The toxicity of staphylococcal enterotoxin B in mice is mediated by T cells

In vivo effects of superantigens

Superantigens are potent immunostimulatory molecules that activate both T cells and antigen presenting cells. The consequences of superantigen exposure range from induction of T cell proliferation, massive cytokine release and systemic shock to immunosuppression and tolerance. Superantigens have been directly implicated in a number of human conditions including food poisoning and toxic shock. In addition, there is evidence to suggest that superantigens are involved in the initiation of autoimmunity, and the immune dysfunction associated with HIV infection. Because of their possible role in human disease, and their potential use in immune therapy, it is important that we more completely understand the in vivo effects of superantigens.

Staphylococcal enterotoxin A has two cooperative binding sites on major histocompatibility complex class II

The superantigen staphylococcal enterotoxin A (SEA) binds to major histocompatibility complex (MHC) class II molecules at two sites on either side of the peptide groove. Two separate but cooperative interactions to the human class II molecule HLA-DR1 were detected. The first high affinity interaction to the DR1 beta chain is mediated by a zinc atom coordinated by H187, H225, and D227 in SEA and H81 in the polymorphic DR1 beta chain. The second low affinity site is to the DR1 alpha chain analogous to SEB binding and is mediated by residue F47 in SEA. Binding of one SEA to the DR1 beta chain enhances the binding of a second SEA molecule to the DR1 alpha chain. The zinc site is on the opposite side of the SEA molecule from residue F47 so that one SEA molecule can readily bind two class II molecules. Both binding sites on SEA are required for maximal activity. Thus, unlike, SEB, SEA requires two separate binding sites for optimal activity, which may allow it to stabilize SEA interaction with T cell receptors, as well as to activate the antigen-presenting cell by cross-linking MHC class II.

Multiple binding sites for bacterial superantigens on soluble class II MHC molecules

We used surface plasmon resonance to study the binding of a set of soluble mouse I-E class II major histocompatibility molecules, each occupied by a different single peptide, to the staphylococcal enterotoxin superantigens, SEA and SEB. The rates of association and dissociation to SEA varied greatly depending on the I-E-bound peptide. By contrast, binding to SEB yielded fast association and dissociation rates, which were relatively peptide independent. The results also indicated nonoverlapping binding sites for SEB and SEA on class II and raised the possibility of enhanced SAg presentation to T cells by cross-linking of cell surface class II.

Humoral immunity to aerosolized staphylococcal enterotoxin B (SEB), a superantigen, in monkeys vaccinated with SEB toxoid-containing microspheres

Staphylococcal enterotoxin B (SEB) toxoid-containing microspheres were tested for efficacy in rhesus monkeys as a vaccine candidate for respiratory SEB toxicosis and toxic shock. Forty monkeys were randomly separated into 10 groups of four monkeys each: 9 groups were vaccinated with the microspheres via combinations of mucosal and nonmucosal routes, and 1 group served as nonvaccinated controls. Both vaccinated and nonvaccinated monkeys were then challenged with a high lethal dose of SEB aerosol. Monkeys primed with an intramuscular dose of the microspheres followed by an intratracheal booster all survived the SEB challenge. Overall, monkeys with an intratracheal booster generally had the highest antibody levels, which is consistent with their high survival rate and lower rate of illness. Protective immunity was correlated with antibody levels in both the circulation and the respiratory tract. The protection was not due to the depletion or anergy of SEB-reactive T cells, since SEB-induced proliferation in cultures of circulating lymphocytes was not significantly reduced after the microsphere vaccination. It is evident that the nonsurvivors did not die of systemic anaphylaxis or hypersensitivity because the monkeys did not die immediately after SEB challenge and there were no significant differences in histamine levels between the vaccinated and control monkeys before and after SEB challenge. The antibodies seemed to neutralize the SEB that got into the airway and the circulation.

Proliferation is a prerequisite for bacterial superantigen-induced T cell apoptosis in vivo

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen that binds to major histocompatibility complex class II molecules and selectively interacts with T cells that bear certain T cell receptor (TCR) V beta domains. Administration of SEB in adult mice results in initial proliferation of V beta 8+ T cells followed by a state of unresponsiveness resulting from a combination of clonal deletion and clonal anergy in the SEB-reactive population. At this time, it is unclear what relationship exists between the T cells that have proliferated and those that have been deleted or have become anergic. Here we show that only a fraction of the potentially reactive V beta 8+ T cells proliferate in response to SEB in vivo, and that all the cells that have proliferated eventually undergo apoptosis. Virtually no apoptosis can be detected in the nonproliferating V beta 8+ T cells. These data demonstrate a causal relationship between proliferation and apoptosis in response to SEB in vivo, and they further indicate that T cells bearing the same TCR V beta segment can respond differently to the same superantigen. The implications of this differential responsiveness in terms of activation and tolerance are discussed.

T cells made deficient in interleukin-2 production by exposure to staphylococcal enterotoxin B in vivo are primed for interferon-gamma and interleukin-10 secretion

The superantigen staphylococcal enterotoxin B (SEB) induces a defect in interleukin (IL)-2 production by T cells expressing specific T cell receptor V beta domains. The present study was undertaken to determine the capacity of T cells, made deficient in IL-2 production by exposure to SEB in vivo, to secrete interferon (IFN)-gamma and IL-10 and to induce pathology upon SEB rechallenge. For this purpose, BALB/c mice received two intraperitoneal injections of 100 micrograms SEB with a 48-h interval. First, we compared peak serum levels of IL-2, IFN-gamma and IL-10 after SEB rechallenge with those measured after a single SEB injection in control mice. The expected defect in IL-2 production in SEB-pretreated mice was associated with a major increase in IL-10 and IFN-gamma levels which were about fivefold higher than in controls. Experiments in mice depleted of CD4+ or CD8+ cells as well as studies in which purified T cell populations were rechallenged with SEB in vitro indicated that both CD4+ and CD8+ cells from SEB-pretreated mice were primed for IL-10 and IFN-gamma production. Furthermore, SEB-pretreated mice were sensitized to the toxic effects of the superantigen as indicated by a 30-70% lethality rate (vs. 0% in naive mice) within 48 h after SEB rechallenge. IFN-gamma was involved in the lethal syndrome as it could be prevented by injection of neutralizing anti-IFN-gamma monoclonal antibody. We conclude that SEB-reactive T cells made deficient for the production of IL-2 by exposure to SEB in vivo are primed for IFN-gamma and IL-10 production, and that IFN-gamma up-regulation is involved in the shock syndrome occurring upon SEB rechallenge.

Lethally irradiated normal strains of mice radioprotected with SCID bone marrow develop sensitivity to low doses of staphylococcal enterotoxin B

Normal strains of mice are rendered sensitive to small amounts (3-10 micrograms) of staphylococcal enterotoxin B (SEB) by transplanting bone marrow cells of SCID donor mice to lethally irradiated recipients. Four to 12 weeks post-transplantation, SEB induces 56-100% lethality. Transplantation of normal mouse bone marrow cells, either alone or with the SCID mouse selected bone marrow cells, does not confer SEB sensitivity. These data imply that either irradiation ablates certain cell population(s), that confer resistance to SEB in normal mice (populations that are absent in the SCID donor mice) or that the donor cells selectively repopulate recipients with SEB-sensitive cells. This model will help elucidate the cells, cytokines and the SEB peptide fragments responsible for SEB toxicity and will be useful in identifying promising vaccine candidates and in developing preventive medicines to protect against this potent toxin.

Staphylococcal enterotoxin B toxicity in BALB/c mice: effect on T-cells, plasma cytokine levels and biochemical markers

Groups of BALB/c mice were treated with a sub-lethal dose (60 micrograms) of staphylococcal enterotoxin B (SEB) intraperitoneally and were sacrificed at 2, 5, 8, or 10 h post-injection. Organ, blood plasma and lymph node samples from these mice were analyzed. Plasma levels of urea, creatinine and alanine aminotransferase were significantly raised above normal by 5 h post-injection. However, alkaline phosphatase levels showed an erratic increase after toxin administration and, after administration of 10-40 microgramS SEB per mouse, were consistently at least 30% below normal levels at 24 h post-injection. Weight change was also monitored but found to be inconsistent. Lung, spleen and kidney samples appeared normal on histopathological examination, but liver samples showed minor polymorph infiltration and congestion. TNF-alpha, and IL-1 alpha levels in the plasma were raised by 8 h to picogram levels per ml of plasma, whereas IFN-gamma and IL-2 were raised by 2 h to nanogram levels per ml of plasma. Lymph node cells taken from mice treated with toxin were given a secondary stimulation with toxin in vitro. Although the response of the cells was lower than normal on assay at four days, a time response curve showed a peak in cell responsiveness to secondary stimulation with toxin at three days. These data indicate that biochemical markers and cytokine levels are affected by the administration of SEB to mice and may be used as indicators of toxicity.

Biological activity of toxic shock syndrome toxin 1 and a site-directed mutant, H135A, in a lipopolysaccharide-potentiated mouse lethality model

A recombinant of toxic shock syndrome toxin 1 (TSST-1) which contains a single histidine-to-alanine mutation at residue 135 (H135A) was analyzed for toxicity and vaccine potential in a lipopolysaccharide (LPS)-potentiated mouse lethality model. The 50% lethal dose (LD50) of TSST-1 in BALB/c mice was 47.2 micrograms/kg, but H135A was not lethal when tested at a dose equivalent to 10 LD50s of TSST-1. Levels of tumor necrosis factor (TNF) and gamma interferon (IFN-gamma) in serum were, respectively, 10- and 50-fold higher in LPS-potentiated mice injected with 15 LD50s of TSST-1 than in mice given H135A. Mice injected with only TSST-1 did not have elevated levels of TNF or IFN-gamma in serum, while H135A plus LPS or LPS alone elicited identical, yet very low, levels of TNF and IFN-gamma. An enzyme-linked immunosorbent assay of H135A and TSST-1 with anti-TSST-1 serum yielded very similar dose-response curves, which strongly suggests that H135A serologically and conformationally resembles the native toxin. Mice immunized with H135A developed antibodies that recognized TSST-1 in an enzyme-linked immunosorbent assay and afforded protection against a 15-LD50 challenge of TSST-1 plus LPS. The pooled sera of mice immunized with either TSST-1 or H135A also prevented lymphocyte proliferation due to TSST-1.

Anti-gamma interferon and anti-interleukin-6 antibodies affect staphylococcal enterotoxin B-induced weight loss, hypoglycemia, and cytokine release in D-galactosamine-sensitized and unsensitized mice

Administration of staphylococcal enterotoxin B (SEB) to BALB/c mice was found to induce a cytokine release syndrome hallmarked by weight loss and hypoglycemia. A neutralizing monoclonal antibody against gamma interferon (IFN-gamma) given before SEB counteracted weight loss and prevented hypoglycemia. This protective effect of anti-IFN-gamma antibody was associated with decreased IFN-gamma levels in serum; tumor necrosis factor (TNF) and interleukin-6 (IL-6) levels remained unchanged. A monoclonal anti-IL-6 antibody, known for its ability to cause accumulation of biologically active IL-6 in the circulation, did not modify SEB-induced body weight loss or hypoglycemia. Levels of TNF, IFN-gamma, and IL-6 in serum were all more elevated in anti-IL-6-treated mice than in corresponding SEB-challenged control mice. In D-galactosamine-sensitized mice, SEB-induced weight loss but not hypoglycemia was more severe, resulting mostly in death within 24 h. Higher levels of biologically active TNF and IFN-gamma in serum were noted in these mice than in mice receiving SEB only. In D-galactosamine-sensitized mice, anti-IFN-gamma antibody did prevent hypoglycemia but failed to reduce the severity of the syndrome. Again, TNF levels in anti-IFN-gamma-treated mice remained unchanged. Pretreatment with anti-IL-6 antibody temporarily attenuated SEB-induced hypoglycemia in sensitized mice. Thus, at 6 h post-SEB injection, anti-IL-6-treated mice were less hypoglycemic than corresponding controls. However, at 24 h, hypoglycemia was significantly aggravated. Concomitantly, IL-6 levels were dramatically increased. Neither anti-IFN-gamma nor anti-IL-6 antibody treatment modulated mortality levels in D-galactosamine-sensitized mice. The data obtained with anti-IFN-gamma antibody clearly indicate that endogenous IFN-gamma is instrumental in bringing about hypoglycemia and body weight loss in mice exposed to SEB but also that hypoglycemia is not a crucial determinant of mortality in D-galactosamine-sensitized mice. The data obtained with anti-IL-6 antibody indicate that endogenous IL-6 is involved in regulating the levels of TNF and IFN-gamma in serum.

Staphylococcal enterotoxin B increases the severity of type II collagen induced arthritis in mice

OBJECTIVE

To observe the influence of T cell subset changes on the development of experimental arthritis, by using the bacterial superantigen staphylococcal enterotoxin B (SEB) to modulate the T cell repertoire during the arthritogenic response to type II collagen (CII) in vivo.

METHODS

DBA/1 mice were injected with SEB before immunisation with CII, and assessed for the development of collagen induced arthritis (CIA) and an immune response to CII. Mice with established arthritis were also treated therapeutically with SEB. Flow cytometry was used to evaluate the effect of the therapy on T cell subsets and T cell receptor (TCR) V beta expression.

RESULTS

Mice injected with SEB developed arthritis significantly faster than saline treated control animals, and developed more severe clinical features. Mice treated with SEB after the onset of CIA were also observed to progress more rapidly to a severe arthritis than mice treated with saline alone. The level of anti-CII antibody was not affected by SEB injection. Flow cytometric analysis of TCR expression in mice 21 days after injection of CII showed decreased expression of V beta 6 and V beta 8 cells in SEB treated mice, compared with collagen immunised control mice. Injection of SEB alone caused a decrease in V beta 8, but not V beta 6 T cells compared with the values in normal DBA/1 mice. No significant variations in the T cell repertoire were detected 70 days after CII immunisation.

CONCLUSIONS

Treatment with the bacterial enterotoxin SEB before the induction of arthritis did not suppress the immunological or arthritogenic response to CII in DBA/1 mice, despite the modulation of the V beta 8 T cell subset. Treatment of mice with established arthritis using SEB provoked a more severe disease course.

V beta gene repertoire in the aging mouse: a developmental perspective

To define age-associated alterations in the immune system at the molecular level, we have analyzed TCR V beta gene expression patterns at the fetal, neonatal, adult, and advanced ages of mice. In contrast to V gamma and VH genes, V beta genes rearranged without any preference related to their chromosomal organization. Endogenous superantigen-mediated clonal deletions were registered for the first time at the neonatal stage, presumably reflecting the late developmental appearance of these molecules. Such deletions, once established, were maintained throughout life with little, if any, leakage in this process. Furthermore, bone marrow transplantation and other studies indicated that an involuted thymus maintained its capacity to perform both its functions, i.e. positive and negative selection. Although overall V beta repertoires showed remarkable stability with advanced age, modifications in expression levels for some V beta, particularly those associated with the CD8 subset and presumably reflecting antigenic stimulation, were recorded. Mice with lupus and early-life thymic involution were fully capable of deleting endogenous superantigen-reactive V beta clones, and even lupus mice with a genetic defect in the apoptosis-promoting Fas gene were normal in this regard. The results indicate that, aside from some anticipated clonal expansions induced by antigenic stimulation, age-associated alterations in immune functions are not caused by any profound changes in the overall TCR repertoire.

Autocrine feedback death and the regulation of mature T lymphocyte antigen responses

Antigen-induced T cell death is an important regulatory mechanism in the peripheral immune system. Evidence suggests that this process depends on T cell growth-inducing lymphokines such as IL-2 and occurs in proportion to the degree of T cell receptor occupancy. Strong T cell receptor stimulation leads to the synthesis of death molecules such as Fas ligand and tumor necrosis factor that cause T cell suicide. We propose that T cell death under these circumstances is the culmination of a feedback control mechanism termed propriocidal regulation or autocrine feedback death that regulates the expansion of specific T cell clones under conditions of high lymphokine and antigen load. In a quasi-stochastic system such as the antigen receptor repertoire, feedback information may be essential for the appropriate regulation of peripheral immune responses. Our understanding of this feedback mechanism affords a means to manipulate antigen-specific T cell death in vivo. The application of this approach to the therapy of T cell-medicated immunological diseases is discussed.

Staphylococcal enterotoxin B modulates V beta 8+ TcR-associated T-cell memory against conventional antigen

Primary in vivo challenge with the superantigen staphylococcal enterotoxin B (SEB) induces polyclonal proliferation of an unusually large proportion of circulating T-cells that bear the V beta 8-T-cell receptor (TcR) domain. Early and vigorous proliferation of V beta 8+ T-cells precedes their selective deletion, leaving the host unresponsive upon rechallenge with the native immunogen SEB. Nonetheless, this induction of anergy is incompletely understood. Recently we demonstrated that more cells than just V beta 8+ T-cells undergo clonal proliferation after challenge with SEB (Cell. Immunol. 154, 440, 1994). These findings suggested that non-V beta 8+ T-cells may have a role in the induction of superantigen-induced anergy. To further investigate this, we enumerated CD4+ and CD8+ T-cells in lymph nodes and spleens from Balb/c mice at various times after primary and secondary challenge with either a high or a low dose of SEB. Using these kinetic data we investigated whether challenge with SEB would modulate antigen-specific V beta 8-associated T-memory responses. To this end, the V beta 8+ T-cell-associated responses induced by SEB were compared with the V beta 8+ TcR-associated memory responses induced by the nominal antigen sperm whale myoglobin (SWM). Results indicated that challenge of SWM-primed mice with SEB abrogated the V beta 8-associated SWM-specific T-cell memory for an extended but transient period of time. Moreover, prechallenge with SEB blocked the establishment of de novo V beta + T-cell-mediated immunity. These findings suggest that administration of low and controlled doses of microbial superantigen could provide long-term suppression of antigen-specific cell-mediated immunity.

Amelioration of autoimmune reactions by antigen-induced apoptosis of T cells

We have shown that T cells vigorously cycling in response to growth lymphokines are driven into apoptosis by potent TCR restimulation. This process, termed propriocidal regulation, appears to be a normal feedback inhibitory mechanism to prevent excessive T cell proliferation and lymphokine production. Exposure of T cells to repeated high dose antigen treatments creates the conditions just described by activating T cells, and stimulating the production of growth lymphokines and their receptors. High growth lymphokine levels induced by the large amount of antigen present, stimulate vigorous cycling. The continued presence of high antigen levels subjects the cycling T cells to strong TCR restimulation as they enter the vulnerable S phase, inducing apoptosis in T cells responsive to the administered antigen. Thus, simple, repetitive, intravenous administration of high dose antigen may be used to delete potentially destructive clones of T cells, resulting in a state of peripheral tolerance. This has obvious therapeutic potential in disorders where the elimination of pathogenic T cell clones could be beneficial. We have described in EAE, an animal model for MS, that high dose MBP therapy is effective in preventing CNS pathology and the onset of disease as well as reducing the severity of the clinical symptoms of established EAE. We are currently involved in expanding this approach to other animal models of autoimmunity and graft rejection, as well as refining the immunotherapy in the EAE model with the objective of developing a clinical therapy for human demyelinating disease.

Toxic shock syndrome toxin-1 complexed with a class II major histocompatibility molecule HLA-DR1

The three-dimensional structure of a Staphylococcus aureus superantigen, toxic shock syndrome toxin-1 (TSST-1), complexed with a human class II major histocompatibility molecule (DR1), was determined by x-ray crystallography. The TSST-1 binding site on DR1 overlaps that of the superantigen S. aureus enterotoxin B (SEB), but the two binding modes differ. Whereas SEB binds primarily off one edge of the peptide binding site of DR1, TSST-1 extends over almost one-half of the binding site and contacts both the flanking alpha helices of the histocompatibility antigen and the bound peptide. This difference suggests that the T cell receptor (TCR) would bind to TSST-1:DR1 very differently than to DR1:peptide or SEB:DR1. It also suggests that TSST-1 binding may be dependent on the peptide, though less so than TCR binding, providing a possible explanation for the inability of TSST-1 to competitively block SEB binding to all DR1 molecules on cells (even though the binding sites of TSST-1 and SEB on DR1 overlap almost completely) and suggesting the possibility that T cell activation by superantigen could be directed by peptide antigen.

T cell receptor-major histocompatibility complex class II interaction is required for the T cell response to bacterial superantigens

Bacterial and retroviral superantigens (SAGs) stimulate a high proportion of T cells expressing specific variable regions of the T cell receptor (TCR) beta chain. Although most alleles and isotypes bind SAGs, polymorphisms of major histocompatibility complex (MHC) class II molecules affect their presentation to T cells. This observation has raised the possibility that a TCR-MHC class II interaction can occur during this recognition process. To address the importance of such interactions during SAG presentation, we have used a panel of murine T cell hybridomas that respond to the bacterial SAG Staphylococcal enterotoxin B (SEB) and to the retroviral SAG Mtv-7 when presented by antigen-presenting cells (APCs) expressing HLA-DR1. Amino acid substitutions of the putative TCR contact residues 59, 64, 66, 77, and 81 on the DR1 beta chain showed that these amino acids are critical for recognition of the SAG SEB by T cells. TCR-MHC class II interactions are thus required for T cell recognition of SAG. Moreover, Mtv-7 SAG recognition by the same T cell hybridomas was not affected by these mutations, suggesting that the topology of the TCR-MHC class II-SAG trimolecular complex could be different from one TCR to another and from one SAG to another.

Localization of binding sites of staphylococcal enterotoxin B (SEB), a superantigen, for HLA-DR by inhibition with synthetic peptides of SEB

Staphylococcal enterotoxins are major causes of food poisoning and toxic shock syndrome. Their ability to bind to major histocompatibility complex (MHC) class II molecules has been suggested to be the first step in the mechanism whereby they cause illness. By flow cytometric analysis, the sites of interaction of staphylococcal enterotoxin B (SEB) with HLA-DR molecules were probed in the present study by inhibiting the binding of biotinylated SEB to a human T-cell line (HUT-78) with synthetic peptides of SEB. Five peptides of SEB gave significant inhibition of binding: a peptide containing amino acids 9 to 20 [SEB(9-20)], SEB(30-38), SEB(61-70), SEB(90-114), and SEB(169-181). One peptide, SEB(39-51), enhanced binding. Among the inhibitory peptides, SEB(90-114), a peptide spanning the entire disulfide loop, showed the most efficient inhibition of binding. Peptides SEB(9-20) and SEB(39-51) include amino acid residues that have been identified by previous mutation studies (J.W. Kappler, A. Herman, J. Clements, and P. Marrack, J. Exp. Med. 175:387-396, 1992) as being important in binding to MHC class II. Amino acids lining the alpha 5 groove of SEB have also been postulated to be involved in binding to MHC class II molecules. However, only two of the residues that line the alpha 5 groove of SEB, His-12 and Tyr-17, are on peptide SEB(9-20) that inhibits binding. These results confirm previous studies that implicated the amino-terminal portion of the molecule in binding to MHC class II molecules and further indicate an important role for residues in other regions, particularly the disulfide loop.

Increased susceptibility to staphylococcal enterotoxin B intoxication in mice primed with actinomycin D

Mice (BALB/cJ, C3H/HeN, and C3H/HeJ) primed with actinomycin D became highly susceptible to lethal intoxication with staphylococcal enterotoxin B (SEB). The mice underwent toxicosis and toxic shock and died. Actinomycin D-primed C3H/HeN and C3H/HeJ mice showed equal sensitivity to SEB, suggesting that bacterial lipopolysaccharide derived from gram-negative bacteria in the gut may not be an important cofactor in intoxication. In a time course study of the illness, prominent pathological changes characterized by blood congestion and thickening of alveolar septa were seen in the lung, while blood congestion, inflammation, epithelial cell flattening, and villous blunting were seen in the small intestine. In lymphoid tissues, such as the spleen, congestion, inflammation, and lymphoid cell depletion were the major reactions. The pathological features of the mice had many similarities to those of rhesus monkeys intoxicated with intravenous SEB. The actinomycin D-primed C3H/HeJ mice are thus an ideal mouse model for studying SEB toxicosis and toxic shock.

Lymphatic mast cell response and effect of compound 48/80 on popliteal lymph node reaction in rats following intracutaneous injection of Staphylococcus aureus

To investigate the significance of mast cells in the popliteal lymph node during the development of an inflammatory response, rats were inoculated with 12 x 10(7) colony-forming units of Staphylococcus aureus in the hind foot pad. Numerical changes in mast cells were then measured in the corresponding popliteal lymph node. Six days after inoculation, despite the enlargement of the responding lymph node, a marked decrease in granulated mast cell number, relative to the contralateral node, was observed in the cortical and medullary compartments. Popliteal lymph nodes from rats treated with compound 48/80 and then inoculated with S. aureus showed a higher cortical and medullary hypertrophic response and a significant increase in degranulated/weakly basophilic mast cell number in the lymph node tissue. The findings suggest that (1) Staphylococcus aureus induces a reduction in granulated mast cell number in the cortical and medullary compartments of regional lymph nodes; (2) pretreatment with compound 48/80 appears to contribute to the lymphoid cell proliferation and the hypertrophic response of lymph nodes induced by S. aureus; and (3) granulated mast cells have a regulatory role on lymphoid cell proliferation.

Early expression of cytokines in lymph nodes after treatment in vivo with Staphylococcus enterotoxin B

Excessive cytokine expression induced by superantigen may be one aspect of the pathophysiology associated with Gram positive bacteremia. We have undertaken a study of the kinetics of cytokine production in lymph nodes obtained from in vivo Staphylococcus enterotoxin B (SEB) treated animals. This study was designed to evaluate the short term cytokine profile observed using immunohistochemistry (IHC) in BALB/c mice injected intraperitoneally (i.p.). The observed immunohistochemical kinetic profiles were corroborated using reverse transcription-polymerase chain reaction (RT-PCR) RNA analysis. We report here that TNF, IL-2, and IFN-gamma are the principal cytokines which were detected within hours of SEB administration, and that other cytokines such as IL-3, IL-4, IL-5, IL-6, IL-10, GM-CSF and M-CSF were undetectable. TNF and IL-2 appeared very early following SEB priming, and were observed by 1 h. IFN-gamma which appeared later (maximally at 14 h) was produced predominantly by CD8+ cells. In contrast, the TNF and IL-2 were produced primarily by CD4+ cells. Identical results were obtained by IHC and RT-PCR; the kinetics of mRNA expression slightly preceded the appearance of protein. The TNF and IFN-gamma staining patterns observed in lymph node sections were indicative of Golgi-localized cytokine. The IL-2 staining pattern observed in lymph node sections was distinctive, covering a significant local area of cells. This local regional concentration of IL-2, which may result from cytokine attached to extracellular binding components, may be an important aspect of the activation phase of a developing immune response. Rapid induction and excessive cytokine production elicited by superantigen in vivo, may ultimately help to explain the shock and death associated with SEB.

Monoclonal antibodies defining functional sites on the toxin superantigen staphylococcal enterotoxin B

Four monoclonal antibodies (mAbs) were produced binding to four nonoverlapping epitopes on the superantigen staphylococcal enterotoxin B (SEB). The mAbs were tested for their ability to detect SEB bound to major histocompatibility complex (MHC) class II, to inhibit SEB binding to MHC class II, to inhibit SEB stimulation of T cell hybridomas, to bind to various nonfunctional mutants of SEB, and to capture and present SEB and its mutants to T cells in the absence of MHC class II. We concluded that two mAbs, B344 and B327, bound to epitopes not required for superantigen function, one mAb, 2B33, blocked an MHC interaction site on SEB, and the fourth mAb, B87, blocked the T cell recognition site on SEB. Moreover, two mAbs (B344 and 2B33) were capable of presenting SEB, although much less efficiently than APC, to CD4- but not CD4+ T cell hybridomas. The results confirm the functional domains on SEB originally defined by mutation and show that MHC class II is not always an essential component of the superantigen ligand.

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.

Three-dimensional structure of a human class II histocompatibility molecule complexed with superantigen

The structure of a bacterial superantigen, Staphylococcus aureus enterotoxin B, bound to a human class II histocompatibility complex molecule (HLA-DR1) has been determined by X-ray crystallography. The superantigen binds as an intact protein outside the conventional peptide antigen-binding site of the class II major histocompatibility complex (MHC) molecule. No large conformational changes occur upon complex formation in either the DR1 or the enterotoxin B molecules. The structure of the complex helps explain how different class II molecules and superantigens associate and suggests a model for ternary complex formation with the T-cell antigen receptor (TCR), in which unconventional TCR-MHC contacts are possible.

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.

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.

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.

Cytoplasmic membrane-associated protein (CAP) isolated from Streptococcus pyogenes: as a new bacterial superantigen

A protein isolated from the cytoplasmic membranes of Streptococcus pyogenes (cytoplasmic membrane-associated protein, CAP) stimulated human T cells in vitro to induce their mitogenic response. This CAP-induced T cell proliferation required the presence of nylon-adherent accessory cells (AC) of either autologous or allogeneic origin in the reaction mixtures. In addition, the reaction was inhibited by monoclonal antibodies (mAbs) against major histocompatibility complex (MHC) class II molecules, HLA-DR and -DQ, but not -DP. Human lymphoid cell lines positive for HLA-DR but not those lacking it were also effective as AC for the reaction. A binding test using fluorescein-labeled protein revealed that CAP bound to the adherent monocytes and HLA-DR+ but not to -DR- lymphoid cell lines. The proliferative response of T cells to CAP was, however, not inhibited by the addition of the lysosomotrophic agent NH4Cl to the reaction mixtures. These results suggest that the presentation of CAP by AC to human T cells is mediated through binding of the protein to the MHC class II molecules but without being processed in the AC. The proliferative response of T cells was also found to be inhibited by addition of anti-CD2, -CD3 or -T cell receptor (TcR) mAbs. A major population responding to CAP was CD3+4+8- T cells. CAP also appears to stimulate T cells bearing V beta 8 sequences much more selectively than T cells bearing other V beta s. These results indicate that this streptococcal membrane protein, CAP, may be a new protein belonging to a group of bacterial superantigens.

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.

Apoptosis defects analyzed in TcR transgenic and fas transgenic lpr mice

Although autoreactive T cells are thought to play a prominent role in autoimmune disease in MRL-lpr/lpr mice, it has been difficult to directly determine if autoreactive T cells escape from the thymus and react with self-antigens in the periphery. Defective expression of the Fas apoptosis antigen in MRL-lpr/lpr mice results from the insertion of the ETn retrotransposon. The fas defect can be partially corrected in CD2-fas transgenic mice in which the expression of fas is corrected in T cells. To identify a possible defect in clonal deletion or clonal anergy induction of auto-specific T cells, we have studied C57BL/6-lpr/lpr transgenic mice that express TcR genes that recognize a known self-antigen, the male H-Y antigen. In addition, we have analyzed clonal deletion and tolerance induction after neonatal tolerance induction and superantigen-induced arthritis with the class II MHC reactive superantigen staphylococcal enterotoxin B (SEB) in V beta 8 TcR transgenic and non-transgenic MRL-lpr/lpr mice. Neonatal tolerance induction to SEB was normal in lpr/lpr mice. However, over time a loss of tolerance (thymic or peripheral) was observed in lpr/lpr mice but not in +/+ TcR transgenic mice. This defect in lpr/lpr mice was thymic-dependent and was due to increased CD28/CTLA4 signaling. These results suggest that an apoptosis defect involving both thymocytes and peripheral lymphoid cells leads to autoimmune disease in lpr/lpr mice. The challenge in the future will be to determine the role of defective apoptosis in other autoimmune diseases.

Toxicity of staphylococcal enterotoxins potentiated by lipopolysaccharide: major histocompatibility complex class II molecule dependency and cytokine release

The biological effects of staphylococcal enterotoxins (SE), potentiated by bacterial lipopolysaccharide (LPS), were studied with mice. Control animals survived the maximum dose of either SE or LPS, while mice receiving both agents died. SEA was 43-fold more potent than SEB and 20-fold more potent than SEC1. The mechanism of toxicity was further examined with transgenic mice deficient in major histocompatibility complex class I or II expression. Class II-deficient mice were resistant to SEA or SEB. However, class I-deficient animals were less susceptible to SEA (30% lethality) than wild-type mice (93% lethality). In vitro stimulation of T cells from the three mouse phenotypes by SEA correlated well with toxicity. T cells from transgenic or wild-type mice were similarly responsive to SEA when presented by irradiated, wild-type mononuclear cells. These data confirmed that the toxicity of SE was mainly exerted through a mechanism dependent on the expression of major histocompatibility complex class II molecules. Toxicity was also linked to stimulated cytokine release. Levels in serum of tumor necrosis factor alpha, interleukin-6, and gamma interferon peaked 2 to 4 h after the potentiating dose of LPS but returned to normal within 10 h. Concentrations of interleukin-1 alpha were also maximal after 2 h but remained above the background for up to 22 h. Relative to the levels in mice given only SEA or LPS, the levels in serum of tumor necrosis factor alpha, interleukin-6, and gamma interferon increased 5-, 10-, and 15-fold, respectively, after injections of SEA plus LPS. There was only an additive effect of SEA and LPS on interleukin-1 alpha concentrations.

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.

Modification of the anti-CD3-induced cytokine release syndrome by anti-interferon-gamma or anti-interleukin-6 antibody treatment: protective effects and biphasic changes in blood cytokine levels

Anti-interferon-gamma (IFN-gamma) antibodies were found to protect mice against pathological changes induced by injection of anti-CD3 antibody: incidence of diarrhea, severity of hypothermia and mortality rates were dramatically reduced. In anti-IFN-gamma antibody-treated mice, IFN-gamma blood levels were significantly reduced at 1.5 h post anti-CD3 challenge, but more elevated levels were found from 4 to 24 h. This rebound-like IFN-gamma response coincided with more profound hypoglycemia. Tumor necrosis factor and interleukin (IL)-6 levels were not affected by anti-IFN-gamma treatment. Exogenous IFN-gamma, administered within 3 h (but not later) of the anti-CD3 challenge made the syndrome worse. Furthermore, inter-mouse strain differences in sensitivity to the anti-CD3 syndrome correlated with the ability of the strain to produce IFN-gamma. Anti-IL-6 antibodies provided only marginal protection against hypothermia and mortality, but did markedly reduce hypoglycemia. Levels of biologically active IL-6 in serum were not influenced by anti-IL-6 antibody treatment during the first few hours after anti-CD3 challenge, but were significantly increased at later times. The data provide evidence that endogenous IFN-gamma is a critical element in the early phase of the anti-CD3 syndrome; endogenous IL-6, while possibly being involved in hypoglycemia, seems of lesser importance for the outcome of the syndrome.

Linomide, a novel immunomodulator that prevents death in four models of septic shock

Intravenous injections of 50 micrograms Staphylococcus aureus enterotoxin B (SEB) or bacterial lipopolysaccharide (LPS) are lethal, provided that mice are simultaneously sensitized with either N-galactosamine (GalN) or the anti-glucocorticoid RU-38486. Similar to the synthetic glucocorticoid (GC) receptor agonist dexamethasone, pharmacological doses of the immunomodulator linomide (quinoline-3-carboxamide) prevent death in all four models of lethal septic shock (LPS + GalN, LPS + RU-38486, SEB + GalN, and SEB + RU-38486) and inhibit the secretion of tumor necrosis factor, one of the major intermediate effector molecules of SEB and LPS toxicity. In this system, cyclosporine A (CsA), although effective in suppressing SEB toxicity, fails to counteract the lethal effect of LPS. This observation, together with the fact that linomide acts in the presence of excess amounts of GC receptor antagonist, indicates that linomide functions in a different way to that of known immunosuppressive agents like CsA and GC.

A novel superantigen isolated from pathogenic strains of Streptococcus pyogenes with aminoterminal homology to staphylococcal enterotoxins B and C

Streptococcus pyogenes (group A Streptococcus) has re-emerged in recent years as a cause of severe human disease. Because extracellular products are involved in streptococcal pathogenesis, we explored the possibility that a disease isolate expresses an uncharacterized superantigen. We screened culture supernatants for superantigen activity with a major histocompatibility complex class II-dependent T cell proliferation assay. Initial fractionation with red dye A chromatography indicated production of a class II-dependent T cell mitogen by a toxic shock-like syndrome (TSLS) strain. The amino terminus of the purified streptococcal superantigen was more homologous to the amino termini of staphylococcal enterotoxins B, C1, and C3 (SEB, SEC1, and SEC3), than to those of pyrogenic exotoxins A, B, C or other streptococcal toxins. The molecule, designated SSA, had the same pattern of class II isotype usage as SEB in T cell proliferation assays. However, it differed in its pattern of human T cell activation, as measured by quantitative polymerase chain reaction with V beta-specific primers. SSA activated human T cells that express V beta 1, 3, 15 with a minor increase of V beta 5.2-bearing cells, whereas SEB activated V beta 3, 12, 15, and 17-bearing T cells. Immunoblot analysis of 75 disease isolates from several localities detected SSA production only in group A streptococci, and found that SSA is apparently confined to only three clonal lineages as defined by multilocus enzyme electrophoresis typing. Isolates of one of these lineages, (electrophoretic type 2) are strongly associated with TSLS. The data identify SSA as a novel streptococcal superantigen that appears to be more related structurally to staphylococcal enterotoxins than to streptococcal exotoxins. Because abundant SSA production is apparently confined to only three streptococcal clonal lineages, the data also suggest that the SSA gene has only recently been acquired by S. pyogenes.

Immunopharmacology of the superantigen staphylococcal enterotoxin A in T-cell receptor V beta 3 transgenic mice

The response of mouse T cells to the superantigen staphylococcal enterotoxin A (SEA) requires 1000-fold higher concentrations compared to human T cells. In order to develop a sensitive model for SEA studies in mice, the immunopharmacology has been studied in T-cell receptor (TcR) V beta 3 transgenic (TGV beta 3) and non-transgenic (non-TG) C57Bl/6 mice. The frequency of SEA-responsive T cells in the TGV beta 3 mice exceeded 90%, whereas a 10-fold lower frequency was seen in normal C57Bl/6 mice. Nanograms of SEA injected intravenously into TGV beta 3 mice induced strong cytolytic T lymphocyte (CTL) activity against SEA-coated major histocompatibility complex (MHC) class II+ B-lymphoma cells, whereas administration of 1000-fold higher amounts of SEA to non-TG littermates or normal C57Bl/6 mice induced only a moderate response. Kinetic analysis demonstrated that the CTL activity was more rapidly detectable in TG mice, but substantial levels were seen 2 days after SEA injection in both TGV beta 3 and non-TG mice. The cytotoxic T-cell response induced by SEA in TGV beta 3 and non-TG mice was completely MHC class II dependent, as SEA-coated MHC class II-transfected syngeneic B16 melanoma cells but not untransfected B16 cells were sensitive to lysis. Large amounts of tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) accumulated in serum of TGV beta 3 mice after injection of 10 ng SEA, whereas only marginal amounts were recorded in non-TG even after injection of 100 micrograms SEA. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrated that SEA-induced TNF-alpha and IFN-gamma mRNA reached maximal levels 1 hr after SEA administration in TGV beta 3 mice, whereas peak serum levels of TNF-alpha and IFN-gamma proteins were recorded after 2 hr. Comparison of the mRNA levels of a panel of cytokines in the TGV beta 3 and non-TG mice revealed that almost similar amounts of interleukin-1 (IL-1) were induced in both strains, whereas IL-4 was only detected at significant levels in the TGV beta 3 mouse. The results suggest that TGV beta 3 mice are suitable for studying in vivo immune responses to superantigens at concentrations comparable to the potent effects elicited in humans. Moreover, this model is useful for detailed studies on the dynamic regulation of T-cell activation and anergy induced by superantigens.

Genotypic heterogeneity of node based peripheral T-cell lymphoma

PTCL represents a diverse group of histological entities that defy classification schemes based on normal T cell differentiation, differ in their clinical presentation and behave unpredictably. Genetic analyses of this phenotypically heterogeneous group have clearly shown that histologically defined PTCL may be subdivided on the basis of clonal gene rearrangements. The absence of clonal gene rearrangements in a significant proportion of PTCL cases has increased the complexity of classification. The data presented in this review suggest that a molecular classification would allow true reflection of PTCL aetiology, but carefully coordinated studies are required to evaluate the clinical usefulness of such a classification scheme.

Concomitant loss of conformation and superantigenic activity of staphylococcal enterotoxin B deletion mutant proteins

The T-cell-stimulating activity of staphylococcal enterotoxin B (SEB) is an important factor in the pathogenesis of certain staphylococcal diseases. To investigate the immunologically active domains of the SEB molecule, we have produced truncated fragments of recombinant SEB by C-terminal and N-terminal deletions. The fragments were expressed as fusion proteins with protein A, including a cleavage site to remove the protein A part. Mutant proteins were tested for the ability to stimulate human resting T cells and SEB-reactive T-cell clones. Deletion of only 9 amino acids from the C terminus leads to complete loss of T-cell-stimulating activity. Removing further amino acids from the SEB molecule did not lead to a reexpression of T-cell-mitogenic activity. A mutant protein, however, in which the 9 C-terminal amino acids were replaced with a tail of 68 amino acids encoded by the vector was fully active. Two mutant proteins with N-terminal deletions of 60 and 81 amino acids were inactive as well. A neutralizing monoclonal antibody against a conformational epitope lost binding with all the inactive mutant proteins only, whereas a monoclonal antibody recognizing an epitope involved in emetic activity reacted with all mutant proteins. These results suggest that even small deletions at the C terminus affect the three-dimensional conformation of the SEB molecule.

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.

Lectins and superantigens: membrane interactions of these compounds with T lymphocytes affect immune responses

1. Lectins and superantigens belong to two different families of macromolecules which are able to interact with cells of the immune system. 2. The principal mechanisms by which they modulate immune responses are presented in this review. 3. Possible similarities shared by these proteins and their common mechanisms of action upon immunocytes will be presented along with a brief discussion regarding the role of these molecules in physiological immune responses and human diseases.

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.

Inhibition of allostimulated HLA-DQ and DP-specific T cells by staphylococcal enterotoxin A

Bacterial superantigens have two immunologically important features. They bind MHC class II molecules and stimulate T cells bearing certain V beta TCR phenotypes. Superantigens such as SEA, SEB, and TSST bind to each of the three HLA class II isotypes (DR, DQ, and DP). Allotypic variation seems to play an important role in superantigen binding to class II molecules, but the functional implications of these differences remain largely unknown. In the present investigation, we studied the effects of SEA, SEB, and TSST on allostimulation of HLA-DR-, DQ-, and DP-allospecific T-cell clones. To avoid direct stimulation of T-cell responses by the superantigens, SEA and/or SEB nonresponsive T-cell clones were selected. We show that SEA strongly inhibited DQ- and DP-specific T-cell responses. In contrast, SEB and TSST had only weak inhibitory effects. DR-specific T-cell responses were unaffected or only weakly inhibited by the superantigens tested. The inhibition appeared not to be due to induction of cytotoxicity or suppression of either T cells or EBV-LCLs by SEA. In conclusion, the bacterial superantigen SEA can block alloantigen-specific stimulation of T clones in vitro. These results suggest that SEA binds to certain MHC class II molecules in a way that prevents MHC-TCR interactions.

Characterization of T cell repertoire changes in acute Kawasaki disease

Kawasaki disease (KD) is an acute multisystem vasculitis of unknown etiology that is associated with marked activation of T cells and monocyte/macrophages. Using a quantitative polymerase chain reaction (PCR) technique, we recently found that the acute phase of KD is associated with the expansion of T cells expressing the V beta 2 and V beta 8.1 gene segments. In the present work, we used a newly developed anti-V beta 2 monoclonal antibody (mAb) and studied a new group of KD patients to extend our previous PCR results. Immunofluorescence analysis confirmed that V beta 2-bearing T cells are selectively increased in patients with acute KD. The increase occurred primarily in the CD4 T cell subset. The percentages of V beta 2+ T cells as determined by mAb reactivity and flow cytometry correlated linearly with V beta expression as quantitated by PCR. However, T cells from acute KD patients appeared to express proportionately higher levels of V beta 2 transcripts per cell as compared with healthy controls or convalescent KD patients. Sequence analysis of T cell receptor beta chain genes of V beta 2 and V beta 8.1 expressing T cells from acute KD patients showed extensive junctional region diversity. These data showing polyclonal expansion of V beta 2+ and V beta 8+ T cells in acute KD provide additional insight into the immunopathogenesis of this disease.

Activation of mucosal V beta 3+ T cells and tissue damage in human small intestine by the bacterial superantigen, Staphylococcus aureus enterotoxin B

Staphylococcus aureus enterotoxin B (SEB) was added to explants of fetal human intestine in organ culture or administered into the lumen of fetal small intestine prior to culture. Both routes produced a massive increase in lamina propria T cells expressing V beta 3, and to a lesser extent, those expressing V beta 5 and V beta 12. SEB-activated lamina propria T cells produced interleukin-2 and interferon-gamma and T cell activation was accompanied by tissue damage, which was inhibited by FK506.