The role of anergy in peripheral T cell unresponsiveness

Contribution of MicroRNAs to autoimmune diseases

MicroRNAs are a class of evolutionarily conserved, short non-coding RNAs that post-transcriptionally modulate the expression of multiple target genes. They are implicated in almost every biological process, including pathways involved in immune homeostasis, such as immune cell development, central and peripheral tolerance, and T helper cell differentiation. Alterations in miRNA expression and function can lead to major dysfunction of the immune system and mediate susceptibility to autoimmune disease. Here, we discuss the role of miRNAs in the maintenance of immune tolerance to self-antigens and the gain or loss of miRNA functions on tissue inflammation and autoimmunity.

Ndrg1 is a T-cell clonal anergy factor negatively regulated by CD28 costimulation and interleukin-2

Induction of T-cell clonal anergy involves serial activation of transcription factors, including NFAT and Egr2/3. However, downstream effector mechanisms of these transcription factors are not fully understood yet. Here we identify Ndrg1 as an anergy factor induced by Egr2. Ndrg1 is upregulated by anergic signalling and maintained at high levels in resting anergic T cells. Overexpression of Ndrg1 mimics the anergic state and knockout of the gene prevents anergy induction. Interestingly, Ndrg1 is phosphorylated and degraded by CD28 signalling in a proteasome-dependent manner, explaining the costimulation dependence of anergy prevention. Similarly, IL-2 treatment of anergic T cells, under conditions that lead to the reversal of anergy, also induces Ndrg1 phosphorylation and degradation. Finally, older Ndrg1-deficient mice show T-cell hyperresponsiveness and Ndrg1-deficient T cells aggravate inducible autoimmune inflammation. Thus, Ndrg1 contributes to the maintenance of clonal anergy and inhibition of T-cell-mediated inflammation.

Long-term interleukin-10 presence induces the development of a novel, monocyte-derived cell type

Interleukin (IL)-10 is one of the most crucial immunoregulatory cytokines. Its short-term effects have been analysed extensively, but little is known about its long-term effects. This is of considerable importance, as high systemic IL-10 levels are present for long periods in patients with persistent viral infections, certain cancers and in critical care patients. Our study investigated the effects of the long-term presence of IL-10 on human peripheral blood monocytes. In vitro, IL-10 treatment of these cells for 7 days induced the development of a novel cell type characterized by unique phenotypical and functional characteristics. These cells showed high HLA-DR expression and low expression of CD86 and other co-stimulatory molecules on their surface. The mRNA levels of both HLA-DR and CD86 were high, but no intracellular accumulation of CD86 protein was observed. With respect to its function, these cells showed strongly diminished tumour necrosis factor-alpha production following lipopolysaccharide stimulation, strongly diminished allogenic CD4(+) T cell stimulatory capacity, and even induced a hyporesponsive state in CD4(+) T cells. The phenotype remained stable despite the removal of IL-10. In vivo, we found monocytic cells from patients exhibiting this phenotype after long-term IL-10 exposure. These results complement our knowledge further about the biological effects of IL-10 and may provide an explanation for the sustained immunodeficiency in cases of the persistent presence of systemic IL-10.

Therapeutic use of Aldara in chronic myeloid leukemia

The potent clinical responses seen in patients with chronic myeloid leukemia (CML) after administration of donor-specific lymphocytes, as well as the correlation between the presence of antigen specific T cells and prolonged remission in these patients, suggests a role for the immunological control of CML. Here we propose Aldara™, a clinically used formulation of imiquimod, as an agent for augmenting immune responses to CML antigens. Our proposition is based upon 3 tenets: 1) Endogenous dendritic cells (DC) of CML patients, which are known to be derived from the malignant clone, express and present various leukemic antigens; 2) CML-antigen reactive T cell clones exist in the patient but in many situations are ineffectively stimulated to cause significant hematological responses; and 3) Antigen presentation by mature, activated DC, which endogenously express CML-antigens may endow the pre-existing ineffective T cell responses with ability to control CML progression. The practical use of Aldara™ as a localized activator of DC in the context of present day leukemic therapeutics, as well as various properties of this unique immune modulator will be discussed.

Plasmodium chabaudi adami: use of the B-cell-deficient mouse to define possible mechanisms modulating parasitemia of chronic malaria

Our previous observation that B-cell-deficient JH-/- mice utilize T cell-dependent immunity to suppress acute Plasmodium chabaudi adami-induced malaria but then develop chronic low-level parasitemia prompted this study of control mechanisms for chronic parasitemia. When we infected JH-/- mice with blood-stage parasites, chronic parasitemia exacerbated after the 6th month and persisted for up to 17 months. This exacerbation of parasitemia could not be attributed to host aging because the time-course of acute infection in naïve aged mice was nearly identical to that seen in young mice. Nor could exacerbated parasitemia be attributed to mutation in the parasite genome resulting in increased virulence; when subinoculated into naïve JH-/- mice, parasites from chronically infected JH-/- mice with exacerbated parasitemia produced acute stage parasitemia profiles in most recipients comparable to those seen in JH-/- mice upon infection with the original stabilate material. Of the pro-inflammatory cytokines measured, including IFNgamma, TNFalpha, IL-12p70, and MCP-1beta, none were significantly different in the sera of mice with exacerbated parasitemia compared to uninfected controls. Levels of IL-6 were significantly (P=0.002) less in the sera of mice with exacerbated parasitemia. Serum levels of the anti-inflammatory cytokine, TGFbeta, were significantly depressed in chronically infected JH-/- mice compared to uninfected controls. In contrast, IL-10 levels were markedly increased. These findings suggest that the cytokine balance may be disturbed during chronic malaria, thereby impacting on mechanisms that modulate levels of parasitemia.

Barbiturates Directly Inhibit the Calmodulin/Calcineurin Complex: a Novel Mechanism of Inhibition of Nuclear Factor of Activated T Cells

Barbiturates are frequently used for the treatment of intracranial hypertension after brain injury but their application is associated with a profound increase in the infection rate. The mechanism of barbiturate-induced failure of protective immunity is still unknown. We provide evidence that nuclear factor of activated T cells (NFAT), an essential transcription factor in T cell activation, is a target of barbiturate-mediated immunosuppression in human T lymphocytes. Treatment of primary CD3+ lymphocytes with barbiturates inhibited the PMA and ionomycin induced increase in DNA binding of NFAT, whereas the activity of other transcription factors, such as Oct-1, SP-1, or the cAMP response element-binding protein, remained unaffected. Moreover, barbiturates suppressed the expression of a luciferase reporter gene under control of NFAT (stably transfected Jurkat T cells), and of the cytokine genes interleukin-2 and interferon-gamma that contain functional binding motifs for NFAT within their regulatory promotor domains (human peripheral blood CD3+ lymphocytes). Neither GABA receptor-initiated signaling nor direct interactions of barbiturates with nuclear proteins affected the activity of NFAT. In contrast, barbiturates suppressed the calcineurin-dependent dephosphorylation of NFAT in intact T cells and also inhibited the enzymatic activity of calcineurin in a cell-free system, excluding upstream regulation. Thus, our results demonstrate a novel mechanism of direct inhibition of the calcineurin/calmodulin complex that may explain some of the known immunosuppressive effects associated with barbiturate treatment.

Inflammatory cytokines and antigen presenting cell activation

Immune responses are stimulated in response to threats against health. In animals, defense against infectious agents, particularly rapidly growing viruses and bacteria, requires an immediate response to limit growth and dissemination, and then stimulation of a more prolonged, specific immunity to prevent re-infection. The process by which animals meet the dual needs of an immediate response to danger and initiation of long-term protection is substantially influenced by inflammatory cytokines produced primarily by macrophages and professional antigen presenting cells (APCs). Inflammatory cytokines mobilize the immune system in response to danger and increase the efficiency of an immune response as effectors of APC function. Here we review the evidence for the involvement of inflammatory cytokines in immune induction and as mediators of APC activity, with a particular emphasis on swine and on the induction of immunity at mucosal surfaces. The vast majority of infections occur at mucosal surfaces of the enteric, respiratory and reproductive tracts, and induction of protective immunity at these sites is particularly challenging. Induction of immunity at mucosal surfaces of the small intestine is greatly facilitated by the oral adjuvant, cholera toxin (CT). CT potentiates inflammatory cytokine and costimulatory molecule expression in macrophages, and stimulates humoral and cell-mediated immune responses both locally and systemically. These observations are consistent with the hypothesis that activation of APCs is a key step in the induction of antigen-specific immunity, and that inflammatory cytokine expression is a hallmark of activated APC function. The efficacy of vaccine adjuvants, particularly in the context of mucosal immunity, may be determined by their ability to induce a controlled inflammatory response in gut-associated lymphoid tissue, characterized by the expression of various costimulatory molecules and inflammatory cytokines. Thus, elucidation of the patterns of inflammatory cytokine expression and features of APC activation will help to facilitate the rational development of more efficacious vaccines.

CD4+ T cells specific for factor VIII as a target for specific suppression of inhibitor production

The studies we reviewed here have begun to clarify the complex cellular mechanisms involved in the immune response to fVIII, and the circumstances under which fVIII inhibitors develop. Further characterization and comparison of the immune response to fVIII in both hemophilia patients and healthy subjects will help to further elucidate these mechanisms. The murine hemophilia model will hopefully provide further insights into the mechanisms of inhibitor formation, and prove to be a suitable tool for the design and testing of therapeutic strategies aimed at preventing the development of fVIII inhibitors.

Myelin-specific tolerance attenuates the progression of a virus-induced demyelinating disease: implications for the treatment of MS

Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a multiple sclerosis (MS) model, is a central nervous system (CNS) demyelinating disease characterized by early peripheral T cell responses to virus epitopes which spreads to myelin epitopes during chronic disease. We show that CD4(+) T cells isolated from the spinal cords of chronically infected SJL mice proliferate and secrete pro-inflammatory cytokines upon in vitro challenge with both TMEV epitopes and proteolipid protein (PLP(139-151)). Importantly, myelin-specific tolerance induced by intravenous administration of MP4, a fusion of the myelin proteins myelin basic protein (MBP) and PLP, to SJL mice with ongoing TMEV-IDD attenuated disease progression and resulted in significantly less demyelination and decreased inflammatory cell infiltration in the CNS. Paradoxically, peptide-specific splenic T cell proliferative and IFN-gamma responses were enhanced in the tolerized mice. Collectively, these results indicate that myelin-specific T cell responses contribute to chronic disease progression in this virus-induced model of MS, and suggest caution in the use of antigen-specific tolerance for treatment of ongoing autoimmune disease.

Lack of CD80 expression by fibroblast-like synoviocytes leading to anergy in T lymphocytes

OBJECTIVE

To investigate whether contact with HLA-DR+, but CD80-, fibroblast-like synoviocytes (FLS) in the presence of antigen leads to the induction of anergy in, rather than stimulation of, T cells.

METHODS

Cell surface expression of activation and costimulatory markers on FLS were studied by flow cytometry. Functional changes were investigated by T cell proliferation to tuberculin purified protein derivative or allogeneic responses to FLS, in the presence or absence of DAP3.B7 cells, a human CD80-transfected mouse fibroblast cell line. Induction of anergy was investigated by a 2-stage culture system. T cells were cocultured with allogeneic FLS in the primary culture, rested, and restimulated in the secondary culture by FLS in the presence or absence of DAP3.B7 cells or interleukin-2 (IL-2).

RESULTS

Direct contact between T cells and FLS caused up-regulation of CD69 on T cells and HLA-DR on FLS in both the allogeneic and autologous cultures. The addition of DAP3.B7 cells to FLS-T cell cocultures restored the depressed allogeneic responses of T cells. The allogeneic response by T cells to FLS in the presence of DAP3.B7 cells could be completely inhibited by blocking CD80 with CTLA-4 Ig. Indirect evidence that T cells cocultured with FLS were anergic was the up-regulation of CD25, negligible T cell proliferation, and the restoration of proliferation by the addition of exogenous IL-2. Direct evidence of anergy was obtained when T cells from the primary cultures with FLS remained unresponsive to secondary culture with FLS even in the presence of DAP3.B7 cells. In contrast, primary culture of T cells with FLS plus DAP3.B7 cells initiated a good allogeneic response in all subsequent cultures.

CONCLUSION

It is possible that T cells within the synovium may be anergized by contact with HLA-DR+ CD80- FLS.

Mechanisms of vaccine adjuvanticity at mucosal surfaces

The vast majority of pathogens invade via mucosal surfaces, including those of the intestine. Vaccination directly on these surfaces may induce local protective immunity and prevent infection and disease. Although vaccine delivery to the gut mucosa is fraught with obstacles, immunization can be enhanced using adjuvants with properties specific to intestinal immunity. In this review, we present three general mechanisms of vaccine adjuvant function as originally described by Freund, and we discuss these principles with respect to intestinal adjuvants in general and to the prototypical mucosal adjuvant, cholera toxin. The key property of intestinal adjuvants is to induce an immunogenic context for the presentation of the vaccine antigen. The success of oral vaccine adjuvants is determined by their ability to induce a controlled inflammatory response in the gut-associated lymphoid tissues, characterized by the expression of various costimulatory molecules and cytokines. An understanding of the specific molecular mechanisms of adjuvanticity in the gut will allow the rational development of safe and effective oral vaccines.

Lymph node metastases: the importance of the microenvironment

BACKGROUND

Although, to the authors' knowledge, no prospective randomized clinical trial has demonstrated improvement in survival following the radical dissection of lymph nodes in the treatment of cancer patients, lymphadenectomy is still routinely performed for curative purposes. For many years, regional lymph nodes (RLNs) in tumor-bearing hosts have been considered anatomic barriers to the systematic dissemination of tumor cells. More recently, the belief has been held that lymph nodes play a completely passive role, by virtue of the observations that many lymphatic and lymphaticovenous shunts bypass RLNs and allow both lymphatic and hematogenous dissemination of malignant cells at an early stage in the vast majority of cancers. Furthermore, surgical removal of RLNs apparently has no effect, deleterious or beneficial, on the well-being of the host.

METHODS

A comprehensive and critical review of the scientific literature was conducted to evaluate, from a biologic point of view, the role played by RLNs during the interactions between the tumor and the host's immune system.

RESULTS

Recent advances in our understanding of the molecular events of antigen recognition by T cells and T-cell activation have provided strong experimental evidence to demonstrate that these secondary lymphoid organs constitute the primary sites where the specific recognition of tumor antigens and the proper activation of the immune system take place. Indeed, the notion that naive T cells are induced or silenced by tumor cells in the periphery may today be questioned, because effective induction can only occur in these secondary lymphoid organs where cell-to-cell interactions are properly guided and cells can meet in an appropriate cytokine-enriched microenvironment.

CONCLUSIONS

Promising results obtained in the human setting with the use of dendritic cells as novel immunotherapeutic tools have recently renewed interest in active immunotherapy for the treatment of solid tumors. However, for accomplishing this goal, the maintenance of the integrity of the immune system remains a crucial issue. Studies showing that radical tumor-draining RLN dissections exert a markedly negative influence on the efficacy of postoperative immunotherapy protocols in mice as well as in humans seem to support adoption of a more conservative approach regarding uninvolved RLNs in the treatment of cancer patients.

T-cell anergy induced by clonotype-specific antibodies: modulation of an autoreactive human T-cell clone in vitro

Monoclonal antibodies (mAb) specific for the clonotype of an autoreactive T cell may be useful reagents in the modulation of autoimmune disease. We have previously reported the generation of a set of mAb specific for the clonotypic structure of a human T-cell clone recognizing an epitope of human cartilage gp-39. This glycoprotein was recently identified as a candidate autoantigen in rheumatoid arthritis. Here, we demonstrate for the first time that small amounts of immobilized anticlonotype mAb can induce anergy in the autoreactive clone. Following the anergic stimulus, T cells failed to proliferate upon restimulation as a result of a lack of interleukin-2 (IL-2) gene transcription. In addition, a diminished interferon-gamma (IFN-gamma) production was found. Our data indicate that anergy was not a result of T-cell receptor (TCR) downmodulation or the absence of free TCR. The anergic state was induced independent of costimulation or the presence of IL-2 and no protein synthesis was required for the induction of anergy. Anticlonotype mAb-induced anergy was prevented by cyclosporin A, suggesting that active signalling via the calcium/calcineurin pathway was required for the induction of anergy. In coculture experiments, anergic T cells were found to suppress the response of reactive cells from the same clone. This bystander suppression led to 90% inhibition of peptide-induced proliferation. Together, these findings suggest that mAb to the clonotypic structure of autoreactive T cells may be suitable reagents for the functional inactivation of these T cells in autoimmune diseases.

Role of macrophage cytokines in mucosal adjuvanticity

Delivery of protein antigens to the GALT can result in immunity or oral tolerance depending on the circumstances of the encounter. One mechanism by which mucosal adjuvants can affect these circumstances is by the induction of macrophage cytokines, including IL-1 and IL-12. These cytokines can directly affect the immune response by their effects on antigen-specific T cells and by the induction of IFN-gamma by T cells or NK cells. This IFN-gamma also activates macrophages to up-regulate MHC or costimulatory molecules and by further inducing IL-1 and IL-12. In effect, mucosal adjuvants function both directly and indirectly as activators of antigen presenting cells, resulting in stimulation of the immune response to coincidental antigens. Our studies in swine have shown CT is a potent mucosal adjuvant for CT-B. CT also increased IL-1 and IL-12 mRNA in cultured macrophages, especially after activation with IFN-gamma. The effect of CT on the secretion of bioactive IL-12 protein is currently being investigated. While the mucosal adjuvanticity of CT involves a variety of mechanisms, these findings suggest a role for the induction of the macrophage cytokines IL-1 and IL-12.

Viral immune evasion due to persistence of activated T cells without effector function

We examined the regulation of virus-specific CD8 T cell responses during chronic lymphocytic choriomeningitis virus (LCMV) infection of mice. Our study shows that within the same persistently infected host, different mechanisms can operate to silence antiviral T cell responses; CD8 T cells specific to one dominant viral epitope were deleted, whereas CD8 T cells responding to another dominant epitope persisted indefinitely. These virus-specific CD8 T cells expressed activation markers (CD69(hi), CD44(hi), CD62Llo) and proliferated in vivo but were unable to elaborate any antiviral effector functions. This unresponsive phenotype was more pronounced under conditions of CD4 T cell deficiency, highlighting the importance of CD8- CD4 T cell collaboration in controlling persistent infections. Importantly, in the presence of CD4 T cell help, adequate CD8 effector activity was maintained and the chronic viral infection eventually resolved. The persistence of activated virus-specific CD8 T cells without effector function reveals a novel mechanism for silencing antiviral immune responses and also offers new possibilities for enhancing CD8 T cell immunity in chronically infected hosts.

Viral immune evasion due to persistence of activated T cells without effector function

We examined the regulation of virus-specific CD8 T cell responses during chronic lymphocytic choriomeningitis virus (LCMV) infection of mice. Our study shows that within the same persistently infected host, different mechanisms can operate to silence antiviral T cell responses; CD8 T cells specific to one dominant viral epitope were deleted, whereas CD8 T cells responding to another dominant epitope persisted indefinitely. These virus-specific CD8 T cells expressed activation markers (CD69(hi), CD44(hi), CD62Llo) and proliferated in vivo but were unable to elaborate any antiviral effector functions. This unresponsive phenotype was more pronounced under conditions of CD4 T cell deficiency, highlighting the importance of CD8- CD4 T cell collaboration in controlling persistent infections. Importantly, in the presence of CD4 T cell help, adequate CD8 effector activity was maintained and the chronic viral infection eventually resolved. The persistence of activated virus-specific CD8 T cells without effector function reveals a novel mechanism for silencing antiviral immune responses and also offers new possibilities for enhancing CD8 T cell immunity in chronically infected hosts.

T:T Antigen Presentation by Activated Murine CD8+ T Cells Induces Anergy and Apoptosis

Using an IL-2-secreting, noncytolytic, H-Y-specific, CD8+ T cell clone, the functional consequences of Ag presentation by T cells to T cells were investigated. Incubation of the T cells with H-Y-soluble peptide led to nonresponsiveness to Ag rechallenge. This was due to the simultaneous induction of apoptosis, involving approximately 40% of the T cells, and of anergy in the surviving cells. These effects were strictly dependent upon bidirectional T:T presentation, in that exposure of C6 cells to peptide-pulsed T cells from the same clone induced proliferation but not apoptosis or anergy. The inhibitory effects of T:T presentation were not due to a lack of costimulation, since the T cells expressed levels of CD80 and CD86 higher than those detected on cultured dendritic cells and equipped them to function as efficient APCs for primary CD8+ T cell responses. Following incubation with soluble peptide, CD80 expression increased, and high levels of CTLA-4 (CD152) expression were induced. Although addition of anti-CTLA-4 Ab augmented proliferation in response to soluble peptide, no protection from apoptosis or anergy was observed. Neither Fas nor TNF-α was expressed/produced by the C6 cells, and coligation of MHC class I molecules and TCR failed to reproduce the effects of T:T presentation. Taken together, these data suggest that T:T Ag presentation induces anergy and apoptosis in murine CD8+ T cells and may reflect the regulatory consequences of T:T interactions in the course of clonal expansion in vivo.

The role of dendritic cells in T cell activation

Dendritic cells (DC) are distinguishable from other antigen-presenting cells by their potent antigen-presenting capacity. They are not only efficient at presenting peptide antigen but can also process and present soluble protein antigen sto antigen-specific T cells and cloned T cell lines. They are very strong stimulators of both allogeneic and syngeneic mixed lymphocyte reactions and have a unique capacity to stimulate naive T cells. The potent functional capacity of DC is related to a high-level expression of major histocompatibility complex class I/II molecules and constitutive expression of costimulatory molecules, such as CD80/CD86, as well as heat stable antigen, CD40 and the leucocyte function antigen (LFA) family of adhesion molecules. Recent studies have shown that DC are also involved in regulation of the immune response via induction of both central and peripheral tolerance.

Anergic TH1 clones specific for hepatitis B virus (HBV) core peptides are inhibitory to other HBV core-specific CD4+ T cells in vitro

A strong and transient hepatitis B virus core (HBc)-specific CD4+ T-cell response has been shown to be associated with viral elimination in acute self-limited hepatitis B but to be absent in chronic hepatitis B. So far, little is known about immunological mechanisms involved in the regulation of the HBc-specific CD4+ T-cell response. We studied 28 patients with acute hepatitis B, and frequently a sudden decrease in the HBc-specific CD4+ T-cell response was found between 4 and 8 weeks after disease onset. Thirty-two CD4+ T-cell clones specific for amino acids 50 to 69, 81 to 105, 117 to 131, or 141 to 165 of HBc were isolated from a patient shortly before the peripheral blood mononuclear cell response to most HBc-derived peptides abruptly disappeared. TH1 clones, but not TH0 clones, could be anergized in vitro by stimulation with specific peptides even in the presence of costimulatory cells. Moreover, when anergic cells were mixed with responsive cells, the proliferation of HBc-specific TH1 or TH0 clones was inhibited antigen specifically by anergic cells. The unusual susceptibility of HBc-specific TH1 clones to anergy induction in vitro as well as their potential to inhibit other HBc-specific TH1 and TH0 clones suggests that anergy induction may be involved in the downregulation of the virus-specific immune response during acute hepatitis B in vivo.

Immune deviation of 2C transgenic intraepithelial lymphocytes in antigen-bearing hosts

The present study examined self-tolerance for T cell receptor (TCR) alpha beta intestinal intraepithelial lymphocytes (iIELs) using the 2C transgenic (Tg) mouse model specific for a peptide antigen (Ag) presented by the class I major histocompatibility complex H-2Ld. Although Tg+ T cells were largely deleted from the periphery of Ag+ mice, equivalent numbers of Tg iIELs were present in Ag+ compared to Ag- mice. Tg iIELs in Ag- mice contained CD8 alpha beta, CD8 alpha alpha, and CD4-CD8- subsets, whereas only CD8 alpha alpha and CD4-CD8- Tg iIEL subsets were detected in Ag+ mice. Analysis of surface markers revealed that Tg iIELs in Ag+ mice expressed decreased levels of Thy-1 and increased CD45R/B220 as compared to Ag- Tg iIELs. In response to activation with exogenous peptide or immobilized anti-TCR mAB, iIELs from Ag- mice proliferated at high levels and produced interleukin (IL)-2 and interferon (IFN)-gamma, while Tg+ iIELs from Ag+ mice proliferated at low levels and failed to produce detectable IL-2 or IFN-gamma. Activation of sorted iIEL subsets from Ag- mice revealed that CD8 alpha alpha and CD4-CD8- subsets produced low levels of IL-2 and IFN-gamma in response to activation with antigen-presenting cells and added peptide or immobilized anti-TCR mAb, while CD8 alpha beta + iIELs responded to endogenous levels of peptide. In response to APC and exogenous peptide, sorted iIEL subsets from Ag+ mice produced IL-2 and IFN-gamma, and proliferated at greatly reduced levels compared to corresponding subsets from Ag- mice. Analysis of cytokine mRNA levels revealed that activation in vitro induced IL-2 mRNA only in Ag-, but not Ag+ iIELs, whereas a high level of IL-4 mRNA induction was detected in Tg+ iIELs from Ag+ mice, and to a lesser degree, from Ag- mice. These data suggest that tolerance for Tg+ iIELs resulted in the deletion of CD8 alpha beta + subsets and the persistence of Tg+ iIEL subsets with decreased sensitivity to endogenous levels of self-peptide. A comparison of the cytokine profiles expressed by Tg+ iIEL subsets in Ag- and Ag+ mice suggested that tolerance induction had involved the functional deviation of cells from TC1 (T helper-1-like) to a less inflammatory TC2 (T helper-2-like) phenotype capable of mediating humoral immune responses in the mucosa.

Autoreactive T cells in healthy individuals show tolerance in vitro with characteristics similar to but distinct from clonal anergy

Peripheral tolerance to self antigens has been suspected to play an important role in the regulation of the immune response in humans since autoreactive T cells can be isolated from the peripheral blood of healthy individuals. The mechanism of this tolerance is not known, but a number of groups have shown that autoreactive T cells can be induced to proliferate in vitro by the addition of their specific antigen and exogenous interleukin (IL)-2. In this report, we present the analysis of autoreactive T cells, isolated from healthy individuals, to the autoantigen GpIIb-IIIa present on circulating bone-marrow-derived cells and on thymic epithelial cells. We found that the response of GpIIb-IIIa autoreactive T cells in vitro, when stimulated with GpIIb-IIIa, shares characteristics with the response found for anergic T cells. In response to GpIIb-IIIa, the GpIIb-IIIa-autoreactive T cells are neither able to proliferate nor produce IL-2 on their own, but do express IL-2 receptors alpha on their cell surface and produce IFN-gamma. This state of unresponsiveness can be broken by the addition of exogenous IL-2 and IL-7, as in the case of anergic T cells. However, GpIIb-IIIa-autoreactive T cells differ from anergic T cells in their capacity to be stimulated by IL-12 and by their production of IL-2 mRNA. Interestingly, once the unresponsive state to GpIIb-IIIa has been broken by the addition of IL-2, GpIIb-IIIa autoreactive T cells can produce IL-2 and proliferate when restimulated by GpIIb-IIIa alone. Altogether, these results suggest that the tolerance of GpIIb-IIIa autoreactive T cells from healthy individuals could involve post-transcriptional regulation of IL-2 expression.