[ENTEROTOXIGENICITY OF STAPHYLOCOCCUS AUREUS STRAINS, ISOLATED FROM BREAST MILK OF WOMEN, FEEDING CHILDREN WITH INFECTIOUS PATHOLOGY]

AIM

Determination of enterotoxigenicity and ability to synthesize TSST-1 in S. aureus strains, isolated from breast milk of women, feeding children with infectious pathology.

MATERIALS AND METHODS

35 S. aureus strains, isolated from breast milk of women feeding children with varying infectious pathology in hospitals and as outpatients were studied for the presence of staphylococci enterotoxins (SE) of types A and B and toxic shock syndrome toxin (TSST-1). Determination of SEA, SEB and TSST-1 was carried out by enzyme immunoassay.

RESULTS

Toxins were detected in 94.2% of S. aureus strains. SEB was synthesized by 86.7%, SEA--34.3%, TSST-1--42.8% of S. aureus strains. Toxins were detected with equal frequencies in healthy women and women with inflammatory diseases of breasts. Differences in frequency of colonization of intestines of children receiving breast milk, infected with toxigenic and non-toxigenic staphylococci strains was not detected.

CONCLUSION

A high frequency of occurrence of enterotoxins and TSST-1 in S. aureus, isolated from breast milk of the mother during infectious pathology in the child was discovered. Enterotoxigenic strains can be detected in breast milk in healthy women. Study of the role of breast milk, infected with S. aureus, producing SEA, SEB And TSST-1 in development of child pathology is necessary.

PHENOTYPIC AND GENOTYPIC DETECTION OF ENTEROTOXINS, TOXIC SHOCK SYNDROME TOXIN-1 AND OF METHICILLIN RESISTANCE IN STAPHYLOCOCCUS AUREUS ISOLATED FROM RETAIL READY-TO-EAT FOODS IN NORTHEASTERN THAILAND

Toxigenic Staphylococcus aureus contamination of ready-to-eat (RTE) foods is a leading cause of foodborne illness in Thailand. From 151 RTE food samples randomly collected from food vendors and food shops in Khon Kaen municipality, Thailand and after culture-based identification of S. aureus isolates, pentaplex PCR was used for simultaneous detection of super-antigenic toxin (SE) genes (sea, seb, sec, sed and tst-1) and presence of their toxins by reversed passive latex agglutination assay. S. aureus was identified in 57 isolates, of which 60% and 25% was positive for presence of super-antigenic toxin genes and toxins, respectively; and among the former isolates sea was the most common (46%), as well as its product (SEA) (14%) among the latter group. Methicillin resistance S. aureus mecA was not found in any of the isolates using both PCR and disk diffusion methods. These results showed that pentaplex PCR is a useful tool for detection of SE-encoding genes in S. aureus isolates from RTE food.

[Toxic shock syndrome developed after scalding with water]

Toxic shock syndrome (TSS) is a potentially lethal condition most often caused by Staphylococcus aureus. The diagnostic criteria for TSS are high fever, hypotension, rash, desquamation 1-2 weeks after onset of illness, and involvement of three or more organ systems. Most patients are young menstruating women, and most burn patients with TSS are children. A 66-year-old woman was scalded with water and developed TSS four days later. She was admitted to an intensive care unit where she received adequate treatment. She was discharged after 15 days in hospital.

Report of toxic shock syndrome toxin 1 (TSST-1) from Staphylococcus aureus isolated in food handlers and surfaces from foodservice establishments

A set of 53 Staphylococcus aureus isolates collected from food handlers and foodservice establishments in Spain was analyzed for toxic shock syndrome toxin (TSST-1) production. S. aureus strains were isolated from 908 samples collected from different surfaces such as dish towels, workers' hands, cutting boards, stainless steel tables and slicers, but they were not detected neither in clean plates nor in kitchen knives. Only one food worker hand has been reported to be contaminated by TSST-1 in a restaurant. Despite this, proper hygiene practices should be respected for the surfaces of contact with food, as well as for the hands of the manipulators This is the first article, in Spain, that reports the detection of TSST-1 in a restaurant worker hand.

First evidence of a food poisoning outbreak due to staphylococcal enterotoxin type E, France, 2009

At the end of 2009, six food poisoning outbreaks caused by staphylococci were reported in France. Soft cheese made from unpasteurized milk was found to be the common source of the outbreaks. Staphylococcal enterotoxin type E was identified and quantified in the cheese using both official and confirmatory methods of the European Union Reference Laboratory (EU-RL). To our knowledge, this is the first report of food poisoning outbreaks caused by staphylococcal enterotoxin type E in France.

Screening of bovine coagulase-negative staphylococci from milk for superantigen-encoding genes

A collection of 102 coagulase-negative staphylococci (CNS), isolated from cases of subclinical and clinical bovine mastitis and belonging to 10 different species, were screened by PCR for the presence of genes encoding enterotoxins and enterotoxin-like toxins (sea, seb, sec, sed, see, seg, seh, sei, sej, selk, sell, selm, seln, selo, selp, selq and selu), toxic shock syndrome toxin-1 (tst), and exfoliative toxins A and B (eta and etb). No toxin gene sequences were amplified from any of the isolates, indicating that superantigens encoded by genes detectable by the PCR tests used were not involved in the development of subclinical and clinical mastitis in cattle infected with the CNS isolates tested.

[Staphylococcal toxin of toxic shock syndrome]

Literature data on toxic shock syndrome staphylococcal toxin (TSST-1) are summarized; properties of Staphylococcus aureus strains producing TSST-1, nutrient media, and factors influencing on production of TSST-1 are reviewed. Physical and chemical properties of the toxin, its molecular characteristics, genetic regulation of its production, mechanism of action, and diseases which it causes are also discussed. Clinical and histologic signs of toxic shock syndrome (TSS), its diagnostic criteria, susceptibility of people to TSS, antigenic and serologic properties of the toxin, epidemiology of the infection caused by TSST-1-producing strains of staphylococci, methods of TSST-1 extraction and identification are described.

Mycoplasma arthritidis-derived superantigen (MAM) displays DNase activity

Bacterial superantigens are potent stimulators of the immune system. In this study, we expressed recombinant superantigens, which were then affinity purified and used for growth curves and DNase activity assays. Overexpression of Mycoplasma arthritidis-derived superantigen in Escherichia coli reduced bacterial growth. This is unique, as staphylococcal enterotoxin A and toxic shock syndrome toxin-1, expressed in the same vector system, showed no growth impairment. The observed growth inhibition was caused by the DNase activity of recombinant M. arthritidis-derived superantigen, thus describing the first superantigen showing enzymatic activity, which may be a result of the separate evolution of this toxin.

Novel multiplex PCR for the detection of the Staphylococcus aureus superantigen and its application to raw meat isolates in Korea

A multiplex PCR assay that allows for the rapid screening of the 19 genes that encode staphylococcal enterotoxins (SEs) (sea to see, and seg to sei), SE-like (SEl) toxins (sej to ser, and seu), and toxic shock syndrome toxin-1 (TSST-1) (tst) was developed in this study. These toxins are included in the pyrogenic toxin superantigen (PTSAg) family and are responsible for many diseases such as staphylococcal food poisoning (SFP) and TSS. The primers were designed based on dual priming oligonucleotide (DPO) technology to detect all of the 19 SAg genes in three sets of PCR. The developed multiplex PCR was applied to 143 Staphylococcus aureus strains isolated from pork and chicken meat in Korea. Almost 50% of the strains possessed at least one of the 19 SAg genes. The most frequently found genes were seg, sei, sem, and sen (53 isolates, 37%), which were often found simultaneously in the same isolate. In those isolates, the seo (39 isolates, 27%) or seu (6 isolates, 4%) genes were frequently found together and this combination (seg, sei, sem, sen, and seo or seu) was considered to be a part of the enterotoxin gene cluster (egc). The sea gene (10 isolates, 7%) was the gene most frequently detected out of all the classical SE genes (sea to see). Although these classical SEs are considered to be major etiological factors in SFP, newly described SE or SEl genes (seg to ser, and seu) were more frequently detected than the classical SE genes in this study. There was no isolate detected containing the seb, sec, sek, sel, or seq genes. S. aureus possessing mobile genetic elements known to encode these SAg genes, such as egc, were presumed to be widely distributed among pork and chicken meats in Korea. The multiplex PCR developed in this study could be applied to the investigation of SAg genes in S. aureus strains isolated from various sources.

A quantitative real-time immuno-PCR approach for detection of staphylococcal enterotoxins

Bacterial intoxications represent a substantial public health concern with enterotoxins produced by Staphylococcus aureus among the most common causes of food poisoning. In addition to their role in the pathogenicity of food poisoning, staphylococcal enterotoxins have profound effects on the immune system as members of the family of pyrogenic toxin superantigens. As the classical diagnostic bioassays as well as the routinely used immunological methods are hampered by several drawbacks regarding sensitivity, specificity, and practicability, there is a need for the timely identification of toxins by highly sensitive and specific methods. To combine the versatility of an enzyme immunoassay (EIA) with the amplification power of the PCR, a quantitative real-time immuno-PCR (qRT-iPCR) was developed for the detection of staphylococcal enterotoxins A and B and compared to a commercially available EIA. A broadly applicable tool for signal amplification of pre-formed immunocomplexes was established by covalent binding of a reporter DNA to secondary detection antibodies. Therefore, the amino-modified reporter DNA was coupled successfully to N-succinimidyl-S-actyl-thioacetate-activated secondary detection antibodies. The qRT-iPCR was able to detect highly reproducibly as low as approximately 0.6 to 6 pg (4 to 40 amol/microl) of staphylococcal enterotoxin B and staphylococcal enterotoxin A, respectively. In conclusion, the qRT-iPCR approach was shown to overcome clearly the sensitivity limit of traditional immunological detection procedures for bacterial toxins, as demonstrated in this study for staphylococcal enterotoxins. The development of a stable antibody-DNA conjugate providing a universal signal amplification offers a versatile as well as a highly sensitive and specific tool for diagnostic and research purposes generally applicable for pre-formed antibody-antigen complexes.

Targeting of hepatoma cell and suppression of tumor growth by a novel 12mer peptide fused to superantigen TSST-1

Hepatocellular carcinoma (HCC), one of the most common and malignant tumors worldwide, is unresponsive to any of the available therapies. Using intact HCC cells as therapeutic targets, we isolated a novel peptide, denoted HCC79 (KSLSRHDHIHHH), from a phage display peptide library. HCC79 can bind to hepatoma cell membranes with high affinity and specificity. Remarkably, competitive binding assays demonstrated that HCC79 competed with HAb25, a specific antibody for HCC, in binding to hepatoma cells. The corresponding synthetic peptide did not inhibit tumor proliferation directly, but repressed tumor invasion significantly in a cell migration assay. Moreover, we explored the potential of the selected peptide to deliver a superantigen (SAg) to cancer cells, to attain a significant cell-targeting effect. When the peptide is fused to the TSST-1 SAg, the resulting fusion protein could bind to hepatoma cells with high affinity in vitro and improved the tumor inhibition effect by activating T lymphocyte cells in vitro and in vivo, compared with TSST-1 alone. Taken together, our results indicate that this peptide and its future derivatives may have the potential to be developed into highly specific therapeutic agents against cancer.

[Yersinia pseudotuberculosis toxins]

The review of publications about protein toxins Y. pseudotuberculosis are presented. It includes the main data obtained by domestic and foreign investigators as well as the results of our own elaboration in the study of Y. pseudotuberculosis protein toxins. The guestions of isolation, purification, characterization of physico-chemical and biological properties, the mechanism action and role of toxins on pathogenesis of infection were discussed.

Expression, purification and crystallization of Streptococcus dysgalactiae-derived mitogen

Superantigens are bacterial or viral toxins with potent immunostimulatory properties. Streptococcus dysgalactiae-derived mitogen, a 25 kDa protein, is a recently discovered superantigen isolated from S. dysgalactiae culture supernatant. Sequence considerations suggest that it belongs to a new superantigen family distinct from other superantigens. The protein was expressed in Escherichia coli cells and purified to homogeneity. Crystals were grown at pH 4.2-4.4 in the presence of 18-20%(w/v) PEG 3350 and 0.4 M lithium nitrate. A complete data set to 2.4 A resolution was collected from a single crystal at liquid-nitrogen temperatures using synchrotron radiation. The crystals belong to space group P3/P3(1)/P3(2), with unit-cell parameters a = b = 52.7, c = 62.4 A, gamma = 120 degrees and one molecule in the crystallographic asymmetric unit.

[Presence of enterotoxin C and toxic shock syndrome toxin--1 (TSST-1) genes in population of Staphylococcus aureus phage type 187]

The aim of this study was to examine whether Staphylococcus aureus of phage type 187 possess the genes of enterotoxins and toxic shock syndrom toxin. Sixteen phage type 187 strains were isolated from the hospital patients (12) and the carriers (4) in twelve medical centres in Poland during 1991 and 2005. Biotyping, phage typing, antibiotic susceptibility, detection of the genes of enterotoxins (sea--sed) and toxic shock syndrome toxin (tst) was tested. The results of this study showed that all staphylococci of phage type 187 belonged to the human biotype (A) and appeared to be sensitive to all of the tested antibiotics, including methicillin (MSSA). Almost all of them (93.8%) had the enterotoxin C gene and TSST-1 gene. This fact allows to consider them the strains of potentially high virulence.

Mixed bacterial infection model of sepsis in rabbits and its application to evaluate superantigen-adsorbing device

BACKGROUND

Superantigens are suspected to be the potent and lethal pathogens of gram-positive sepsis, and a new therapy that targeted to superantigens are required.

METHODS

A mixed infection model was developed in rabbits by the cecal ligation and puncture associated with the intraperitoneal injection of Staphylococcus aureus, which produces toxic shock syndrome toxin 1 (TSST-1). Animals were also hemoperfused with a superantigen-adsorbing device (SAAD), or a control column.

RESULTS

The model animals revealed multiple organ failure and died 6-12 h after the injection of S. aureus. The plasma levels of TSST-1, but not of lipopolysaccharide (LPS), significantly (p < 0.01) and inversely correlated with mean arterial pressure (r = -0.63). Plasma TSST-1 level was significantly reduced and shock-onset time was significantly retarded in the SAAD treated group, although the survival time was not significantly affected.

CONCLUSIONS

The animal model developed could serve as a model for sepsis. It is suggested that there is the potential application of SAAD in treating superantigen-related sepsis.

Enterotoxins and toxic shock syndrome toxin in Staphylococcus aureus recovered from human nasal carriers and manually handled foods: epidemiological and genetic findings

A set of 269 Staphylococcus aureus isolates recovered from nasal carriers and manually handled foods in a region of Spain was analyzed for pyrogenic toxin production and toxin genes. Fifty-seven isolates producing at least one of four enterotoxins (SEA, SEB, SEC, SED), 10 isolates producing only toxic shock syndrome toxin (TSST-1), and 10 isolates producing both toxin types were found. The 77 toxigenic isolates were discriminated into 36 SmaI genomic and 13 EcoRI plasmid profiles. A strong relationship between toxin profiles with both SmaI genomic and EcoRI plasmid profiles was revealed. SmaI genomic profiles showing six or less mismatching fragments and similarity coefficient > or =0.7 were included in a lineage. Eight lineages were differentiated; six of them grouped both human and food isolates and two of these also included outbreak-implicated isolates. Two lineages, represented by TSST-SEA and TSST-1, on the one hand, and SEC and SEC-SED isolates, on the other hand, were the most frequent, but only the second was outbreak-related. When SmaI genomic and EcoRI plasmid profiles were hybridized with tst, sea, seb, and sec toxin probes, it was observed that each probe mapped on a different SmaI fragment from isolates falling into the same lineage. All of the probes only mapped on genomic fragments, but sed also mapped on three plasmid fragments. When sej and ser probes were included, they mapped together with sed on the chromosome and on the plasmids. Two plasmids (ca. 33 and 36 kb) carried the expected sed-sej-ser genes, while the other (ca. 53.5 kb) carried sed-sej and ser-like genes. The latter plasmid and the chromosomal location of sed-sej-ser are new findings from this study.

[Toxic shock syndrome in 3 children]

A 16-year-old and a 10-year-old girl were admitted with general signs of illness, and respectively a green vaginal discharge and a panaritium. They recovered following antibiotic treatment and surgical relief of the panaritium. A 2-year-old boy became ill the morning after eating tainted cold meat; he died in the course of the following night. In all 3 patients Staphylococcus aureus was incubated with the toxic-shock-toxin-1-gene and/or the enterotoxin-A-gene. These 3 cases occurred within one year in a general hospital. TSS probably occurs more frequently than is generally assumed. Given that it is a life-threatening disease, rapid diagnosis is of major importance.

Enterotoxin B Is the Predominant Toxin Involved in Staphylococcal Scarlet Fever in Taiwan

This study retrospectively reviewed all pediatric cases of staphylococcal scarlet fever (SSF) that occurred during a 10-year period in a 1400-bed tertiary medical center in northern Taiwan. All 20 cases of SSF occurred in previously healthy individuals. Skin and soft-tissue infections predominated among children from whom Staphylococcus aureus was isolated. Polymerase chain reaction testing was used to detect known staphylococcal toxin genes, and of the isolates studied, most (18 [90%] of 20) contained only the staphylococcal enterotoxin B. One of the other strains was positive for staphylococcal enterotoxin A only, and the last strain was positive for both staphylococcal enterotoxin G and staphylococcal enterotoxin I. Pulsed-field gel electrophoresis identified a small cluster of isolates (6 [30%] of 20) that were genetically related, but these strains came from epidemiologically unrelated patients during a 3-year period.

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.

Preparation of a superantigen-adsorbing device and its superantigen removal efficacies in vitro and in vivo

OBJECTIVE

A new superantigen-adsorbing device (SAAD) was developed, and its characteristics and efficacy in septic animals were evaluated.

METHODS

The SAAD was prepared by stepwise chemical modification of a polystyrene-based composite fiber reinforced with polypropylene. Adsorption affinities for several factors and the biological effect of superantigen (SAg) removal were measured in vitro. Also, superantigen-infused rabbits were treated with SAAD, and the efficacy was evaluated in vivo.

RESULTS

When the SAAD was evaluated for its ability to adsorb SAg in human plasma (1 ng/mL each), the adsorption rates were 74%, 76% and 85% for staphylococcal enterotoxins A, B and C, respectively, and 80% and 72% for toxic shock syndrome toxin-1 (TSST-1) and streptococcal pyrogenic exotoxin A, respectively. In addition, the SAAD showed some affinity towards other molecules, such as streptococcal pyrogenic exotoxin B, beta2-microglobulin, and vancomycin. Residual activities in whole blood samples containing TSST-1 (1 ng/mL) after incubation with the SAAD were 125 pg/mL for tumor necrosis factor alpha (TNF-alpha) production, and 359 pg/mL for interleukin-8 (IL-8) production (the initial activities: 194 pg/mL for TNF-alpha production, and 1029 pg/mL for IL-8 production). When TSST-1/lipopolysaccharide (LPS)-infused rabbits were subjected to extracorporeal blood purification with a SAAD column, 50% of the animals survived for a 14-day period after the infusion. In contrast, all control animals died within 3 days after the infusion.

CONCLUSION

These results indicate that the SAg-adsorbing device may be useful in treating SAg-related diseases.

Characterization of a novel staphylococcal enterotoxin-like superantigen, a member of the group V subfamily of pyrogenic toxins

Staphylococcus aureus is an important human pathogen, causing a variety of diseases. Major virulence factors of this organism include staphylococcal enterotoxins (SEs) that cause food poisoning and toxic shock syndrome. Our study identified a novel enterotoxin-like protein that is a member of the new subfamily (group V) of pyrogenic toxin superantigens (PTSAgs) and examined its biochemical and immunobiological properties. The gene encoding the SE-like protein is directly 5' of another recently identified PTSAg, SEK. The SE-like protein had a molecular weight of 26000 and an experimentally determined isoelectric point between 7.5 and 8.0. We demonstrated that the PTSAg had many of the biological activities associated with SEs, including superantigenicity, pyrogenicity, and ability to enhance endotoxin shock, but lacked both lethality in rabbits when administered in subcutaneous miniosmotic pumps and emetic activity in monkeys. Recombinant protein stimulated human CD4 and CD8 T cells in a T cell receptor variable region, beta chain (TCRVbeta) specific manner. T cells bearing TCRVbeta 2, 5.1, and 21.3 were significantly stimulated.

Basic streptococcal superantigens (SPEX/SMEZ or SPEC) are responsible for the mitogenic activity of the so-called mitogenic factor (MF)

The mitogenic factor (MF) of group A streptococci has been reported to be a superantigen stimulating human T cells carrying Vbeta2, 4 and 8 and has been designated streptococcal pyrogenic exotoxin F (SPEF). MF was also shown to possess DNase activity. Here we have purified MF from culture supernatants of different Streptococcus pyogenes strains. Surprisingly, the MF preparations from different strains showed different Vbeta specificities depending on the expression of SPEC or SMEZ3 by the producing strain. Their mitogenic activity decreased upon further purification. In addition, the mitogenic activity could be only neutralized by antibodies against the basic streptococcal superantigens SPEC or SPEX (SMEZ3) but not by antibodies against MF itself although the latter were able to neutralize completely the DNase activity of MF. We found that streptodornase type B (SDB) was expressed in two molecular forms (SDBI and SDBII), differing only by one additional N-terminal arginine at SDBI. MF was found identical to the enzyme SDBII but is devoid of superantigenic properties and should no longer be called a superantigen or a pyrogenic exotoxin.

Binding of Mycoplasma arthritidis-derived mitogen to human MHC class II molecules via its N terminus is modulated by invariant chain expression and its C terminus is required for T cell activation

Mycoplasma arthritidis-derived mitogen (MAM) is considered to be a member of the super-antigen family despite the fact that there is no evidence until now indicating its binding to MHC class II molecules. To demonstrate its direct binding and to determine the regions involved in MHC class II and TCR interactions, we generated a recombinant wild-type and two truncated forms of the MAM protein. Data obtained in the course of the present investigation show that MAM binds specifically and significantly to human MHC class II molecules. Evidence is also provided that MAM bears two distinct binding regions: one is located within its N terminus and interacts with MHC class II molecules, while the second region which is located in its C terminus mediates its recognition by the TCR. Association of the MHC class II-associated invariant chain peptide with the peptide binding groove on the cell surface completely abolished MAM binding and presentation. This inhibitory effect is restored by the expression of HLA-DM molecules, suggesting that the nature of the peptide within the binding groove and/or the stability of the MHC class II molecules on the cell surface may modulate MAM/MHC class II interactions.

The superantigenic activity of streptococcal pyrogenic exotoxin B is independent of the protease activity

The nature of the mitogenic activity of pyrogenic streptococcal exotoxin B, also known as streptococcal cysteine protease, has been debated in the literature. Streptococcal exotoxin B has been shown to cleave interleukin-1beta precursor and create biologically active interleukin-1beta, a major cytokine mediating inflammation and shock. This activity could mimic the mitogenicity and cytokine release induced by superantigens in lymphocyte stimulating experiments. In this study, the protease activity of streptococcal exotoxin B was irreversibly inhibited by covalent binding of a tripeptide and the superantigenic properties of streptococcal exotoxin B were found not to be influenced by this inactivation. Native as well as protease-inactivated streptococcal exotoxin B was shown to stimulate T-cell proliferation without a need of metabolically active antigen presenting cells. Furthermore, streptococcal exotoxin B-induced T-cell proliferation was shown to require HLA-DQ since addition of HLA-DQ monoclonal antibodies totally inhibited the mitogenic activity of streptococcal exotoxin B, indicating that streptococcal exotoxin B, as other superantigens, makes direct contact with the T-cell receptor via HLA class II. The aim of this study was to characterize the relationship between the proteolytic and superantigenic properties of streptococcal exotoxin B.

The crystal structure of exfoliative toxin B: a superantigen with enzymatic activity

The exfoliative toxins (ETs) cause staphylococcal scalded skin syndrome, a disease characterized by specific separation of layers of the skin. Evidence suggests that the toxins act as serine proteases, though the specific substrate and mode of action are not known for certain. The crystal structure of exfoliative toxin A (ETA) was reported earlier and shown to be similar to that of the chymotrypsin-like serine proteases. Here, we report the 2.4 A resolution crystal structure of the other exfoliative toxin, ETB, which is 40% identical to ETA. The overall structures of ETA and ETB are similar including the positions of key residues within the active site. The structure of ETB supports the previous findings that the ETs are serine proteases that cleave substrates after glutamic acid residues. In this study we also discuss a number of structural differences including a large 14 residue loop insertion which may be a key feature involved in the differing biological properties of the ETs, particularly the pyrogenic and lethal activities of ETB not shared by ETA.

Peripheral blood T-cell receptor beta-chain V-repertoire in atopic dermatitis patients after in vitro exposure to Pityrosporum orbiculare extract

The yeast Pityrosporum orbiculare belongs to the normal cutaneous flora but is also considered to be one of the factors that may contribute to atopic dermatitis (AD). In the present study we investigated the possibility that P. orbiculare can act with superantigen activity in AD. P. orbiculare-reactive T-cell lines (TCLs) were obtained after stimulation of peripheral blood mononuclear cells (PBMC) with P. orbiculare extract. T-cell receptor beta-chain V-segment (TCRBV) usage was investigated using monoclonal antibodies and flow cytometry. We could not find any difference in TCRBV usage between AD patients (n = 10) and healthy controls (n = 5), either in fresh PBMC or in P. orbiculare-reactive TCLs. Compared with their original PBMCs the P. orbiculare-reactive TCLs showed a decreased usage of several TCRBVs, although increased usage of certain TCRBVs could be seen in some of the individuals. Further analysis of the CDR3-length polymorphism exhibited a shift in CDR3-length distribution, indicating oligoclonal expansion of T cells specific to different antigens in the P. orbiculare extract. In conclusion we have not found any evidence for superantigen activity in P. orbiculare extract, but our data support the importance of classical major histocompatibility complex (MHC)-restricted allergens in P. orbiculare.

Molecular characterization of the putative T-cell receptor cavity of the superantigen staphylococcal enterotoxin B

A number of investigators have utilized a variety of methods to identify the structural basis for the interaction of superantigens with the T-cell receptor beta-chain. The previous studies strongly suggest that a region of the toxin near residues N23, Y61, Y91 and D209 is important for this binding activity. Examination of crystal structure data shows that these residues line the rim of one side of a shallow cavity in the toxin. In an attempt further to define the face of the staphylococcal enterotoxin B (SEB) molecule involved in the interaction with the beta-chain, we have employed a polymerase chain reaction (PCR)-based, site-specific mutagenesis method to generate amino acid substitutions of residues on the opposite side of this putative T-cell receptor interaction cavity. Our results show that Y175 and N179 appear to be involved in the function of this superantigen, since each of several substitutions at this position exhibits a significantly reduced ability to induce T-cell proliferation. At the same time, mutation of the proximal Y186 does not alter the superantigen activity of SEB. Binding analysis of these mutants shows that class II binding activity is not significantly altered. Analysis of the responding T cells shows that the mutant toxins maintain T-cell receptor V beta selectivity. However, responses of T cells bearing the V beta 8.1 allele appear to be particularly diminished. When viewed in the context of other results reported in the literature, our results suggest that the T-cell receptor interaction site involves SEB residues which ring both the Y175/N179-side and the N23-side of a cavity on one side of the toxin molecule.

Purification, characterization and cloning of a novel variant of the superantigen Yersinia pseudotuberculosis-derived mitogen

The novel superantigen designated as Yersinia pseudotuberculosis-derived mitogen typeB (YPMb) was purified from the cell lysate of Y. pseudotuberculosis O:6 strain (R-104). Proliferative response of human peripheral blood mononuclear cells to the purified YPMb was detectable at a concentration of as low as 1 pg/ml, that is comparable to the previously documented YPM (YPMa). The Vbeta repertoire specificity (3, 9, 13.1 and 13.2) of YPMb was also the same as that of YPMa. A gene (ypmB) encoding YPMb was cloned and its nucleotide sequence was determined. The open reading frame (ORF 453 bp) of the ypmB encodes a protein with 150 amino acid residues, though the precursor protein of YPMa consists of 151 amino acid residues. There is a nucleotide sequence homology of 88.9% between ypmB and ypmA. The low homology in the downstream of the structural gene between ypmB and ypmA and the difference in the GC content in the ORF of ypmB and ypmA from that of the base usage of Y. pseudotuberculosis suggest that the ypm gene originates from another organism. The alignment of the amino acid sequences of mature proteins of YPMb and YPMa revealed that there is 83% homology (108 amino acid residues are identical). Between YPMa and YPMb, the central region is less homologous than the N- and C-terminal regions. Based on the functional similarity of two superantigen molecules, the less homology suggested that the central region is less important for the function of both YPM molecules.

Superantigenicity of helper T-cell mitogen (SPM-2) isolated from culture supernatants of Streptococcus pyogenes

A superantigen (Streptococcus pyogenes mitogen-2; SPM-2) that stimulates human helper T cells bearing unique types of variable domains of T-cell receptor beta-chain (TCR V beta) was isolated from the culture supernatant of S. pyogenes strain T12. The active molecule isolated by diethylaminoethyl (DEAE)-cellulose chromatography and isoelectric focusing was a protein with a molecular weight (MW) of 29,000 and isoelectric point (pl) of 6.0. This new superantigen was found to activate preferentially V beta 4+, 7+, and 8+ T cells, whereas recombinant streptococcal pyrogenic exotoxin A and C activated V beta 12+ and V beta 2+ T cells, respectively, as determined by flow cytometry and reverse transcriptase-polymerase chain reaction (RT-PCR) methods. This proliferative response was significantly inhibited by anti-HLA-DR monoclonal antibody, and required paraformaldehyde-fixed antigen-presenting cells (APC), indicating that this action is dependent on major histocompatibility complex (MHC) class II molecules without processing. Analysis of the amino-terminal amino acid sequence of the molecule failed to find any identical or significantly homologous proteins. We have previously reported that cytoplasmic membrane-associated protein (CAP), a streptococcal superantigen isolated from the cell membranes of S. pyogenes T12 strain, stimulated mainly V beta 8+ T cells. Both SPM-2 and CAP preferentially stimulated helper T cells, and rabbit antiserum against SPM-2 completely neutralized the T-cell-stimulating activities of CAP, suggesting that SPM-2 and CAP belong to a family of streptococcal mitogenic proteins. The SPM-2 activity with stimulation of V beta 8+ T cells was detected extensively in the culture fluids of group A streptococci, but not in those of other streptococcal species, including groups B and D streptococci, and most of the activities detected were completely inhibited by anti-SPM-2 serum. These results indicate that SPM-2 may be a newly discovered superantigen molecule, which can be commonly synthesized by group A streptococci.

Isolation of a new superantigen with potent mitogenic activity to murine T cells from Streptococcus pyogenes

A mitogenic substance on murine lymphocytes was detected in the culture supernate of Streptococcus pyogenes type 12 strain. This substance had a molecular weight of 28,000 and pI 9.2, and was designated as S. pyogenes mitogen (SPM). The proliferative response of C3H/HeN spleen cells began at 1 ng ml-1 and reached a maximal response at 100 ng ml-1 of SPM for 4 days culture. Anti-Thy 1.2 mAb and complement-treated spleen cells abrogated the proliferative response to any dose of SPM. Although the anti-major histocompatibility complex class 1 mAbs had no blocking effect on proliferation by SPM, this proliferation was substantially inhibited by the addition of either anti-I-A or anti-I-E mAb, and complete inhibition was produced by the addition of both mAbs. Fixed antigen-presenting cells still induced T cell proliferation by SPM. A significant expansion of T cells bearing V beta 13 T-cell receptor was observed up to 73% among the Thy 1.2+ cells in cultures stimulated with SPM, indicating expansion in a V beta-specific manner. Immunoblotting of IEF-separated proteins showed that anti-streptococcal pyrogenic exotoxin (SPE) C reacted with a protein of pI 6.9 and anti-SPEB did not show any reactivity. SPEA was reported to expand V beta 8.1 and 8.2 bearing murine T cells, and SPM did not. SPM also exhibited potent mitogenic activity on human T cells and V beta 21+ T cells were selectively expanded. These results lead to the conclusion that SPM was neither SPEA, B nor C, but a new protein belonging to a group of streptococcal superantigens with activity on not only human but also murine lymphocytes.

A V beta 4-specific superantigen encoded by a new exogenous mouse mammary tumor virus

The superantigen (SAg) expressed by mouse mammary tumor virus (MMTV) has been shown to play an essential role in the course of the viral life cycle. In the present study, we describe a V beta 4-specific SAg encoded by a new exogenous MMTV carried by the SIM mouse strain. This is the first report of a viral or bacterial SAg reacting with mouse V beta 4+ T cells. Injection of MMTV(SIM) into adult BALB/c mice leads to a rapid and strong stimulation of V beta 4+ CD4+ T cells, followed by a slow deletion of these cells. Neonatal exposure to the virus also leads to a progressive deletion of V beta 4+ T cells. In contrast to other strong MMTV SAg, this new SAg requires the presence of major histocompatibility complex class II I-E molecules to be presented efficiently to T cells. Sequence analysis revealed a new predicted amino acid sequence in the C-terminal polymorphic region of this SAg. Furthermore, sequence comparisons to the most closely related SAg with different V beta specificities hint at the specific residues involved in the interaction with the T cell receptor.

Isolation of HLA-DR1.(staphylococcal enterotoxin A)2 trimers in solution

Mutational studies indicate that the superantigen staphylococcal enterotoxin A (SEA) has two separate binding sites for major histocompatibility complex (MHC) class II molecules. Direct evidence is provided here for the formation of SEA-MHC class II trimers in solution. Isoelectric focusing separated SEA-HLA-DR1 complexes into both dimers and HLA-DR1.SEA2 trimers. The molar ratio of components was determined by dual isotope labeling. The SEA mutant SEA-F47S, L48S, Y92A, which is deficient in MHC class II alpha-chain binding, formed only dimers with HLA-DR1, whereas a second SEA mutant, SEA-H225A, which lacks high-affinity MHC class II beta-chain binding was incapable of forming any complexes. Thus SEA binding to its MHC receptor is a two-step process involving initial beta-chain binding followed by cooperative binding of a second SEA molecule to the class II alpha chain.

Mitogenicity of M5 protein extracted from Streptococcus pyogenes cells is due to streptococcal pyrogenic exotoxin C and mitogenic factor MF

M proteins of Streptococcus pyogenes are virulence factors which impede phagocytosis, bind to many plasma proteins, and induce formation of cross-reactive autoimmune antibodies. Recently, it has been reported that some M proteins, extracted with pepsin from streptococci (pep M), are superantigens. One of these, pep M5, was investigated in detail and was shown to stimulate human T cells bearing V beta 2, V beta 4, and V beta 8. In the present study, we extracted and purified M5 protein by different biochemical methods from two M type 5 group A streptococcal strains. The crude extracts were fractionated by affinity chromatography and ion-exchange chromatography. All fractions were tested in parallel for M protein by immunoblotting and for T-cell-stimulating activity. Although several crude preparations of M5 protein were associated with mitogenicity for V beta 2 and V beta 8 T cells, the M5 proteins, irrespective of the extraction method, could be purified to the extent that they were no longer mitogenic. The mitogenic activity was not destroyed during the purification procedures but was found in fractions separated from M protein. In these fractions, streptococcal pyrogenic exotoxin C and mitogenic factor MF could be detected by protein blotting and enzyme-linked immunosorbent assay. Moreover, anti-M protein sera did not inhibit the mitogenic activity of crude extracts, but antisera which contained anti-streptococcal pyrogenic exotoxin C antibodies showed inhibition. The inability of M5 protein to stimulate T cells was confirmed with recombinant pep M5 produced in Escherichia coli. Our data strongly suggest that the mitogenic activity in M protein preparations is caused by traces of streptococcal superantigens different from M protein.

Negative-acting factor and superantigen are separable activities of the mouse mammary tumor virus long terminal repeat

The open reading frame contained within the long terminal repeat (LTR) of mouse mammary tumor virus encodes Naf, a negative regulator of transcription, as well as a superantigen activity, Sag, which causes the deletion of specific classes of T cells. In the present study, the effect of Naf expression on different promoters and the coding requirements for Naf and Sag have been investigated. Sag activity was found to require only sequences in the LTR, whereas sequences located within the gag gene were additionally required for functional Naf activity. Surprisingly, both the classic promoter and a recently described promoter located in the LTR can give rise to both functional Naf and Sag. Further analysis of Naf revealed that the downregulatory effect was mediated by sequences located in the LTR and that heterologous promoters were also affected by Naf.

Purification and characterization of a novel superantigen produced by a clinical isolate of Yersinia pseudotuberculosis

A superantigen designated as Yersinia pseudotuberculosis-derived mitogen (YPM) was purified in an equal manner from both the culture supernatant and cell lysate of a clinical isolate (KUR-1) of Y. pseudotuberculosis serotype 4b. A significant proliferative response of human peripheral blood mononuclear cells to purified YPM was detectable even at a concentration of 1 pg/ml. The N-terminal sequence of YPM which included 23 amino acid residues was determined, by automated Edman degradation, as Thr-Asp-Tyr-Asp-Asn-Thr-Leu-Asn-Ser-Ile-Pro-Ser-Leu-Arg-Ile-Pro-Asn-Il e-Ala-Thr-Tyr-Thr-Gly-. This sequence differed from not only all the, hitherto, reported superantigens but also known proteins. While molecular weights of known bacterial superantigens are more than 22,000, electrospray ionization mass spectrometry showed that the molecular weight of YPM was 14524.4. These results indicate that YPM comprises a novel superantigen with substantial structural differences from other bacterial superantigens produced by Gram-positive cocci.

Evidence for a superantigen in human tuberculosis

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

Processing and major histocompatibility complex binding of the MTV7 superantigen

Mouse mammary tumor viruses produce superantigens (vSAGs) which interact with class II major histocompatibility complex (MHC) proteins and stimulate T cells. vSAGs are synthesized as Type II membrane proteins, but at least one of these proteins (vSAG7) is found on the cell surface in a proteolytically processed form. Monoclonal antibodies (MAbs) were used to characterize vSAG7 and its binding to class II molecules. vSAG7 is synthesized in the endoplasmic reticulum (ER) as a 45 kd glycoprotein containing N-asparagine-linked oligomannosyl carbohydrates. vSAG7 transits the golgi complex, where it is modified by the addition of complex-type glycans and proteolysed at three positions. After proteolysis, the amino and carboxyl termini remain noncovalently associated. The ER, golgi, and surface forms of vSAG7 are stably bound to class II, but one of the proteolysed forms comprises the majority of the class II-bound material.

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.