Purification and characterization of streptococcal erythrogenic toxin type A produced by Streptococcus pyogenes strain NY-5 cultured in the synthetic medium NCTC-135. Comparison with the dialyzed medium (TP medium)-derived toxin

Activation of mouse liver natural killer cells and NK1.1(+) T cells by bacterial superantigen-primed Kupffer cells

Although bacterial superantigens have been well characterized as potent stimulators of T cells, their role in natural killer (NK)-type cells remains largely unknown. In the present study, we examined the effect of bacterial superantigens on mouse liver NK cells and NK1.1 Ag(+) (NK1(+)) T cells. C57BL/6 mice were intravenously injected with staphylococcal enterotoxin B (SEB) or streptococcal pyrogenic exotoxin A (SPE-A), and mononuclear cells (MNC) of various organs were obtained from mice 4 hours after being injected with superantigen. MNC were cultured for 48 hours, and interferon gamma (IFN-gamma) levels of supernatants were measured. The antitumor cytotoxicities of the liver and spleen MNC were also evaluated 24 hours after the mice were injected with superantigen. Liver MNC produced more IFN-gamma than did splenocytes, and peripheral blood and lung MNC did not produce any detectable IFN-gamma. In addition, liver MNC acquired a potent antitumor cytotoxicity by the SEB injection, and both NK cells and NK1(+)T cells but not cluster of differentiation (CD)8(+) T cells were responsible for the cytotoxicity as demonstrated by either in vivo or in vitro cell depletion experiments, and the NK-type cells were partly responsible for the increased serum IFN-gamma. Activation of liver NK-type cells was also supported by the fact that liver NK cells proportionally increased and NK1(+) T cells augmented their CD11a expressions after SEB injection. The pretreatment of mice with anti-IFN-gamma Ab and/or with anti-interleukin-12 (IL-12) Ab diminished the SEB-induced cytotoxicity of liver MNC. Furthermore, the in vivo depletion of Kupffer cells decreased the SEB-induced cytotoxicity of liver MNC. Consistent with these results, liver MNC stimulated with superantigens in the presence of Kupffer cells in vitro produced a greater amount of IFN-gamma than did the liver MNC without Kupffer cells or splenocytes. Our results suggest that bacterial superantigen-primed Kupffer cells produce IL-12 and other monokines, while also nonspecifically activating both NK cells and NK1(+) T cells to produce IFN-gamma.

Inhibition of IL-12 synthesis of peripheral blood mononuclear cells (PBMC) stimulated with a bacterial superantigen by pooled human immunoglobulin: implications for its effect on Kawasaki disease (KD)

The aim of this study was to further assess the role of pooled human immunoglobulin (PHIG) on cytokine production from PBMC stimulated with a bacterial superantigen. Human PBMC were cultured with Streptococcus pyrogenic exotoxin A (SPE-A) with or without PHIG and several proinflammatory cytokine levels of culture supernatants were measured. Serum cytokine levels of KD patients before and after PHIG therapy were also examined. PHIG greatly reduced the production of IL-12, interferon-gamma (IFN-gamma) and other cytokines from SPE-A-stimulated PBMC, while exogenous IL-12, but neither IL-1 nor tumour necrosis factor-alpha (TNF-alpha), restored IFN-gamma production inhibited by PHIG. Although PHIG partially adsorbed SPE-A, its inhibitory effect on cytokine production was not played by anti-SPE-A antibody. Although purified CD4+ T cells cultured with human HLA-DR-transfected mouse L cells and SPE-A could not effectively produce IFN-gamma, they produced large amounts of IFN-gamma if exogenous IL-12 was introduced. KD patients in the acute phase had higher levels of serum IFN-gamma than did controls and patients with bacterial infection. Although IL-12 levels of children with or without KD were not significantly different, IL-12 levels of children were much higher than those of adults. However, serum levels of IL-12 of KD patients were transiently but significantly decreased by PHIG therapy and IFN-gamma amounts subsequently reverted to basal levels thereafter. These findings indicate that PHIG inhibits IL-12 production of SPE-A-activated monocytes and thereby decreases IFN-gamma synthesis by T cells and suggest that inhibition of IL-12 and IFN-gamma production is an important part of the mechanisms underlying PHIG therapy on KD.

Mutational analysis of superantigen activity responsible for the induction of skin erythema by streptococcal pyrogenic exotoxin C

Streptococcal pyrogenic exotoxin C (SPEC), when injected intradermally, induces erythema in unsensitized rabbits. In the present study, we examined whether this erythema induction is due to the T-cell stimulatory activity of SPEC as a superantigen. Analysis by using single-residue mutant SPECs indicated that mutant SPECs Y15I, A16E, and Y17I, in which tyrosine 15, alanine 16, and tyrosine 17 were replaced with isoleucine, glutamic acid, and isoleucine, respectively, exhibited significantly reduced mitogenic activity for Vbeta2(+) human T cells in vitro, and Y15I showed as much as a 1, 000-fold reduction. Y15I mutant SPEC, however, retained the ability to bind to major histocompatibility complex class II antigen and to form a homodimer, implying that residue 15 is critically important for the interaction of SPEC with T-cell antigen receptor beta chains. When injected intradermally into normal rabbits, wild-type SPEC induced a characteristic erythema after 3 h in a dose-dependent fashion, which was associated with polymorphonuclear and mononuclear cell infiltration. This erythema formation was found to be severely suppressed by systemic pretreatment with cyclosporin A, suggesting the involvement of host T cells. Y15I mutant SPEC exhibited nearly 1, 000-fold less erythema induction in vivo than wild-type SPEC. Altogether, the present results strongly suggest that erythema induction in rabbits by SPEC is attributable mostly to its T-cell stimulatory activity as a superantigen.

Exclusion of bioactive contaminations in Streptococcus pyogenes erythrogenic toxin A preparations by recombinant expression in Escherichia coli

The streptococcal erythrogenic exotoxin A (SPEA) belongs to the family of bacterial superantigens and has been implicated in the pathogenesis of a toxic shock-like syndrome and scarlet fever. Concerning its biological activity, mainly T-cell-stimulatory properties, conflicting data exist. In this study, we show that most of the SPEA preparations used so far contain biologically active contaminations. Natural SPEA from the culture supernatant of Streptococcus pyogenes NY-5 and recombinant SPEA purified from the culture filtrate of S. sanguis are strongly contaminated with DNases. We show that natural SPEA induces more tumor necrosis factor alpha (TNF-alpha) than recombinant SPEA, but we also show that DNases are able to induce TNF-alpha. In commercial SPEA preparations, we identified a highly active protease, which was shown not to be SPEB. To exclude these contaminations, we overexpressed SPEA cloned in the effective high-level expression vector pIN-III-ompA2 in Escherichia coli. The expressed SPEA shows the same amino acid composition as natural SPEA, whereas functional studies reported so far were carried out with toxins containing an incorrect amino terminus. We describe the rapid purification of lipopolysaccharide-, DNase-, and protease-free SPEA in two steps from the host's periplasm and its structural characterization by circular dichroism. Our results represent for the first time the production in E. coli of recombinant SPEA with the authentic N-terminal sequence and a proven superantigenic activity. Collectively, our results indicate that immunological studies of superantigens require highly purified substances free of biologically active contaminations.

Streptococcal mitogenic exotoxin Z, a novel acidic superantigenic toxin produced by a T1 strain of Streptococcus pyogenes

Streptococcus pyogenes T1 was previously found to produce an acidic mitogenic exotoxin, designated A beta, antigenically distinct from erythrogenic toxin type A (ETA) of strains T1 and NY5. Following chemical analysis and biological characterization, we have renamed this toxin streptococcal mitogenic exotoxin Z (SMEZ). Physicochemical separation of SMEZ from ETA was successfully performed on a hydrophobic chromatograph. The isoelectric point was pH 5.3, and the molecular size was estimated to be 28 kDa. These values were similar to those of ETA, but the amino acid composition and the NH2-terminal sequence of SMEZ were distinct from those of any mitogenic exotoxins hitherto described. Its mitogenic activity was found to be more potent than that of ETA in rabbit lymphocyte cultures. A specific antiserum raised against SMEZ did not cross-react with ETA, ETB, or ETC in the neutralization tests of mitogenic and erythrogenic activities. Its superantigenic nature was evident from the reverse transcriptase PCR findings of the T-cell receptor Vbeta profiles of rabbit lymphocytes stimulated in vitro. The Vbeta 8 subfamily was unique to SMEZ, while the Vbeta 2 and 6 subfamilies were found to be common among lymphocytes stimulated with ETA, ETB, ETC, or SMEZ. The results from this study provide an additional example of the diversity that exists among mitogenic or superantigenic exotoxins of streptococcal origin.

A new procedure for the purification of streptococcal pyrogenic exotoxin A from Streptococcus pyogenes supernatant

An important role in the pathogenesis of invasive group A streptococcal disease has been ascribed to the production of streptococcal pyrogenic exotoxin A. We present a new technique for the purification of streptococcal pyrogenic exotoxin A from Streptococcus pyogenes NY-5 supernate, which is highly efficient with respect to yield (35%), purity (> or = 99%), and time.

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.

Analysis of the superantigenic activity of mutant and allelic forms of streptococcal pyrogenic exotoxin A

Infections with Streptococcus pyogenes (group A streptococcus) can result in the recently described streptococcal toxic shock syndrome (STSS), which is characterized by rashes, hypotension, multiorgan failure, and a high mortality rate. S. pyogenes isolates associated with STSS usually produce streptococcal pyrogenic exotoxin A (SpeA), a bacterial superantigen capable of stimulating host immune cells. Most of the symptoms of STSS are believed to result from cytokine release by the stimulated cells. To better understand the pathogenesis of STSS, we began studies on the SpeA-immune cell interaction. We generated 20 mutant forms of SpeA1 (SpeA encoded by allele 1), and the mutant toxins were analyzed for mitogenic stimulation of human peripheral blood mononuclear cells, affinity for class II major histocompatibility complex molecules (DQ), and disulfide bond formation. Residues necessary for each of these functions were identified. There are four alleles of speA, and STSS strains usually contain either allele 2 or allele 3. The product of allele 2, SpeA2, had slightly higher affinity for the class II MHC molecule compared with SpeA1 but not significantly greater mitogenic activity. SpeA3, however, was significantly increased in mitogenic activity and affinity for class II MHC compared with SpeA1. Thus, we have evidence that the toxin encoded by some of the highly virulent S. pyogenes STSS-associated isolates is a more active form of SpeA.

Kinetics and regulation of erythrogenic toxins type A and C during growth of Streptococcus pyogenes

The production of erythrogenic toxins type A (ETA) and C (ETC) is described as a function of growth kinetics. Group A streptococcal strains C 203 S and NY 5 were cultivated in yeast-peptone extract, Todd-Hewitt medium and a synthetic medium. Two main growth phases occurred during growth: a first logarithmic phase and a second linear phase. These phases were separated by a short stationary interphase caused by limitation of the amino acids L-serine and L-leucine. Maximum production of ETC was observed during the logarithmic phase, it was correlated to a high level of viable cells. ETA was produced mainly during the short stationary interphase. The production of ETC is regulated by L-isoleucine. A stagnation or reduction of the concentration of viable cells was observed during the interphase. The phosphate limitation caused during streptococcal growth induced expression of the extracellular protein phosphatase and surprisingly, of a serine proteinase activity. The association between these results and the pathogenicity of streptococci is discussed.

Streptococcal erythrogenic toxin type C is not a phosphorylated protein. Description of two different purification procedures and investigation of its phosphorylation state

Erythrogenic toxin type C (ETC) from different streptococcal group A strains was successively purified by absorption on phenylsepharose, acidic dialysis of the eluate at 40% saturated ammonium sulphate solution, CM-Sepharose chromatography, finally by immunoaffinity chromatography on monoclonal antibodies. Second, after growing of bacteria in the presence of [32P]orthophosphate to phosphorylate ETC, the ETC was purified with phenylsepharose following immunoaffinity chromatography. The occurrence of phosphoamino acids in the purified ETC was investigated by an immunoassay. No phosphoamino acids could be detected in the ETC molecule. Also after radiolabelling with 32P it was not possible to demonstrate a radioactive signal. The treatment with alkaline phosphatase has no influence on the mitogenicity or position of ETC in isoelectric focusing. The results obtained led to the conclusion that in contrast to the literature, ETC is not a phosphorylated protein.

Mechanism of stimulation of T cells by Streptococcus pyogenes: isolation of a major mitogenic factor, cytoplasmic membrane-associated protein

Our previous studies established that heat-killed Streptococcus pyogenes, as well as other gram-positive cocci, when incubated with human peripheral blood leukocytes (PBLs) in culture, induced polyclonal activation of T lymphocytes. The activated T lymphocytes included CD4+ CD8- helper T cells and CD3+ and CD4- CD8- double-negative T cells with gamma delta T-cell receptors. In the present study, we isolated a major factor with this unique mitogenic activity against human T lymphocytes from S. pyogenes. This active fraction was found in the cytoplasmic membrane (CM) of the heat-killed organisms but not in other cellular fractions such as cell walls, peptidoglycan, lipoteichoic acids, or cytoplasmic soluble fractions. An active molecule(s) was further isolated from the CM by cholic acid extraction followed by Sephacryl S-200 chromatography. The molecule was protease labile but highly resistant to heat, had a pI of greater than or equal to 9.3 and a molecular weight of 10,000 to 15,000 according to gel filtration experiments, and was termed CM-associated protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the protein purified by anion-exchange chromatography showed a single band with a molecular weight of 15,000, corresponding to mitogenically active regions. Purified CM-associated protein induced activation of T lymphocytes, which consisted of CD4+ CD8- T cells and CD4- CD8- double-negative T-cell receptor gamma/delta + T-cell populations, as did the whole cells of S. pyogenes.

Increased vascular permeability, erythema, and leukocyte emigration induced in rabbit skin by streptococcal erythrogenic toxin type A

A highly purified streptococcal erythrogenic toxin type-A (SET-A) caused increased vascular permeability, erythema, and leukocyte emigration when injected into the skin of rabbits. A blueing reaction indicating increased vascular permeability appeared at 1 h, reaching the highest intensity between 4 and 5 h, decreasing thereafter and completely disappearing at 12 h after toxin injection. The intensity of the increase in permeability was found to be dose dependent. The erythematous reaction began later and persisted longer than the blueing. The time course of leukocyte emigration was found roughly to parallel that of the blueing reaction. The skin reaction to SET-A in rabbits can be characterized as having an acute non-specific exudative inflammatory nature.