The V beta-specific superantigen staphylococcal enterotoxin B: stimulation of mature T cells and clonal deletion in neonatal mice

T-cell antigen receptors in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic disease of unknown etiology characterized by chronic inflammation mainly in the joints. Several lines of evidence suggest that T cells are involved in the pathogenesis of the disease. RA is associated with certain HLA-DR alleles. Studies analyzing T-cell receptor transcripts in RA have found biased or preferential usage of certain V alpha and/or V beta gene segments by T cells infiltrating the synovial membrane or extravasating into the synovial fluid compared to peripheral blood. In certain patients few T-cell antigen receptor (TCR) clones dominated the infiltrating T cells, suggesting that T cells from the synovial membrane or the synovial fluid comprise oligoclonal populations of T cells. However, other studies have found a polyclonal population of T cells. In interpreting these results the phase of the disease (early vs. late RA), the source of T cells and the limitations of the methods used in these studies should be taken into consideration. However, it appears that synovial T cells comprise oligoclonal populations of T cells and that there is a bias towards particular TCR gene segments, although a specific TCR gene segment in RA has not emerged.

Immunity to T cell receptor peptides: theory and applications

In this review, we describe an anti-idiotypic regulatory mechanism that is naturally induced by the autoimmune disease process, and that can be boosted by injection of TCR peptides that mimic epitopes generated naturally from germline sequences. The striking similarities in the induction and characteristics of rodent and human T cells specific for TCR peptides support the generality of the observation, and enhance the probability that this immunoregulatory mechanism will have application in human organ-specific autoimmune diseases that are characterized by oligoclonal expression of TCR V genes. The major challenges that remain to be resolved to make the TCR peptide therapy more widely applicable include (1) establishing disease-relevant V gene biases in individual patients, (2) identifying biologically active TCR peptide sequences, and (3) demonstrating that the induction of anti-TCR peptide immunity in humans can reduce the pernicious activity of autoreactive T cells putatively directed at organ-specific target antigens.

T cells of staphylococcal enterotoxin B-tolerized autoimmune MRL-lpr/lpr mice require co-stimulation through the B7-CD28/CTLA-4 pathway for activation and can be reanergized in vivo by stimulation of the T cell receptor in the absence of this co-stimulatory signal

The CD28/CTLA-4 receptors on T cells interact with the B7 molecule on antigen-presenting cells (APC) to produce a co-stimulatory signal that determines the outcome of activation. The role of this co-stimulatory signal in T cell activation and loss of tolerance in autoimmune MRL-lpr/lpr mice has not been investigated previously. The present study examines the contribution of the CD28/CTLA-4 co-stimulatory pathway to the loss of T cell tolerance in V beta 8 transgenic MRL-lpr/lpr and (-)+/+ mice in which neonatal tolerance has been induced by the superantigen staphylococcal enterotoxin B (SEB). An artificial APC transfected with the murine B7 gene, and a CTLA-4-Ig fusion protein were used to analyze the significance of the CD28/CTLA-4 pathway in vitro. The CTLA-4-Ig fusion protein was also used to inhibit the pathway in vivo. Our results demonstrate that CD28 and CTLA-4 mRNA was overexpressed in the lymph nodes of lpr/lpr mice (MRL, C57BL/6, C3H and AKR), but not in +/+ mice of the same background strain. Lymph node T cells and thymocytes from SEB neonatally tolerized MRL-lpr/lpr mice that had undergone tolerance loss, proliferated when cultured with SEB and B7+ fibroblasts in vitro, but did not proliferate when the SEB was presented in the context of B7- fibroblasts. This in vitro tolerance loss could be prevented by blocking of B7 signaling by CTLA-4-Ig. This loss of tolerance did not occur in lymph node T cells from thymectomized MRL-lpr/lpr mice. SEB challenge of tolerized MRL-lpr/lpr mice in vivo led to weight loss, increased serum cytokine levels and depletion of V beta 8+ T cells. These effects were blocked by blocking of the co-stimulatory pathway by treatment with the CTLA-4-Ig fusion protein prior to and during challenge with SEB. T cells from thymus and lymph nodes of these mice did not proliferate later in response to stimulation in vitro with SEB even in the presence of B7+ APC. Nonresponsiveness was not due to deletion of V beta 8+ CD28+ T cells, as the number of these cells was increased after treatment with SEB and the CTLA-4-Ig fusion protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Clonal expansion of T lymphocytes causes arthritis and mortality in mice infected with toxic shock syndrome toxin-1-producing staphylococci

Erosive arthritis is a common and feared complication of staphylococcal infection. The reason(s) for the progressive course of the arthritis is unknown. It has been recently established that enterotoxins produced by Staphylococcus aureus display superantigen properties leading to stimulation of T cells carrying distinct T cell receptor V beta elements. This finding provides a potential connection between staphylococcal exoproteins and endogenous immune mechanisms participating in the infectious process. We have recently describe successful induction of infections arthritis in mice after intravenous inoculation of a toxic shock syndrome toxin-1 (TSST-1)-producing S. aureus LS-1 strain. Using this model we have now found a clonal expansion of T cells expressing V beta 11+ T cell receptor in the synovial tissue of arthritic mice. The role of TSST-1 as a superantigen inducing oligoclonal expansion was confirmed in an in vitro culture system. The expansion of V beta 11+ T cells proved to be of arthritogenic significance since mice genomically deleted of the V beta 11+ T cells did not develop arthritis and since pretreatment of healthy mice with anti-CD4 or anti-V beta 11 monoclonal antibodies inhibited arthritis. In addition, CD4+ and V beta 11+ T cells showed themselves to be of pathogenic significance in staphylococcal-induced mortality, since mice depleted of such populations showed increased survival. We propose that in hematogenously spread S. aureus-induced arthritis the TSST-1-dependent clonal expansion of CD4+ V beta 11+ T cells is a driving pathogenic force.

Evidence for a superantigen in human tuberculosis

T cells are not only required for resistance to tuberculosis, but they likely contribute to the tissue damage characteristic of the disease. To define better the T cell populations that contribute to the immunopathogenesis of human tuberculosis, we investigated the T cell receptor (TCR) beta chain repertoire expressed in patients with tuberculous pleuritis. Analysis by polymerase chain reaction and flow cytometry indicated an expansion of V beta 8+ T cells at the site of disease in some donors, suggesting the possibility that Mycobacterium tuberculosis contains a superantigen. M. tuberculosis induced strong T cell proliferative responses in tuberculin-negative healthy donors in vitro, with preferential expansion of V beta 8+ T cells, independent of the CDR3 region. T cell stimulation was MHC class II-dependent and did not require antigen processing by the antigen-presenting cells. These findings are consistent with the presence of a superantigen in M. tuberculosis, aspects of which may contribute to the immunopathology of tuberculosis and to the adjuvant properties of M. tuberculosis.

Stimulation with specific antigen can block superantigen-mediated deletion of T cells in vivo

The T-cell response to pigeon cytochrome c peptide, residues 88-104 (pcytC), in B10.BR mice is mediated largely by cells bearing both V beta 3 and V alpha 11 variable regions of the T-cell antigen receptor. These cells are, therefore, reactive with the superantigen staphylococcal enterotoxin A (SEA). Recent reports have shown that in vivo exposure to superantigen can lead to deletion of superantigen-reactive T cells from the pool of mature T cells in the periphery. Here we show that upon cotreatment of animals with both SEA and pcytC, bulk deletion of the population of SEA-reactive cells is maintained, while the subpopulation of SEA-reactive T cells that also responds to pcytC is not deleted but instead proliferates in response to pcytC. These results are discussed with regard to mechanisms regulating the balance between T-cell tolerance and T-cell activation in vivo.

Antagonism of superantigen-stimulated helper T-cell clones and hybridomas by altered peptide ligand

T-cell activation by an immunogenic peptide can be antagonized by nonstimulatory analogs of that peptide. We investigated this T-cell receptor antagonism by using staphylococcal enterotoxin superantigen to stimulate hemoglobin-specific helper T (Th) cells because its activation pathway may differ from that of conventional antigen. Interestingly, superantigen activation of these Th cells was antagonized by hemoglobin peptide analogs even though agonist (superantigen) and antagonist (analog peptide) bind at different sites on the major histocompatibility complex-encoded molecule and the T-cell receptor. The antagonism appeared to be a fundamental block in T-cell activation, as phosphoinositol generation, cytokine production, and proliferation were reduced in Th1 clones, and, similarly, proliferative and cytokine responses were inhibited in Th2 cells. Even T-cell hybridoma activation (cytokine production and apoptosis) was inhibited by peptide antagonists. Furthermore, analog peptides that functioned as partial agonists for these Th cells also antagonized superantigen-induced proliferation and thus were a subset of the peptide antagonists. In summary, our results demonstrate that analogs of immunogenic peptide are potent antagonists for Th cell responses induced by superantigen as well as immunogenic peptide.

Absence of peripheral clonal deletion and anergy in immune responses of T cell-reconstituted athymic mice

Superantigens induce clonal deletion of reactive T cells in the thymus and clonal deletion and anergy in the periphery of euthymic mice. In this report we have assessed the ability of Staphylococcal enterotoxin B (SEB) to induce peripheral tolerance in nude mice reconstituted with normal, syngeneic T cells. Immunization of reconstituted nude mice with SEB resulted in lethal toxic shock in a large fraction of the animals. Such lethality was never observed in the normal donor mouse strain. Analysis of lymphokine production in response to SEB showed that reconstituted nude mice produced higher levels of interleukin-2 and tumor necrosis factor-alpha, but lower levels of interleukin-4, than euthymic control mice. Furthermore, SEB was unable to promote either clonal elimination or induction of anergy in the SEB-responsive peripheral T cells, despite the fact that reconstituted nude mice did produce high levels of corticosterone upon treatment with SEB. These results imply a lack of control over immune responses to superantigen in T cell-reconstituted athymic mice.

Analysis of the T-cell receptor beta-chain variable-region (V beta) repertoire in monozygotic twins discordant for human immunodeficiency virus: evidence for perturbations of specific V beta segments in CD4+ T cells of the virus-positive twins

We analyzed the T-cell receptor (TCR) V beta repertoire in human immunodeficiency virus type 1 (HIV-1)-infected individuals at different stages of disease. To circumvent the effect of HLA and other loci on the expressed TCR repertoire, we compared the TCR repertoire in nine pairs of monozygotic twins who were discordant for HIV infection. A semiquantitative polymerase chain reaction (PCR) assay and flow cytometry enabled us to show distinct differences in the V beta repertoire in the HIV-positive twin compared with the HIV-negative twin. By combining PCR and cytofluorometry, these differences were restricted to a specific set of TCR V beta segments, with members of the V beta 13 family perturbed in six out of seven cases and those of the V beta 21 family perturbed in four out of seven cases studied. Most of the other V beta families remained unchanged. Our results provide direct evidence for a skewed TCR repertoire in HIV infection.

Selective anergy of V beta 8+ T cells in human immunodeficiency virus-infected individuals

We have analyzed the V beta usage by CD4+ and CD8+ T cells from human immunodeficiency virus (HIV)-infected individuals in response to an in vitro stimulation with the superantigenic erythrogenic toxin A (ETA) of Streptococcus pyogenes. ETA amplifies specifically CD4+ and CD8+ T cells from control donors expressing the V beta 8 and the V beta 12 elements. When peripheral T cells from asymptomatic HIV-infected individuals were stimulated with ETA, there was a complete lack of activation of the V beta 8+ T cell subset, whereas the V beta 12+ T cell subset responded normally to the superantigen. This V beta-specific anergy, which was also observed in response to staphylococcal enterotoxin E (SEE), affected both CD4+ and CD8+ T cells and represented an intrinsic functional defect rather than a specific lack of response to bacterial superantigens since it was also observed after a stimulation with V beta 8 monoclonal antibodies. The V beta 8 anergic T cells did not express interleukin 2 receptors (IL-2Rs) and failed to proliferate in response to exogenous IL-2 or IL-4, suggesting that this anergy was not a reversible process, at least by the use of these cytokines. The unresponsiveness of the V beta 8 T cell subset is frequent since it was found in 56% of the patients studied, and comparison of the clinical status of responder vs. anergic patients indicated that the only known common factor between them was HIV infection. In addition, it is noteworthy that the anergy of the V beta 8 subset may be a very early phenomenon since it was found in a patient at Centers for Disease Control stage I of the disease. These data provide evidence that a dominant superantigen may be involved in the course of HIV infection and that the contribution of HIV has to be considered.

Activation of human T cells by the superantigen Staphylococcus enterotoxin B: analysis on a cellular level

Superantigens interact with and activate a sizeable fraction of T cells characterized by expression of specific V beta gene segments of their antigen receptor. The massive activation of T cells in an organism is considered responsible for clinical symptoms associated with superantigen-producing bacteria. Here we studied the in vitro activation of human T cells by the superantigen Staphylococcus Enterotoxin B on a cell by cell basis. Superantigen-reactive T cells were stained with a V beta 12-specific monoclonal antibody and analyzed in a cytofluorograph. Blast formation of SEB-reactive T cells occurs within 12 h and reaches a plateau after 24 h. Double-staining of V beta 12+ T cells with antibodies against different T cell activation or adhesion surface molecules revealed a time-dependent differential upregulation for CD2, CD11 = LFA-1, CD25, CD28, CD69, and HLA-DR. The expression of CD3, CD4 and CD5 was not influenced by the superantigen. The rapid phenotypic changes of superantigen reactive T cells in terms of marker expression and cell size could provide early tools in diagnosing diseases caused by superantigens.

Differential effects of superantigen-induced "anergy" on priming and effector stages of a T cell-dependent antibody response

The in vitro T cell nonresponsiveness or anergy to restimulation with staphylococcal enterotoxin B (SEB) following the in vivo injection of the superantigen is well characterized. Here we use mice transgenic for a V beta 8.2+ T cell receptor (TcR) (reactive with SEB) to establish a large population of anergic T cells in vivo. As expected, peripheral T cells from the SEB injected transgenic mice failed to proliferate or produce interleukin (IL)-2 following restimulation with the superantigen in vitro. However, in this system superantigen reactivity could be restored by either addition of exogenous IL-2, or stimulation with immobilized anti-TcR antibody. To evaluate the effects of superantigen-induced anergy in vivo, SEB-injected or noninjected control transgenic mice were immunized and boosted with the T cell-dependent antigen tetanus toxin (TT). SEB injection of the V beta 8.2+ transgenic mice 5 days prior to the TT immunization inhibited the anti-TT antibody response as measured over a 100-day period, whereas injection of a superantigen which does not interact with the V beta 8.2% TcR (such as SEA) did not. Furthermore, SEB injection of control nontransgenic mice did not interfere with the induction of a high titer anti-TT antibody response. In contrast to the inhibition seen when SEB was given prior to TT immunization, injection of transgenics with SEB either after the priming TT immunization or after the recall booster injection did not significantly influence the titers of anti-TT antibodies produced. These results demonstrate that the establishment of peripheral T cell anergy to superantigens inhibits the specific antigenic priming of helper T cells in vivo, but does not prevent primed T cells from helping B cells to mount an effective antibody response.

Interferon gamma-treated keratinocytes activate T cells in the presence of superantigens: involvement of major histocompatibility complex class II molecules

During inflammation in the skin keratinocytes can express major histocompatibility complex class II molecules but are unable to present nominal antigens to resting T cells. Certain bacteria including staphylococci produce a new class of antigens termed superantigens that are very potent T-cell activators. Using an in vitro model with cultured normal human keratinocytes and purified allogeneic T cells, we demonstrated that major histocompatibility complex class II+ keratinocytes can activate T cells in the presence of the superantigen staphylococcal enterotoxin B. Major histocompatibility complex class II+ keratinocytes activated T cells at concentrations of staphylococcal enterotoxin B as low as 100 pg/ml. The activation required contact between keratinocytes and T cells, was inhibited with a monoclonal antibody to human leukocyte antigen DR, -DQ, and was not affected by fixation of the keratinocytes. These data show that major histocompatibility complex class II+ keratinocytes activate T cells in the presence of the superantigen staphylococcal enterotoxin B.

Hepatic injury and lethal shock in galactosamine-sensitized mice induced by the superantigen staphylococcal enterotoxin B

BACKGROUND/AIMS

Staphylococcal enterotoxin B (SEB) acts as a superantigen binding to class II major histocompatibility complex proteins, and this complex stimulates T cells. The aim of this study was to investigate the pathogenic effects of SEB on hepatic injury and lethal shock in mice.

METHODS

SEB was administered to D-galactosamine (GalN)-sensitized mice, and the degree of liver injury and levels of circulating cytokines were determined. In vitro cytokine production in response to SEB was also investigated.

RESULTS

Intraperitoneal administration of SEB (50 micrograms) caused lethal shock (50% mortality) associated with massive hepatic necrosis in GalN-sensitized mice, with no mortality on injection of up to 100 micrograms SEB alone. Within 2 hours after injection of SEB, serum tumor necrosis factor alpha (TNF-alpha) levels reached a peak, followed by high levels of serum interferon-gamma (IFN-gamma) up to 10 hours after injection. Passive immunization with anti-TNF-alpha/beta-neutralizing monoclonal antibody (mAb) protected GalN-sensitized mice from the lethal effects of SEB, with less protection with anti-IFN-gamma-neutralizing mAb. SEB induced the production of TNF-alpha and IFN-gamma in a dose-dependent manner from splenic mononuclear cells in vitro.

CONCLUSIONS

The results show that SEB contributes to lethal shock associated with severe hepatic injury in GalN-sensitized mice and suggest that TNF-alpha and IFN-gamma produced in response to SEB may be mediators of the lethal toxicity and hepatotoxicity of SEB.

Prominent T lymphocyte response to Borrelia burgdorferi from peripheral blood of unexposed donors

The proliferative response of peripheral blood T cells to the spirochete, Borrelia burgdorferi, can be as pronounced in unexposed normal individuals as it is in Lyme disease patients. This finding was observed using three geographically distinct isolates of B. burgdorferi. The response is not due to a lipopolysaccharide effect of the spirochete, is sensitive to Proteinase K, and requires antigen processing. It does not result from cross-reactivity of memory T cells that may be reactive to another antigen; the proliferative response to B. burgdorferi is equally distributed between naive (CD29-, CD45RO-) and memory (CD29+, CD45RO+) T cells, whereas the tetanus response is confined to the memory subset. In support of this notion, cord blood specimens that contain almost entirely naive T cells, respond as vigorously to B. burgdorferi as T cells from normal adult peripheral blood. A large panel of CD4+ T cell clones has been derived that are specific for B. burgdorferi. The majority of these clones are reactive to B. burgdorferi in the presence only of autologous HLA-DR molecules. Collectively, these data suggest that the T cell response from normal individuals is more likely due to multiple antigenic epitopes within Borrelial proteins than a superantigen response.

Structural basis of superantigen action inferred from crystal structure of toxic-shock syndrome toxin-1

Superantigens stimulate T cells bearing particular T-cell receptor V beta sequences, so they are extremely potent polyclonal T-cell mitogens. T-cell activation is preceded by binding of superantigens to class II major histocompatibility complex (MHC) molecules. To further the structural characterization of these interactions, the crystal structure of a toxin associated with toxic-shock syndrome, TSST-1, which is a microbial superantigen, has been determined at 2.5 A resolution. The N- and C-terminal domains of the structure both contain regions involved in MHC class II association; the C-terminal domain is also implicated in binding the T-cell receptor. Despite low sequence conservation, the TSST-1 topology is similar to the structure reported for the superantigen staphylococcal enterotoxin B4. But TSST-1 lacks several of the structural features highlighted as central to superantigen activity in the staphylococcal enterotoxin B and we therefore reappraise the structural basis of superantigen action.

T cell influence on superantigen-induced arthritis in MRL-lpr/lpr mice

OBJECTIVE

To define the influence of the T cell receptor (TCR) and the lpr autoimmune gene on the induction and progression of superantigen-induced arthritis in V beta 8 transgenic MRL-lpr/lpr mice.

METHODS

The time to onset and the extent of synovial hyperplasia after the induction of arthritis by intraarticular injection of staphylococcal enterotoxin B (SEB) were compared in mice having T cells that bear the V beta 8 transgene alone (V beta 8 TCR transgenic MRL-+/+), the lpr gene without the V beta 8 gene (nontransgenic MRL-lpr/lpr), both the V beta 8 gene and the lpr gene (V beta 8 transgenic MRL-lpr/lpr), or neither gene (nontransgenic MRL-+/+). Synovial hyperplasia was compared in SEB-injected V beta 8 transgenic MRL-lpr/lpr mice after treatment with cyclosporin A (CSA), anti-V beta 8 and anti-CD4 monoclonal antibodies, and in V beta 8 transgenic MRL-lpr/lpr mice after injection of a non-V beta 8-reactive superantigen, staphylococcal enterotoxin A (SEA).

RESULTS

At day 30, increased synovial cells were observed in all SEB-treated mice, but the increase was greatest in the V beta 8 transgenic MRL-lpr/lpr mice. T cell involvement was indicated by the inability of either heat-denatured SEB or SEA to induce severe arthritis, the reduction in the severity of the arthritis on systemic treatment with CSA or anti-V beta 8, and the correlation of synovial hyperplasia with in vitro SEB reactivity of T cells.

CONCLUSION

These observations suggest that superantigens can induce chronic arthritis and that the induction and progression of the arthritis requires an underlying T cell defect in anergy induction in addition to exposure to the superantigen.

Linomide inhibits programmed cell death of peripheral T cells in vivo

Programmed cell death (PCD) is involved in the physiological regulation of lymphocyte turnover, as well in the antigen-driven selection of T and B cells. Here it is shown that the immunomodulator linomide (quinoline-3-carboxamide) inhibits the apoptotic decay of peripheral T lymphocytes in response to three different stimuli. First, linomide reduces the superantigen-mediated apoptosis and deletion of specific T lymphocytes of both the CD4+ and the CD8+ subsets without affecting other superantigen-triggered phenomena such as T cell expansion and anergy. Second, linomide abolishes the T lymphopenia and inhibits PCD of splenic CD4+ and CD8+ T cells induced by exogenous glucocorticoids. This effect is restricted to peripheral T lymphocytes and does not concern thymocytes. Finally, linomide abolishes the development of lymphopenia that follows infection with vaccinia virus, while reducing PCD of CD4+ and CD8+ peripheral T cells. The anti-apoptotic effect of linomide could account for its immunostimulatory properties and might be relevant to the treatment of immunodeficiencies associated with an increased apoptotic decay of T lymphocytes.

A study of mast cells in autoimmune mice: the proliferative response of autoimmune mast cells to cytokines

To investigate the mechanisms underlying the increased number of mast cells in autoimmune mice, the proliferative response of autoimmune mast cells to cytokines was examined. Bone marrow cells from autoimmune NZB mice produced scarcely any bone marrow derived mast cells (BMMCs) in the presence of interleukin 3 (IL-3), but were able to generate BMMCs when cultured with pokeweed mitogen-stimulated spleen cell conditioned medium (PWM-SCM). In contrast, NZB BMMCs showed very little proliferation in the presence of PWM-SCM, but proliferated strongly when cultured with stem cell factor (SCF). Non-autoimmune NZW BMMCs showed a strong proliferative response to both IL-3 and PWM-SCM, but proliferated weakly in culture with SCF. Autoimmune NZB x NZW F1 (B/W) BMMCs shared the proliferative activities of both NZB and NZW BMMCs, showing strong proliferation in response to IL-3, PWM-SCM and SCF. All strains (including other non-autoimmune strains) except for NZW demonstrated synergism between PWM-SCM and SCF. This study suggests that the strong proliferative response of autoimmune mast cells to SCF plays a major role in, and that other cytokines are partially responsible for, increasing the number of mast cells in autoimmune mice. These mechanisms are discussed in relation to both constitutive and inducible hematopoiesis.

Superantigenic staphylococcal exotoxins induce T-cell proliferation in the presence of Langerhans cells or class II-bearing keratinocytes and stimulate keratinocytes to produce T-cell-activating cytokines

Several staphylococcal toxins are among a growing number of immunostimulatory molecules called "superantigens" because of their ability, when presented by appropriate major histocompatibility complex class II+ accessory cells, to activate essentially all T cells bearing particular T-cell receptor V beta gene segments. We have examined the ability of murine epidermal Langerhans cells and/or keratinocytes to act as accessory cells in the T-cell response to the superantigens staphylococcal enterotoxin B and exfoliative toxin, also known as epidermolysin. Purified murine splenic T cells were stimulated with staphylococcal enterotoxin B or exfoliative toxin in the presence of Langerhans cells--enriched epidermal cells from normal mice or epidermal cells isolated from mice pretreated with recombinant interferon-gamma, a procedure that induces the expression of major histocompatibility complex class II molecules on keratinocytes. The data show that both Langerhans cells and class II-bearing keratinocytes can act as accessory cells in the T-cell response to staphylococcal enterotoxin B and exfoliative toxin. We also observed that both human and murine keratinocytes cultured in the presence of staphylococcal enterotoxin B or exfoliative toxin produce increased amounts of cytokine(s) capable of stimulating thymocytes and D10 cells, and that this toxin activity is independent of the level of expression of class II on keratinocytes. Studies by enzyme-linked immunosorbent assay showed that staphylococcal enterotoxin B stimulates keratinocytes to produce tumor necrosis factor-alpha but not interleukin-1, suggesting tumor necrosis factor-alpha and perhaps other cytokines are responsible for the T-cell proliferative activity. These results demonstrate that two distinct epidermal constituents (i.e. Langerhans cells and keratinocytes) can serve as accessory cells in the responses of T cells to superantigenic bacterial toxins. It is possible that such toxins contribute to the pathogenesis of a variety of skin diseases by either locally activating T cells bearing particular V beta genes and/or enhancing keratinocyte production of immunomodulatory cytokines.

Superantigens

"Superantigens" is the term for a group of molecules that have in common an extremely potent stimulatory activity for T lymphocytes of several species. They stimulate CD4+, CD8+ and gamma delta + T cells by a unique mechanism: they cross-link variable parts of the T-cell receptor (TCR) with MHC class II molecules on accessory or target cells. The interaction site on the class II molecule and on the TCR is different from the peptide binding site; on the TCR it is the variable part of the beta chain (V beta). The prototype superantigen is the staphylococcal enterotoxin B (SEB), member of a family of genetically related proteins produced by Staphylococcus aureus and Streptococcus pyogenes. These are soluble exotoxins of approximately 27 kd molecular mass. It is intriguing that this molecular mechanism of T-cell stimulation has been independently produced at least three times in evolution. Other pathogens producing superantigens are retroviruses (the Mouse Mammary Tumor Viruses) and a mycoplasma (Mycoplasma arthritidis). Many additional candidate superantigens have been proposed, but in most cases unequivocal evidence for superantigen activity is still missing. There are several reasons why these molecules have aroused such tremendous interest in recent years. First, they have provided key information on tolerance mechanisms, both on the deletion of T cells in the thymus and on the induction of peripheral tolerance by anergy and apoptosis. Second, of all polyclonal T-cell stimulators they are the ones that most closely mimic the recognition of specific antigen. Finally, they have been recognized as important factors in the pathogenicity of the producing pathogens, inducing shock and immunosuppression. Whilst there is evidence that superantigens could be involved in the pathogenesis of certain human diseases, in most cases this is still very preliminary and indirect.

Human T-cell responses to Mycoplasma arthritidis-derived superantigen

When injected into mice, Mycoplasma arthritidis causes a chronic arthritis that resembles rheumatoid arthritis, histologically. The organism produces a superantigen termed Mycoplasma arthritidis mitogen or MAM, that in humans preferentially expands T cells whose antigen receptors express V beta 17. T cells with this phenotype appear to be increased in rheumatoid synovial effusions. We describe a novel approach to isolating and characterizing human MAM-reactive T-cell lines and determining their T-cell receptor (TCR) V beta usage. Lines were prepared from T cells that clustered with dendritic cells during a 2-day exposure to MAM. Cluster and noncluster fractions of T cells were then expanded by using feeder cells and a polyclonal mitogen. Most of the MAM reactivity was found in dendritic T-cell clusters, as were most of the T cells expressing TCR V beta 17. After expansion, 76% of the cluster-derived T-cell lines were MAM reactive, while no reactivity was seen in cell lines derived from the noncluster fraction. Of the MAM-reactive lines, 49% expressed V beta 17 on some or all of the cells. Cell lines from both cluster and noncluster fractions were analyzed for TCR V beta mRNA expression by PCR amplification. Other V beta genes (5.1, 7, 8, 12, and 20) were found to be expressed by lines that were MAM reactive, although these were not a major component of the cluster-derived T cells. Some non-cluster-derived lines expressed V beta s 17, 12, and 7, but these proved to be nonreactive to MAM. Therefore, dendritic cells can be used to immunoselect and characterize T cells that express superantigen-reactive TCRs.

Structure of toxic shock syndrome toxin 1

The three-dimensional structure of toxic shock syndrome toxin 1 (TSST-1) from Staphylococcus aureus has been determined and refined to an R value of 0.226 for data between 8- and 2.5-A resolution. Overall, the structure of TSST-1 is similar to that of another superantigen, staphylococcal enterotoxin B (SEB). The key differences between these molecules are in the amino termini and in the degree to which a long central helix is covered by surface loops. The region around the carboxyl end of this central helix is proposed to govern the superantigenic properties of TSST-1. An adjacent region along this helix is proposed to be critical in the ability of TSST-1 to induce toxic shock syndrome.

HLA class II molecule-mediated signal transduction mechanism responsible for the expression of interleukin-1 beta and tumor necrosis factor-alpha genes induced by a staphylococcal superantigen

Superantigens including staphylococcal enterotoxins (SE) bind to major histocompatibility complex class II molecules and interact with T cells bearing particular V beta chains. SEB was shown to induce the expression of interleukin (IL)-1 beta and tumor necrosis factor (TNF)-alpha genes in human peripheral blood monocytes bearing HLA class II molecules. Monoclonal antibodies directed against HLA-DR and -DQ abolished the SEB-induced expression of both the IL-1 beta and TNF-alpha genes, suggesting that the HLA class II molecules mediated the gene expression. Therefore, we investigated the signal transduction mechanism responsible for the expression of IL-1 beta and TNF-alpha genes induced by binding of SEB to the HLA class II molecules. Three protein tyrosine kinase (PTK) inhibitors, genistein, herbimycin A, and tyrphostin, each of which has a different mechanism of action, strongly inhibited the expression of the monokine mRNA induced by SEB. Analyses of PTK activity revealed that SEB induced a rapid increase of membrane-associated PTK activity and this was blocked by tyrphostin. Furthermore, H-7 inhibited the expression of the monokine mRNA induced by SEB, suggesting the involvement of protein kinase C (PKC) in the signaling pathway. The involvement of PKC was confirmed by the observations that phorbol 12-myristate 13-acetate (PMA), a direct activator of PKC, induced the expression of the monokine mRNA and that SEB evoked the activation of membrane-associated PKC. Both activation of PKC and expression of the monokine mRNA induced by SEB appeared to be inhibited by tyrphostin, but those induced by PMA were not. Taken together, these findings indicate that both PTK and PKC play essential roles in HLA class II molecule-mediated signal transduction elicited by SEB and that PTK activation may precede PKC activation in the signaling pathway.

Superantigen mediated shock: a cytokine release syndrome

Treatment of animals with superantigens results in profound immunological changes. A major fraction of all peripheral T cells becomes activated in vivo. Subsequently, successive waves of cytokines are produced with TNF playing a central pathophysiologic role. In addition, if the liver is damaged by an as yet poor defined mechanism the consequences of the cytokine syndrome are life threatening. However, TNF alone is not sufficient to cause death, instead synergizing interactions with cytokines like IL-1, IL-6, and IFN-gamma are probably involved. On the other hand, certain experimental conditions prevent these waves of cytokines and consequently lethal shock. Furthermore, a significant fraction of SA reactive T cells are deleted by programmed cell death 10 to 24 hours after treatment. Thereafter the surviving cells proliferate vigorously until day 2 or 3, followed by a second wave of apoptosis resulting in reduced SA reactive T cell numbers as compared to pretreatment levels. Of course, many aspects of the complicated events are only marginally understood and deserve further investigation.

Identification of an endogenous mammary tumor virus involved in the clonal deletion of V beta 2 T cells

Expression of V beta (beta-chain variable region) gene segments was investigated in the Mus m. domesticus DDO strain, which possesses a large genomic deletion encompassing 20 of the 29 V beta gene segments known in BALB/c. Stainings using V beta-specific monoclonal antibodies revealed that up to 60% of the peripheral T cells use 3 V beta gene segments. Variable frequencies of V beta 2 T cells were observed among DDO individuals. Segregation analyses of F2 crosses between V beta 2-deletor mice and mammary tumor virus (Mtv)-free mice led to the identification of a new endogenous Mtv, named Mtv-DDO, mediating V beta 2 T cell clonal deletion. Mtv-DDO structure is conserved with the exception of the carboxy-terminal region as compared to other Mtv. Comparison between Mtv sharing the same V beta specificity and isolated from laboratory or wild mice confirms that a stretch of 11 amino acids, defined as the V beta-specific region, is required for the V beta-specific interaction. Limited substitutions in this region account for the shift of the Mtv specificity towards different V beta.

Interleukin 10 protects mice against staphylococcal enterotoxin B-induced lethal shock

We investigated the ability of interleukin 10 (IL-10) to protect mice against lethal shock induced by staphylococcal enterotoxin B (SEB). Treatment of mice with IL-10 prevented the death of mice injected with SEB in a dose-dependent manner. IL-10-mediated protection was apparent when administered either prior to or concurrent with SEB but was less effective when administered following SEB injection. This observation indicates that IL-10 is capable of regulating T-cell activation in vivo.

Distribution and kinetics of superantigen-induced cytokine gene expression in mouse spleen

The polyclonal stimulation of T cells by bacterial superantigens is involved in the pathogenesis of the toxic shock syndrome in certain staphylococcal and streptococcal infections. Here we describe the onset and kinetics of superantigen-induced cytokine production in situ in spleens of normal BALB/c mice monitored at the level of cytokine mRNA expression by in situ hybridization. Messenger RNAs for interleukin 2 (IL-2), interferon gamma, and tumor necrosis factors (TNF) alpha and beta were not expressed at detectable levels in spleens of unstimulated animals but became visible already 30 min after intraperitoneal application of 50 micrograms staphylococcal enterotoxin B. All mRNA levels showed peak expression approximately 3 h after injection and a slow decrease up to 24 h after injection. Expression of the mRNAs was restricted to the T cell-dependent area of the periarteriolar lymphatic sheets of the spleen. Interestingly, TNF-alpha mRNA showed a biphasic response, the early appearing mRNA had the same localization as the other mRNAs, whereas after 3 h TNF-alpha mRNA showed a broader distribution indicating a second cell population producing TNF-alpha. The expression of IL-2 and TNF proteins in the serum increased in parallel to the observed mRNA changes with a slight delay. The presence of macrophages was not required for the expression of the cytokine mRNAs in the spleen as the expression was unchanged in macrophage-depleted mice. Only the second phase of TNF-alpha mRNA expression was abrogated in such animals. The expression of all mRNAs was completely suppressed by prior administration of cyclosporin A. These data show that nonphagocytic cells are the essential superantigen-presenting cells in vivo and indicate that at least part of the pathogenetic TNF-alpha is T cell derived.

Nitric oxide production from a macrophage cell line: interaction with autologous and allogeneic lymphocytes

The indirect stimulation of macrophages to produce nitrite was examined by using the macrophage cell line J774.J774 spontaneously produced nitrite, when cultured at high concentration. J774 cultured in low concentration (< 10(4) cells in 100 microliters) barely produced nitrite. J774 cultured in low concentration produced a large amount of nitrite by the co-culture of nonadherent spleen cells or nonadherent peritoneal exudate cells, which were stimulated with con A, anti-CD3, or staphylococcal enterotoxin A. J774 (BALB/c derived: H-2d) cultured with either syngeneic (BALB/c) or allogeneic (B6; H-2b B10BR; H-2k) nonadherent lymphocytes, which were stimulated with conA or anti-CD3, produced nitric oxide. However, J774 produced nitric oxide by stimulation with SEA only when co-cultured with SEA-reactive T lymphocytes. Peritoneal exudate cells from mice, which did not proliferate by the stimulation of conA or anti-CD3, proliferated well by the addition of L-arginine homologue, NG-monomethyl-L-arginine. The proliferation of nonadherent peritoneal exudate cells stimulated with conA or anti-CD3 was suppressed by the addition of peritoneal macrophages. This suppression was abolished by the addition of NG-monomethyl-L-arginine.

Induction of relapsing paralysis in experimental autoimmune encephalomyelitis by bacterial superantigen

The role of infection in the pathogenesis of clinical relapses that occur in most autoimmune diseases, including multiple sclerosis, remains to be established. Experimental autoimmune encephalomyelitis (EAE) serves as a model for multiple sclerosis, with episodes of relapsing paralysis. In certain strains of mice, T-lymphocytes expressing the V beta 8 T-cell receptor (TCR) engage the amino-terminal epitope Ac1-11 of myelin basic protein, leading to EAE. The bacterial superantigen staphylococcal enterotoxin B (SEB) activates V beta 8-expressing T cells. Here we show that after immunization with Ac1-11, or after transfer of encephalitogenic T-cell lines or clones reactive to Ac1-11, SEB induces exacerbation or relapses of paralytic disease in mice that are in clinical remission following an initial episode of paralysis, and triggers paralysis in mice with subclinical disease. Tumour necrosis factor has a critical role in the mechanism underlying SEB-induced exacerbation of disease, because anti-tumour necrosis factor antibody given in vivo delays the onset of paralysis triggered by SEB. On reactivation of autoaggressive cells through their T-cell receptor, superantigens may induce clinical relapses of autoimmune disease.

Clonal anergy to staphylococcal enterotoxin B in vivo: selective effects on T cell subsets and lymphokines

Injection of bacterial superantigens such as staphylococcal enterotoxin B (SEB) in adult mice results in initial proliferation of SEB-responsive V beta 8+ T cells followed by induction of a state of non-responsiveness frequently referred to as clonal anergy. We show here that SEB-induced anergy involves selective changes in lymphokine production and that it affects CD4+ V beta 8+ and CD8+ V beta 8+ T cells in different fashions. Whereas both CD4+ V beta 8+ and CD8+ V beta 8+ cells from anergic mice exhibit strongly reduced proliferative capacity and interleukin(IL)-2 production upon restimulation with SEB either in vivo or in vitro the CD8+ subset from SEB-injected mice produces other lymphokines (such as interferon(IFN)-gamma) at normal or slightly increased levels in response to SEB. Changes in the levels of production of IL-2 and IFN-gamma protein correlated well with mRNA accumulation both in vivo and in vitro. Collectively these data suggest that superantigen-induced anergy involves selective changes in signal transduction and/or gene regulation in T lymphocytes.

Cloning, characterization and overexpression of a Streptococcus pyogenes gene encoding a new type of mitogenic factor

A new type of mitogenic factor, termed MF, has been found in the culture supernatant of Streptococcus pyogenes and its N-terminal amino acid sequence has been determined. On the basis of this sequence, an S. pyogenes gene encoding MF was cloned and its nucleotide sequence was determined. The MF gene includes a long, open reading frame with 813 nucleotides capable of encoding the MF precursor protein with 271 amino acids. Removal of the putative 43 residues as a signal peptide results in the mature MF protein with 228 amino acids. The molecular mass of the mature MF is calculated as 25,363 which is consistent with the previously determined value of 25,370 for MF secreted from S. pyogenes. Neither nucleotide nor amino acid sequence homology was found between the mature MF and other streptococcal pyrogenic exotoxins, such as SPE A, SPE B and SPE C. The mature MF was recombinantly overexpressed as a fusion protein with glutathione S-transferase in Escherichia coli. The recombinant protein showed mitogenic activity in rabbit peripheral blood lymphocytes and immunoreactivity with the rabbit antiserum raised against the secreted MF from S. pyogenes. These data indicate that a unique gene encoding MF was cloned from S. pyogenes.

Autoimmune syndrome after induction of neonatal tolerance to I-E antigens

Neonatal injection of semiallogeneic spleen cells induces a state of specific tolerance to the parental alloantigens, but also the development of an autoimmune syndrome known as host-versus-graft disease (HVGD). The autoimmune features are a consequence of the allogeneic cooperation between persisting alloreactive host T helper type 2 (TH2) cells and donor semiallogeneic B cells. It has been established that I-A alloantigens play a central role in the triggering of this HVGD. Here it was investigated if I-E antigens, which have shown functional differences, regarding autoimmunity and alloreactivity, with respect to I-A antigens, are also able to trigger this autoimmune syndrome. The injection of spleen cells from [B10.A(4R) x B10.A(2R)]F1 (I-E+) hybrid mice into newborn B10.A(4R) (I-E-) mice was accompanied by the establishment of chimerism and also by the development of a characteristic, but moderated, HVGD. The weak intensity of this HVGD is likely due to the moderation of the alloreactive responses induced against I-E molecules. Moreover, the marked increase in the levels of IgE and in the titers of anti-DNA IgG1 antibodies strongly suggest that alloreactive TH2 cells play also a main role in the autoimmune syndrome following tolerization to I-E antigens. Therefore, it is concluded that the I-E and I-A isotypes are functionally similar with respect to the allogeneic cellular interactions that account for the HVGD.

Lack of selective V beta deletion in peripheral CD4+ T cells of human immunodeficiency virus-infected infants

To investigate the possibility of super-antigen-mediated deletions of T cells expressing particular T cell receptor V beta (TcR V beta) gene segments during human immunodeficiency virus (HIV) infection, TcR V beta usage in CD4+ and CD8+ subsets was analyzed in a cohort of infants maternally infected by HIV and in a group of healthy neonates. We used a semi-quantitative anchored polymerase chain reaction technique together with cytofluorographic analysis with anti-V beta monoclonal antibodies. The representation of the 24 V beta families in CD4+ and CD8+ T cells from normal neonates was very similar to that in adults. Preferential expression of V beta 2 in the CD4+ subset was observed in both the neonates and in healthy adults. The representation of the 24 V beta families in peripheral CD4+ T cells from the HIV-infected infants showed no selective V beta deletion, even when the CD4+ subset was globally depleted. Moreover, the main characteristics of the control group (predominance of certain V beta families and V beta 2 skewing towards the CD4+ subset) were also present in all the HIV-infected infants.

T cell immunity after a viral infection versus T cell tolerance induced by soluble viral peptides

The fate of in vivo activated CD8+ cytotoxic T cells was studied in transgenic mice expressing a T cell receptor (TCR) specific for the lymphocytic choriomeningitis virus (LCMV) glycoprotein peptide 33-41 presented by major histocompatibility complex (MHC) class I molecules. LCMV infection of TCR transgenic mice induced LCMV-specific effector and memory T cells whereas injection of soluble LCMV glycoprotein peptide 33-41 resulted in tolerance by peripheral deletion and anergy of LCMV-specific T cells after an initial expansion phase. Similarly, LCMV peptide 33-41-specific tolerance could be achieved in normal C57BL/6 mice and was not abrogated by an LCMV infection. These results obtained with a classically MHC-restricted peptide antigen parallel previous findings with retroviral or bacterial superantigens and indicate a possibility to modulate specifically mature peripheral cytotoxic T lymphocytes in vivo.

Activation with superantigens induces programmed death in antigen-primed CD4+ class II+ major histocompatibility complex T lymphocytes via a CD11a/CD18-dependent mechanism

Staphylococcal enterotoxin superantigens (SAg) bind class II major histocompatibility complex (MHC) molecules on antigen-presenting cells (APC) and upon cell-to-cell contact stimulate proliferation of T cells expressing appropriate V beta gene products. In addition, SAg can also deliver negative signals to Ag-specific T cells resulting in a state of unresponsiveness or a loss of viability. The present study examines the functional consequences of a direct interaction of SAg with alloAg-specific class II MHC+ CD4+ T cell lines (TCL). Our results demonstrate that SAg induce programmed death (apoptosis) in a majority of Ag-specific CD4+ T cells accompanied by genomic DNA fragmentation. SAg binding to Ag-specific TCL resulted in a rapid mobilization of intracellular free calcium ([Ca2+]i) and transcription of a number of cytokine genes including interleukin-2(IL-2), IL-4, interferon-gamma (IFN-gamma), granulocyte-macrophage colony-stimulating factor (GM-CSF), and granzyme B indicating the activation of primed T cells. Both SAg-induced cytokine gene expression as well as subsequent death were significantly inhibited by a tyrosine kinase inhibitor herbimycin A and also by cyclosporin A. SAg-induced death of primed T cells was also inhibited by monoclonal antibodies (mAb) directed at the CD11a/CD18 molecule but not those reactive with other T cell surface molecules such as CD2, CD7, CD28, CD29 or CD49d. None of these mAb, including anti-CD11a/CD18, had any effect on SAg-induced expression of IL-2 and IL-4 genes or SAg-induced [Ca2+]i response. Addition of cytokines such as IL-1 alpha, IL-2, IL-4, IL-6, GM-CSF, IFN-gamma, tumor necrosis factor (TNF-alpha, or TNF-beta), or neutralizing Ab to these cytokines had no effect on SAg-induced death of Ag-specific TCL. The T cells which survived the death-inducing effects of SAg showed down-regulation of the CD3/T cell receptor and up-regulation of CD2 and HLA-DR expression, and upon re-exposure to the same SAg upregulated expression of mRNA for IL-2 and IFN-gamma. Presentation of SAg by B7+ ICAM-1+ LFA-3+ DR+ professional APC was also able to induce the death of Ag-specific TCL. Together these results suggest that the activation with SAg causes programmed death of Ag-specific TCL cells via a mechanism that requires late participation of the CD11a/CD18 molecule.

Triggering and exacerbation of autoimmune arthritis by the Mycoplasma arthritidis superantigen MAM

OBJECTIVE

It has been postulated that superantigens might play a role in the human rheumatic diseases, by activation of self-reactive T cells or by induction of autoantibodies. The Mycoplasma arthritidis superantigen MAM, which is derived from a naturally occurring murine arthitogenic mycoplasma, uses certain V beta chains of the murine T cell receptor (TCR) that have been proposed to be involved in murine collagen-induced arthritis (CIA). The present study was designed to determine whether MAM influences the course of arthritis mediated by immunization with porcine type II collagen (PII).

METHODS

MAM or phosphate buffered saline (PBS) was injected locally or systemically into mice convalescing from CIA or mice suboptimally immunized with collagen.

RESULTS

In contrast to PBS, MAM caused an exacerbation of arthritis in mice that were recovering from CIA. MAM also triggered arthritis onset in mice that had been suboptimally immunized with PII up to 160 days previously. Injection of MAM during the onset phase of CIA also triggered and enhanced the severity of arthritis in mice given low doses of PII.

CONCLUSION

MAM can both trigger and exacerbate murine autoimmune arthritis induced by immunization with type II collagen. Since T cells bearing the same V beta TCRs as are used by MAM have been found to comprise a major portion of the activated cells in the synovial tissue of patients with rheumatoid arthritis, it is possible that superantigens similar to MAM may play a role in this human disease.

An alternative method for T-cell receptor repertoire analysis: clustering of human V-beta subfamilies selected in responses to staphylococcal enterotoxins B and E

We have designed a convenient procedure for the analysis of V beta repertoire expression in polyclonal T-cell populations. In this procedure T-cell RNA is converted to cDNA, polydC-tailed with terminal deoxynucleotidyl transferase and submitted to one-side specificity PCR amplification with a constant region oligonucleotide primer. The amplified material is then analysed by reverse spot-test hybridization: after 32P-labelling, the amplification product is put to hybridize on a membrane where specially designed V beta subfamily-specific probes are immobilized. The radioactivity fixed on each probe can then be easily quantified and the signal obtained is directly proportional to the initial amount of homologous RNA. We applied this technique to the study of V beta gene selection following T-cell stimulation by staphylococcal enterotoxins B and E. We show that with these toxins two almost non-overlapping sets of T-cells are recruited and that this selection is likely to be dependent on specific amino acid residues shaping the fourth complementarity determining region of the TCR-beta chain. These residues constitute two tandemly-conserved tripeptide sequences (Asp39Pro40Gly41)-(Val69Ser70Arg71) and (Arg66Phe67Ser68)-(Asp88Ser89Ala90) in the SEB- and the SEE-responsive V beta gene clusters respectively.

Pathogenesis of the toxic shock syndrome: T cell mediated lethal shock caused by the superantigen TSST-1

The pathogenesis of the toxic shock syndrome (TSS) is only incompletely understood. We now present evidence that TSS toxin-1 (TSST-1), one of the superantigens produced by Staphylococcus aureus, induces lethal shock in D-galactosamine sensitized mice. In this model TSS is dependent on T cells, since cyclosporin A (CsA) completely blocked development of shock, and since T cell-deficient SCID mice did not show signs of disease upon injection with TSST-1. However, SCID mice repopulated with T cells succumbed to lethal shock. The disease is characterized by a burst of lymphokines like interleukin-2 (IL-2) and tumor necrosis factor (TNF) released into the sera of TSST-1-treated animals. Already 1-2 h after TSST-1 application TNF serum levels peaked and IL-2 levels peaked around 4 h after treatment. TNF appears as key mediator of TSS, because anti-TNF monoclonal antibodies protected TSST-1-challenged mice. Interestingly, the burst of TNF in serum was noted well in advance of detectable markers of T cell activation. Thus, about 5% of all peripheral T cells started to express the IL-2 receptors as late as 4 h after treatment. Comparing TSST-1- and endotoxin-induced shock we conclude that TNF effects shock in both diseases. However, the type of cells involved appears distinct in that T cells cause TSS triggered by the exotosin TSST-1 while macrophages mediate the shock induced by endotoxins.

T cell receptor targeting to thymic cortical epithelial cells in vivo induces survival, activation and differentiation of immature thymocytes

We report that targeting of T cell receptors (TcR) to non-major histocompatibility complex (MHC) molecules on thymic cortical epithelial cells by hybrid antibodies in vivo and in fetal thymic organ cultures results in phenotypic and functional differentiation of thymocytes. A single pulse with hybrid antibodies rescues immature, CD4/8 double-positive thymocytes from their programmed death in vivo, induces expression of the early activation antigen CD69 followed by TcR up-regulation, concomitant down-regulation of CD8 or CD4 and their conversion to functional mature T cells by day 3. This temporal sequence of maturation only affects small thymocytes without co-induction of blastogenesis. TcR targeting to MHC class II-positive epithelial cells predominantly induces CD4-positive T cells. This generation of CD4 single-positive T cells occurs also in MHC class II-deficient mice and thus is independent of CD4-MHC class II interactions. Moreover, in the presence of a specific deleting antigen (Mls 1a), TcR targeting results in transient activation of immature thymocytes, however, not in subsequent TcR (V beta 6) up-regulation and development of single-positive T cells. Our findings imply that TcR cross-linking to cortical epithelial cells is sufficient to confer a differentiation signal to immature thymocytes. Furthermore, this approach distinguishes two independent TcR-mediated intrathymic events: activation and subsequent deletion of the same thymocyte subset.

Staphylococcal enterotoxin enhances the activation of rat encephalitogenic T cells by myelin basic protein

It is generally believed that the activation of autoreactive T cells is an essential step in the pathogenesis of autoimmune diseases; however, autologous antigens are often weak immunogens and their detectable levels in vivo are much lower than required for T-cell activation. In experimental autoimmune encephalomyelitis, encephalitogenic T cells specific for myelin basic protein (MBP) react weakly to autologous rat myelin basic protein (RBP) but strongly to guinea pig-derived basic protein, even though both ligands possess the essential epitope (MBP(68-88)). Here we demonstrate that RBP is converted to a strong immunogen in the presence of a small dose of bacterial superantigen, staphylococcal enterotoxin E (SEE). The enhancing effect of SEE on the rat protein was apparent with all encephalitogenic T-cell lines examined in this study, including those not responding to RBP alone. It depended, moreover, on the simultaneous presence of RBP and SEE; delaying the addition of SEE for 8-12 h greatly decreased the potency of RBP. None of a series of major cytokines was able to replace SEE as an enhancer. Our results indicate that two T ligands, one a bacterial superantigen, can interact to enhance the activation of autoreactive T cells. This observation has implications for the involvement of bacterial and viral infections in the pathogenesis of multiple sclerosis.

Leishmania major-specific, CD4+, major histocompatibility complex class II-restricted T cells derived in vitro from lymphoid tissues of naive mice

Several studies indicate that the outcome of experimental murine cutaneous leishmaniasis caused by Leishmania major (Lm) is determined by immunological events occurring shortly after infection. These events lead to outgrowth of either protective CD4+ T cells in the C57BL/6 mouse, which cures, or exacerbative cells in the BALB/c mouse, which succumbs to disease. Potential factors influencing the outgrowth of protective or exacerbative T cells include antigen-presenting cells (APC), cytokines, and parasite antigens. An in vitro system, in which one could precisely control the factors shaping early events in the T cell response to Lm, would be very useful. To this end, we have examined the in vitro response of naive lymphocytes to Lm promastigotes. The data presented here show that Lm-specific CD4+ T cell receptor alpha/beta + T cells can be generated in vitro from spleen and lymph node cell populations of naive mice. Furthermore, they can be obtained from the CD44low (unprimed) population of T lymphocytes, indicating that in vitro priming occurs. The ability to generate these T cells is dependent on the presence of live parasites and is not due to a parasite-derived nonspecific T cell mitogen. Restimulation, as assayed by proliferation, requires APC bearing syngeneic I-A. Optimal restimulation of the in vitro derived T cells is achieved only when live promastigotes are used. The T cells do not proliferate in response to a frozen-and-thawed lysate of promastigotes, yet they exhibit mild reactivity to lysates prepared from heat-shocked promastigotes. Furthermore, they do not recognize two predominant antigens on the promastigote surface, lipophosphoglycan and gp63. T cells derived in vitro with Lm show crossreactivity with live L. donovani, less crossreactivity with live L. mexicana, and no crossreactivity with live Bacillus-Calmette-Guerin or live Brugia malayi microfilariae. Finally, these early T cells, whether derived from healing C57BL/6 or nonhealing BALB/c mice, produce interleukin 2 (IL-2), IL-4, and interferon gamma.

Effects of staphylococcal enterotoxin B on T cell receptor V beta utilization and clinical manifestations of experimental allergic encephalomyelitis

Staphylococcal enterotoxin B (SEB) is a superantigen (SA) that up-regulates and then subsequently down-regulates and deletes T cells expressing V beta 8 T cell receptor (TcR) chains (Marrack and Kappler, 1990; Johnson et al., 1991). We have investigated the effect of SEB on experimental allergic encephalomyelitis (EAE) in PL/J mice, where the predominant encephalitogenic T cells are V beta 8+ (Acha Orbea et al., 1988; Zamvil et al., 1988). SEB did not enhance induction of EAE when administered prior to or after immunization for EAE. PL/J mice pretreated with SEB developed anergy and deletion of V beta 8 bearing cells and concomitant reduction in the incidence of EAE. Following SEB pretreatment, a redistribution in the TcR utilization of MBP-specific lymphocytes occurred. As a result, there was a low frequency of V beta 8 and expansion of other, normally less frequent, myelin basic protein (MBP)-specific clones. These observations indicate that systemic exposure to superantigen can influence organ-specific autoimmune diseases. We observed V beta-specific elimination, rather than activation, of autoimmune clones, a finding of potential therapeutic value. Modification of the TcR repertoire by systemic exposure to this SA indicates plasticity of immune reactivity and demonstrates a mechanism by which an environmental exposure (SEB) can influence a genetically determined, T cell mediated autoimmune disease.

Glucocorticoid-mediated control of the activation and clonal deletion of peripheral T cells in vivo

Poly- and oligoclonal T cell stimuli like anti-CD3 epsilon monoclonal antibody or Staphylococcus aureus enterotoxin B (SEB), injected at doses that per se are not lethal, provoke acute death within less than 24 h, provided that endogenous glucocorticoids (GC) are depleted by adrenalectomy or by injection of saturating amounts of the GC receptor antagonist RU-38486 (mifepristone). Pharmacological doses of the GC agonist dexamethasone (DEX) alter the in vivo response of splenic V beta 8+ T cells to SEB, thus impeding the expansion of such cells and causing their rapid (3 d) clonal deletion. In contrast, coadministration of RU-38486 counteracts a SEB-induced early (12 h) reduction of V beta 8+CD4+ and V beta 8+CD8+ spleen cells. In vivo T cell stimulation by injection of bacterial superantigen induces a rapid (peak at 90-120 min) increase in corticosterone serum levels, suggesting that endogenous GC might control early T cell activation. Accordingly, kinetic studies revealed that RU-38486 has to be administered within 2 h after superantigen administration to exert its lethal effect. Similarly, exogenous GC must be injected during this critical phase (2 h) to rescue animals from acute death induced by coinjection of SEB and D-galactosamine (GalN). Adrenalectomy, injection of RU-38486 and priming with GalN per se provoke the programmed death of peripheral CD4+ and CD8+ T cells. Thus, three manipulations that sensitize mice for the lethal effect of T cell stimulation also exert a proapoptotic effect on peripheral T cells. In synthesis, endogenous and exogenous GC regulate T cell responses and determine the propensity of peripheral T cells to undergo apoptosis.

Staphylococcal enterotoxin type A internal deletion mutants: serological activity and induction of T-cell proliferation

Previous findings indicate that the N-terminal region of staphylococcal enterotoxin type A (SEA) is required for its ability to induce T-cell proliferation. To better localize internal peptides of SEA that are important for induction of murine T-cell proliferation, SEA mutants that had internal deletions in their N-terminal third were constructed. A series of unique restriction enzyme sites were first engineered into sea; only one of these changes resulted in an amino acid substitution (the aspartic acid residue at position 60 of mature SEA was changed to a glycine [D60G]). Because the D60G substitution had no discernible effect on serological or biological activity, the sea allele encoding this mutant SEA was used to construct a panel of mutant SEAs lacking residues 3 to 17, 19 to 23, 24 to 28, 29 to 49, 50 to 55, 56 to 59, 61 to 73, 68 to 74, or 74 to 85. Recombinant plasmids with the desired mutations were constructed in Escherichia coli and transferred to Staphylococcus aureus. Staphylococcal culture supernatants containing the mutant SEAs were examined. Western immunoblot analysis with polyclonal anti-SEA antiserum revealed that each of the recombinant S. aureus strains produced a mutant SEA of the predicted size. All the mutant SEAs exhibited increased sensitivity to monkey stomach lavage fluid in vitro, which is consistent with these mutants having conformations unlike that of wild-type SEA or the SEA D60G mutant. In general, deletion of internal peptides had a deleterious effect on the ability to induce T-cell proliferation; only SEA mutants lacking either residues 3 to 17 or 56 to 59 consistently produced a statistically significant increase in the incorporation of [3H]thymidine. In the course of this work, two monoclonal antibodies that had different requirements for binding to SEA in Western blots were identified. The epitope for one monoclonal antibody was contained within residues 108 to 230 of mature SEA. Binding of the other monoclonal antibody to SEA appeared to be dependent on the conformation of SEA.