Activation of human T cells by toxic shock syndrome toxin-1: the toxin-binding structures expressed on human lymphoid cells acting as accessory cells are HLA class II molecules

Neonatal toxic shock syndrome-like exanthematous disease (NTED)

The author and colleagues recently discovered an emerging neonatal infectious disease: neonatal toxic shock syndrome-like exanthematous disease (NTED), which is induced by the superantigen toxic shock syndrome toxin-1 (TSST-1), produced by methicillin-resistant Staphylococcus aureus (MRSA). The massively expanded Vbeta2+ T cells were rapidly deleted in the peripheral blood of patients with NTED. A marked depletion of Vbeta2+ T cells was also observed in the peripheral blood before the expansion of these T cells. Anergy is specifically induced in the TSST-1 reactive T cells of patients with NTED. Rapid recovery from NTED without complications is expected to be related to the induction of immunologic tolerance in neonatal patients. Anti-TSST-1 IgG antibody of maternal origin was found to play a protective role in preventing the development of NTED. The number of hospitals that have experience caring for patients with NTED has increased threefold in the past 5 years. Most MRSA isolates from neonatal intensive care units in Japan were found to be a single clone of coagulase type II and to possess TSST-1 and staphylococcal enterotoxin C genes. The timing and increased incidence of NTED suggest the emergence of a new MRSA clone. By recognizing that TSST-1 can induce NTED, healthcare providers may give increased attention to this disease in neonatal wards.

Streptococcus dysgalactiae-derived mitogen (SDM), a novel bacterial superantigen: characterization of its biological activity and predicted tertiary structure

A mitogenic substance, designated Streptococcus dysgalactiae-derived mitogen (SDM), was purified from S. dysgalactiae culture supernatant, and the gene encoding the mitogen was cloned. Both native and recombinant SDM expressed in Escherichia coli significantly activated human V beta 1+ and V beta 23+ T cells in association with major histocompatibility complex (MHC) class II molecules on accessory cells, indicating that SDM possesses superantigenic properties. The sdm gene consists of two segments encoding a signal peptide and a mature 25 kDa protein composed of 212 amino acids. Three of 34 S. dysgalactiae strains but none of 28 Streptococcus pyogenes strains examined carried sdm. Phylogenetic analysis indicated that SDM belongs to a family distinct from established bacterial superantigens. SDM showed around 30% homology with other superantigens at the amino acid sequence level. The tertiary structure of SDM was predicted by modelling onto streptococcal pyrogenic exotoxin C and streptococcal mitogenic exotoxin Z-2, both of which share highly homologous structure-determining regions. SDM showed overall structural similarity to both these superantigens. This is the first study to characterize fully a bacterial superantigen from S. dysgalactiae.

Continuous exposure of mice to superantigenic toxins induces a high-level protracted expansion and an immunological memory in the toxin-reactive CD4+ T cells

We analyzed the responses of several T cell fractions reactive with superantigenic toxins (SAGTs), staphylococcal enterotoxin A (SEA), or Yersinia pseudotuberculosis-derived mitogen (YPM) in mice implanted with mini-osmotic pumps filled with SEA or YPM. In mice implanted with the SEA pump, SEA-reactive Vbeta3(+)CD4(+) T cells exhibited a high-level protracted expansion for 30 days, and SEA-reactive Vbeta11(+)CD4(+) T cells exhibited a low-level protracted expansion. SEA-reactive CD8(+) counterparts exhibited only a transient expansion. A similar difference in T cell expansion was also observed in YPM-reactive T cell fractions in mice implanted with the YPM pump. Vbeta3(+)CD4(+) and Vbeta11(+)CD4(+) T cells from mice implanted with the SEA pump exhibited cell divisions upon in vitro restimulation with SEA and expressed surface phenotypes as memory T cells. CD4(+) T cells from mice implanted with the SEA pump exhibited high IL-4 production upon in vitro restimulation with SEA, which was due to the enhanced capacity of the SEA-reactive CD4(+) T cells to produce IL-4. The findings in the present study indicate that, in mice implanted with a specific SAGT, the level of expansion of the SAGT-reactive CD4(+) T cell fractions varies widely depending on the TCR Vbeta elements expressed and that the reactive CD4(+) T cells acquire a capacity to raise a memory response. CD8(+) T cells are low responders to SAGTs.

Immunopathophysiological aspects of an emerging neonatal infectious disease induced by a bacterial superantigen

We recently discovered an emerging neonatal infectious disease, neonatal toxic shock syndrome-like (TSS-like) exanthematous disease (NTED), which is induced by a superantigen, TSS toxin-1 (TSST-1), produced by methicillin-resistant Staphylococcus aureus (MRSA). Here, we analyzed the activation and the response of TSST-1-reactive Vss2(+) T cells in NTED patients during the acute and recovery phases and in asymptomatic infants exposed to MRSA. In the acute phase, Vss2(+) T cells were anergic to stimulation with TSST-1 and underwent marked expansion, but by 2 months after disease onset, their numbers had declined to about 10% of the control level. Although the percentage of Vss2(+) T cells in the ten asymptomatic neonatal MRSA carriers was within the control range, these individuals could be divided into two groups on the basis of Vss2(+) T-cell activation. Vss2(+)CD4(+) T cells from three of these infants (Group 1) highly expressed CD45RO and were anergic to TSST-1, whereas in the other seven asymptomatic neonatal MRSA carriers (Group 2), these cells expressed CD45RO at the control level and were highly responsive to stimulation with TSST-1. The serum anti-TSST-1 IgG Ab titer was negligible in the four NTED patients in the acute phase and the three asymptomatic neonatal MRSA carriers in Group 1, but it was high in the seven asymptomatic carriers in Group 2. We suggest that maternally derived anti-TSST-1 IgGs helps to suppress T-cell activation by TSST-1 and protects infants from developing NTED.

Comparison of pathogenic factors expressed by group A Streptococci isolated from patients with streptococcal toxic shock syndrome and scarlet fever

Streptococcal toxic shock syndrome (STSS) is an illness with high mortality. To obtain clues to understanding the pathogenesis of STSS, we investigated the expression of several pathogenic factors in ten group A streptococcus (GAS) isolates from ten patients with STSS in Japan, in comparison with ten GAS isolates from children with scarlet fever. The ten scarlet fever-derived GAS isolates were equally low in lethality and anti-phagocytic activity in mice and in the production of streptolysin O (SLO), and equally high in production of superantigenic exotoxins (SAGTs) and cysteine proteinase. By comparison, the ten STSS-derived GAS isolates were heterogeneous in the expression of the above pathogenic factors, which ranged from low to high values. Most of the ten STSS-derived isolates were higher in lethality and anti-phagocytic activity and production of SLO, and lower in the production of SAGTs and cysteine proteinase than the ten scarlet fever-derived isolates. The results suggest that the lethality and anti-phagocytic activity examined in mice and SLO may be involved mainly in the development of most of the ten STSS cases.

Analysis of the superantigen-producing ability of Yersinia pseudotuberculosis strains of various serotypes isolated from patients with systemic or gastroenteric infections, wildlife animals and natural environments

Yersinia pseudotuberculosis is a pathogen causing gastroenteritis as well as acute and systemic infections. This organism produces a superantigenic exotoxin, designated Y. pseudotuberculosis-derived mitogen (YPM). We consider this exotoxin to be the primary pathogen of the systemic type infection. In this study, we examined 101 Y. pseudotuberculosis strains isolated from various sources, patients with the systemic or the gastroenteric type of infections, wildlife animals and natural environments for the presence of the YPM gene and the production of YPM or other related superantigens. We found that all of the strains isolated from patients with systemic type infection carried the YPM gene and produced YPM. A certain proportion of the organisms isolated from patients with the gastroenteric type infection, wildlife animals or natural environments did not carry the YPM gene nor produced superantigens. These results suggest that YPM is involved in the pathogenesis of the systemic type of Y. pseudotuberculosis infection.

Exanthematous disease induced by toxic shock syndrome toxin 1 in the early neonatal period

BACKGROUND

We have seen a number of patients who developed systemic exanthema and thrombocytopenia in the first week of life. Although nearly 100% of the patients were carriers of meticillin-resistant Staphylococcus aureus (MRSA), no clear link between MRSA and this exanthematous disease has yet been made.

METHODS

20 neonates with exanthema and thrombocytopenia were selected for study. To see whether superantigenic exotoxins from MRSA are involved in the pathogensis of the exanthematous disease, we studied the production of these exotoxins by MRSA isolates from the neonates. We studied the expression of T-cell-receptor Vbeta and CD45RO in T cells taken from four of the neonates. We also analysed the DNA sequences of 16 cloned Vbeta2-positive T-cell-receptor-chain genes taken from two of the neonates.

FINDINGS

Although most of the patients recovered within 5 days of onset of the exanthematous disease without any active treatment, two preterm infants died in the recovery phase. All patients showed colonisation by MRSA. The MRSA produced toxic shock syndrome toxin-1 (TSST-1). The number of T cells positive for T-cell-receptor Vbeta2, reactive to TSST-1, was increased in the four patients studied (p<0.0001), and these T cells expressed CD45RO (p=0.0185). None of the Vbeta2 clones had the same junctional sequences.

INTERPRETATION

The polyclonal expansion of Vbeta2-positive T cells in patients colonised by TSST-1-producing MRSA suggests that the pathogenic micro-organism of this neonatal exanthematous disease is S aureus, mainly MRSA, and that in its pathogenesis it activates T cells by TSST-1. Although the pathogenesis of both this exanthematous disease and toxic shock syndrome are fundamentally the same, a diagnosis of toxic shock syndrome cannot be made in this case, based on the clinical criteria for toxic shock syndrome. We propose neonatal toxic-shock-syndrome-like exanthematous disease (NTED) as the name for this disease.

Post-Thymic Maturation of Migrating Human Thymic Single-Positive T Cells: Thymic CD1a− CD4+ T Cells Are More Susceptible to Anergy Induction by Toxic Shock Syndrome Toxin-1 than Cord Blood CD4+ T Cells

To determine whether human CD4+ T cells undergo post-thymic maturation, we compared the susceptibility to anergy induction in human thymic CD1a− CD4+ single-positive (CD4+), cord blood (CB) CD4+, and adult peripheral blood (APB) CD4+ T cells by stimulation with toxic shock syndrome toxin-1 (TSST-1). Most TSST-1-induced T cell blasts derived from either T cell preparation expressed TCR Vβ2, which determines the potential reactivity to TSST-1. Most thymic CD4+ T cell blast preparations exhibited little or no production of IL-2 and IL-4 after restimulation with TSST-1 and only marginal responses after stimulation with rIL-2 or a combination of PMA and calcium ionophore, while the APB CD4+ T cell blasts showed high responses to these stimuli. The responses of CB CD4+ T cell blasts to these stimuli varied, ranging from minimal to relatively high. Studies of DNA fragmentation showed that there was no significant cell death of thymic CD4+ T cell blasts. Most thymic CD1a− CD4+ and CB CD4+ T cells were CD38 positive. APB CD4+ T cell blasts derived from the CD38+ fraction and from the CD38− fraction exhibited equally high responses to restimulation with TSST-1. These results indicate that thymic CD1a− CD4+ and CB CD4+ T cells are inherently highly susceptible to anergy induction by bacterial superantigens and that thymic CD1a− CD4+ T cells are less mature than CB CD4+ T cells, suggesting that post-thymic maturation in thymic T cells migrating to the periphery is required for acquisition of full reactivity to antigenic stimulation.

Synovial mononuclear cells consist with T cells which produce high levels of tumor necrosis factor alpha

To determine whether synovial mononuclear cells include a population of tumor necrosis factor alpha-producing T cells, we measured tumor necrosis alpha levels in culture supernatants of synovial mononuclear cells by ELISA and analyzed tumor necrosis alpha mRNA-positive cell frequencies. There were no significant differences in the spontaneous levels of TNF alpha between synovial mononuclear cells and peripheral mononuclear cells. The frequency of tumor necrosis factor alpha mRNA-positive cells in synovial mononuclear cells was higher than that of peripheral mononuclear cells. When stimulated with a superantigen, mononuclear cells from the synovial fluid of rheumatoid arthritis patients showed higher levels of tumor necrosis factor alpha production (1,035 +/- 817 pg/ml) than did mononuclear cells from their peripheral blood (236 +/- 180 pg/ml). In addition, we observed that a few T cell clones were resistant to superantigenic restimulation in vitro. We conclude that when these types of T cells persist in the synovium, they play a role in the development of rheumatoid arthritis via a mechanism involving tumor necrosis factor alpha production.

Expression of T-cell receptor V beta 2 and type 1 helper T-cell-related cytokine mRNA in streptococcal pyrogenic exotoxin-C-activated human peripheral blood mononuclear cells

Streptococcal pyrogenic exotoxin type C (SPE C) is a member of the bacterial superantigens that are potent stimulants of T cells. We expressed SPE C in Escherichia coli and characterized its selective stimulation properties on human T cells bearing specific V beta chains of T-cell receptors (TCRs). Cytokine profiles induced by SPE C were also examined. Recombinant SPE C significantly enhanced proliferation of human peripheral blood mononuclear cells (PBMCs) at concentrations as low as 10(-12)-10(-14)M. Reverse transcription of RNA, from SPE-C-stimulated PBMCs followed by polymerase chain reaction, revealed selective induction of TCR V beta 2 chain expression. SPE C raised the mRNA level of type 1 helper T cell (TH1) related cytokines, such as interferon gamma (IFN-gamma), interleukin 2 (IL-2), and tumor necrosis factor beta (TNF beta). The expression of TNF alpha was also increased. In contrast, the increase in mRNA levels of the p35 small fragment of IL-12 and type 2 helper T cell (TH2) related cytokines (i.e., IL-4 and IL-10) was not significantly affected by SPE C. The mRNA level of proinflammatory cytokine IL-6 was increased marginally. Consistent with the mRNA accumulation, protein concentrations of IFN gamma, IL-2, and TNF were increased in SPE-C-stimulated PBMCs, but IL-4 was not. From these results, we conclude that the stimuli of SPE C preferentially causes the TH1 responses in human T cells bearing TCR V beta 2.

Identification from a phage display library of peptides that bind to toxic shock syndrome toxin-1 and that inhibit its binding to major histocompatibility complex (MHC) class II molecules

Phage display technique is a powerful tool with which to identify novel binding sequences for antibody and receptor targets. Few studies, however, have used this technology to select affinity peptides for ligand molecules. Here, we screened a peptide phage library for binding to toxic shock syndrome toxin 1 (TSST-1) to examine whether peptide ligands for TSST-1 which mimic the structure of major histocompatibility complex (MHC) class II receptors could be identified. After three cycles of biopanning, four potent sequences reactive with TSST-1 were isolated (designated phages 2, 3, 8, and 11). Selected phage were found to react specifically with TSST-1 but not with other staphylococcal exotoxins. A synthetic peptide (pep3) corresponding to the most frequently identified sequence (phage3) was shown to inhibit binding of all four isolated phage to TSST-1, suggesting that they bind to a common site on TSST-1. Furthermore, pep3 was shown to compete with MHC class II molecules for binding to TSST-1 in a concentration-dependent manner. Comparison of their sequences with MHC class II molecules revealed that phage8 shared sequence homology with two regions of the beta chain of MHC class II molecules: amino acids 57-62, containing a residue (Tyr-60) involved in TSST-1 binding as suggested by X-ray crystallographic data of TSST-1-MHC class II complex; and amino acids 188-193, a region not previously known as a contact domain. These results suggest that the selected sequences recognized the MHC class II binding site on TSST-1. Thus, affinity selection for peptides binding to ligand molecules (e.g., TSST-1) rather than their cognate receptors (e.g., MHC class II) from a random phage display library represents a useful approach to understanding receptor-ligand interactions.

Correlation between serum TNF alpha and IL6 levels and severity of group A streptococcal infections

The multiorgan failure syndrome caused by group A streptococci (GAS) designated streptococcal toxic shock syndrome (STSS) is believed to be mediated by cytokines induced by superantigens. In order to study the relationship between superantigen production, cytokine levels in patient sera, and clinical GAS manifestation we examined acute-phase sera and strains from 25 patients with GAS bacteremia. The patients had various disease manifestations, including STSS (44%), erysipelas (28%), septicemia (24%), wound infections (16%), and pneumonia (12%). Serotype T1M1 dominated, representing 56% of the isolates, but also strains of other serotypes were identified. The strains were found to produce the streptococcal pyrogenic exotoxins (Spe) A, B, and F, as determined by immuno-blot analyses. There was no difference in amounts of toxin produced between strains isolated from patients with different manifestations of disease. Levels of TNF alpha, IL1 alpha, IL6, IL8, and IFN gamma in acute-phase sera were determined by use of ELISA and RIA assays. The analyses showed higher levels of IL6 in sera from patients with STSS than in sera from patients with bacteremia without shock. TNF alpha was elevated in sera from patients with STSS, as compared to sera from patients with uncomplicated pharyngotonsillitis. No increase in the levels of IL1 alpha, IL8, and IFN gamma could be found in the patient sera and there was no difference in the level of those cytokines between the various patient categories.

Superantigenic properties of the group A streptococcal exotoxin SpeF (MF)

Streptococcal pyrogenic exotoxin F (SpeF), previously referred to as mitogenic factor, is a newly described potent mitogen produced by group A streptococci. To investigate whether this protein belongs to the family of microbial superantigens, we analyzed the cellular and molecular requirements for its presentation to T cells and compared it with the known streptococcal superantigen pyrogenic exotoxin A (SpeA) and the nonspecific polyclonal T-cell mitogen phytohemagglutinin (PHA). SpeF and SpeA were efficiently presented by autologous antigen-presenting cells (APCs) and an allogeneic B lymphoma cell line, Raji. In contrast, the monocytic cell line U937, which does not express major histocompatibility complex (MHC) class II molecules, failed to present SpeF as well as SpeA but supported the response to PHA. Thus, the presentation of SpeF by APCs was class II dependent but not MHC restricted. The requirement for HLA class II was further supported by the ability of anti-HLA-DQ monoclonal antibody to block the SpeF-induced proliferative response by 75 to 100%. Paraformaldehyde (PFA) fixation of autologous APCs resulted in an impaired ability of SpeF and SpeA to induce optimal T-cell proliferation. In contrast, fixation of Raji cells did not affect the induced proliferation. The stimulatory effect of PHA remained unaffected by both the use of PFA-fixed APCs and the addition of the HLA class II-specific monoclonal antibodies. The addition of a supernatant enriched in interleukin 1 and interleukin 6 to fixed autologous APCs resulted in an increased SpeF-induced response; thus, the impairment was not due to a requirement for processing, but, rather, costimulatory factors produced by metabolically active APCs were needed. SpeF was found to preferentially activate T cells bearing V beta 2, 4, 8, 15, and 19, as determined by quantitative PCR. The data presented clearly show that SpeF is a superantigen. We also studied the prevalence of the speF gene in clinical isolates by Southern blot analyses, and the gene could be detected in 42 group A streptococcal strains, which represented 14 serotypes.

Similar cytokine induction profiles of a novel streptococcal exotoxin, MF, and pyrogenic exotoxins A and B

The cytokine production induced by a newly discovered streptococcal exotoxin, MF, and the pyrogenic exotoxins SpeA and SpeB was determined by in vitro stimulation of peripheral blood mononuclear cells (PBMCs) obtained from healthy blood donors. The induction and kinetics of interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-1 receptor antagonist, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-10, gamma interferon, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and granulocyte-macrophage colony-stimulating factor were studied at the single-cell level by use of cytokine-specific monoclonal antibodies and intracellular immunofluorescent juxtanuclear staining. The cytokine-producing cells, with the exception of IL-1-expressing cells, had a characteristic morphology generated by the accumulation of cytokines in the Golgi organelle. MF, SpeA, and SpeB induced a massive gamma interferon and TNF-beta response in 10 to 16% of the PBMCs after 48 to 96 h of cell stimulation. In contrast, IL-2 and TNF-alpha production was detected in only 1 to 3% of the PBMCs. The induction of a lymphocyte TH2 phenotype response, including production of IL-3, IL-4, IL-5, and IL-10, was weak. However, the monokines, IL-1 alpha, IL-1 beta, IL-1 receptor antagonist, and IL-8, were consistently found and gradually produced, peaking at 24 h in approximately 5 to 8% of the PBMCs. MF showed extensive cytokine- and proliferation-inducing capacities equal to those of SpeA and SpeB, which suggests that MF is also a superantigen. A marked interindividual variation could be noted both in the proliferative response and in the cytokine induction of lymphocytes isolated from different individuals, which may be one explanation for the varying clinical severity noticed during group A streptococcal infections.

Production of tumour necrosis factors by human T cells stimulated by a superantigen, toxic shock syndrome toxin-1

The capacity of human T cell subsets, CD4+ or CD8+ T cells, to produce tumour necrosis factors (TNF-alpha and TNF-beta) upon stimulation with toxic shock syndrome toxin-1 (TSST-1) and the requirement for MHC class II molecules on accessory cells (AC) in the response were investigated. The capacity of CD4+ T cells was much higher than that of CD8+ T cells in TSST-1-induced production of TNF-alpha and TNF-beta. The expression of MHC class II molecules on AC was required in the response.

Purification and partial characterization of a product from Yersinia pseudotuberculosis with the ability to activate human T cells

We tried to purify a substance exhibiting mitogenicity for human peripheral blood lymphocytes from Yersinia pseudotuberculosis isolated from patients with Y. pseudotuberculosis infection manifesting acute and systemic clinical symptoms. The supernatant of a suspension of the bacteria disrupted by sonication was serially chromatographed on DEAE-Sepharose fast-flow, Sephacryl S-100 HR, and TSK-gel G2000SW high-pressure liquid chromatography columns. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that the purified mitogenically active substance migrated as a single band corresponding to a molecular mass of 21 kDa. We designated the purified substance Y. pseudotuberculosis-derived mitogen (YPM). YPM stimulated human peripheral T cells to proliferate and produce interleukin-2 at 0.1 ng/ml or more. YPM-induced T-cell activation required the expression of HLA class II molecules on accessory cells.

Relative abilities of distinct isotypes of human major histocompatibility complex class II molecules to bind streptococcal pyrogenic exotoxin types A and B

The relative ability of distinct isotypes of human leukocyte antigen class II molecules to bind streptococcal pyrogenic exotoxins A and B (SPE A and SPE B, respectively) was investigated by a direct-binding assay with 125I-labeled toxin for SPE A and by a functional assay system measuring the accessory cell activity of human leukocyte antigen class II transfectants in toxin-induced T-cell activation for SPE A and SPE B. SPE A binding was observed in L cells transfected with DQw1 genes. By contrast, it was not detected in L cells transfected with DR2, DR4, DPw4 or DP(Cp63) genes. All the transfectants supported SPE-induced interleukin-2 production by human T cells except the DP transfectants for SPE B. Levels of accessory cell activity were low in the DP transfectants induced by stimulation with SPE A and in the DR and DP transfectants induced by SPE B. The results indicate that SPE A and SPE B bind well to DQ molecules, less well to DR molecules, and very weakly to DP molecules.

Direct activation of murine T cells by staphylococcal enterotoxins

The capacity of staphylococcal enterotoxins to stimulate all T cells bearing certain TCR variable region alleles has generated a great deal of interest. This stimulation appears to involve specific binding of the toxin to class II molecules and subsequent stimulation of the T cell via the TCR V beta elements. Recent studies from our laboratory have focused on the ability of staphylococcal enterotoxins to directly activate purified lymph node T cells and a panel of T cell clones and hybridomas. A T cell costimulation assay was performed to assess cellular activation requirements and cytokine receptor expression. Activation of highly purified lymph node T cells by staphylococcal enterotoxin B (SEB) required costimulatory signals which could be provided by IL-1, IL-2, IL-4, or IL-6, whereas SEB alone demonstrated no significant proliferative response. Using a panel of TH1 and TH2 cell clones and T cell hybridomas possessing various responsive and nonresponsive V beta alleles, it was possible to demonstrate that SEA and SEB costimulate T cells via the TCR complex. Additionally, enterotoxin-pretreated T cells demonstrated a significant proliferative response upon exposure to class II-bearing accessory cells, suggesting that these toxins bind directly to T cells. Highly purified T cells cultured with both SEB and IL-1 exhibit significantly increased levels of IL-2 receptor, whereas cells cultured with SEB or IL-1 alone demonstrated low levels of this receptor. These results do not exclude an association of the staphylococcal enterotoxins with class II molecules in a manner which results in a high avidity binding to the TCR required for transduction of the appropriate activation signals. In the absence of class II molecules, however, these superantigens can still bind to T cells, and the activation signal is delivered in the presence of cytokines that trigger T cell growth and lymphokine production.

Involvement of HLA class II molecules in acquisition of staphylococcal enterotoxin A-binding activity and accessory cell activity in activation of human T cells by related toxins in vascular endothelial cells

Human umbilical vascular endothelial cells (HUVEC) express HLA class II molecules upon stimulation with recombinant human interferon-gamma (IFN-gamma). Staphylococcal enterotoxin (SE) A (SEA)-binding assay using [125I]-SEA showed the presence of specific SEA binding in HUVEC stimulated with IFN-gamma but not in unstimulated HUVEC. Levels of HLA class II expression and SEA-binding increased as the IFN-gamma concentration and the period of stimulation were increased. Binding of [125I]-SEA to the IFN-gamma-stimulated HUVEC was reduced markedly by an anti-DR/DP MoAb. T cells produced IL-2 upon stimulation with a group of SEs (SEA, SEB, SEC, SED and SEE) in the presence HUVEC stimulated with IFN-gamma but not in the presence of control HUVEC. The level of accessory cell activity in the IFN-gamma-stimulated HUVEC was related to the level of HLA class II expression and SEA-binding activity. Antibodies to HLA class II molecules almost completely inhibited the response. These results indicate that HLA class II molecules are directly involved in the acquisition of these activities in HUVEC.

Relative ability of distinct isotypes of human major histocompatibility complex class II molecules in binding staphylococcal enterotoxin A

Relative ability of distinct isotypes of human major histocompatibility complex class II molecules to bind staphylococcal enterotoxin A (SEA) was investigated. SEA-binding was observed in L cells transfected with DR2 and DQw1 genes. By contrast, it was not detected in L cells transfected with DPw4 and DP (Cp63) genes. All the transfectants supported SEA-induced IL-2 production by human T cells. Levels of the accessory activity were low in the DPw4 and DP (Cp63) transfectants compared with the DR2 and DQw1 transfectants. In view of the observation that all the transfectants express well the transfected gene products on their surface, the results indicate that DR and DQ molecules bind SEA with high affinity, while DP molecules bind it with fairly low affinity.

The superantigen Pseudomonas exotoxin A requires additional functions from accessory cells for T lymphocyte proliferation

We have examined the functions required of accessory cells (AC) for murine thymocyte proliferation induced by Pseudomonas exotoxin A (PE) and have compared these functions to those required of a known superantigen, staphylococcal enterotoxin B (SEB). We demonstrate that PE, like SEB, preferentially stimulates PNA+ thymocytes expressing a specific V beta element within the T cell receptor. However, PE requires functions from AC that are distinct from those required by SEB. AC treated with paraformaldehyde (PCHO) prior to stimulation supported thymocyte proliferation induced by SEB but not PE. However, when AC were treated with PCHO subsequent to stimulation with PE, thymocyte proliferation was observed, which suggests that PE requires antigen processing in addition to presentation. Furthermore, treatment of AC with lysosomotropic agents abrogated thymocyte proliferation induced by PE but not SEB. Antibodies to MHC class II molecules inhibited thymocyte proliferation induced by both PE and SEB. In addition, we observed that interleukin 1 alpha (IL-1 alpha) participated in the proliferation of thymocytes induced by PE but not SEB. Thus, our data indicate that PE is a unique microbial superantigen that requires additional AC functions for T lymphocyte proliferation.

Activation of murine T cells by staphylococcal enterotoxin E: requirement of MHC class II molecules expressed on accessory cells and identification of V beta sequence of T cell receptors in T cells reactive to the toxin

We investigated a mechanism leading to activation of murine T cells by staphylococcal enterotoxin E (SEE). L cells transfected with I-Ab genes but not control L cells supported IL-2 production by SEE-induced C57BL/6 T lymphoblasts upon restimulation with SEE. mAb to I-Ab markedly inhibited the above response. Flow cytometric analyses showed that SEE-induced C57BL/6 T lymphoblasts are composed of both CD4+ T cells and CD8+ T cells, and that larger parts of them bore V beta 11 (40-75%). mAb to V beta 11 markedly inhibited the SEE-induced proliferative response and IL-2 production by T cells. Analysis of SEE-induced IL-2 production in spleen cells from various mouse strains showed that C57BL/6 and B10.A(4R) mice (I-E, not expressed; V beta 11+ T cells, normally generated) are highly responsive to SEE. In contrast, BALB/c, C3H/HeN, (C57BL/6 x BALB/c or C3H/HeN) F1 mice (I-E, normally expressed and V beta 11+ T cells, deleted), and SJL and C57L mice (V beta 11 genes, deleted) are weakly responsive to SEE. The results indicate that SEE activates mainly T cells bearing V beta 11 in physical association with MHC class II molecules expressed on AC. In addition, the results indicate that SEE activates both CD4+ T cells and CD8+ T cells.

Relative activities of distinct isotypes of murine and human major histocompatibility complex class II molecules in binding toxic shock syndrome toxin 1 and determination of CD antigens expressed on T cells generated upon stimulation by the toxin

Relative abilities of murine and human major histocompatibility complex class II molecules to bind toxic shock syndrome toxin 1 (TSST-1) and T-cell subsets activated by the toxin were investigated. TSST-1 binding was observed in L cells transfected with I-Ab, I-Ak, DR2, and DQw1 genes. Scatchard plot analysis showed similar Kd values (1 x 10(-8) to 3 x 10(-8) M) for these cells. By comparison, binding was not detected in L cells transfected with I-Ek, DPw4, and DP(Cp63) genes. All of the transfectants supported TSST-1-induced proliferative response and interleukin-2 production by murine and human T cells. Levels of accessory activity were lower in the I-Ek transfectants and the DPw4 and DP(Cp63) transfectants than in the I-Ab and I-Ak transfectants and the DR2 and DQw1 transfectants, respectively. The results indicate that I-A, DR, and DQ molecules bind TSST-1 with similar affinities, whereas I-E and DP molecules bind it with fairly low affinity. TSST-1-activated T cells consisted of both CD4+ and CD8+ T cells, indicating that TSST-1 activates these two T-cell subsets.