimulating factor as an adjuvant. These peptides were 15-18 amino acids in length and designed to elicit a CD4 T helper-specific immune response. Patients underwent intradermal immunization once a month for a total of two to six immunizations. To date, all of the patients immunized with HER-2/neu peptides developed HER-2/neu peptide-specific T-cell responses. The majority of patients (six of eight) also developed HER-2/neu protein-specific responses. Responses to HER-2/neu protein occurred with epitope spreading. Immune T cells elicited by vaccination were shown to migrate outside the peripheral circulation by virtue of generating delayed type hypersensitivity responses distant from the vaccine site, which indicated the potential ability to traffic to the site of tumor. The use of peptide-based vaccines may be a simple, yet effective, vaccine strategy for immunizing humans to oncogenic self-proteins.

Cd1-Reactive Natural Killer T Cells Are Required for Development of Systemic Tolerance through an Immune-Privileged Site

Abstract: Systemic tolerance can be elicited by introducing antigen into an immune-privileged site, such as the eye, or directly into the blood. Both routes of immunization result in a selective deficiency of systemic delayed type hypersensitivity. Although the experimental animal model of anterior chamber–associated immune deviation (ACAID) occurs in most mouse strains, ACAID cannot be induced in several mutant mouse strains that are coincidentally deficient in natural killer T (NKT) cells. Therefore, this model for immune-privileged site–mediated tolerance provided us with an excellent format for studying the role of NKT cells in the development of tolerance. The following data show that CD1-reactive NKT cells are required for the development of systemic tolerance induced via the eye as follows: (a) CD1 knockout mice were unable to develop ACAID unless they were reconstituted with NKT cells together with CD1+ antigen-presenting cells; (b) specific antibody depletion of NKT cells in vivo abrogated the development of ACAID; and (c) anti-CD1 monoclonal antibody treatment of wild-type mice prevented ACAID development. Significantly, CD1-reactive NKT cells were not required for intravenously induced systemic tolerance, thereby establishing that different mechanisms mediate development of tolerance to antigens inoculated by these routes. A critical role for NKT cells in the development of systemic tolerance associated with an immune-privileged site suggests a mechanism involving NKT cells in self-tolerance and their defects in autoimmunity.

A two-step, two-signal model for the primary activation of precursor helper T cells

Abstract: I present here a new model for the primary activation of precursor helper T cells. Observations demonstrate that the immune system learns not to respond to extrathymic, organ-specific self-antigens because of their early appearance in development. The immune system thus discriminates between peripheral self-antigens and foreign antigens and, when mature, usually makes an immune response against only the latter. Contemporary models for the activation and inactivation of T helper (Th) function do not account for such discrimination. The model proposed here is consistent with contemporary findings and incorporates a mechanism of peripheral self–nonself discrimination.

HLA-G-mediated inhibition of antigen-specific cytotoxic T lymphocytes.

Abstract: In the present study, we demonstrate that the non-classical MHC class I molecule HLA-G impairs specific cytolytic T cell functions in addition to its well-established inhibition of NK lysis. The antigen-specific cytotoxic T lymphocyte (CTL) response analyzed was mediated by CD8(+) T cells specific for the influenza virus matrix epitope, M58-66, presented by HLA-A2. The transfection of HLA-G1 cDNA in target cells carrying the M58-66 epitope reduced their lysis by these virus-specific CTL. This HLA-G-mediated inhibition of antigen-specific CTL lysis was (i) peptide dose dependent, (ii) reversed by blocking HLA-G with a specific mAb and (iii) still observed despite the blockade of HLA-E/CD94/NKG2A interaction. By inhibiting both CTL and NK functions, HLA-G appears to have an extensive role in immune tolerance.

Tumor-induced immune dysfunction.

Abstract: Immune system-based approaches for the treatment of malignant disease over the past decades have often focused on cytolytic effector cells such as cytotoxic T lymphocytes (CTL), and natural killer (NK) cells. It has also been demonstrated that tumor-bearing mice can be cured using a wide variety of approaches, some of which involve cytokine-mediated enhancement of CTL and NK cell activity. However, the apparent success in mice stands in contrast to the current situation in the clinic, wherein only a minority of patients have thus far benefited from CTL- or NK cell-based antitumor approaches. The underlying causes of tumor-associated immune suppression of CTL and NK cell activity are discussed, and features of interest shared with HIV infection, leprosy, and rheumatoid arthritis are also be mentioned. Remarkable and very recent observations have shed more light upon the causes of dysfunctional alterations in CTL and NK cells often associated with these diseases, that in turn have suggested new immunotherapeutic approaches for cancer and infectious disease.

Transforming growth factor-β in breast milk: A potential regulator of atopic disease at an early age

Abstract: Background: According to data from animal and in vitro studies, transforming growth factor-β (TGF-β) has a crucial effect on 2 essential parts of the mucosal immune system: IgA production and oral tolerance induction. Objective: We sought to ascertain whether TGF-β in breast milk is associated with specific IgA production and atopic disease in human subjects. Methods: Forty-seven infants with several atopic family members were followed during their first year of life. The concentrations of TGF-β1 and TGF-β2 in maternal colostrum, mature milk, and the infants' sera were determined. The enzyme-linked immunospot assay was used to assess the infants' specific IgA production in response to β-lactoglobulin, casein, gliadin, and ovalbumin. Results: At 12 months, atopic dermatitis was confirmed in 29 of 47 infants; in 11, atopic disease had begun during exclusive breast-feeding (preweaning onset), whereas in 18 the disease manifested itself after weaning (postweaning onset). The concentrations of both TGF-β1 and TGF-β2 were higher in maternal colostrum, but not in mature milk and infants' serum, in infants with postweaning-onset atopic disease compared with those with preweaning-onset disease ( P = .0008 and P = .015, respectively). The concentration of TGF-β2 was, and that of TGF-β1 tended to be, higher in the colostrum of mothers whose infants had specific IgA-secreting cells at 3 months in response to at least one of the dietary antigens tested compared with those who did not have such cells ( P = .048 and P = .076, respectively). Conclusion: TGF-β in colostrum may prevent the development of atopic disease during exclusive breast-feeding and promote specific IgA production in human subjects. (J Allergy Clin Immunol 1999;1251-7.)

Mucosal immunity and tolerance: relevance to vaccine development

Abstract: The mucosal immune system of mammals consists of an integrated network of lymphoid cells which work in concert with innate host factors to promote host defense. Major mucosal effector immune mechanisms include secretory antibodies, largely of immunoglobulin A (IgA) isotype, cytotoxic T cells, as well as cytokines, chemokines and their receptors. Immunologic unresponsiveness (tolerance) is a key feature of the mucosal immune system, and deliberate vaccination or natural immunization by a mucosal route can effectively induce immune suppression. The diverse compartments located in the aerodigestive and genitourinary tracts and exocrine glands communicate via preferential homing of lymphocytes and antigen-presenting cells. Mucosal administration of antigens may result in the concomitant expression of secretory immunoglobulin A (S-IgA) antibody responses in various mucosal tissues and secretions, and under certain conditions, in the suppression of immune responses. Thus, developing formulations based on efficient delivery of selected antigens/tolerogens, cytokines and adjuvants may impact on the design of future vaccines and of specific immunotherapeutic approaches against diseases associated with untoward immune responses, such as autoimmune disorders, allergic reactions, and tissue-damaging inflammatory reactions triggered by persistent microorganisms.

Induction of Glutamic Acid Decarboxylase 65-Specific Th2 Cells and Suppression of Autoimmune Diabetes at Late Stages of Disease Is Epitope Dependent

Abstract: Peptide-based immunotherapy is one strategy by which to selectively suppress the T cell-mediated destruction of β cells and treat insulin-dependent diabetes mellitus (IDDM). Here, we investigated whether a panel of T cell epitopes derived from the β cell autoantigen glutamic acid decarboxylase 65 (GAD65) differ in their capacity to induce Th2 cell function in nonobese diabetic (NOD) mice and in turn prevent overt IDDM at different preclinical stages of disease development. The panel consists of GAD65-specific peptides spanning aa 217–236 (p217), 247–265 (p247), 290–309 (p290), and 524–543 (p524). Our studies revealed that all of the peptides effectively prevented insulitis and diabetes when administered to NOD mice before the onset of insulitis. In contrast, only a mixture of p217 and p290 prevented progression of insulitis and overt IDDM in NOD mice exhibiting extensive β cell autoimmunity. Immunization with the GAD65-specific peptides did not block IDDM development in NOD mice deficient in IL-4 expression. These findings demonstrate that GAD65-specific peptide immunotherapy effectively suppresses progression to overt IDDM, requires the production of IL-4, and is dependent on the epitope targeted and the extent of preexisting β cell autoimmunity in the recipient.

Impaired Immune Responses and B-Cell Proliferation in Mice Lacking the Id3 Gene

Abstract: B-lymphocyte activation and proliferation induced by the B-cell receptor (BCR) signals are important steps in the initiation of humoral immune responses. How the BCR signals are translated by nuclear transcription factors into cell cycle progression is poorly understood. Id3 is an immediate-early gene responding to growth and mitogenic signals in many cell types including B cells. The primary function of the Id3 protein has been defined as that of inhibitor of basic-helix-loop-helix (bHLH) transcription factors. The interaction between Id3 and bHLH proteins, many of which are essential for cellular differentiation, has been proposed as a key regulatory event leading to cellular proliferation instead of differentiation. To further investigate the role of Id3 in tissue and embryo development and the mechanism of Id3-mediated growth regulation, we generated and analyzed Id3-deficient mice. While these mice display no overt abnormality in tissue and embryo development, their humoral immunity is compromised. The amounts of immunoglobulins produced in Id3-deficient mice immunized with a T-cell-dependent antigen and a type 2 T-cell-independent antigen are attenuated and severely impaired, respectively. Further analysis of lymphocytes isolated from Id3-deficient mice reveals a B-cell defect in their proliferation response to BCR cross-linking but not to lipopolysaccharide or a combination of BCR cross-linking and interleukin-4. Analyses of cultured lymphocytes also suggest involvement of Id3 in cytokine production in T cells and isotype switching in B cells. Finally, the proliferation defect in Id3-deficient B cells can be rescued by ectopic expression of Id1, a homologue of Id3. Taken together, these results define a necessary and specific role for Id3 in mediating signals from BCR to cell cycle progression during humoral immune responses.

NF-κB1 (p50) Is Upregulated in Lipopolysaccharide Tolerance and Can Block Tumor Necrosis Factor Gene Expression

Abstract: Monocytes respond to lipopolysaccharide (LPS) stimulation with a rapid expression of the tumor necrosis factor (TNF) gene. Upon repeated LPS stimulation there is, however, little production of TNF mRNA and protein; i.e., the cells are tolerant to LPS. Analysis of NF-κB proteins in gel shift assays demonstrated that the DNA binding activity that is induced by LPS stimulation in tolerant cells consists mainly of p50-p50 homodimers. Since p50 can bind to DNA but lacks a transactivation domain, this may explain the blockade of TNF gene expression. We now show that in the monocytic cell line Mono Mac 6, this inability to respond can be largely ascribed to NF-κB, since a reporter construct directed by a trimeric NF-κB motif is strongly transactivated by LPS stimulation of naive cells whereas LPS-tolerant cells exhibit only low activity. Also, Western blot analyses of proteins extracted from purified nuclei showed mobilization of threefold-higher levels of p50 protein in tolerant compared to naive cells, while mobilization of p65 was unaltered. Overexpression of p50 in HEK 293 cells resulted in a strong reduction of p65-driven TNF promoter activity at the levels of both luciferase mRNA and protein. These data support the concept that an upregulation of p50 is instrumental in LPS tolerance in human monocytes.

Mechanisms of brain-mediated systemic anti-inflammatory syndrome causing immunodepression.

Abstract: Overwhelming inflammatory immune response can result in systemic inflammation and septic shock. To prevent excessive and deleterious action of proinflammatory cytokines after they have produced their initial beneficial effects, the immune system can release several anti-inflammatory mediators, including interleukin-10, interleukin-1 receptor antagonist, and soluble tumor necrosis factor receptors, thus initiating a compensatory anti-inflammatory response syndrome. However, in vivo the delicate balance between pro- and anti-inflammatory responses is additionally controlled by the central nervous system. Therefore, proinflammatory cytokines stimulate the hypothalamic-pituitary-adrenal axis and enhance sympathetic nerve system activity. The mediators of these neuroimmune pathways can again suppress immune cell functions to control systemic inflammation. The question is, however, what happens if the immunoinhibitory CNS pathways are activated without systemic inflammation? This can result from production of cytokines in the brain following infection, injury, or ischemia or in response to various stressors (e.g., life events, depression, anxiety) or directly from brainstem irritation. The answer is that this may generate a brain-mediated immunodepression. Many animal and clinical studies have demonstrated a stress and brain cytokine mediated decrease in the cellular immune response at the lymphocyte level. More recently, the importance of monocytes in systemic immunocapacity has been shown. Monocytic inactivation with decreased capability of antigen presentation and depressed secretion of proinflammatory cytokines increases the risk of infectious complications. Interestingly, cytokines in the brain and other stressors can also generate systemic immunodepression at the monocyte level. In this scenario the catecholamine-induced release of the potent anti-inflammatory cytokine interleukin-10 is a newly discovered mechanism of the brain-mediated monocyte deactivation in addition to the "well known" immunosuppressive action of glucocorticoids. Furthermore, other neuropeptides such as alpha-melanocyte-stimulating hormone and beta-endorphin which can be released in stressful situations have also inhibitory effects on immune cells. Thus mediators of the CNS are implicated in the regulation of immune functions and may play a role in both conditioning the host's response to endogenous or exogenous stimuli and generating a "brain-mediated" immunodepression.

Corticosteroids inhibit the production of inflammatory mediators in immature monocyte-derived DC and induce the development of tolerogenic DC3.

Abstract: Corticosteroids (CS) are potent immunosuppressive agents that are known to affect T cell-mediated inflammation by the inhibition of proliferation and cytokine production, as well as the immunostimulatory function of monocytes and macrophages. Not much is known of the effect of corticosteroids on dendritic cells (DC), the professional T cell stimulatory antigen-presenting cells. We report that the endogenous CS hydrocortisone and the synthetic CS clobetasol-17-propionate strongly inhibited the production of the inflammatory mediators interleukin (IL)-12 p70, tumor necrosis factor alpha (TNF-alpha), and IL-6 by lipopolysaccharide (LPS)-stimulated monocyte-derived immature DC (iDC) in vitro. In contrast, the stimulatory capacity, antigen uptake, and the expression of costimulatory molecules were not affected. In accordance with the decreased production of IL-12 p70, CS-treated iDC induced less production of the inflammatory Th1 cytokine interferon-y and enhanced levels of the Th2 cytokines IL-10 and IL-5 in staphylococcal enterotoxin B-stimulated CD4+ Th cells. Furthermore, CS inhibited the maturation of iDC as assessed by the lack of expression of CD83 as well as by the prevention of the loss of antigen uptake capacities. These type 3 DC (DC3) matured in the presence of CS produce less IL-12 p70 and have a decreased T cell stimulatory capacity. Moreover, uncommitted T cells that encounter the CS-induced DC3 develop into Th2-biased cells, which may additionally decrease the Th1-mediated tissue damage but, on the other hand, Th2 cytokines may promote undesirable elevation of IgE and eosinophilia. These findings indicate that suppression of T cell-mediated inflammation by CS not only relies on direct effects on T cells, but also on various effects on DC, their professional antigen-presenting cells.

Tat as one key to HIV-induced immune pathogenesis and Pat toxoid as an important component of a vaccine

Abstract: HIV-induced immune pathogenesis is more complex than simple infection of CD4+ T cells, their subsequent death, replacement by new CD4+ T cells, and eventual immune exhaustion. Even from the earliest period of HIV research, it was clear from in vitro results that the bulk of T cells did not respond properly to antigenic stimuli and even ultimately to mitogenic stimuli, despite the fact that only a small percent of T cells were infected (1, 2). These results, however, were not limited to in vitro experiments. Other studies showed abnormalities of proliferation and sometimes “bystander” apoptosis of uninfected cells in simian immunodeficiency virus-infected macaques (3) and, more recently, regenerative abnormalities that include more generalized effects on hematopoiesis of HIV infected people (4). Consequently, a direct infection and cell killing of CD+ T cells followed by their rapid replacement and ultimate immune exhaustion as suggested in some models does not encompass the overall reality of HIV-induced immune pathogenesis. HIV immune pathogenesis also clearly involves extracellular factors, which have an effect on uninfected cells (Fig. 1). Candidates may include the aberrant production of normal cellular factors, such as the over-production of some cytokines and/or their production at the wrong time and place. In fact, in studies chiefly performed by my collaborator D. Zagury, we have presented evidence that IFN-α may be one such candidate because of its over-production after HIV infection (5), its known anti-proliferative effects (6–8) (Fig. 2), and because we could partially restore T-cell proliferation in vitro to normal when HIV infected peripheral blood mononuclear cell cultures were treated with antibodies to IFN-α (8). Viral proteins, of course, also may be extracellular toxins, and D. Zagury, his collaborators, and I have proposed that Tat is one such toxin and perhaps the most important one (8 …

De Novo Autoimmunity to Cardiac Myosin After Heart Transplantation and Its Contribution to the Rejection Process

Abstract: Allograft rejection is initiated by an immune response to donor MHC proteins. We recently reported that this response can result in breakdown of immune tolerance to a recipient self Ag. However, the contribution of this autoimmune response to graft rejection has yet to be determined. Here, we found that after mouse allogeneic heart transplantation, de novo CD4 + T cell and B cell autoimmune response to cardiac myosin (CM), a major contractile protein of cardiac muscle, is elicited in recipients. Importantly, CM is the autoantigen that causes autoimmune myocarditis, a heart autoimmune disease whose histopathological features resemble those observed in rejected cardiac transplants. Furthermore, T cell responses directed to CM peptide myhc α 334–352, a known myocarditogenic determinant, were detected in heart-transplanted mice. No responses to CM were observed in mice that had received an allogeneic skin graft or a syngeneic heart transplant, demonstrating that this response is tissue specific and that allogeneic response is necessary to break tolerance to CM. Next, we showed that sensitization of recipient mice with CM markedly accelerates the rejection of allogeneic heart. Therefore, posttransplant autoimmune response to CM is relevant to the rejection process. We conclude that transplantation-induced autoimmune response to CM represents a new mechanism that may play a significant role in cardiac transplant rejection.

T-cell reactivity and its predictive role in immunosuppression after burns

Abstract: Objective To obtain further insight into the constitutional, phenotype-dependent changes of T-helper-1 and T-helper-2 signature lymphokine synthesis after trauma. Design Prospective, descriptive study. Setting Intensive care unit of a burn center in a community hospital. Patients Ten patients 1, 3, 5, and 7 days after major burn injury and 15 healthy individuals. Interventions Peripheral blood mononuclear cells were separated and incubated (5 hrs) for cytokine production induced by the accessory cell-independent stimulus of ionomycin and phorbol 12-myristate 13-acetate. After fixation and permeabilization, cell samples were immunofluorescently stained for cell surface antigens (CD4 and CD8), intracellular interferon (IFN)-gamma, and interleukin (IL)-4 synthesis. Results were correlated with corresponding enzyme-linked immunosorbent assay measurements of the culture supernatants. Measurements and main results The phenotypic analysis of the composition of the helper (CD4) and suppressor/cytotoxic (CD8) T-cell subset demonstrated that patients suffering from major burns and healthy controls express these antigens in similar percentages. The ratio of CD4 positive to CD8 positive/CD16 negative T-cell subsets showed no significant changes after trauma compared with controls. The production of IL-4 was excessively up-regulated while the release of IFN-gamma was only slightly increased. The predominant cell source of IL-4 after burn trauma was the CD8+ cell with nearly five-fold increased production on day 5 (7.2+/-2.6%) vs. 1.5+/-0.4% in controls. While CD8+ cells are also capable of enhancing their IFN-gamma synthesis under stress by about 60% due to the significant participation of the naive CD45RA+ subset, the CD4+ IFN-gamma release remained largely unchanged. With this study, we demonstrated that in nonsurvivors the number of CD8+ IL-4-producing cells was significantly higher compared with controls; also, the number of IFN-gamma-releasing memory/effector CD45RO+ cells was lower compared with survivors. Conclusions In previous experiments, we show that a shift to T(H)2 dominated phenotypes increases the risk for postburn infection. The current study confirms that major burns induce a significant shift of cytokine response in the T(H)2 direction and demonstrates that the CD8+, rather than the CD4+ phenotype, is present. Increased IL-4 production is associated with the T(H)2 lymphocyte. These diagnostic tests may help to differentiate patients with compensatory anti-inflammatory response syndrome and immunosuppression from those patients in the proinflammatory state associated with the systemic inflammatory response syndrome. The profile described in this article is associated with immunosuppression and may contraindicate attempts at anti-inflammatory therapy for sepsis.

Ocular immunosuppressive microenvironment.

Abstract: Over the past 30 years, it has become evident that within the ocular microenvironment there are active mechanisms of immunoregulation and immunosuppression. The immunoregulation and immunosuppressio

Altered Helper T Lymphocyte Function Associated with Chronic Hepatitis B Virus Infection and its Role in Response to Therapeutic Vaccination in Humans

Abstract: Theradigm-hepatitis B virus (HBV) is an experimental lipopeptide vaccine designed to stimulate induction of HBV-specific CTL responses in HLA-A2 individuals. Previous studies had demonstrated high immunogenicity in healthy volunteers, but comparatively weak CTL responses in chronically infected HBV patients. Herein, we examined helper T lymphocyte (HTL) responses in chronically infected patients. Despite normal proliferation and IL-2 secretion, IL-12 and IFN-gamma secretion in vitro in response to the vaccine was reduced compared with healthy volunteers. A similar pattern of cytokine secretion was observed following mitogen stimulation, suggesting a general altered balance of Th1/Th2 responses. Further analysis indicated that HTL recall responses to whole tetanus toxoid protein were reduced in chronically infected subjects, and reduced responsiveness correlated with the outcome of Theradigm-HBV immunization. Finally, experiments in HBV transgenic mice indicated that the nonnatural Pan DR HTL epitope, PADRE, is capable of inducing high levels of IFN-gamma secretion and that its inclusion in a lipopeptide incorporating an immunodominant Ld-restricted CTL epitope resulted in breaking tolerance at the CTL level. Overall, our results demonstrate an alteration in the quality of HTL responses induced in chronically infected HBV patients and suggest that use of a potent HTL epitope may be important to overcome CTL tolerance against specific HBV Ags.

Peritransplant tolerance induction in macaques: early events reflecting the unique synergy between immunotoxin and deoxyspergualin.

Abstract: Background Day of transplant T cell depletion with anti-CD3 immunotoxin or F(Ab)2 immunotoxin induces stable tolerance to renal allografts in rhesus monkeys given 15-deoxyspergualin (DSG), a NF-kappaB inhibitor that suppresses proinflammatory cytokine (PC) production. Because PC and NF-kappaB are involved in dendritic cell (DC) maturation, we asked if impaired DC maturation and Th2-type cytokine deviation might be related to the synergistic effect of DSG in this novel model. Methods Immunosuppression was initiated 4 hr before transplanting a major histocompatibility complex mismatched renal allograft. Some groups received a supplemental 5-day course of cyclosporine A or DSG or a 15-day course of DSG. Peripheral lymph nodes were sequentially examined for presence of mature DC. In vitro effects of DSG on PC-induced maturation of DC were also examined. Results Allografts survived without rejection in 87% of recipients given immunotoxin or F(Ab)2 immunotoxin with DSG x 15 days, in 50% with DSG x 5 days, and 0% with cyclosporine A. The longest DSG survivors are >1000 days with normal graft function and tolerance validated, including acceptance of challenge second donor kidneys without treatment. DSG-treated recipients were unique in developing polarized Th2-type plasma cytokines. In DSG recipients, mature DC were significantly reduced in day +5 lymph node biopsies, with complete repopulation by 30 days. In vitro studies verified an inhibitory effect of DSG on DC maturation. Conclusions The study suggests DSG arrests DC maturation. The unusual synergy of immunotoxin and DSG apparently involves coincidental reduction in lymph node T cell mass and mature DC, a transient circumstance favoring development of stable tolerance.

Mixed chimerism induced without lethal conditioning prevents T cell– and anti-Galα1,3Gal–mediated graft rejection

Abstract: Galα1,3Gal–reactive (Gal-reactive) antibodies are a major impediment to pig-to-human xenotransplantation. We investigated the potential to induce tolerance of anti-Gal–producing cells and prevent rejection of vascularized grafts in the combination of α1,3-galactosyltransferase wild-type (GalT+/+) and deficient (GalT–/–) mice. Allogeneic (H-2 mismatched) GalT+/+ bone marrow transplantation (BMT) to GalT–/– mice conditioned with a nonmyeloablative regimen, consisting of depleting CD4 and CD8 mAb’s and 3 Gy whole-body irradiation and 7 Gy thymic irradiation, led to lasting multilineage H-2bxd GalT+/+ + H-2d GalT–/– mixed chimerism. Induction of mixed chimerism was associated with a rapid reduction of serum anti-Gal naturally occurring antibody levels. Anti-Gal–producing cells were undetectable by 2 weeks after BMT, suggesting that anti-Gal–producing cells preexisting at the time of BMT are rapidly tolerized. Even after immunization with Gal-bearing xenogeneic cells, mixed chimeras were devoid of anti-Gal–producing cells and permanently accepted donor-type GalT+/+ heart grafts (>150 days), whereas non-BMT control animals rejected these hearts within 1–7 days. B cells bearing receptors for Gal were completely absent from the spleens of mixed chimeras, suggesting that clonal deletion and/or receptor editing may maintain B-cell tolerance to Gal. These findings demonstrate the principle that induction of mixed hematopoietic chimerism with a potentially relevant nonmyeloablative regimen can simultaneously lead to tolerance among both T cells and Gal-reactive B cells, thus preventing vascularized xenograft rejection.

Placental Fas ligand expression is a mechanism for maternal immune tolerance to the fetus.

Abstract: Fas ligand (FasL) is a peptide that plays an important immunoregulatory role in limiting the host immune response. Several studies have shown that the expression of FasL in the anterior chamber of the eye and the testis allows these tissues to be immunoprivileged sites. Immunotolerance is achieved by binding of FasL to its receptor (Fas) on activated immune cells, which results in cell apoptosis. To determine whether FasL has a role in maternal immune tolerance to the fetus, we looked for the expression of FasL in the human placenta. Immunoperoxidase staining localized FasL to both syncytiotrophoblast and cytotrophoblast in placental villi and chorionic extravillous trophoblast. Western analysis demonstrated FasL in placental villi and a human first-trimester trophoblast cell line (ED27). In contrast, Fas was colocalized to CD45 (leukocyte common antigen) positive cells found in maternal decidua. When isolated peripheral blood lymphocytes were induced to express Fas with phytohemagglutinin (PHA) and interleukin-2 (IL-2) and then cocultured with trophoblast, 30% of the lymphocytes underwent apoptosis, as determined by the in situ death (TUNEL) assay. Neutralizing antibodies to FasL inhibited apoptosis by 40% in these studies. In contrast, activated lymphocytes cocultured with non-FasL-expressing fibroblasts or unactivated non-Fas-expressing lymphocytes cocultured with ED27 trophoblast showed little evidence of apoptosis. These findings suggest that FasL expressed by fetal trophoblast cells can induce apoptosis in activated lymphocytes there by providing a mechanism for maternal immune tolerance to the fetus.

Anti-CD154 or CTLA4Ig obviates the need for thymic irradiation in a non-myeloablative conditioning regimen for the induction of mixed hematopoietic chimerism and tolerance.

Abstract: Background. Thymic irradiation (TI) or repeated administration of T cell-depleting monoclonal antibodies (TCD mAbs) is required in a previously described nonmyeloablative regimen allowing allogeneic marrow engraftment with stable mixed chimerism and tolerance. As both treatments might be associated with toxicity in the clinical setting, we evaluated whether T-cell costimulatory blockade could be used to replace them. Methods. C57BL/6 mice received depleting anti-CD4 and anti-CD8 mAbs on day 25, 3 Gy whole body irradiation (day 0), and 15310 6 fully MHC-mismatched, B10.A bone marrow cells. In addition, hosts were injected with an anti-CD154 mAb (day 0) and/or CTLA4Ig (day 12). Chimerism in peripheral blood was followed by flow cytometric (FACS) analysis, and tolerance was assessed by skin grafting, and also by mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML) assays. The frequency of certain Vb families was determined by FACS to assess deletion of donorreactive T cells. Results. Chimerism was transient and tolerance was not present in animals receiving TCD mAbs on day 25 without costimulatory blockade. The addition of antiCD154 and CTLA4Ig, alone or in combination, reliably permitted induction of high levels of stable (>6 months) multi-lineage chimerism, with specific tolerance to skin grafts and donor antigens by MLR and CML assays. Long-term chimeras showed deletion of donor-reactive CD4 1 peripheral blood lymphocytes, splenocytes, and mature thymocytes. Administration of TCD mAbs only 1 day before bone marrow transplantation plus anti-CD154 also allowed induction of permanent chimerism and tolerance. Conclusions. One injection of anti-CD154 or CTLA4Ig overcomes the need for TI or prolonged host TCD in a preclinical model for the induction of mixed chimerism and deletional tolerance and thus further decreases the toxicity of this protocol. Achievement of tolerance with conditioning given over 24 hr suggests applicability to cadaveric organ transplantation.