Induction of specific clonal anergy in human T lymphocytes by Staphylococcus aureus enterotoxins

Blocking Superantigen-Mediated Diseases: Challenges and Future Trends

Superantigens are virulence factors secreted by microorganisms that can cause various immune diseases, such as overactivating the immune system, resulting in cytokine storms, rheumatoid arthritis, and multiple sclerosis. Some studies have demonstrated that superantigens do not require intracellular processing and instated bind as intact proteins to the antigen-binding groove of major histocompatibility complex II on antigen-presenting cells, resulting in the activation of T cells with different T-cell receptor Vβ and subsequent overstimulation. To combat superantigen-mediated diseases, researchers have employed different approaches, such as antibodies and simulated peptides. However, due to the complex nature of superantigens, these approaches have not been entirely successful in achieving optimal therapeutic outcomes. CD28 interacts with members of the B7 molecule family to activate T cells. Its mimicking peptide has been suggested as a potential candidate to block superantigens, but it can lead to reduced T-cell activity while increasing the host's infection risk. Thus, this review focuses on the use of drug delivery methods to accurately target and block superantigens, while reducing the adverse effects associated with CD28 mimic peptides. We believe that this method has the potential to provide an effective and safe therapeutic strategy for superantigen-mediated diseases.

Antigen specific activation of cytotoxic CD8+ T cells by Staphylococcus aureus infected dendritic cells

Staphylococcus aureus (S. aureus) is a pathogen associated with a wide variety of diseases, from minor to life-threatening infections. Antibiotic-resistant strains have emerged, leading to increasing concern about the control of S. aureus infections. The development of vaccines may be one way to overcome these resistant strains. However, S. aureus ability to internalize into cells - and thus to form a reservoir escaping humoral immunity - is a challenge for vaccine development. A role of T cells in the elimination of persistent S. aureus has been established in mice but it remains to be established if CD8+ T cells could display a cytotoxic activity against S. aureus infected cells. We examined in vitro the ability of CD8+ T cells to recognize and kill dendritic cells infected with S. aureus. We first evidenced that both primary mouse dendritic cells and DC2.4 cell line can be infected with S. aureus. We then generated a strain of S. aureus expressing a model CD8 epitope and transgenic F5 CD8+ T cells recognizing this model epitope were used as reporter T cells. In response to S. aureus-infected dendritic cells, F5 CD8+ T cells produced IFN-γ in an antigen-specific manner and displayed an increased ability to kill infected cells. Altogether, these results demonstrate that cells infected by S. aureus display bacteria-derived epitopes at their surface that are recognized by CD8+ T cells. This paves the way for the development of CD8+ T cell-based therapies against S. aureus.

Examining pathogenic concepts of autoimmune hepatitis for cues to future investigations and interventions

BACKGROUND

Multiple pathogenic mechanisms have been implicated in autoimmune hepatitis, but they have not fully explained susceptibility, triggering events, and maintenance or escalation of the disease. Furthermore, they have not identified a critical defect that can be targeted. The goals of this review are to examine the diverse pathogenic mechanisms that have been considered in autoimmune hepatitis, indicate investigational opportunities to validate their contribution, and suggest interventions that might evolve to modify their impact. English abstracts were identified in PubMed by multiple search terms. Full length articles were selected for review, and secondary and tertiary bibliographies were developed. Genetic and epigenetic factors can affect susceptibility by influencing the expression of immune regulatory genes. Thymic dysfunction, possibly related to deficient production of programmed cell death protein-1, can allow autoreactive T cells to escape deletion, and alterations in the intestinal microbiome may help overcome immune tolerance and affect gender bias. Environmental factors may trigger the disease or induce epigenetic changes in gene function. Molecular mimicry, epitope spread, bystander activation, neo-antigen production, lymphocytic polyspecificity, and disturbances in immune inhibitory mechanisms may maintain or escalate the disease. Interventions that modify epigenetic effects on gene expression, alter intestinal dysbiosis, eliminate deleterious environmental factors, and target critical pathogenic mechanisms are therapeutic possibilities that might reduce risk, individualize management, and improve outcome. In conclusion, diverse pathogenic mechanisms have been implicated in autoimmune hepatitis, and they may identify a critical factor or sequence that can be validated and used to direct future management and preventive strategies.

Phagocyte subsets and lymphocyte clonal deletion behind ineffective immune response to Staphylococcus aureus

Lack of known mechanisms of protection against Staphylococcus aureus in humans is hindering development of efficacious vaccines. Preclinical as well as clinical data suggest that antibodies play an important role against S. aureus. For instance, certain hypogammaglobulinaemic patients are at increased risk of staphylococcal infections. However, development of effective humoral response may be dampened by converging immune-evasion mechanisms of S. aureus. We hypothesize that B-cell proliferation induced by staphylococcal protein A (SpA) and continuous antigen exposure, without the proper T-cell help and cytokine stimuli, leads to antigen-activated B-cell deletion and anergy. Recent findings suggest an important role of type I neutrophils (PMN-I) and conventionally activated macrophages (M1) against S. aureus, while alternatively activated macrophages (M2) favour biofilm persistence and sepsis. In addition, neutrophil-macrophage cooperation promotes extravasation and activation of neutrophils as well as clearance of bacteria ensnared in neutrophil extracellular traps. Activation of these processes is modulated by cytokines and T cells. Indeed, low CD4(+) T-cell counts represent an important risk factor for skin infections and bacteraemia in patients. Altogether, these observations could lead to the identification of predictive correlates of protection and ways for shifting the balance of the response to the benefit of the host through vaccination.

Superantigens in Staphylococcus aureus isolated from prosthetic joint infection

Staphylococcus aureus is a common cause of prosthetic joint infection (PJI). The prevalence of superantigens (SAgs) among PJI-associated S. aureus is unknown. Eighty-four S. aureus isolates associated with PJI isolated between 1999 and 2006 were studied. SAg genes, sea, seb, sec, sed, see, seg, seh, sei, and tst, were assayed by PCR. Seventy-eight (92.9%) isolates carried at least 1 SAg gene studied, with 61 (72.6%) harboring more than 1. seg was most commonly (70.2%), and seh was least frequently (4.8%) detected. tst-positive isolates were associated with early infection and increased erythrocyte sedimentation rate at diagnosis (P=0.006 and P=0.021, respectively). seg and sei were associated with methicillin resistance (P=0.008 and P=0.002, respectively). A majority of PJI-associated isolates studied produced biologically active SAgs in both planktonic and biofilm growth modes. SAg genes are prevalent in S. aureus causing PJI.

Uncoupling of T cell receptor zeta chain function during the induction of anergy by the superantigen, staphylococcal enterotoxin A

Staphylococcus aureus enterotoxins have immunomodulatory properties. In this study, we show that Staphylococcal enterotoxin A (SEA) induces a strong proliferative response in a murine T cell clone independent of MHC class II bearing cells. SEA stimulation also induces a state of hypo-responsiveness (anergy). We characterized the components of the T cell receptor (TCR) during induction of anergy by SEA. Most interestingly, TCR zeta chain phosphorylation was absent under SEA anergizing conditions, which suggests an uncoupling of zeta chain function. We characterize here a model system for studying anergy in the absence of confounding costimulatory signals.

TCR dynamics in human mature T lymphocytes lacking CD3 gamma

The contribution of CD3gamma to the surface expression, internalization, and intracellular trafficking of the TCR/CD3 complex (TCR) has not been completely defined. However, CD3gamma is believed to be crucial for constitutive as well as for phorbol ester-induced internalization. We have explored TCR dynamics in resting and stimulated mature T lymphocytes derived from two unrelated human congenital CD3gamma-deficient (gamma(-)) individuals. In contrast to gamma(-) mutants of the human T cell line Jurkat, which were selected for their lack of membrane TCR and are therefore constitutively surface TCR negative, these natural gamma(-) T cells constitutively expressed surface TCR, mainly through biosynthesis of new chains other than CD3gamma. However, surface (but not intracellular) TCR expression in these cells was less than wild-type cells, and normal surface expression was clearly CD3gamma-dependent, as it was restored by retroviral transduction of CD3gamma. The reduced surface TCR expression was likely caused by an impaired assembly or membrane transport step during recycling, whereas constitutive internalization and degradation were apparently normal. Ab binding to the mutant TCR, but not phorbol ester treatment, caused its down-modulation from the cell surface, albeit at a slower rate than in normal controls. Kinetic confocal analysis indicated that early ligand-induced endocytosis was impaired. After its complete down-modulation, TCR re-expression was also delayed. The results suggest that CD3gamma contributes to, but is not absolutely required for, the regulation of TCR trafficking in resting and Ag-stimulated mature T lymphocytes. The results also indicate that TCR internalization is regulated differently in each case.

P59(fyn) is upregulated in anergic CD8+ T cells

The ultimate goal in clinical transplantation is achievement of graft tolerance. Despite long-term immunosuppression, alloantigens on transplants elicit alloresponses that can initiate organ rejection. Acute rejection is mediated by CD8(+) cytotoxic T cells, whereas chronic rejection is a result of many factors including non-immunological events. The aim of this study was to examine the molecular requirements of T cell anergy, a cellular state that is an integral component of tolerance in vivo. In vitro, the tolerant state is usually best represented by T cell anergy, which is defined by loss of the ability of T cells to produce and secrete interleukin-2 upon restimulation. In the literature, molecular changes in anergic CD4(+) T cells have been studied in great detail, but only little is known about functional and biochemical characteristics of anergic CD8(+) T lymphocytes. In this study, we demonstrate, that CD8(+) T cells are rendered anergic by TCR stimulation without costimulation. They exhibit impaired interleukin-2 production and tyrosine-phosphorylation, but markedly upregulated p59(fyn) expression, which could be shown to be an early event during anergization. Anergic CD8(+) T lymphocytes show elevated surface expression of early activation markers as well as costimulatory molecules, especially that of CTLA4. These results, are an important component for the discovery of potential molecular targets, which contribute to the development and maintenance of tolerance.

P2Y(13): identification and characterization of a novel Galphai-coupled ADP receptor from human and mouse

We have identified an orphan G protein-coupled receptor, SP174, that shares a high degree of homology with the recently described ADP receptor P2Y(12). mRNA for SP174 is abundant in the brain and in cells of the immune system. In the present study, we demonstrate that SP174 is also a receptor for ADP, which is coupled to Galphai. ADP potently stimulates SP174 with an EC(50) of 60 nM, and other related nucleotides are active as well, with a rank order of potency 2-methylthio-ADP tetrasodium = adenosine 5'-O-2-(thio)diphosphate = 2-methylthio-ATP tetrasodium > ADP > AP3A >ATP > IDP. This pharmacological profile is similar to that for P2Y(12). We have also identified the murine homolog of SP174, which exhibits 75% homology to the human receptor. ADP is also a potent agonist at the murine receptor, and its pharmacological profile is similar to its human counterpart, but ADP and related nucleotides are more potent at the murine receptor than the human receptor. In keeping with the general nomenclature for the purinergic receptors, we propose designating this novel receptor P2Y(13).

Cross-linking HLA-DR molecules on Th1 cells induces anergy in association with increased level of cyclin-dependent kinase inhibitor p27(Kip1)

HLA class II molecules play pivotal roles in antigen presentation to CD4+ T cells. We investigated signaling via HLA-DR molecules expressed on CD4+ T cells. When HLA-DR or CD3 molecules on cloned CD4+ T cells were cross-linked by solid-phase mAbs, T cells proliferated, and this resulted in anergy. Whereas cross-linking of HLA-DR and CD3 resulted in secretion of the same levels of IFN-gamma and IL-8, secretion of IL-10 induced by cross-linking of HLA-DR was less than that induced by cross-linking of CD3 on CD4+ T cells. Interestingly, expression of p27(Kip1) but not p21(Cip1) increased after stimulation by either anti-HLA-DR or anti-CD3 mAb. This was indeed the case, when T cells were rendered anergic using a soluble form of antigenic peptide. In contrast, T cells stimulated by peptide-pulsed PBMC expressed little p27(Kip1). We propose that signaling via HLA-DR molecules on CD4+ T cells at least in part contributes to the induction of T cell anergy, through the upregulated expression of the p27(Kip1). The implication of our finding is that HLA-DR molecules play a role in human T cell anergy induced by a soluble form of antigenic peptide.

The potential of peptide immunotherapy in allergy and asthma

Allergic conditions contribute significantly to the burden of chronic disease in the industrialized world. Current treatments offer varying degrees of palliation. The sole proven disease-modifying strategy, specific or whole-allergen immunotherapy, is limited because of the associated risk of systemic adverse effects, such as anaphylaxis. Short, linear allergen-derived peptides, corresponding to T cell epitopes, offer the possibility of a safer approach as they are capable of inducing allergen-specific hyporesponsiveness without cross-linking mast cell-bound IgE. This review evaluates the scientific basis of peptide immunotherapy and clinical experience in allergy up to the present time.

Superantigens: microbial agents that corrupt immunity

Microbial superantigens are a family of protein exotoxins that share the ability to trigger excessive and aberrant activation of T cells. The best characterised are the staphylococcal enterotoxins and the streptococcal pyrogenic exotoxins that trigger the staphylococcal and streptococcal toxic shock syndromes. It is now apparent that superantigens have a wider role in the pathology of infectious diseases than has previously been appreciated. Staphylococcus aureus and Streptococcus pyogenes together produce 19 different superantigens. The range of microorganisms known to produce superantigens has expanded to include Gram negative bacteria, mycoplasma, and viruses. Research is beginning to shed light on the more subtle parts these molecules play in causing disease and to produce some real possibilities for specific treatment of superantigen-induced toxicity. We aim to highlight these new developments and review the science behind these fascinating molecules.

Possible role of organ-specific autoantigen for Fas ligand-mediated activation-induced cell death in murine Sjögren's syndrome

Activation-induced cell death (AICD) is a well-known mechanism of peripheral T cell tolerance that depends upon an interaction between Fas and Fas ligand (FasL). In this study, we demonstrate that the administration of a soluble form of anti-FasL Ab, FLIM58, results in severe destructive autoimmune exocrinopathy in the murine model of human Sjögren's syndrome (SS), and we found that an organ-specific autoantigen may play an important role on down-modulation of AICD. A high titer of serum autoantibodies against 120-kDa alpha-fodrin autoantigen was detected in the FLIM58-treated mice, and splenic T cell culture supernatants contained high levels of IFN-gamma. In vitro T cell apoptosis assay indicated that FasL-mediated AICD is down-regulated by autoantigen stimulation in spleen cells from the murine SS model, but not from Fas-deficient MRL/lpr mice and FasL-deficient MRL/gld mice. FasL undergo metalloproteinase-mediated proteolytic processing in their extracellular domains, resulting in the release of soluble trimeric ligands (soluble FasL). We showed that the processing of soluble FasL occurs in autoantigen-specific CD4(+) T cells, and that a significant increase in expressions of metalloproteinase-9 mRNA was observed in spleen cells from SS model mice. These findings indicate that the increased generation of soluble FasL inhibits the normal AICD process, leading to the proliferation of effector CD4(+) T cells in the murine SS model.

Cell surface CD28 levels define four CD4+ T cell subsets: abnormal expression in rheumatoid arthritis

CD28 is a costimulatory receptor expressed in most CD4(+) T cells. Despite the long-standing evidence for up- and downregulation of surface CD28 expression in vitro, and the key regulatory role assigned to the upregulation of CD28 counterreceptor [the CD152 (CTLA-4) molecule], in vivo CD28 induction has attracted little attention. We studied CD28 and CD152 expression and function in 33 rheumatoid arthritis (RA) patients, 20 clinically active and 13 inactive, and in 24 healthy donors. Four subsets of CD28(-), CD28(low), CD28(int), and CD28(high) peripheral blood human CD4(+) T cells were defined using three-color flow cytometry. The three CD28(+) subsets displayed a one-, two-, or threefold quantitative difference in their relative number of CD28 antibody binding sites, respectively (P < 0.01). RA patients, whether active or inactive, showed a distinct phenotype when compared to healthy donors: (i) the percentage of CD4(+)CD28(high) cells was increased twofold and the CD4(+)CD28(low) subset was reduced twofold (P < 0.01) and (ii) the CD4(+)CD28(high) cells from RA patients showed an in vivo activated phenotype, CD45RO(+)CD5(high)IL-2Ralpha(+) (P < 0.01). Active RA patients were different from inactive patients. They showed a twofold increase in mean CD28 expression (P < 0.05), whereas each of the CD28(+) subsets in the inactive RA patients showed reduced expression when compared to healthy donors. Notably, both active and inactive RA patients showed abnormal CD28 upregulation when T cells were activated in vitro with CD3 antibodies, but only inactive RA patients showed a hypoproliferative response to TCR/CD3 triggering when compared to healthy donors (P < 0.01). This defective proliferation was normalized by concurrent crosslinking with CD28 antibody. No differences were noted in the expression of CD152 or CD80, a CD28 and CD152 shared ligand. The disregulated in vivo expression of CD28 was related to the RA patients' disease activity and suggests that modulation of CD28 surface levels may be an additional mechanism to finely tune the delicate responsiveness/tolerance balance.

Differential requirements for induction of total immunoglobulin and physiological rheumatoid factor production by human peripheral blood B cells

Rheumatoid factors (RFs) are autoantibodies directed against the Fc part of IgG. Considerable evidence exists that there are two classes of RFs, pathological and physiological. Whereas pathological RFs are associated with disease, physiological RFs are considered to be a normal component of the immune response. RF(+) precursor B cells present as part of the B cell repertoire of healthy individuals are held responsible for the production of physiological RFs, which is a transient phenomenon with a clear correlation with an initiating stimulus such as immunization or exposure to an infection. Here we demonstrate a difference in the regulatory control of total Ig and RF production by peripheral blood (PB) B cells of both healthy controls (HC) and patients with rheumatoid arthritis (RA). Highly purified B cells from HC and patients with RA were cocultured with T cells stimulated with immobilized anti-CD3 mAb. Similar to IgM production, IgM-RF production was shown to be dependent on CD40 cross-linking. However, activation of PB B cells in the CD40 system in the presence of IL-2, IL-4, IL-10, combinations of these cytokines or supernatant of anti-CD3-stimulated T cells failed to induce detectable IgM-RF, whereas total IgM production was considerable. From these results we conclude that conditions to activate physiological RF(+) B cells require additional contact besides CD40--CD40L interactions between T and B cells. Since the requirements for RF production were similar using PB B cells from HC and patients with RA it is suggested that the regulatory properties of RF(+) precursors in the PB B cell compartment is equal among these groups. Together, these results indicate that conditions for the induction of total Ig and physiological RFs are different.

Rheumatoid arthritis synovial T cells regulate transcription of several genes associated with antigen-induced anergy

Rheumatoid arthritis (RA) is a chronic, inflammatory synovitis whose pathogenesis may involve autoimmune mechanisms. Anergy is a state of T-cell nonresponsiveness characterized by downregulated IL-2 production. Paradoxically, RA T cells are hyporesponsive and proliferate poorly to antigens and mitogens, thus sharing some characteristics with anergic T cells. We analyzed the molecular basis of anergy in cloned human CD4+ T cells using differential display RT-PCR and subsequently examined the levels of differentially expressed transcripts in RA and, as control, reactive arthritis (ReA) synovium. Several transcriptional events were common to anergic T cells and RA synovium. These included downregulation of CALMODULIN:, which is critical to T-cell activation, and of cellular apoptosis susceptibility protein, which may mediate resistance to apoptosis in RA. Transcription of CALMODULIN: in RA synovium was less than 1% of that in ReA and was lower in RA synovial fluid mononuclear cells than in paired PBMCs. Following anti-TNF-alpha therapy in vivo, RA PBMC CALMODULIN: transcripts increased five- to tenfold. Pharmacological calmodulin blockade in vitro impaired antigen-specific proliferation. These data provide a link between reduced CALMODULIN: transcription and impaired T-cell responsiveness in RA. The identification of transcriptional changes common to anergic and RA synovial T cells should help interpret some of the characteristic RA cellular defects.

NFAT-controlled expression of GFP permits visualization and isolation of antigen-stimulated primary human T cells

We have developed a new method that allows detection and isolation of viable, antigen-specific, human T cells from a heterogeneous pool of T cells. We have engineered a self-inactivating retroviral vector containing multiple (3 or 6) nuclear factor of activated T-cell (NFAT)-binding sites, followed by the minimal IL2 promoter and the reporter gene GFP. Jurkat cells, primary T-cell blasts, and T-cell clones were transduced with high efficiency (20%-40%). Stimulation of the transduced cells with phorbol myristate acetate (PMA) and ionomycin resulted in a high level expression of GFP that was maximal after 12 to 14 hours and remained stable for another 12 hours. Activation of T cells carrying the construct containing 6 NFAT-binding sites resulted in the highest mean fluorescence intensity. Cyclosporin-A and FK506 were able to block the activation-dependent GFP expression. Activation of transduced T-cell blasts with the superantigen staphylococcal enterotoxin B or of transduced antigen-specific T-cell clones with cognate antigen resulted in GFP expression. After an overnight stimulation of a heterogeneous T-cell bulk culture with an HLA mismatched stimulator cell (JY), the GFP expressing cells were cloned. As expected, the cloning frequency of the antigen-specific GFP+ cells was considerably higher than that of the total T-cell population. Most of the T-cell clones were either cytolytic, or proliferative toward JY stimulator cells. Interestingly, we also isolated T-cell clones that were noncytolytic and nonproliferative toward JY cells, but specifically up-regulated GFP after an overnight stimulation with JY.

NFAT-controlled expression of GFP permits visualization and isolation of antigen-stimulated primary human T cells

We have developed a new method that allows detection and isolation of viable, antigen-specific, human T cells from a heterogeneous pool of T cells. We have engineered a self-inactivating retroviral vector containing multiple (3 or 6) nuclear factor of activated T-cell (NFAT)-binding sites, followed by the minimal IL2 promoter and the reporter gene GFP. Jurkat cells, primary T-cell blasts, and T-cell clones were transduced with high efficiency (20%-40%). Stimulation of the transduced cells with phorbol myristate acetate (PMA) and ionomycin resulted in a high level expression of GFP that was maximal after 12 to 14 hours and remained stable for another 12 hours. Activation of T cells carrying the construct containing 6 NFAT-binding sites resulted in the highest mean fluorescence intensity. Cyclosporin-A and FK506 were able to block the activation-dependent GFP expression. Activation of transduced T-cell blasts with the superantigen staphylococcal enterotoxin B or of transduced antigen-specific T-cell clones with cognate antigen resulted in GFP expression. After an overnight stimulation of a heterogeneous T-cell bulk culture with an HLA mismatched stimulator cell (JY), the GFP expressing cells were cloned. As expected, the cloning frequency of the antigen-specific GFP+ cells was considerably higher than that of the total T-cell population. Most of the T-cell clones were either cytolytic, or proliferative toward JY stimulator cells. Interestingly, we also isolated T-cell clones that were noncytolytic and nonproliferative toward JY cells, but specifically up-regulated GFP after an overnight stimulation with JY.

Induction of global anergy rather than inhibitory Th2 lymphokines mediates posttrauma T cell immunodepression

Depressed mitogen-induced IL-2 and IFN-gamma responses after severe mechanical or thermal injury are postulated to result from an expansion of Th2 lymphocytes with concomitant excessive production of IL-4 and/or IL-10. Here, we simultaneously assessed proliferation and Th1 (IFN-gamma) versus Th2 (IL-10, IL-4) lymphokine production in trauma patients' isolated T cells stimulated in a costimulation sufficient, antigen presenting cell independent system (anti CD3 + anti-CD4). T cells with depressed proliferation and IL-2 production simultaneously lost IL-4, IL-10, and IFN-gamma protein and mRNA responses. Exogenous IL-12 addition did not restore IFNgamma responses, but exogenous IL-2 partially restored IL-4, IFN-gamma, and IL-10 production. Although initially partially restored by exogenous IL-2 or stimulation with PMA + ionomycin, patient T cells with persisting anergy progressively lost even these lymphokine and proliferative responses. Development of global T cell anergy was not a result of lost T cell viability or protein synthesis, since it corresponded to predominance of anergic T cells with upregulated expression of CD11b, but downregulated CD28 and CD3 expression. Thus, the subset of posttrauma patients whose isolated T cells become unresponsive experienced progressively worsening global anergy, mediated not by an increased production of Th2 lymphokines, but possibly by T cell incapacity to be activated through TCR triggering or Ca(2+) mobilization.

Threshold signaling of human Th0 cells in activation and anergy: modulation of effector function by altered TCR ligand

Molecular interactions between TCR and its natural ligand, in the presence of costimulatory signals, elicit T cell effector functions, whereas subtle changes in the structure of antigenic peptides may induce only selected T cell effector function including anergy. In this study, we have investigated the immunological activity of an altered TCR ligand (p 2, 28-40A34,36) derived from the immunodominant T cell epitope of the group 2 allergen of house dust mite, in which residues at positions 34 and 36 were substituted by alanine. Elevated IFN-gamma synthesis was induced by equimolar concentrations of the analogue compared with native peptide (p 2, 28-40) and was paralleled by increased down-regulation of cell surface CD3. IL-5 and IL-10 production exhibit the same sensitivity to both peptides, implying that the induction of T cell effector functions are not all proportional to TCR occupancy. Both native peptide and the analogue bound to MHC class II (DRB1*1101) molecules with similar affinities. Furthermore, p 2, 28-40A34,36 induced T cell anergy at lower concentrations than native peptide. During the induction of anergy, TGF-beta production was comparable for both peptides, whereas IL-10 secretion was markedly increased but more so in response to p 2, 28-40A34,36. Membrane expression of costimulatory ligands CD80 and CD86 was similar for native peptide and p 2, 28-40A34,36 and increased in activation, whereas only CD86 was elevated during anergy. The modulation of T cell effector function with altered TCR ligands may have practical applications in reprogramming allergic inflammatory responses through the induction of T cell anergy and/or the promotion of Th1 cytokines.

Single cell analysis of cytokine expression kinetics by human CD4+ T-cell clones during activation or tolerance induction

Exposure to optimal peptide antigen concentrations induces human CD4+ T-cell clones to proliferate and secrete various cytokines. Higher (> 10-fold optimal) antigen concentrations cause long-term proliferative unresponsiveness, which can be reversed by exogenous interleukin-2 (IL-2). We call this condition 'tolerance'. We used intracellular cytokine staining and flow cytometric analysis to investigate the kinetics of interferon-gamma, tumour necrosis factor-alpha, IL-4 and IL-5 production during the initial phase of tolerance induction. Single cell analysis of interferon-gamma and IL-4 or IL-5 coexpression showed functional heterogeneity of cloned human CD4+ T cells. Superstimulation with phorbol 12-myristate 13-acetate and ionomycin (PI) revealed enhanced responsiveness shortly after tolerizing treatment, followed by reduced responsiveness. Both tolerized and activated T cells had similarly reduced cytokine responses when further stimulated with antigen during the following 48 hr, with limited enhancement following additional stimulation with PI. We conclude that cytokine induction is normally followed by a refractory phase, but that the expression of cytokines is enhanced in the initial phase of tolerance induction.

The structural basis of T cell activation by superantigens

Superantigens (SAGs) are a class of immunostimulatory and disease-causing proteins of bacterial or viral origin with the ability to activate large fractions (5-20%) of the T cell population. Activation requires simultaneous interaction of the SAG with the V beta domain of the T cell receptor (TCR) and with major histocompatibility complex (MHC) class II molecules on the surface of an antigen-presenting cell. Recent advances in knowledge of the three-dimensional structure of bacterial SAGs, and of their complexes with MHC class II molecules and the TCR beta chain, provide a framework for understanding the molecular basis of T cell activation by these potent mitogens. These structures along with those of TCR-peptide/MHC complexes reveal how SAGs circumvent the normal mechanism for T cell activation by peptide/MHC and how they stimulate T cells expressing TCR beta chains from a number of different families, resulting in polyclonal T cell activation. The crystal structures also provide insights into the basis for the specificity of different SAGs for particular TCR beta chains, and for the observed influence of the TCR alpha chain on SAG reactivity. These studies open the way to the design of SAG variants with altered binding properties for TCR and MHC for use as tools in dissecting structure-activity relationships in this system.

Understanding the mechanism of action of bacterial superantigens from a decade of research

In the face of the unique diversity and plasticity of the immune system pathogenic organisms have developed multiple mechanisms in adaptation to their hosts, including the expression of a particular class of molecules called superantigens. Bacterial superantigens are the most potent stimulators of T cells. The functional consequences of the expression of superantigens by bacteria can be extended not only to T lymphocytes, but also to B lymphocytes and to cells of the myeloid compartment, including antigen-presenting cells and phagocytes. The biological effects of bacterial superantigens as well as their molecular aspects have now been studied for a decade. Although there is still a long way to go to clearly understand the role these molecules play in the establishment of disease, recently acquired knowledge of their biochemistry now offers unique experimental opportunities in defining the molecular rules of T-cell activation. Here, we present some of the most recent functional and molecular aspects of the interaction of bacterial superantigens with MHC class II molecules and the T-cell receptor.

Role of interleukin-2 in superantigen-induced T-cell anergy

T-cell anergy is a state of immunological tolerance characterized by unresponsiveness to antigenic stimulation. Previous studies have shown that anergy is induced in T cells following stimulation in the absence of adequate costimulatory signals. These cells fail to respond to stimulation via the T-cell receptor (TCR), and fail to produce normal levels of interleukin-2 (IL-2). We present results here which show that low concentrations of the superantigen staphylococcal enterotoxin A (SEA) in the absence of antigen-presenting cells induced both proliferation and anergy in the A.E7 T-cell clone. Furthermore, under these conditions, the A.E7 clone remained responsive to exogenous IL-2. Fluorescence-activated cellular cytometry analysis revealed unaltered expression of the TCR/CD3 complex in the anergized clone; however, both CD4 and CD25 expression increased after 24 hr of stimulation by SEA under these conditions. Interestingly, a low level of IL-2 production was measured during the induction of anergy. Most strikingly, stimulation of the A.E7 clone by SEA in combination with exogenous IL-2 resulted in a more pronounced state of anergy. These results suggest that the induction of anergy is a process that is essentially independent of the production of IL-2.

Immunologic changes associated with allergen immunotherapy

Specific allergen injection immunotherapy is highly effective in selected patients with IgE-mediated disease, including respiratory allergy and venom anaphylaxis. Research in this area provides insight into the immunologic basis of allergic disease and may assist in the development of more highly targeted treatment. Immunotherapy reduces immediate allergen-induced symptoms and concentrations of inflammatory mediators, including histamine and prostaglandin D2, in ragweed-sensitive patients. Similarly, nasal epithelial mast cell numbers are decreased. A characteristic feature of immunotherapy is its ability to inhibit late-phase responses. In the nose it is accompanied by a decrease in eosinophil numbers in lavage during late responses. Characteristic changes in serum immunoglobulins are found, with an initial increase in IgE followed by a blunting of seasonal increases in IgE in pollen-sensitive patients and a gradual decline in allergen-specific IgE levels over several years. This is accompanied by an increase in allergen-specific IgG (blocking antibodies), although neither appear to correlate closely with the clinical response to immunotherapy. One way in which immunotherapy may act is by modifying the T-lymphocyte response to subsequent natural allergen exposure. Studies in peripheral blood and within the target organ have demonstrated a shift in the balance of T-cell subsets away from TH2-type (producing particularly IL-4 and IL-5) in favor of a TH1-type T-lymphocyte response (with the preferential production of IFN-gamma). Studies of the nasal mucosa before and after immunotherapy have demonstrated suppression of the late nasal response and increases in the numbers of cells expressing mRNA for IFN-gamma. It is not clear whether this immune deviation is due to anergy of TH2/TH0 cells or increases in TH0/TH1 T-lymphocyte responses. An alternative may be amplification of suppressor CD8+ T cells, which may have a downregulatory effect. Novel approaches currently being explored include the use of T-cell reactive peptides, which might circumvent the risk of anaphylaxis, and the use of adjuvants such as IL-12 or mycobacterial vaccines to potentiate the effects of allergen in inducing immune deviation.

Class II MHC/peptide complexes on T cell antigen-presenting cells: agonistic antigen recognition inhibits subsequent antigen presentation

Previous studies have shown that tolerogenic anti-CD4 (W3/25) and anti-LFA-1 mAb (LRTC1) which block T cell activation paradoxically enhance T cell-mediated antigen presentation. Lasting T cell APC (T-APC) activity requires and initial exposure of T cells to these mAb in the presence of professional APC and antigen. This study revealed a central mechanism regulating the duration of T-APC activity. T cell recognition of class II MHC complexes of T-APC catalyzed a rapid decay in the presentation of agonistic antigens, whereas partial agonistic signals decayed at a shower rate. Likewise, blockade of agonistic T-T cell autorecognition by these mAb led to the persistence of agonistic MHC/antigen on T-APC. The best predictor of T-APC activity was related to the ability of clonal T cells to respond to antigen presented by neighboring T cells. Strong responders were inefficient T-APC, whereas inefficient responders were strong T-APC. Addition of irradiated myelin basic protein (MBP0-specific responders to T-APC cultures specifically inhibited the subsequent presentation of MBP but not conalbumin, and vice versa. T-APC presentation of antigen to responder T cells also resulted in reduced surface expression of class II MHC I-A glycoproteins on T-APC. These findings indicate that agonistic recognition of antigen of T-APC specifically inhibits subsequent presentation of that antigen, whereas antagonistic MHC/antigen complexes are preserved for an enduring T-APC activity.

Heat shock proteins as potential targets in the therapy of inflammatory arthritis

Whether heat shock proteins (hsp) will be therapeutic targets in arthritis depends on their role in pathogenesis. In this article, three possibilities are considered. Firstly, an excessive immune response to bacterial hsp could be arthritogenic - as may occur in reactive arthritis. In these circumstances therapy would be directed to down-regulating this immune response, or altering the nature of the immune response e.g. by changing cytokine production from interferon-g to IL-4. However this approach depends on the immune response to bacterial hsp not being critical for control of the bacterial infection. Secondly, an immune response to bacterial hsp may induce autoimmunity by cross-reactivity, e.g. with the homologous human. This could also be modulated in the same way with a lower likelihood of interfering with control of the infectious agent, since only a component of the immune response against the bacterial hsp will be cross-reactive with self. Thirdly, recent experiments raise the possibility that joint inflammation might be controlled by T cells which recognizes self hsp, particularly hsp60. Therapies might enhance this response; protection from experimental arthritis by prior immunization with hsp60 is well established. Whether similar approaches will be viable after arthritis is established remains to be seen.

Pattern of cytokine expression in circulation CD57+ T cells from long-term renal allograft recipients

We made a quantitative analysis of the lymphokine mRNA and of proteins produced by CD57+ and CD57- circulating T cells isolated from long-term kidney-transplanted patients with expanded CD4+/CD57+ and CD8+/CD57+ T cells, and from normal individuals. We concentrated on IL-2 and IFN-gamma, which define a Th1-like type of lymphokine production, and on IL-4 which defines a Th-2-like type. We also analysed the production of IL-10 which is endowed with inhibitory effects on IL-2 and IFN-gamma synthesis, and of TNF-alpha, a pleiotropic inflammatory cytokine. On ionomycin + PMA stimulation, which reveals the intrinsic potential of lymphokine production by T cells, the CD57+ T cell subsets from all individuals produced high amounts of IFN-gamma and TNF-alpha mRNA and protein. They also produced IL-2, but to a much lesser extend than their CD57- counterparts, and little IL-4 and IL-10. They were no more capable of producing IL-2 when stimulated through the CD3/TCR in the presence of monocytes, yet still synthesized IFN-gamma. Our data suggest that the in vivo expansion of CD57+ T cells in stable allograft renal recipients might correspond to Th1 energized cells which on triggering of cell surface receptors hardly secrete lymphokines involved in cell cycle progression, but can still exert some effector functions, including IFN-gamma secretion.

Superantigens as immunomodulators: recent structural insights

Superantigens interact with major histocompatibility complex (MHC) class II molecules and T-cell receptors (TcRs) forming a trimolecular complex which is able to induce proliferation and cytokine production in T cells. Although superantigens appear to act through a common mechanism, they very in many of their specific interactions and biological properties. X-ray crystallographic studies and biochemical experiments have now established that cross-linking of MHC class II molecules and the TcR by superantigens can occur in a number of different modes.

Induction of interleukin-2 unresponsiveness and down-regulation of the JAK-STAT system upon activation through the T cell receptor

Full activation of T cells with antigen (Ag) and antigen-presenting cells initiates effector functions and proliferation. When T cells are re-stimulated through the T cell receptor (TCR) after a primary stimulation with Ag, growth arrest and cell death are induced. Activation of a T cell clone by cross-linking of TCR induces interleukin (IL)-2 unresponsiveness and ultimately cell death. While the proliferative signal delivered by IL-2 induces c-myc, bcl-2 and cyclin D3 expression, the expression of bcl-2 and cyclin D3 is completely suppressed upon TCR stimulation. Furthermore, TCR stimulation induces a decrease in the protein levels of JAK3 and STAT5, suggesting that IL-2 unresponsiveness and growth arrest of T cells result from down-regulation of JAK3 and STAT5.

A structural and functional comparison of staphylococcal enterotoxins A and C2 reveals remarkable similarity and dissimilarity

Staphylococcal enterotoxins and toxic shock syndrome toxin-1 are known as superantigens due to their ability to activate a large number of T-cells by crosslinking the major histocompatibility complex class II molecules with the T-cell receptor. Although superantigens seem to act by a common mechanism, they vary in many of their specific interactions and biological properties. A structural comparison of staphylococcal enterotoxins A and C2, members of the staphylococcal superantigens, has shown large conformational differences at the putative TcR interaction site (loops between alphaN-alpha2, alpha4-beta9 and beta10-alpha5 in staphylococcal enterotoxin A) that could explain the variability in their T-cell receptor specificity. A common Zn2(+)-binding site was identified in both staphylococcal enterotoxin A and C2 that is superimposable but differs somewhat in its coordination geometry between the two molecules.

Differential response of CD4+ V7+ and CD4+ V7- T cells to T cell receptor-dependent signals: CD4+ V7+ T cells are co-stimulation independent and anti-V7 antibody blocks the induction of anergy by bacterial superantigen

V7 is a novel cell surface glycoprotein that is expressed on 25% of circulating T lymphocytes. This molecule appears to play a critical role in T cell activation based on the observation that a monoclonal anti-V7 antibody inhibits T cell receptor (TCR)-dependent interleukin-2 (IL-2) production and proliferation of T cells. In the current study, CD4+ V7+ and CD4+ V7- T cells were separated from one another and their response to various stimuli analyzed. Although there were only minor differences between the two subsets in the expression of activation/differentiation markers, including CD45RA and R0 isotypes, when exposed to immobilized anti-CD3 or anti-TCR antibodies in the absence of APC, CD4+ V7+ T cells alone produced IL-2 and proliferated vigorously. By contrast, CD4+ V7- cells responded poorly to such stimuli, but they recovered their capacity to respond if antigen-presenting cells (APC) or anti-CD28-antibody were added to the cultures. The enhancement of the V7- T cell response by APC appears to be related to augmentation of TCR signals because the effect could be blocked by antibodies against molecules on APC [major histocompatibility (MHC) class II, CD86] that are known to up-regulate such signals through their interaction with counter-receptors on T cells. To assess the role of V7 in a system independent of co-stimulation, CD4+ T cells were stimulated with the bacterial superantigens, staphylococcal enterotoxins A and B. The cells responded by proliferating and then becoming anergic. Addition of anti-V7 antibody at the initiation of culture with superantigen did not inhibit cellular proliferation but prevented T cells from becoming anergic, while addition of anti-CD28 antibody had no effect on either proliferation or anergy induction. These results indicate that V7 and CD28 mediate distinct intracellular signals and suggest that V7 functions to preserve T cell reactivity whether the stimulus is mitogenic or anergizing.

Clinical role for a superantigen in Yersinia pseudotuberculosis infection

Yersinia pseudotuberculosis is an enteric pathogen that causes a variety of clinical symptoms in the human. Recently, we reported the production of a superantigen (Y. pseudotuberculosis-derived mitogen, YPM) by this organism and characterized the gene structure of ypm. To further study the potential pathogenic role of YPM in Y. pseudotuberculosis infection, we assayed IgG anti-YPM antibodies and T cell antigen receptor-Vbeta expression of the T cells in peripheral blood and in mesenteric lymph node in patients acutely infected with Y. pseudotuberculosis. 20 out of 33 patients (61%) had an elevated antibody titer compared with healthy controls (P = 0.0001). Patients with systemic symptoms such as lymphadenopathy, transient renal dysfunction, and arthritis had significantly higher titers of anti-YPM than patients with gastrointestinal tract symptoms alone. T cells bearing the Vbeta3 gene segment were significantly increased (P = 0.009) among acute phase patients compared with healthy children. During the convalescence phase of the illness, there was a reduction in the abnormal level of Vbeta3 T cells. Moreover, in the mesenteric lymph node, an elevated level of Vbeta3 T cells compared with peripheral blood and a sequence diversity in the junctional region of the T cell antigen receptor beta-chain containing Vbeta3 element was observed in one patient. Together, these findings suggest that YPM was produced in vivo and played an important role in the pathogenesis of Y. pseudotuberculosis infection.

Defective post-thymic tolerance mechanisms during the chronic progressive stage of multiple sclerosis

We have recently isolated a panel of T-cell clones from chronic progressive multiple sclerosis (MS) patients that are capable of functioning as antigen-presenting cells and of expressing the costimulatory molecules B7-1 and B7-2. In this report we show that these T-cell clones are resistant to inhibitory regulation, including the induction of anergy and sensitivity to tumor growth factor-beta (TGF-beta)-induced growth inhibition. The resistance to anergy induction was associated with expression of B7 costimulatory molecules. These data suggest that lack of responsiveness to peripheral inhibitory signals may account for the entry of autoimmune diseases into a chronic progressive phase.

Proteins in the cell wall and membrane of Cryptococcus neoformans stimulate lymphocytes from both adults and fetal cord blood to proliferate

Cryptococcus neoformans is an encapsulated yeast that infects patients who have defective cell-mediated immunity, including AIDS, but rarely infects individuals who have intact cell-mediated immunity. Studies of the immune response to C. neoformans have been hampered by a paucity of defined T-lymphocyte antigens, and hence, the understanding of the T-cell response is incomplete. The goal of this study was to separate C. neoformans into its component parts, determine whether those components stimulate lymphocyte proliferation, perform preliminary characterization of the proteins, and establish the potential mechanism of lymphocyte proliferation. The lymphocyte response to fungal culture medium, whole organisms, disrupted organisms, and the yeast intracellular fraction or cell wall and membrane was studied by determining thymidine incorporation and by determining the number of lymphocytes at various times after stimulation. The cell wall and membrane of C. neoformans stimulated lymphocyte proliferation, while the intracellular fraction and culture filtrate did not. The optimal response occurred on day 7 of incubation, with 4 x 10(5) peripheral blood mononuclear cells per well and with 13 microg of cryptococcal protein per ml. The number of lymphocytes increased with time in culture, indicating that thymidine incorporation was accompanied by proliferation. Proteinase K treatment of the cell wall and membrane abrogated lymphocyte proliferation, indicating that the molecule was a protein. [35S]methionine labeling, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and fluorography were performed to analyze the proteins contained in the cell wall and membrane, intracellular fraction, and culture filtrate. At least 18 discrete bands were resolved from the cell wall and membrane. Since a large percentage of healthy adults responded to the cryptococcal cell wall and membrane, a mitogenic effect was investigated by testing proliferation of fetal cord blood lymphocytes. The percentage of fetal samples that proliferated in response to the cell wall and membrane was similar to the percentage of fetal samples that proliferated in response to Staphylococcus enterotoxin B, a microbial mitogen. Thus, a protein in the cell wall and membrane of C. neoformans is a potent stimulant of lymphocyte proliferation and has mitogenic properties, which may have important implications for cell-mediated immunity to C. neoformans.

Modulation of promiscuous T cell receptor recognition by mutagenesis of CDR2 residues

The T cell receptor (TCR) recognizes a ligand composed of a major histocompatibility complex (MHC) molecule and a peptide antigen. Prior studies of murine T cell clones have demonstrated that residues in the CDR3 region of TCR interact with amino acids in the peptide during MHC-restricted antigen recognition. However, the questions of whether direct TCR MHC contacts are made and where such contact sites might map in the TCR have not been resolved. In this study, we have taken advantage of the promiscuous recognition of a peptide from influenza virus (HA 307-319) by human T cell clones to map sites in the TCR that mediate differences in human leukocyte antigen-D related (HLA-DR) restriction in the presence of a common peptide antigen. Site-specific mutagenesis of cloned TCR genes and transfection into Jurkat cells were used to demonstrate that single amino acid substitutions in CDR2 of the TCR-alpha chain controlled whether a T cell was restricted by the product of a single DR allele (DR7) or would respond to the HA 307-319 peptide when presented by the products of one of several different DR alleles (DR1, DR4, DR5, or DR7). Because the relevant DR alleles are defined by polymorphism in the DR-beta chain, these results also suggest a rotational orientation for recognition in which TCR-alpha interacts with DR beta.

One cause for the apparent inability of human T cell clones to function as professional superantigen-presenting cells is autoactivation

Human T cell clones (TCC) are antigen-presenting cells (APC) able to present peptides and superantigens (SAg) and to process and present intact proteins. TCC express major histocompatibility complex (MHC) class II antigens and molecules involved in the accessory signal delivery, such as B7.1 and B7.2/B70. Notwithstanding these observations, the role of professional APC has been often denied to T cells because anergy of responder T cells rather than proliferation has been observed following the TCC presentation in the absence of added professional APC. Here, we show that upon stimulation with free SAg, TCC undergo proliferative responses followed, after a 1-week culture, by an SAg-dependent unresponsiveness to T cell receptor (TCR)-mediated stimuli, but not to interleukin-2. The anergy induced by the SAg can not be prevented by the addition of autologous Epstein-Barr virus (EBV)-transformed B cells, indicating that the induction of anergy occurs also in the presence of conventional APC. Conversely, if the TCC are stimulated by SAg-prepulsed irradiated APC, either EBV and TCC, the induction of anergy is not observed. After a 1-week culture, in fact, TCC stimulated with APC-bound SAg responded to TCR-mediated stimuli, irrespective of the APC (EBV or TCC) used for the SAg presentation. Stimulation of TCC with free SAg in a semisolid medium that prevents T-T cell contacts resulted in an activation followed by a state of anergy, suggesting that anergy is the consequence of SAg recognition at the single T cell level. These data indicate that the anergy observed in TCC upon a 1-week culture in the presence of soluble SAg is not the result of an inherent inability of TCC to act as professional APC. Rather the phenomenon depends on the presence of soluble SAg, leading to T cell autostimulation.

Effects of antigen presentation on superantigen-induced apoptosis mediated by Fas/Fas ligand interactions in human T cells

Stimulation of T cells with bacterial superantigens has several distinct functional outcomes including proliferation, anergy and apoptosis. At present however, the mechanisms that dictate whether activation, anergy, or apoptosis predominate are unclear. In this study we have investigated the effects of superantigen presentation to mature superantigen-reactive human T-cell lines. Despite expressing major histocompatibility complex (MHC) class II molecules, these lines failed to proliferate in response to superantigen in the absence of antigen-presenting cells (APC) but proliferated when minimal APC were added. In the absence of APC a significant proportion of the T cells underwent apoptosis. This response was rapid, antigen dependent and largely abolished by the addition of cyclosporin A. Interestingly the response was not blocked by the addition of a number of antibodies to cell surface molecules including MHC class II and intracellular adhesion molecule-1. Using both a bioassay and messenger RNA analysis we were able to demonstrate that stimulation of these T cells with superantigen resulted in the induction of Fas-ligand expression on the T cells and furthermore, the ability of these cells to induce apoptosis was inhibited by the addition of blocking Fas antibodies as well as a Fas-Fc fusion protein. These data demonstrate that stimulation of T cells with staphylococcal enterotoxin B induces expression of Fas-ligand resulting in T-cell apoptosis; however, the final outcome of proliferation or apoptosis is determined by the presence of APC.

Regulation of cytokine and chemokine transcription in a human TH2 type T-cell clone during the induction phase of anergy

BACKGROUND

Selected cytokines produced by allergen specific CD4+ T cells from atopic individuals contribute to both the specific and non-specific effector mechanisms of the allergic immune response. The chemokine family of cytokines and tumour necrosis factor (TNF)-alpha are leucocyte regulatory and proinflammatory molecules. The chemokines include interleukin (IL)-8 and the RANTES/SIS cytokines.

OBJECTIVE

There has been no systematic survey of chemokine production in T-cell subtypes. Because of their wide range of biological properties, it might be expected that they would be closely regulated by T cells. This paper illustrates one way (through the characterization of T-cell clones) these questions might be addressed.

METHODS

Northern blot analysis was used to quantitate steady state transcription of selected cytokine genes and enzyme linked immunosorbent assay (ELISA) was used to quantitate soluble product.

RESULTS

mRNA expression of the chemokines (IL-8, HuMIP-1 alpha and HuMIP-1 beta) and TNF alpha is upregulated in TH2-like cloned house dust mite reactive human CD4+ T cells under conditions of activation and during the induction phase of anergy. Although the development of anergy superinduces mRNA for both IL-8 and TNF alpha, protein production is low compared with that released during activation. In contrast, RANTES, a chemoattractant for CD4+/CD45RO+ memory T cells, eosinophils and basophils, is constitutively expressed at the RNA level by the T cells and not modulated by signals of activation and anergy induction. The production of IL-2, IL-4 and IL-5 mRNA and proteins during the induction of anergy peaks at 2 h after stimulation, whereas the kinetics following activation of the T cells is delayed in comparison.

CONCLUSION

These data show that the induction of the anergic state coincides with post-transcriptional regulation of selected cytokine genes. Further study of these phenomena will impact on our understanding of the mechanisms of induction of anergy and the regulation of allergic immune responses in desensitization.

Peptide modulation of allergen-specific immune responses

In vitro peptide stimulation of allergen-reactive T-helper type 1 and type 0 cells, in the absence of costimulatory signals, induces anergy that is accompanied by the modulation of cell surface phenotype and changes in cytokine production. In experimental animal models, the administration of allergen-derived peptides may result in the downregulation of cytokine and antibody production, which is preceded by transient activation of CD4+ T cells, without the induction of effector immunity. Preliminary results of clinical trials using allergen-derived peptides for desensitization are becoming available and should provide some insight into the efficacy of peptide therapy in man.

Differential dependence of TH-0, TH-1 and TH-2 CD4+ T cells on co-stimulatory activity provided by the accessory molecule LFA-1

BACKGROUND

The adhesion molecule LFA-1 contributes to the activation response of peripheral blood human CD4+ T cells. Less is known of its contribution to stimulation of long-term CD4+ T cell lines and clones or of its potential to co-stimulate CD4+ T cells of different functional phenotype.

OBJECTIVE

This study was therefore performed to investigate co-stimulatory properties of the LFA-1 (CD11a/CD18) complex in the activation of human CD4+ T cell lines and clones of TH-0, TH-1 and TH-2 subsets.

METHODS

Co-stimulatory activity was measured by cross-linking antibodies to CD11a or CD18 with anti-CD3 antibodies to plastic and then measuring the proliferative response of CD4+ T cells to these antibodies.

RESULTS

A house duct mite allergen-specific CD4+ T cell line (TH-2) demonstrated much greater dependence on both CD11a and CD18 than a mycobacterial antigen-specific CD4+ T cell line (TH-1). Co-stimulatory activity through LFA-1 was also provided to a house dust mite-specific CD4+ T cell clone (DE-9; TH-2) but not to an influenza haemagglutinin-specific CD4+ T cell clone (HA1-7; TH-0). In contrast, soluble antibodies to CD18 inhibited proliferative responses of both DE-9 and HA1.7 to an immunogenic challenge of antigen and to stimulation by anti-CD3 antibodies. However, the allergen-specific T cells were more susceptible to inhibition. Signal transduction was also observed from the T-cell receptor to LFA-1. Ligation of the T-cell receptor modulated the phenotypic expression of LFA-1 and ICAM-1 on both HA1.7 and DE-9. Phenotypic modulation was observed as a result of both activation and the induction of non-responsiveness.

CONCLUSION

These experiments indicate that CD4+ T cells of TH-2 functional phenotype may have a greater requirement for the co-stimulatory activity of LFA-1 than CD4+ T cells of TH-0 or TH-1 phenotypes.

Staphylococcal enterotoxins modulate interleukin 2 receptor expression and ligand-induced tyrosine phosphorylation of the Janus protein-tyrosine kinase 3 (Jak3) and signal transducers and activators of transcription (Stat proteins)

Staphylococcal enterotoxins (SE) stimulate T cells expressing the appropriate variable region beta chain of (V beta) T-cell receptors and have been implicated in the pathogenesis of several autoimmune diseases. Depending on costimulatory signals, SE induce either proliferation or anergy in T cells. In addition, SE can induce an interleukin-2 (IL-2) nonresponsive state and apoptosis. Here, we show that SE induce dynamic changes in the expression of and signal transduction through the IL-2 receptor (IL-2R) beta and gamma chains (IL-2R beta and IL-2R gamma) in human antigen-specific CD4+ T-cell lines. Thus, after 4 hr of exposure to SEA and SEB, the expression of IL-2R beta was down-regulated, IL-2R gamma was slightly up-regulated, while IL-2R alpha remained largely unaffected. The changes in the composition of IL-2Rs were accompanied by inhibition of IL-2-induced tyrosine phosphorylation of the Janus protein-tyrosine kinase 3 (Jak3) and signal transducers and activators of transcription called Stat3 and Stat5. In parallel experiments, IL-2-driven proliferation was inhibited significantly. After 16 hr of exposure to SE, the expression of IL-2R beta remained low, while that of IL2R alpha and IL2R gamma was further up-regulated, and ligand-induced tyrosine phosphorylation of Jak3 and Stat proteins was partly normalized. Yet, IL-2-driven proliferation remained profoundly inhibited, suggesting that signaling events other than Jak3/Stat activation had also been changed following SE stimulation. In conclusion, our data suggest that SE can modulate IL-2R expression and signal transduction involving the Jak/Stat pathway in CD4+ T-cell lines.

Modification of immediate hypersensitivity responses by staphylococcal enterotoxin B

The staphylococcal enterotoxins have been termed superantigens based on their ability to stimulate polyclonal proliferative responses of murine and human T lymphocytes expressing particular T-cell receptor V beta gene products. Certain of these toxins have been shown both to activate and to induce anergy in reactive T cells. Staphylococcal enterotoxin B is known to interact with murine T cells bearing V beta 3, -7, -8.1, -8.2, -8.3, and -17. In BALB/c mice V beta 3+ and V beta 17+ T cells are deleted; V beta 7+ T cells are low in frequency. BALB/c mice sensitized to ovalbumin via the skin and airways develop immediate hypersensitivity including IgE/IgG1 antiovalbumin antibodies, immediate cutaneous reactivity to ovalbumin and, increased airway responsiveness. In both in vitro and in vivo studies, the development of these responses has been associated with the V beta 8+ subset of T cells and controlled by V beta 2 + T cells. In view of the central role of V beta 8+ T cells in these responses, we tested the effects of staphylococcal enterotoxin B on the development of immediate hypersensitivity in this system. Intradermal injection of staphylococcal enterotoxin B prevented the development of these responses in the absence of a major deletion of V beta 8+ T cells. The data suggest that the administration of staphylococcal enterotoxin B prevented the antigen-induced expansion of V beta 8+ T cells resulting in a state of responsiveness or anergy, thus preventing the manifestations of immediate hypersensitivity. Bacterial toxins may provide a novel approach to intervention in allergic or autoimmune diseases.

Differential effects of interleukin-10 on the expression of HLA class II and CD1 molecules induced by granulocyte/macrophage colony-stimulating factor/interleukin-4

Interleukin (IL)-10 down-regulates HLA class II molecules, whether constitutively expressed or up-regulated by interferon-gamma or IL-4 on monocytes but not on B lymphocytes. In this study we show that IL-10 does not inhibit HLA class II expression induced by the combination granulocyte/macrophage colony-stimulating factor and IL-4 on monocytes, although it simultaneously abrogates the expression of CD1 molecules induced by the same combination of cytokines. CD1 molecules can act as element of genetic restriction for CD4- CD8- T lymphocytes, and the suppression of CD1 expression by IL-10 abolished antigen presentation to CD1-restricted CD4- CD8- T cell receptor-positive T cells. Although HLA class II expression was not down-regulated by IL-10, the antigen specific proliferative response of CD4+ T cells was nevertheless decreased. This was not caused by down-regulation of known co-stimulatory molecules such as B7.1, B7.2 and ICAM-1. IL-10 decreased the antigen specific proliferative response further by directly influencing the T lymphocytes. Our results indicate that IL-10 exerts some of its immunoregulatory functions by differential modulation of antigen presenting molecules, induced by the same combination of cytokines.