Models of T cell anergy: is there a common molecular mechanism?

Hepatitis C virus core protein induces an anergic state characterized by decreased interleukin-2 production and perturbation of mitogen-activated protein kinase responses

Alterations of cytokine responses are thought to favor the establishment of persistent hepatitis C virus (HCV) infections, enhancing the risk of liver cirrhosis and hepatocellular carcinoma. Here we demonstrate that the expression of the HCV core (C) protein in stably transfected T cells correlates with a selective reduction of interleukin-2 (IL-2) promoter activity and IL-2 production in response to T-cell receptor triggering, whereas the activation of IL-4, IL-10, gamma interferon, and tumor necrosis factor alpha was moderately increased. This altered cytokine expression profile was associated with a perturbation of mitogen-activated protein (MAP) kinase responses. Extracellular regulated kinase and p38 were constitutively phosphorylated in C-expressing cells, while triggering of the costimulatory c-Jun N-terminal kinase (JNK) signaling cascade and activation of the CD28 response element within the IL-2 promoter appeared to be impaired. The perturbations of MAP kinase phosphorylation could be eliminated by cyclosporine A-mediated inhibition of nuclear factor of activated T cells, suggesting that the inactivation of JNK signaling and hyporesponsiveness to IL-2 induction were downstream consequences of C-induced Ca(2+) flux in a manner that mimics the induction of clonal anergy.

Administration of tolerogenic dendritic cells induced by interleukin-10 prolongs rat splenic allograft survival

The risk and intensity in splenic graft rejection are greater than in other types of transplants, because the spleen is the largest peripheral lymphoid organ and the immunosuppressive drugs administered can cause splenic dysfunction. In this study, we demonstrate that intravenous injection of interleukin-10-treated donor-type dendritic cells into recipient rats prolongs the survival of splenic allografts. Although the mechanisms are not clear, the induction of tolerance to grafted spleens seems to rely mainly on blockage of expression of the costimulatory molecule CD86, by interleukin-10, leading to enhanced apoptosis of allospecific T cells by immature and tolerogenic dendritic cells. Administration of tolerogenic cells induced by interleukin-10 may thus represent a useful approach for protection of splenic allografts. Further study is required to investigate the operative pathways and to optimize the strategy targeting dendritic cells to induce tolerance in splenic allografts.

The influence of the major histocompatibility complex on development of autoimmune diabetes in RIP-B7.1 mice

The most important genetic susceptibility factor for type 1 diabetes is encoded in the major histocompatibility complex (MHC). The nonobese diabetic (NOD) mouse, which develops spontaneous diabetes, expresses H-2g7 comprising the MHC class I molecules Kd and Db and the MHC class II molecule I-Ag7. However, neither B6.H-2g7 mice, in which H-2g7 is expressed on the C57BL/6 genetic background, nor the nonobese resistant (NOR) mouse, in which H-2g7 is expressed on a genetic background that is 88% similar to NOD mice, develop diabetes. Immune tolerance can be broken in these diabetes-resistant mice expressing H-2g7 if the costimulatory molecule B7.1 is present on the islet beta cells. This does not occur if only single MHC class I components of the H-2g7 haplotype are present, such as Kd in BALB/c mice or Db in C57BL/6 mice, both of which develop only a low level of diabetes when B7.1 is expressed. The presence of I-Ag7 leads to the development of an autoimmune T-cell repertoire, and local costimulation of CD8 T-cells precipitates aggressive diabetes. This implies that a major role of the MHC class II molecules in diabetes is the development of an autoreactive T-cell repertoire.

A pivotal role for the multifunctional calcium/calmodulin-dependent protein kinase II in T cells: from activation to unresponsiveness

Stimulation of the TCR leads to an oscillatory release of free calcium that activates members of the calcium/calmodulin-dependent protein kinase II (CaMKII) family. The CaMKII molecules have profound and lasting effects on cellular signaling in several cell types, yet the role of CaMKII in T cells is still poorly characterized. In this report we describe a splice variant of CaMKIIbeta, CaMKIIbeta'e, in mouse T cells. We have determined its function, along with that of CaMKIIgamma, by introducing the active and kinase-dead mutants into activated P14 TCR transgenic T cells using retroviral transduction. Active CaMKII enhanced the proliferation and cytotoxic activity of T cells while reducing their IL-2 production. Furthermore, it induced a profound state of unresponsiveness that could be overcome only by prolonged culture in IL-2. These results indicate that members of the CaMKII family play an important role in regulation of CD8 T cell proliferation, cytotoxic effector function, and the response to restimulation.

In Vivo Modulation of T Cell Responses and Protective Immunity by TCR Antagonism during Infection

Infectious agents are known to express altered peptide ligands that antagonize T cells in vitro; however, direct evidence of TCR antagonism during infection is still lacking, and its importance in the context of infection remains to be established. In this study, we used a murine model of infection with recombinant Listeria monocytogenes and addressed three issues that are critical for assessing the role of TCR antagonism in the modulation of the immune response. First, we demonstrated that the antagonist peptide efficiently inhibited the ability of the agonist to prime naive TCR-transgenic T cells in vivo. Second, we showed clonal memory T cells were antagonized during recall responses, resulting in loss of protective immunity. Lastly, we observed that even in the context of a polyclonal response, TCR antagonism greatly inhibits the agonist-specific response, leading to altered hierarchy of immunodominance and reduced T cell memory and protective immunity. These results provide direct evidence of clonal TCR antagonism of naive and memory CD8 T cells during infection and demonstrate the effect of TCR antagonism on protective immunity. Thus, agonist/antagonist interactions may play an important role in determining the immunodominance and repertoire of T cell targets, and evaluation of immune responses and vaccine strategies may require examination of not only agonists but also antagonists and their interactions during an infection.

Systemic immunomodulation of autoimmune disease using MHC-derived recombinant TCR ligands

Human autoimmune disease involves local activation of antigen-specific CD4(+) T cells that produce inflammatory Th1 cytokines leading to the further recruitment and activation of lymphocytes and monocytes, resulting ultimately in the destruction of target tissue. Antigen presenting cells (APCs) initiate activation of CD4(+) T cells in a multistep process that minimally involves co-ligation of the TCR and CD4 by the MHC class II/peptide complex and costimulation through additional T cell surface molecules such as CD28. Disruption of this highly orchestrated series of events can result in the direct modulation of CD4(+) T cell behavior. The interaction between MHC and TCR holds unique promise as a focal point for therapeutic intervention in the pathology of CD4(+) T cell-mediated diseases, and MHC class II-derived Recombinant TCR Ligands ("RTLs") have emerged as a new class of therapeutics with potent clinical efficacy in a diverse set of animal models for multiple sclerosis. Here I review the systemic effect that RTL therapy has on the intact immune system and present an overview of a molecular mechanism by which RTL therapy could induce these systemic changes.

Regulatory T cells in rheumatoid arthritis

Apart from the deletion of autoreactive T cells in the thymus, various methods exist in the peripheral immune system to control specific human immune responses to self-antigens. One of these mechanisms involves regulatory T cells, of which CD4+CD25+ T cells are a major subset. Recent evidence suggests that CD4+CD25+ T cells have a role in controlling the development of autoimmune diseases in animals and in humans. The precise delineation of the function of CD4+CD25+ T cells in autoimmune inflammation is therefore of great importance for the understanding of the pathogenesis of autoimmune diseases. Moreover, the ability to control such regulatory mechanisms might provide novel therapeutic opportunities in autoimmune disorders such as rheumatoid arthritis. Here we review existing knowledge of CD4+CD25+ T cells and discuss their role in the pathogenesis of rheumatic diseases.

Operationally tolerant and minimally immunosuppressed kidney recipients display strongly altered blood T-cell clonal regulation

Most kidney transplant recipients who discontinue immunosuppression reject their graft. Nevertheless, a small number do not, suggesting that allogeneic tolerance state (referred to operational tolerance) is achievable in humans. So far, however, the rarity of such patients has limited their study. Because operational tolerance could be linked to anergy, ignorance or to an active regulatory mechanism, we analyzed the blood T-cell repertoire usage of these patients. We report on comparison of T-cell selection in drug-free operationally tolerant kidney recipients (or with minimal immunosuppression), recipients with stable graft function, chronic rejection and healthy individuals. The blood T cells of operationally tolerant patients display two major characteristics: an unexpected strongly altered T-cell receptor (TCR) Vbeta usage and high TCR transcript accumulation in selected T cells. The cytokine transcriptional patterns of sorted T cells with altered TCR usage show no accumulation of cytokine transcripts (IL10, IL2, IL13, IFN-gamma), suggesting a state of hyporesponsiveness in these patients. Identification of such a potential surrogate pattern of operational tolerance in transplant recipients under life-long immunosuppression may provide a new basis and rationale for exploration of tolerance state. However, these data obtained in a limited number of patients require further confirmation on larger series.

Transduction of naive CD4 T?cells with kinase-deficient Lck-HIV-Tat fusion protein dampens T?cell activation and provokes a switch to regulatory function

We show here that T cell differentiation can be altered by exposing naive mouse CD4 T cells to altered T cell receptor signaling, achieved by transducing them with a fusion protein consisting of a modified Lck protein lacking the kinase domain and the HIV-Tat protein transduction domain. The Lck-HIV-Tat fusion protein is internalized into naive mouse T cells within 30 min after application to the medium. Activation of transduced cells in vitro resulted in strongly reduced intracellular calcium mobilization, alterations in cytokine profile, and sustained up-regulation of CD25. The cells had suppressive activity in vitro, but no Foxp3 expression. Our data indicate that signals encountered by a naive T cell during its initial activation can profoundly influence its subsequent functional behavior and elicit T cells, which can have regulatory activity.

Rationally designed mutations convert complexes of human recombinant T cell receptor ligands into monomers that retain biological activity

Single-chain human recombinant T cell receptor ligands derived from the peptide binding/TCR recognition domain of human HLA-DR2b (DRA*0101/DRB1*1501) produced in Escherichia coli with and without amino-terminal extensions containing antigenic peptides have been described previously. While molecules with the native sequence retained biological activity, they formed higher order aggregates in solution. In this study, we used site-directed mutagenesis to modify the β-sheet platform of the DR2-derived RTLs, obtaining two variants that were monomeric in solution by replacing hydrophobic residues with polar (serine) or charged (aspartic acid) residues. Size exclusion chromatography and dynamic light scattering demonstrated that the modified RTLs were monomeric in solution, and structural characterization using circular dichroism demonstrated the highly ordered secondary structure of the RTLs. Peptide binding to the `empty' RTLs was quantified using biotinylated peptides, and functional studies showed that the modified RTLs containing covalently tethered peptides were able to inhibit antigen-specific T cell proliferation in vitro, as well as suppress experimental autoimmune encephalomyelitis in vivo. These studies demonstrated that RTLs encoding the Ag-binding/TCR recognition domain of MHC class II molecules are innately very robust structures, capable of retaining potent biological activity separate from the Ig-fold domains of the progenitor class II structure, with prevention of aggregation accomplished by modification of an exposed surface that was buried in the progenitor structure.

The quantal theory of how the immune system discriminates between "self and non-self"

In the past 50 years, immunologists have accumulated an amazing amount of information as to how the immune system functions. However, one of the most fundamental aspects of immunity, how the immune system discriminates between self vs. non-self, still remains an enigma. Any attempt to explain this most intriguing and fundamental characteristic must account for this decision at the level of the whole immune system, but as well, at the level of the individual cells making up the immune system. Moreover, it must provide for a molecular explanation as to how and why the cells behave as they do. The "Quantal Theory", proposed herein, is based upon the "Clonal Selection Theory", first proposed by Sir McFarland Burnet in 1955, in which he explained the remarkable specificity as well as diversity of recognition of everything foreign in the environment. The "Quantal Theory" is built upon Burnet's premise that after antigen selection of cell clones, a proliferative expansion of the selected cells ensues. Furthermore, it is derived from experiments which indicate that the proliferation of antigen-selected cell clones is determined by a quantal, "all-or-none", decision promulgated by a critical number of cellular receptors triggered by the T Cell Growth Factor (TCGF), interleukin 2 (IL2). An extraordinary number of experiments reported especially in the past 20 years, and detailed herein, indicate that the T cell Antigen Receptor (TCR) behaves similarly, and also that there are several critical numbers of triggered TCRs that determine different fates of the T cells. Moreover, the fates of the cells appear ultimately to be determined by the TCR triggering of the IL2 and IL2 receptor (IL2R) genes, which are also expressed in a very quantal fashion. The "Quantal Theory" states that the fundamental decisions of the T cell immune system are dependent upon the cells receiving a critical number of triggered TCRs and IL2Rs and that the cells respond in an all-or-none fashion. The "Quantal Theory" accounts fully for the development of T cells in the thymus, and such fundamental cellular fates as both "positive" and "negative" selection, as well as the decision to differentiate into a "Regulatory T cell" (T-Reg). In the periphery, the "Quantal Theory" accounts for the decision to proliferate or not in response to the presence of an antigen, either non-self or self, or to differentiate into a T-Reg. Since the immune system discriminates between self and non-self antigens by the accumulated number of triggered TCRs and IL2Rs, therapeutic manipulation of the determinants of these quantal decisions should permit new approaches to either enhance or dampen antigen-specific immune responses.

Allergen-specific immunotherapy induces Th1 shift in dogs with atopic dermatitis

Allergen-specific immunotherapy has been applied to canine atopic dermatitis. Despite the accumulated clinical evidence of its effect for atopic dogs, the basic immunologic mechanisms were not fully understood. In this study, the cytokine profile ex vivo in canine atopic dermatitis before and after allergen-specific immunotherapy was characterized using competitive reverse transcription-polymerase chain reaction (RT-PCR). Blood samples were collected from 10 dogs with atopic dermatitis and peripheral blood mononuclear cells were stimulated with house dust mite antigen. The levels of IFN-gamma and IL-4 mRNA were lower in atopic dogs compared with non-atopic controls. The ratio of IFN-gamma/IL-4 was low in atopic dogs indicating a cytokine profile polarized to Th2. The level of IFN-gamma after immunotherapy was significantly higher than that before (P < 0.05) whereas that of IL-4 mRNA was not changed. Consequently, the ratio of IFN-gamma/IL-4 after immunotherapy was significantly higher than that before immunotherapy (P < 0.05). These results indicate a Th2 cytokine bias is the dominant state in atopic dogs and allergen-specific immunotherapy causes a shift to wards a Th1 bias by enhancing IFN-gamma expression.

Uptake of membrane molecules from T cells endows antigen-presenting cells with novel functional properties

Although intercellular transfer of cell surface molecules has been observed between several cells of the immune system, the physiological relevance of this phenomenon remained obscure. Until now the transfer of molecules between antigen-presenting cells (APC) and T cells has been described as a unidirectional process from APC to T cells. However, here we show that T cells in turn donate molecules to APC, and that T cell-derived vesicles can mediate this transfer. The transferred proteins are incorporated into the APC as active molecules. Our data provide evidence that T cells use intercellular molecule transfer to mediate cell contact-dependent regulation of T cell responses via modulation of the APC.

Naive T cells are resistant to anergy induction by anti-CD3 antibodies

Anti-CD3 mAbs are potent immunosuppressive agents used in clinical transplantation. It has been generally assumed that one of the anti-CD3 mAb-mediated tolerance mechanisms is through the induction of naive T cell unresponsiveness, often referred to as anergy. We demonstrate in this study that naive T cells stimulated by anti-CD3 mAbs both in vivo and in vitro do not respond to the superantigen staphylococcal enterotoxin B nor to soluble forms of anti-CD3 mAbs and APC, but express increased reactivity to plastic-coated forms of the same anti-CD3 mAbs and to their nominal Ag/class II MHC, a finding that is difficult to rationalize with the concept of anergy. Phenotypic and detailed kinetic studies further suggest that a strong signal 1 delivered by anti-CD3 mAbs in the absence of costimulatory molecules does not lead to anergy, but rather induces naive T cells to change their mitogen responsiveness and acquire features of memory T cells. In marked contrast, Ag-experienced T cells are sensitive to anergy induction under the same experimental settings. Collectively, these studies demonstrate that exposure of naive T cells in vivo and in vitro to a strong TCR stimulus does not induce Ag unresponsiveness, indicating that sensitivity to negative signaling through TCR/CD3 triggering is developmentally regulated in CD4(+) T cells.

Allogeneic vaccination with a B7.1 HLA-A gene-modified adenocarcinoma cell line in patients with advanced non-small-cell lung cancer

PURPOSE

To determine the safety, immunogenicity, and clinical response to an allogeneic tumor vaccine for non-small-cell lung cancer, we conducted a phase I trial in patients with advanced metastatic disease.

PATIENTS AND METHODS

We treated 19 patients with a vaccine based on an adenocarcinoma line (AD100) transfected with B7.1 (CD80) and HLA A1 or A2. Patients were vaccinated intradermally with 5 x 10(7) cells once every 2 weeks. Three vaccinations represented one course of treatment. If patients had complete response, partial response, or stable disease, they continued with the vaccinations for up to three courses (nine vaccinations). Immune response was assessed by a change between pre-study and postvaccination enzyme-linked immunospot frequency of purified CD8 T-cells secreting interferon-gamma in response to in vitro challenge with AD100.

RESULTS

Four patients experienced serious adverse events that were unrelated to vaccine. Another four patients experienced only minimal skin erythema. All but one patient had a measurable CD8 response after three immunizations. The immune response of six surviving, clinically responding patients shows that CD8 titers continue to be elevated up to 150 weeks, even after cessation of vaccination. Overall, one patient had a partial response, and five had stable disease. Median survival for all patients is 18 months (90% CI, 7 to 23 months), with corresponding estimates of 1-year, 2-year, and 3-year survival of 52%, 30%, and 30%, respectively. HLA matching of vaccine, age, sex, race, and pathology did not bear a significant relation to response.

CONCLUSION

Minimal toxicity and good survival in this small population suggest clinical benefit from vaccination.

Poor immunogenicity of a self/tumor antigen derives from peptide-MHC-I instability and is independent of tolerance

Understanding the mechanisms underlying the poor immunogenicity of human self/tumor antigens is challenging because of experimental limitations in humans. Here, we developed a human-mouse chimeric model that allows us to investigate the roles of the frequency and self-reactivity of antigen-specific T cells in determination of the immunogenicity of an epitope (amino acids 209-217) derived from a human melanoma antigen, gp100. In these transgenic mice, CD8+ T cells express the variable regions of a human T cell receptor (hTCR) specific for an HLA-A*0201-restricted gp100(209-217). Immunization of hTCR-transgenic mice with gp100(209-217) peptide elicited minimal T cell responses, even in mice in which the epitope was knocked out. Conversely, a modified epitope, gp100(209-217(2M)), was significantly more immunogenic. Both biological and physical assays revealed a fast rate of dissociation of the native peptide from the HLA-A*0201 molecule and a considerably slower rate of dissociation of the modified peptide. In vivo, the time allowed for dissociation of peptide-MHC complexes on APCs prior to their exposure to T cells significantly affected the induction of immune responses. These findings indicate that the poor immunogenicity of some self/tumor antigens is due to the instability of the peptide-MHC complex rather than to the continual deletion or tolerization of self-reactive T cells.

Genes of tolerance

Activation-induced cell death, anergy and/or immune response modulation by T-regulatory cells (T(Reg)) are essential mechanisms of peripheral T-cell tolerance. There is growing evidence that anergy, tolerance and active suppression are not entirely distinct, but rather, represent linked mechanisms possibly involving the same cells and multiple suppressor mechanisms. Skewing of allergen-specific effector T cells to T(Reg) cells appears as a crucial event in the control of healthy immune response to allergens and successful allergen-specific immunotherapy. The T(Reg) cell response is characterized by abolished allergen-induced specific T-cell proliferation and suppressed T helper 1 (Th1)- and Th2-type cytokine secretion. In addition, mediators of allergic inflammation that trigger cAMP-associated G-protein coupled receptors, such as histamine receptor 2 may contribute to peripheral tolerance mechanisms. The increased levels of interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) that are produced by T(Reg) cells potently suppress immunoglobulin E (IgE) production, while simultaneously increasing production of noninflammatory isotypes IgG4 and IgA, respectively. In addition, T(Reg) cells directly or indirectly suppress effector cells of allergic inflammation such as mast cells, basophils and eosinophils. In conclusion, peripheral tolerance to allergens is controlled by multiple active suppression mechanisms. It is associated with regulation of antibody isotypes and effector cells to the direction of a healthy immune response and opens a window for novel therapies of allergic diseases.

Expression of indoleamine 2,3-dioxygenase by plasmacytoid dendritic cells in tumor-draining lymph nodes

One mechanism contributing to immunologic unresponsiveness toward tumors may be presentation of tumor antigens by tolerogenic host APCs. We show that mouse tumor-draining LNs (TDLNs) contained a subset of plasmacytoid DCs (pDCs) that constitutively expressed immunosuppressive levels of the enzyme indoleamine 2,3-dioxygenase (IDO). Despite comprising only 0.5% of LN cells, these pDCs in vitro potently suppressed T cell responses to antigens presented by the pDCs themselves and also, in a dominant fashion, suppressed T cell responses to third-party antigens presented by nonsuppressive APCs. Adoptive transfer of DCs from TDLNs into naive hosts created profound local T cell anergy, specifically toward antigens expressed by the transferred DCs. Anergy was prevented by targeted disruption of the IDO gene in the DCs or by administration of the IDO inhibitor drug 1-methyl-D-tryptophan to recipient mice. Within the population of pDCs, the majority of the functional IDO-mediated suppressor activity segregated with a novel subset of pDCs coexpressing the B-lineage marker CD19. We hypothesize that IDO-mediated suppression by pDCs in TDLNs creates a local microenvironment that is potently suppressive of host antitumor T cell responses.

Expression of indoleamine 2,3-dioxygenase by plasmacytoid dendritic cells in tumor-draining lymph nodes

One mechanism contributing to immunologic unresponsiveness toward tumors may be presentation of tumor antigens by tolerogenic host APCs. We show that mouse tumor-draining LNs (TDLNs) contained a subset of plasmacytoid DCs (pDCs) that constitutively expressed immunosuppressive levels of the enzyme indoleamine 2,3-dioxygenase (IDO). Despite comprising only 0.5% of LN cells, these pDCs in vitro potently suppressed T cell responses to antigens presented by the pDCs themselves and also, in a dominant fashion, suppressed T cell responses to third-party antigens presented by nonsuppressive APCs. Adoptive transfer of DCs from TDLNs into naive hosts created profound local T cell anergy, specifically toward antigens expressed by the transferred DCs. Anergy was prevented by targeted disruption of the IDO gene in the DCs or by administration of the IDO inhibitor drug 1-methyl-D-tryptophan to recipient mice. Within the population of pDCs, the majority of the functional IDO-mediated suppressor activity segregated with a novel subset of pDCs coexpressing the B-lineage marker CD19. We hypothesize that IDO-mediated suppression by pDCs in TDLNs creates a local microenvironment that is potently suppressive of host antitumor T cell responses.

Gammadelta T cells enhance the expression of experimental autoimmune encephalomyelitis by promoting antigen presentation and IL-12 production

Using an adoptive transfer model of experimental autoimmune encephalomyelitis (EAE) induced by myelin basic protein (MBP)-reactive lymph node cells (LNC), we have shown that depletion of gammadelta T cells from LNC resulted in diminished severity of EAE in recipient mice, both clinically and histopathologically. The reduced potency of gammadelta T cell-depleted LNC to induce EAE correlated with decreased cell proliferation in response to MBP. The gammadelta T cell effect upon the threshold of MBP-induced LNC proliferation and EAE transfer was restored by reconstitution of gammadelta T cells derived from either MBP-immunized or naive mice, indicating that this effect was not Ag specific. The enhancing effect of gammadelta T cells on MBP-induced proliferation and EAE transfer required direct cell-to-cell contact with LNC. The gammadelta T cell effect upon the LNC response to MBP did not involve a change in expression of the costimulatory molecules CD28, CD40L, and CTLA-4 on TCRalphabeta(+) cells, and CD40, CD80, and CD86 on CD19(+) and CD11b(+) cells. However, depletion of gammadelta T cells resulted in significant reduction in IL-12 production by LNC. That gammadelta T cells enhanced the MBP response and severity of adoptive EAE by stimulating IL-12 production was supported by experiments showing that reconstitution of the gammadelta T cell population restored IL-12 production, and that gammadelta T cell depletion-induced effects were reversed by the addition of IL-12. These results suggest a role for gammadelta T cells in the early effector phase of the immune response in EAE.

Alterations of the expression of T-cell-related costimulatory CD28 and downregulatory CD152 (CTLA-4) molecules in patients with B-cell chronic lymphocytic leukaemia

In the present study, we have examined the kinetics and magnitude of expression of the CD28 and CD152 molecules on unstimulated and anti-CD3+rIL-2-stimulated peripheral blood CD4+ and CD8+ T cells in patients with chronic lymphocytic leukaemia (B-CLL) and controls. The mean percentages of both CD3+/CD4+/CD28+ and CD3+/CD8+/CD28+ cells were significantly lower in B-CLL than in controls before culture, decreased rapidly, reaching their lowest levels between 24 and 48 h, and returned to basal levels after 72 h of culture. In controls, the lowest proportions of CD3+/CD4+/CD28+ and CD3+/CD8+/CD28+ cells were found after 24 h and returned to prestimulation levels after 48 h of stimulation. We observed significantly higher proportions of unstimulated CD3+/CD4+/CD152+ and CD3+/CD8+/CD152+ cells in B-CLL patients than in controls. The highest percentages of CD3+/CD4+/CD152+ and CD3+/CD8+/CD152+ cells were observed in controls after 72 h, and in B-CLL patients after 24 h, and remained statistically higher after 48, 72 and 96 h of stimulation. CD152 molecule expression returned to prestimulation levels after 96 h of culture in controls, and after 120 h in B-CLL patients. The abnormal kinetics and levels of CD28 and CD152 expression on T cells in B-CLL may lead to a state of hyporesponsiveness or anergy and could be one of the mechanisms of immune deficiency in this disease.

Haematopoietic stem cell transplantation for autoimmune disease: limits and future potential

Stem cell transplantation (SCT) for autoimmune disease is handicapped by a lack of definitive clinical trials able to demonstrate an overall benefit. This deficiency will become more problematic as the impetus grows to introduce and evaluate additional technologies intended to improve the safety and efficacy of the procedure. The development of effective surrogate analyses to predict outcome by measuring resurgent autoimmune clones or by genomic- and proteomic-based technologies to detect early disease recurrence may be of value in assessing the benefits of these modifications without the need for full-scale, long-term, randomized trials. The introduction of safer allogeneic transplantation techniques may increase the effectiveness of the procedure, while work on marrow stem cell plasticity and/or fusion suggests that SCT may serve not simply to halt the autoimmune process, but also to contribute cells capable of healing or regenerating diseased organs. Finally, the introduction of therapeutic transgenes into transplanted cells may further increase the effectiveness of SCT, although the regulatory complexities of gene therapy trials will probably delay this process. All these innovations will ensure that the next decade will see major changes in the practice and purpose of SCT for autoimmune disease.

Induction of T cell anergy by the treatment with IL-10-treated dendritic cells

In order to apply for reducing graft versus host disease in allogeneic stem cell transplantation, the study concerning the induction of specific T cell anergy was designed. Normal allogeneic lymphocytes, which were co-cultured with IL-10-treated immature dendritic cells in the first mixed leukocyte culture (MLC), were cultured with mature dendritic cells of the same origin as IL-10-treated immature dendritic cells in the second MLC. By co-culturing with IL-10-treated immature dendritic cells, the response of normal lymphocytes to mature dendritic cells cultured from the same individual as that of IL-10-treated dendritic cells was markedly reduced, compared with the lymphocytes cultured with non-treated dendritic cells or IL-10-treated dendritic cells from a third party individual. The present study demonstrated that antigen specific T cell anergy was generated by priming allogeneic lymphocytes with IL-10-treated immature dendritic cells. These data suggested the applicability of IL-10-treated recipient dendritic cells for the induction of recipient cell-specific donor T cell anergy in donor graft.

Rheumatologic disease with peripheral eosinophilia

Eosinophilia is not common in connective tissue diseases, so the frequency and clinical importance of eosinophilia in rheumatologic disease are not known. The purpose of the present review was to explore its prevalance in rheumatologic disease together with a MEDLINE database search.

Eosinophilia in rheumatologic diseases: a prospective study of 1000 cases

The role of eosinophilia in connective tissue diseases and the relationship between symptoms of rheumatic disease and eosinophilia have not been clearly established. The purpose of the present study was to explore the prevalence of eosinophilia in rheumatologic disease and determine its relationship to the symptoms. One thousand patients who applied to our rheumatology outpatient clinic between 2001 and 2002 were prospectively studied. The upper limit of normal blood eosinophil numbers was determined as 500 cells/microl of blood. A detailed history was obtained from all patients and careful physical examination was done. A negative correlation was observed between eosinophilia and dryness of the mouth, vitiligo, and fatigue (P < 0.05). Nonsteroidal anti-inflammatory drug usage correlated positively with eosinophilia, which was also statistically meaningful (P < 0.05). Twenty-six of our patients with fibromyalgia (n = 293), three of our subjects with rheumatoid arthritis who were using methotrexate (n = 182), 15 of whom who were not on methotrexate therapy, and one of the 26 with vasculitis had eosinophilia, which was not statistically significant (P > 0.05). None of the patients with scleroderma (n = 12) had eosinophilia. Eleven of the patients with gout had eosinophilia, and only one of them was using allopurinol. We conclude that eosinophilia can be seen in various rheumatologic conditions but, as corticosteroids are one of the most common medications used in collagen tissue diseases, the eosinophil numbers found may be lower than expected and eosinophilia may be more frequent than reported.

Antigen-induced regulatory T cells

Regulatory T cells participate in immunologic homeostasis by active suppression of inappropriate immune responses. Regulatory T lymphocytes expressing CD4 and CD25 antigens and naturally present in the peripheral blood were the first to be phenotypically characterized. However, their small number and antigen nonspecific suppression has prompted efforts to identify and dissect antigen-specific regulatory T cells. In this review we discuss how antigen-specific regulatory T cells can be identified, the cellular and molecular mechanisms underlying their induction and activity, and the challenges facing their potential clinical application.

Function and regulation of the CD95 (APO-1/Fas) ligand in the immune system

CD95/CD95L mediated apoptosis is an important mechanism of immune homeostasis. It is instrumental for termination of an immune response and mainly be involved in peripheral tolerance. Dysregulation of the CD95/CD95L system leads to severe diseases. In this review, we present a survey of the role of the CD95/CD95L system in the immune system and, particularly, focus on the signals and transcription factors (NF-AT, Egr, NF-kappaB, AP-1, c-Myc, Nur77, IRFs, SP-1, ALG-4, ROR(gamma)t, and CIITA) involved in CD95L expression. It should also be evident from this review that a profound insight into the molecular mechanisms of CD95L activation should allow to explore potential therapeutic means to treat CD95/CD95L-dependent diseases.

IL-2 is not required for the initiation of CD8 T cell cycling but sustains expansion

Based primarily on in vitro data, IL-2 is believed to be the key cytokine for initiation of the cell cycle of activated T cells. However, the role of IL-2 remains unresolved for T cell responses in vivo. We examined whether the absence of IL-2-mediated signaling in CD8 T cells affected initiation of proliferation. Our results conclusively demonstrated that initial division of Ag-specific CD8 T cells following priming was IL-2 independent, regardless of the context in which Ag was presented. In contrast, the latter stage of the proliferative phase was IL-2-dependent, particularly in nonlymphoid tissues. Thus, activated CD8 T cells initially undergo IL-2-independent proliferation, but reach a critical juncture where the requirement for IL-2 as a growth factor gains prominence.

Conversion of peripheral CD4+CD25- naive T cells to CD4+CD25+ regulatory T cells by TGF-beta induction of transcription factor Foxp3

CD4⁺CD25⁺ regulatory T cells (T_reg) are instrumental in the maintenance of immunological tolerance. One critical question is whether T_reg can only be generated in the thymus or can differentiate from peripheral CD4⁺CD25⁻ naive T cells. In this paper, we present novel evidence that conversion of naive peripheral CD4⁺CD25⁻ T cells into anergic/suppressor cells that are CD25⁺, CD45RB^−/low and intracellular CTLA-4⁺ can be achieved through costimulation with T cell receptors (TCRs) and transforming growth factor β (TGF-β). Although transcription factor Foxp3 has been shown recently to be associated with the development of T_reg, the physiological inducers for Foxp3 gene expression remain a mystery. TGF-β induced Foxp3 gene expression in TCR-challenged CD4⁺CD25⁻ naive T cells, which mediated their transition toward a regulatory T cell phenotype with potent immunosuppressive potential. These converted anergic/suppressor cells are not only unresponsive to TCR stimulation and produce neither T helper cell 1 nor T helper cell 2 cytokines but they also express TGF-β and inhibit normal T cell proliferation in vitro. More importantly, in an ovalbumin peptide TCR transgenic adoptive transfer model, TGF-β–converted transgenic CD4⁺CD25⁺ suppressor cells proliferated in response to immunization and inhibited antigen-specific naive CD4⁺ T cell expansion in vivo. Finally, in a murine asthma model, coadministration of these TGF-β–induced suppressor T cells prevented house dust mite–induced allergic pathogenesis in lungs.

Mycobacterium tuberculosisRecall Antigens Suppress HIV-1 Replication in Anergic Donor Cells via CD8+T Cell Expansion and Increased IL-10 Levels

Mycobacterium tuberculosis (MTb) is the leading cause of death in the setting of AIDS. MTb enhances the pathogenicity and accelerates the course of HIV disease and, furthermore, infection with HIV-1 increases the risk of reactivation or reinfection with MTb. In this study, we show that host-specific recall responses to one pathogen, MTb, has a direct effect upon the regulation of a second pathogen, HIV-1. Using cells from immunocompetent former tuberculosis (TB) patients who displayed either a persistently positive (responsive) or negative (anergic), delayed-type hypersensitivity (DTH) reaction to intradermal injection of purified protein derivative (PPD), we investigated the effect of recall Ags to MTb upon the replication of HIV-1 primary isolates in vitro. We show that HIV-1 replication of a T cell-tropic isolate was significantly impaired in MTb-stimulated PBMC from PPD-anergic donors. Furthermore, these donors displayed a significant increase in CD8(+) T cells and IL-10 levels and lower levels of IL-2 and TNF-alpha relative to PPD-responsive donors in response to PPD stimulation. Strikingly, CD8(+) T cell depletion and blocking of IL-10 significantly increased HIV-1 replication in these PPD-anergic donors, indicating that an immunosuppressive response to MTb recall Ags inhibits HIV-1 replication in PPD-anergic individuals. Therefore, immunotherapeutic approaches aimed at recapitulating Ag-specific MTb anergy in vivo could result in novel and effective approaches to inhibit HIV-1 disease progression in MTb/HIV-1 coinfection.

Cytokines IL-1 alpha, IL-6, and GM-CSF constitutively secreted by oral squamous carcinoma induce down-regulation of CD80 costimulatory molecule expression: restoration by interferon gamma

We previously characterized the expression of CD80 in different murine head and neck squamous cell carcinoma (HNSCC) clones derived following tumor progression in the absence of T cell-mediated immunity in severe combined immunodeficient (SCID) mice. We found that HNSCCs that did not express CD80 grew as progressors, while those that expressed CD80 were regressors when grown in immune-competent animals. In the present study, we characterized expression of a repertoire of immunoregulatory cytokines in these HNSCC lines, and found that HNSCCs that express cytokines IL-1 alpha, IL-6, and GM-CSF do not express CD80, suggesting the hypothesis that these cytokines may down-modulate expression of CD80. Cytokine-conditioned medium from progressor HNSCC and recombinant IL-1 alpha, IL-6, and GM-CSF caused a reduction of CD80 expression in regressor HNSCCs without affecting proliferation. Conversely, the decrease in CD80 expression in progressor HNSCCs could be restored by IFN-gamma, a known inducer of CD80 expression. These data strongly suggest that high levels of cytokines IL-1 alpha, IL-6, and GM-CSF expressed by tumor cells can down-regulate CD80 expression in HNSCC, and that IFN-gamma can independently stimulate expression. These data provide evidence for a novel mechanism of cytokine-mediated down-modulation of CD80 during malignant progression of HNSCC that can be restored by IFN-gamma.

Expression of costimulatory molecules (CD80, CD86, CD28, CD152), accessory molecules (TCR αβ, TCR γδ) and T cell lineage molecules (CD4+, CD8+) in PBMC of leprosy patients using Mycobacterium leprae antigen (MLCWA) with murabutide and T cell peptide of Trat protein

In leprosy, cell-mediated immunity (CMI) is more significant than humoral response to eliminate intracellular pathogen. T cell defect is a common feature in lepromatous leprosy (LL) patients as compared to tuberculoid type (TT) patients. For efficient initiation of CD4+, T cell response requires T cell receptor (TCR) activation and costimulation provided by molecules on antigen-presenting cells (APC) and their counter receptors on T cells. In our previous study, the defective T cell function in LL patients was restored to a proliferating state with the release of TH1 type cytokines using mycobacterial antigen(s) with two immunomodulators (Murabutide (MDP-BE) and T cell epitope of Trat protein of Escherichia coli) by presenting the antigen in particulate form in vitro to PBMC derived from leprosy patients. This observation prompted us to study the expression of the costimulatory molecules (CD80, CD86, CD28, CD152), other accessory molecules (TCR alphabeta/gammadelta) and T cell lineage molecules (CD4+ and CD8+) during constitutive and activated state of peripheral blood mononuclear cells (PBMC) derived from normal and leprosy individuals using different formulations of Mycobacterium leprae total cell wall antigen (MLCWA), Trat and MDP-BE using flow cytometric analysis. An increased surface expression of CD80, CD86 and CD28 but decreased CD152 expression was observed when PBMC of normal, BT/TT (tuberculoid) and BL/LL (lepromatous) patients were stimulated in vitro with MLCWA+MDP-BE+Trat peptide using liposomal mode of antigen delivery, while opposite results were obtained with the antigen alone. Antibody inhibition study using antihuman CD80 or CD86 completely abolished the T cell lymphoproliferation, thereby reconfirming the importance of these costimulatory molecules during T cell activation/differentiation. Though the liposome-entrapped antigen formulation has no effect on expression of alphabeta/gammadelta T cell receptor, the constitutive levels of TCR gammadelta were high in lepromatous patients. Thus, TCR bearing gammadelta appears to have a negligible regulatory role in peripheral blood of leprosy patients. The percentage of cells positive for CD4+ are increased in inducible state in all the three groups, while CD8+-positive cells were decreased in LL patients, thereby reconfirming the fact that priming of CD4+ cells are necessary for producing final effector functions. Lastly, intracellular cytokine staining experiment indicated that CD4+ cells are the major producers of IFN-gamma but not NK cells. The study highlights the reversal of T cell anergy especially in lepromatous patients through the modulation of costimulatory molecule expression under the influence of Th1 cytokines, i.e., IL-2 and IFNgamma.

Distinctive response of naïve lymphocytes from cord blood to primary activation via TCR

Umbilical cord blood (UCB) is now being considered an alternative to bone marrow for restoring hematopoiesis after myeloablative therapy. The lower risk of acute and chronic graft-versus-host disease in patients who received UCB cells seems related to the nature of UCB-T cells. Phenotypically, UCB-CD3+ cells are mostly naive (CD45RA+) and represent a transitional population between thymocytes and adult T cells. We examined the immune reactivity of highly purified, negatively selected CD4+CD45RA+ cells by mimicking activation via T cell receptor (TCR). All experiments included the extensively characterized adult peripheral blood (APB) cells as reference. On the contrary to APB, naive UCB-CD4+ cells were able to proliferate with anti-CD3 stimulation alone. With addition of interleukin (IL)-2 or costimulatory signal, both populations reached similar proliferation. Forty-eight hours after anti-CD3 stimulation, CD4+CD45RA+ from UCB, but not APB, showed characteristic blastic morphology and significant expression of CD25 on the surface. A low concentration of IL-2 was detected at 24 h by anti-CD3-stimulated UCB CD4+CD45RA+, which rapidly disappeared. By 72 h after activation, CD4+CD45RA+ UCB cells showed extensive apoptosis, whereas CD4+CD45RA+ APB cells showed low levels of apoptosis. Using RNase protection assay, we observed that CD95L levels were significantly higher in naive CD4+ cells from UCB than from APB after activation. However, neutralizing Fas-Fc protein was unable to inhibit anti-CD3-induced apoptosis, suggesting that this was a CD95-independent mechanism. These results indicate that UCB-CD4+CD45RA+ cells are able to start proliferating as a result of early IL-2 production after TCR engagement alone, but probably, as a result of the consumption of this IL-2, they undergo cell death.

Interleukin-10 modified dendritic cells induce allo-hyporesponsiveness and prolong small intestine allograft survival

AIM: To investigate whether IL-10-transduced dendritic cells (DCs) could induce tolerogenicity and prolong allograft survival in rat intestinal transplantation.

METHODS: Spleen-derived DCs were prepared and genetically modified by hIL-10 gene. The level of IL-10 expression was quantitated by ELISA. DC function was assessed by MTT in mixed leukocyte reaction. Allogeneic T-cell apoptosis was examined by flow cytometric analysis. Seven days before heterotopic intestinal transplantation, 2 × 10⁶ donor-derived IL-10-DC were injected intravenously, then transplantation was performed between SD donor and Wistar recipient.

RESULTS: Compared with untransduced DC, IL-10-DC could suppress allogeneic mixed leukocyte reaction (MLR). The inhibitory effect was the most striking with the stimulator/effector (S/E) ratio of 1:10. The inhibition rate was 33.25%, 41.19% (P < 0.01) and 22.92% with the S/E ratio of 1:1, 1:10 and 1:50 respectively. At 48 h and 72 h by flow cytometry counting, apoptotic T cells responded to IL-10-DC in MLR were 13.8% and 30.1%, while untransduced group did not undergo significant apoptosis (P < 0.05). IL-10-DC pretreated recipients had a moderate survival prolongation with a mean allograft survival of 19.8 d (P < 0.01), compared with 7.3 ± 2.4 d in control group and 8.3 ± 2.9 d in untransduced DC group. Rejection occurred in the control group within three days. The difference between untreated DC group and control group was not significant.

CONCLUSION: IL-10-DC can induce allogenic T-cell hyporesponsiveness in vitro and apoptosis may be involved in it. IL-10-DC pretreatment can prolong intestinal allograft survival in the recipient.

Ca2+/calcineurin signalling in cells of the immune system

Calcineurin is a serine-threonine - phosphatase that is expressed in a wide variety of tissues and has particularly critical functions in neurons, cardiac and skeletal muscle cells, and lymphocytes. This review focuses on recent studies elucidating the role of Ca(2+)/calcineurin signalling of the immune system.

Analysis of intragraft gene and protein expression of the costimulatory molecules, CD80, CD86 and CD154, in orthotopic liver transplant recipients

CD40-CD154 and/or CD28-CD80/86 costimulatory blockade induces long-term allograft survival in numerous animal models. Studies examining the expression of costimulatory molecules during acute cellular rejection (ACR) have been limited to renal and cardiac allografts. The aim of this study was to describe the relationship between intragraft costimulatory molecule expression in OLT recipients and ACR. Forty-five liver biopsies were obtained at reperfusion and day 7. Gene and protein expression of CD80, CD86 and CD154 were analyzed by RT-PCR and immunohistochemistry. CD154 protein expression was present in 13 of 18 patients with a RAI score of 4, but in only two of 14 patients with a RAI score of <4. There was a strong association between the RAI score and the presence of CD80 and CD154 immunoreactivity. CD86 protein expression did not correlate with the severity of ACR. In reperfusion biopsies CD154, but not CD80 or CD86, protein expression correlated with the total ischaemic time. There was no association between expression of costimulatory molecule genes and ACR. In conclusion, we have demonstrated an association between CD154 and CD80 protein expression and ACR in orthotopic liver allografts.

Induction of antigen-specific regulatory T cells following overexpression of a Notch ligand by human B lymphocytes

In mice, activation of the Notch pathway in T cells by antigen-presenting cells overexpressing Notch ligands favors differentiation of regulatory T lymphocytes responsible for antigen-specific tolerance. To determine whether this mechanism operates in human T cells, we used Epstein-Barr virus-positive lymphoblastoid cell lines (EBV-LCL) as our (viral) antigen-presenting cells and overexpressed the Notch ligand Jagged-1 (EBV-LCL J1) by adenoviral transduction. The EBV-LCL J1s were cocultured with autologous T cells, and the proliferative and cytotoxic responses to EBV antigens were measured. Transduction had no effect on EBV-LCL expression of major histocompatibility complex (MHC) antigens or of costimulatory molecules CD80, CD86, and CD40. However, we observed a 35% inhibition of proliferation and a >65% reduction in cytotoxic-T-cell activity, and interleukin 10 production was increased ninefold. These EBV-LCL J1-stimulated T lymphocytes act as antigen-specific regulatory cells, since their addition to fresh autologous T cells cultured with autologous nontransduced EBV-LCL cells significantly inhibited both proliferation and cytotoxic effector function. Within the inhibitory population, CD4(+)CD25(+) and CD8(+)CD25(-) T cells had the greatest activity. This inhibition appears to be antigen-specific, since responses to Candida and cytomegalovirus antigens were unaffected. Hence, transgenic expression of Jagged-1 by antigen-presenting cells can induce antigen-specific regulatory T cells in humans and modify immune responses to viral antigens.

Anergic T cells exert antigen-independent inhibition of cell-cell interactions via chemokine metabolism

Due to their ability to inhibit antigen-induced T-cell activation in vitro and in vivo, anergic T cells can be considered part of the spectrum of immunoregulatory T lymphocytes. Here we report that both murine and human anergic T cells can impair the ability of parenchymal cells (including endothelial and epithelial cells) to establish cell-cell interactions necessary to sustain leukocyte migration in vitro and tissue infiltration in vivo. The inhibition is reversible and cell-contact dependent but does not require cognate recognition of the parenchymal cells to occur. Instrumental to this effect is the increased cell surface expression and enzymatic activity of molecules such as CD26 (dipeptidyl-peptidase IV), which may act by metabolizing chemoattractants bound to the endothelial/epithelial cell surface. These results describe a previously unknown antigen-independent anti-inflammatory activity by locally generated anergic T cells and define a novel mechanism for the long-known immunoregulatory properties of these cells.

Phenotypic and functional characterization of long-term cultured rhesus macaque spleen-derived NKT cells

Natural killer T cells are immunoregulatory cells, which have important roles in tolerance and autoimmunity, as demonstrated primarily in mice and humans. In this study, we define the phenotype and function of Valpha24(+) T cells derived from the spleens of rhesus macaques, a species increasingly used in models of immune tolerance. Valpha24(+) cells were isolated and expanded with monocyte-derived immature dendritic cells in the presence of alpha-galactosylceramide, IL-2, and IL-15. Rhesus NKT cells were stained with mAbs against both Valpha24 and the invariant complementarity-determining region 3 epitope of the human Valpha24/JalphaQ TCR. The cells were CD4, CD8 double negative and expressed CD56. Rhesus NKT cells also exhibited moderate to high expression of CD95, CD45RO, CD11a, and beta(7) integrin, but did not express CD45 RA, CD62L, CCR7, CD28, and other activation, costimulatory molecules (CD69 and CD40L). By intracellular staining, >90% of unstimulated rhesus NKT cells expressed IL-10, but not IFN-gamma. However, the latter was strongly expressed after stimulation. Rhesus NKT secreted large amounts of TGF-beta, IL-13, and IL-6, and modest levels of IFN-gamma, whereas IL-10 secretion was negligible and no detectable IL-4 was observed either intracellularly or in culture supernatants. Functionally, the NKT cells and their supernatants suppressed T cell proliferation in allogeneic MLR. We conclude that long-term cultured rhesus macaque spleen-derived Valpha24(+) T cells are semi-invariant double-negative cells with effector memory phenotype. These cells are semianergic, polarized to a uniquely Th3 > T regulatory-1 regulatory cell phenotype, and have regulatory/suppressive function in vitro.

T cell anergy

T cell anergy is a tolerance mechanism in which the lymphocyte is intrinsically functionally inactivated following an antigen encounter, but remains alive for an extended period of time in a hyporesponsive state. Models of T cell anergy affecting both CD4(+) and CD8(+) cells fall into two broad categories. One, clonal anergy, is principally a growth arrest state, whereas the other, adaptive tolerance or in vivo anergy, represents a more generalized inhibition of proliferation and effector functions. The former arises from incomplete T cell activation, is mostly observed in previously activated T cells, is maintained by a block in the Ras/MAP kinase pathway, can be reversed by IL-2 or anti-OX40 signaling, and usually does not result in the inhibition of effector functions. The latter is most often initiated in naïve T cells in vivo by stimulation in an environment deficient in costimulation or high in coinhibition. Adaptive tolerance can be induced in the thymus or in the periphery. The cells proliferate and differentiate to varying degrees and then downregulate both functions in the face of persistent antigen. The state involves an early block in tyrosine kinase activation, which predominantly inhibits calcium mobilization, and an independent mechanism that blocks signaling through the IL-2 receptor. Adaptive tolerance reverses in the absence of antigen. Aspects of both of the anergic states are found in regulatory T cells, possibly preventing them from dominating initial immune responses to foreign antigens and shutting down such responses prematurely.

Differential localization and function of ADP-ribosylation factor-6 in anergic human T cells: a potential marker for their identification

Anergy is a state of immunologic tolerance in which T cells are viable but incapable of responding to antigenic stimulation. Recent data indicate that anergic cells have a distinct gene expression program that determines their unique function. In this study we show that anergic human T cells selectively express the small GTPase ADP-ribosylation factor-6 (ARF6), which is involved in membrane traffic and regulation of the cortical actin cytoskeleton. ARF6 was expressed in the GTP-bound form that localizes at the plasma membrane, resulting in a distinct morphologic appearance of anergic cells. Forced expression of ARF6-GTP in Jurkat T cells prevented TCR-mediated reorganization of cortical actin, extracellular signal-regulated kinase1/2 activation, and IL-2 transcription. Forced expression of ARF6-GTP in primary human T cells inhibited extracellular signal-regulated kinase1/2 activation and proliferative responses. Importantly, T cells with the distribution pattern of ARF6-GTP were detected in peripheral blood, suggesting that anergic T cells may constitutively exist in vivo.

Regulation of polyclonal T cell responses by an MHC anchor-substituted variant of myelin oligodendrocyte glycoprotein 35-55

Analogs of immunogenic peptides containing substitutions at TCR contact residues (altered peptide ligands (APLs)) have been used to manipulate Ag-specific T cell responses in models of autoimmunity, including experimental autoimmune encephalomyelitis. However, recent clinical trials with APL of a myelin basic protein epitope revealed limitations of this therapy. In this study, we demonstrate that individual myelin oligodendrocyte glycoprotein (MOG) 35-55-specific T cell clones responded differentially to a MOG 35-55 APL, raising questions about the ability of peptide analogs containing amino acid substitutions at TCR contact residues to control polyclonal populations of T cells. In contrast, we found that a variant peptide containing a substitution at an MHC anchor residue uniformly affected multiple MOG 35-55-specific clones and polyclonal lines. Stimulation of polyclonal MOG 35-55-specific T cells with an MHC variant peptide resulted in the induction of anergy, as defined by a dramatic reduction in proliferation and IL-2 production upon challenge with wild-type peptide. Furthermore, treatment of T cell lines with this peptide in vitro resulted in a significant reduction in their encephalitogenicity upon adoptive transfer. These results indicate that the use of MHC anchor-substituted peptides may be efficacious in the regulation of polyclonal T cell responses such as those found in EAE.

A complicated relationship: fulfilling the interactive needs of the T lymphocyte and the dendritic cell

T cells recognize antigenic peptides displayed on the surface of MHC-bearing antigen-presenting cells (APCs), and with sufficient costimulation become activated. However, the ability of an APC (even bearing the correct peptide) to initiate and fulfill the requirements for T cell activation is not easily achieved. Naive T cells use multiple copies of a single receptor to survey the vast array of peptides presented on an APC, and require multiple receptor engagements to initiate T cell activation. Dendritic cells (DCs) are specialized cells with optimal capabilities for priming naive CD4+ T cells. Activation occurs, after initial antigen recognition by T cells, followed by a rapid dialogue between the T cells and the DCs. The resulting changes in both the cytoskeleton and the expression or regulation of cell-surface molecules on both cell types act to further strengthen engagement. In this report, we review the fundamentals of CD4+ T helper cell : DC interactions and discuss recent data concerning the molecular characteristics of this engagement.

Donor-specific tolerance in a murine model: the result of extra-thymic T cell deletion?

Previously, we established a murine model, that involves the engraftment of fully allogeneic T cell depleted donor bone marrow cells in sublethally irradiated and single dose anti-CD3 treated recipient mice. These mice developed permanent stable multilineage mixed chimerism and donor-specific tolerance without graft-versus-host disease. Recently, we have shown that donor-specific tolerance is not induced and/or maintained by clonal anergy, neither by a Th1/Th2 shift, nor by suppressor or other regulatory processes. In the present study, we investigated whether clonal deletion plays a role in tolerance induction in our model. We studied the kinetics of TCRVbeta8(+) T cells in BALB/c (H-2L(d+))-->dm2 (H-2L(d-)) chimeras, in which combination of mouse strains TCRVbeta8 predominates the anti-donor response. We found that TCRVbeta8(+) T cells were specifically deleted. To our surprise, this deletion was also found in mixed chimeras, thymectomized prior to the conditioning regimen. We conclude that clonal deletion plays a role in the establishment and maintenance of donor-specific tolerance, and that the thymus is not required for this process. In addition, confocal laser-scanning microscopy clearly showed the presence of abundant amounts of donor T cells and some donor antigen presenting cells in the small intestine in thymectomized chimeras and not in other organs, suggesting that T cell selection might take place in this organ in the absence of the thymus.

B cells activated by lipopolysaccharide, but not by anti-Ig and anti-CD40 antibody, induce anergy in CD8+ T cells: role of TGF-beta 1

B cells recognize Ag through their surface IgRs and present it in the context of MHC class II molecules to CD4(+) T cells. Recent evidence indicates that B cells also present exogenous Ags in the context of MHC class I to CD8(+) T cells and thus may play an important role in the modulation of CTL responses. However, in this regard, conflicting reports are available. One group of studies suggests that the interaction between B cells and CD8(+) T cells leads to the activation of the T cells, whereas other studies propose that it induces T cell tolerance. For discerning this dichotomy, we used B cells that were activated with either LPS or anti-Ig plus anti-CD40 Ab, which mimic the T-independent and T-dependent modes of B cell activation, respectively, to provide accessory signals to resting CD8(+) T cells. Our results show that, in comparison with anti-Ig plus anti-CD40 Ab-activated B cells, the LPS-activated B cells (LPS-B) failed to induce significant levels of proliferation, cytokine secretion, and cytotoxic ability of CD8(+) T cells. This hyporesponsiveness of CD8(+) T cells activated with LPS-B was significantly rescued by anti-TGF-beta1 Ab. Moreover, it was found that such hyporesponsive CD8(+) T cells activated with LPS-B had entered a state of anergy. Furthermore, LPS-B expresses a significantly higher level of TGF-beta1 on the surface, which caused the observed hyporesponsiveness of CD8(+) T cells. Therefore, this study, for the first time, provides a novel mechanism of B cell surface TGF-beta1-mediated hyporesponsiveness leading to anergy of CD8(+) T cells.

Ligation of OX40 (CD134) regulates graft-versus-host disease (GVHD) and graft rejection in allogeneic bone marrow transplant recipients

OX40 (CD134) is expressed on activated T cells; its ligand, OX40 ligand (OX40L) is expressed on dendritic cells, B cells, and activated endothelial cells. To determine how OX40-OX40L interaction affects graft-versus-host disease (GVHD), we used antagonistic anti-OX40L monoclonal antibody (mAb) or OX40(-/-) donor or OX40L(-/-) recipient mice. Similar degrees of GVHD reduction were observed with each approach. Despite the fact that OX40 is up-regulated on both CD4(+) and CD8(+) T cells isolated during GVHD, the major effects of OX40 ligation were on CD4(+) and not CD8(+) T-cell-mediated alloresponses as assessed in both GVHD and engraftment model systems. GVHD inhibition by blockade of the OX40/OX40L pathway did not require CD28 signaling. Some studies have indicated OX40 is essential for inducing T-helper type 2 (Th2) responses. However, in vivo blockade of OX40-OX40L interactions reduced GVHD mortality induced by either signal transducer and activator of transcription-6(-/-) (Stat-6(-/-)) (Th2-defective) or Stat-4(-/-) (Th1-defective) major histocompatibility complex (MHC)-disparate splenocytes, indicating that the GVHD-ameliorating effects did not require Stat-4 or Stat-6 signaling. Although OX40L has been reported to be expressed on activated T cells, no effects on GVHD were observed when OX40L(-/-) versus OX40L(+/+) T cells were infused in different models. These data provide insights as to the mechanisms responsible for OX40/OX40L regulation of GVHD.

Apoptotic cell death in conjunction with CD80 costimulation confers uveal melanoma cells with the ability to induce immune responses

Uveal melanoma is a rare malignancy with a poor prognosis despite current therapeutic intervention. The current investigation focuses on the immunogenicity of uveal melanoma cells genetically modified with recombinant adenovirus encoding CD80 (AdCD80) in contrast to their parental counterpart. We demonstrate that costimulation provided by uveal melanoma cells improved immune responses in vitro as determined by mixed lymphocyte tumour cell cultures and cytotoxic T-cell assays using lymphocytes from healthy donors and uveal melanoma patients. Flow cytometry revealed T-cell stimulation by activated CD4+ and CD8+ T cells. Additionally, autologous lymphocytes proliferated in response to CD80-expressing primary uveal melanomas, indicating that this patient group is suitable for immunotherapy. Moreover, this study utilized AdCD80 modified and parental apoptotic tumour cells, loaded onto immature dendritic cells, as a source of tumour antigen. The ability of live or apoptotic tumour cells to stimulate lymphocyte proliferation and activation was determined. Apoptotic uveal melanoma cells expressing CD80 were efficient at inducing an immune response and served as a potent immunogen. The use of apoptotic uveal melanoma cells in combination with expression of costimulatory molecules could prove a novel adjuvant therapy for the treatment of this disease.

Immune function in patients with acute pancreatitis

BACKGROUND

The aim of this study was to clarify the relationship between the balance of T-helper (Th)1 and Th2 cytokines, and the numbers of CD4+ T and CD8+ T-cells, and was investigated, together with the plasma concentration of the antigen, an apoptosis marker, in patients with mild and acute pancreatitis (AP).

METHODS

Plasma concentrations of soluble (s) CD4, sCD8, sIL-2-R, IL-12, IFN-gamma and sFas antigen were measured by ELISA, and CD4+ T, and CD8+ T lymphocyte counts were measured by flow cytometry.

RESULTS

Both CD4+ T and CD8+ T-cells were reduced in number; in the severe cases the reduction in the former was more pronounced. A significant positive correlation was noted among the concentrations of sCD4, sIL-2-R and IL-12, and a significant positive correlation was also found between sCD4 and sFas. During the early stage of AP, the concentrations of sCD4, sCD8, sIL-2-R, IL-12 and IFN-gamma increased more in the severe cases compared with those who had milder symptoms; however, these increases were moderated during the clinical course.

CONCLUSION

We considered that these Th1 type CD4+ T cells probably induce the activation of macrophages and further pro-inflammatory reactions during the early stage of AP, as well as exerting direct cytotoxicity effects through Fas/Fas ligand expression.