Enhancement of host susceptibility to lethal endotoxin shock by staphylococcal pyrogenic exotoxin type C

Superantigen recognition by HLA class II on monocytes up-regulates toll-like receptor 4 and enhances proinflammatory responses to endotoxin

The devastating systemic effects of bacterial superantigens may be explained by powerful proinflammatory synergy with lipopolysaccharide (LPS). However, the mechanism underlying this phenomenon remains unclear and has never been investigated in humans. Specifically, there is no known link between superantigen-induced immune effects and the pattern recognition of LPS at toll-like receptor 4 (TLR4). Here we show that bacterial superantigens induce rapid transcription and increased membrane expression of TLR4 in primary human monocytes by ligation of major histocompatibility complex (MHC) class II. We also demonstrate that superantigens are solely responsible for monocyte TLR4 up-regulation induced by products from Gram-positive bacteria. In parallel with enhanced TLR4 expression, priming of purified monocytes or mixed peripheral blood mononuclear cells with superantigens significantly enhanced the induction of proinflammatory cytokines by known TLR4 ligands. Staphylococcal enterotoxin A constructs containing targeted mutations were used to demonstrate a requirement for MHC class II ligation in both TLR4 up-regulation and enhanced responses to endotoxin. In contrast to results from animal models, superantigen-endotoxin interaction was not dependent on T-cell receptor ligation by superantigen or interferon gamma production. Pattern recognition of bacterial superantigens by MHC class II receptors may exacerbate the proinflammatory response of monocytes to Gram-negative infection or endotoxin by up-regulation of TLR4.

Staphylococcal enterotoxin A-induced hepatotoxicity is predominantly mediated by Fas ligand (CD95L)

OBJECTIVE

To determine the role of tumor necrosis factor alpha (TNF-alpha) and Fas ligand (FasL, CD95L) in superantigen-induced and endotoxin-induced liver injury.

SUMMARY BACKGROUND DATA

Gram-positive bacteria are increasingly common causes of sepsis and multiorgan failure, but the pathophysiologic mechanisms of superantigen-provoked hepatotoxicity remain elusive.

METHODS

Intravital fluorescence microscopy was used to study the liver microcirculation in mice challenged with superantigen (staphylococcal enterotoxin A, SEA) or endotoxin (lipopolysaccharide, LPS) combined with D-galactosamine.

RESULTS

Administration of 10 microg LPS and 50 microg SEA caused similar hepatocellular damage as determined by liver enzymes and apoptosis. Notably, TNF-alpha-deficient mice were completely protected against hepatic injury provoked by LPS, whereas no protection was observed in response to SEA. On the other hand, FasL-deficient mice were protected against liver injury induced by SEA, but no protection was found when challenged with LPS. LPS increased clear-cut leukocyte recruitment, whereas SEA had no significant effect on leukocyte responses in the liver microcirculation. Leukocyte responses to LPS were decreased by >56% in TNF-alpha gene-targeted animals. Moreover, antiadhesive therapy, ie, immunoneutralization of P-selectin, which is an effective inhibitor of leukocyte recruitment, protected against LPS-induced but not against SEA-induced hepatic damage.

CONCLUSIONS

These novel findings demonstrate that the mechanisms of hepatic injury in endotoxin-induced and superantigen-induced sepsis are principally different. On one hand, SEA-provoked hepatotoxicity is mediated by FasL and is not associated with leukocyte recruitment. On the other hand, liver damage provoked by LPS is mediated by TNF-alpha and characterized by prominent leukocyte responses. These data may facilitate development of more specific therapies against sepsis of different origins.

Functional analysis of the TCR binding domain of toxic shock syndrome toxin-1 predicts further diversity in MHC class II/superantigen/TCR ternary complexes

Superantigens (SAGs) aberrantly alter immune system function through simultaneous interaction with lateral surfaces of MHC class II molecules on APCs and with particular variable regions of the TCR beta-chain (Vbeta). To further define the interface between the bacterial SAG toxic shock syndrome toxin-1 (TSST-1) and the TCR, we performed alanine scanning mutagenesis within the putative TCR binding region of TSST-1 along the central alpha helix adjacent to the N-terminal alpha helix and the beta7-beta9 loop as well as with two universally conserved SAG residues (Leu(137) and Tyr(144) in TSST-1). Mutants were analyzed for multiple functional activities, and various residues appeared to play minor or insignificant roles in the TCR interaction. The locations of six residues (Gly(16), Trp(116), Glu(132), His(135), Gln(136), and Gln(139)), each individually critical for functional activity as well as direct interaction with the human TCR Vbeta2.1-chain, indicate that the interface occurs in a novel region of the SAG molecule. Based on these data, a model of the MHC/TSST-1/TCR ternary complex predicts similarities seen with other characterized SAGs, although the CDR3 loop of Vbeta2.1 is probably involved in direct SAG-TCR molecular interactions, possibly contributing to the TCR Vbeta specificity of TSST-1.

Direct hemoperfusion using a polymyxin B immobilized column improves acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by a high mortality rate. We have studied whether direct hemoperfusion using a polymyxin B immobilized fiber column (PMX-DHP) is effective for acute lung injury (ALI) and ARDS. Two ALI and eighteen ARDS patients were evaluated, four congestive heart failure (CHF) patients were evaluated as cardiogenic pulmonary edema, and we retrospectively compared the outcome with ten patients with ARDS who had been hospitalized between 1990 and 1998 as the untreated group. PMX-DHP was carried out twice at a rate of 80-100 ml/minute for 2 hours, with a time interval of approximately 24 hours. We monitored systolic blood pressure (BP), diastolic BP, and the PaO(2)/FIO(2) (PF) ratio before and after PMX-DHP treatment. The mortality was classified if patients were alive at day 30 after initiating PMX-DHP. The mortality of ARDS patients was approximately 20%. Systolic BP increased significantly from 106 +/- 20 to 135 +/- 21 and to 125 +/- 20 mmHg on the following day. Diastolic BP increased from 61 +/- 16 to 78 +/- 15, and to 72 +/- 12 mmHg. The PF ratio increased significantly from 125 +/- 54 to 153 +/- 73, and 163 +/- 78 Torr. CHF patients did not reveal improvement of systolic, diastolic BP, and PF ratio after PMX-DHP. Eight of ten patients in the untreated group died through exacerbated ARDS. In ARDS patients, PMX-DHP improved circulatory disturbance and oxygenation despite the underlying diseases. The mortality improved compared with that before induction of PMX-DHP.

Characterization of Staphylococcus aureus enterotoxin L

Staphylococcus aureus causes a wide variety of diseases. Major virulence factors of this organism include enterotoxins (SEs) that cause both food poisoning and toxic shock syndrome. Recently, a novel SE, tentatively designated SEL, was identified in a pathogenicity island from a bovine mastitis isolate. The toxin had a molecular weight of 26,000 and an isoelectric point of 8.5. Recombinant SEL shared many biological activities with SEs, including superantigenicity, pyrogenicity, enhancement of endotoxin shock, and lethality in rabbits when administered in subcutaneous miniosmotic pumps, but the protein lacked emetic activity. T cells bearing the T-cell receptor beta chain variable regions 5.1, 5.2, 6.7, 16, and 22 were significantly stimulated by recombinant SEL.

Toxic shock syndrome in a horse with Staphylococcus aureus pneumonia

A 3-year-old Thoroughbred gelding was examined because of clinical signs of pneumonia and shock. Mucous membrane petechiation and ventral edema were observed and considered to be a result of vasculitis. Epidermal necrosis developed on the distal portions of the limbs. The horse had a persistent high fever that was unresponsive to nonsteroidal anti-inflammatory treatment, and Staphylococcus aureus was isolated from a nasal swab specimen and 2 transtracheal wash fluid samples. Antimicrobial, anti-inflammatory, and supportive treatment resulted in clinical improvement. However, resolution of the pulmonary infection required long-term (42 days) antimicrobial administration. Staphylococcus aureus strains isolated from this horse were positive for the toxic shock syndrome toxin-1 gene and were shown to produce toxic shock syndrome toxin-1, the causative factor in toxic shock syndrome in humans. The horse's clinical signs were attributed to toxic shock syndrome secondary to pulmonary S. aureus infection.

The zinc-dependent major histocompatibility complex class II binding site of streptococcal pyrogenic exotoxin C is critical for maximal superantigen function and toxic activity

The cocrystal structure of streptococcal pyrogenic exotoxin C (SPE C) with HLA-DR2a (DRA*0101,DRB5*0101) revealed a zinc-dependent interaction site through residues 167, 201, and 203 on SPE C and residue 81 on the beta-chain of HLA-DR2a (DRA*0101,DRB5*0101). Mutation of these SPE C residues resulted in dramatically reduced biological activities. Thus, the zinc-dependent major histocompatibility complex II binding site is critical for maximal biological function of SPE C.

Global repression of exotoxin synthesis by staphylococcal superantigens

Virulent Staphylococcus aureus strains typically produce and secrete large quantities of many extracellular proteins involved in pathogenesis. Such strains cause the classical staphylococcal lesion--local tissue destruction and aggressive inflammation accompanied by the massive influx of polymorphonuclear leukocytes, leading to the formation of pus. Most strains causing toxic shock syndrome, however, produce and secrete very small quantities of most exoproteins although they elaborate high levels of toxic shock syndrome toxin-1 (TSST-1). These strains cause local infections that are remarkably apurulent although potentially fatal owing to the superantigen. We have analyzed this disparity and have found that TSST-1 itself is a negative global regulator of exoprotein gene transcription. TSST-1 not only represses most exoprotein genes but determines its own high expression level by autorepression. We report also that a second superantigen, enterotoxin B, has similar regulatory properties.

Zinc-mediated dimerization and its effect on activity and conformation of staphylococcal enterotoxin type C

Staphylococcal enterotoxins are superantigen exotoxins that mediate food poisoning and toxic shock syndrome in humans. Despite their structural and functional similarities, superantigens display subtle differences in biological properties and modes of receptor binding as a result of zinc atoms bound differently in their crystal structures. For example, the crystal structures of the staphylococcal enterotoxins in the type C serogroup (SECs) contain a zinc atom coordinated by one aspartate and two histidine residues from one molecule and another aspartate residue from the next molecule, thus forming a dimer. This type of zinc ligation and zinc-mediated dimerization occurs in several SECs, but not in most other staphylococcal enterotoxin serogroups. This prompted us to investigate the potential importance of zinc in SEC-mediated pathogenesis. Site-directed mutagenesis was used to replace SEC zinc binding ligands with alanine. SEC mutants unable to bind zinc did not have major conformational alterations although they failed to form dimers. Zinc binding was not essential for T cell stimulation, emesis, or lethality although in general the mutants were less pyrogenic. Thus the zinc atom in SECs might represent a non-functional heavy atom in an exotoxin group that has diverged from related bacterial toxins containing crucial zinc atoms.

Superantigens: microbial agents that corrupt immunity

Microbial superantigens are a family of protein exotoxins that share the ability to trigger excessive and aberrant activation of T cells. The best characterised are the staphylococcal enterotoxins and the streptococcal pyrogenic exotoxins that trigger the staphylococcal and streptococcal toxic shock syndromes. It is now apparent that superantigens have a wider role in the pathology of infectious diseases than has previously been appreciated. Staphylococcus aureus and Streptococcus pyogenes together produce 19 different superantigens. The range of microorganisms known to produce superantigens has expanded to include Gram negative bacteria, mycoplasma, and viruses. Research is beginning to shed light on the more subtle parts these molecules play in causing disease and to produce some real possibilities for specific treatment of superantigen-induced toxicity. We aim to highlight these new developments and review the science behind these fascinating molecules.

Mechanisms of tissue injury in sepsis: contrasts between gram positive and gram negative infection

Sepsis is the systemic response to infection, and is caused by gram positive and gram negative bacteria in approximately equal numbers. In recent years it has become increasingly clear that there are significant differences between sepsis caused by gram positive and gram negative infections, both in the microbial components that initiate the injury, and the host responses that follow it. These differences will assume greater importance in developing targeted therapeutic interventions to severe sepsis.

Role of T cells and gamma interferon during induction of hypersensitivity to lipopolysaccharide by toxic shock syndrome toxin 1 in mice

The superantigenic function of toxic shock syndrome toxin 1 (TSST-1) is generally regarded as an important determinant of its lethal effects in humans or experimental animals. This study examined the role of superantigenicity in a BALB/c mouse model of lethal TSST-1-induced hypersensitivity to lipopolysaccharide (LPS). In this model, TSST-1 greatly potentiated both LPS-induced lethality, as well as LPS-induced serum tumor necrosis factor alpha (TNF-alpha) activity. Although BALB/c-SCID mice were resistant to these LPS enhancement effects of TSST-1, BALB/c-SCID mice reconstituted with T cells were completely susceptible to the enhancement effect of TSST-1 on LPS-induced serum TNF-alpha. Mice pretreated with cyclosporine (Cs) or neutralizing antibodies against gamma interferon (IFN-gamma) did not develop lethal LPS hypersensitivity when injected with TSST-1, and these agents reduced the enhancement effect of TSST-1 on LPS-induced serum TNF-alpha by 99 and 85%, respectively. Cs pretreatment also completely inhibited the known capacity of TSST-1 to amplify LPS-induced levels of IFN-gamma in serum. In contrast, mice given Cs after a priming injection of TSST-1, but before LPS, still exhibited lethal hypersensitivity to LPS. Cs given after TSST-1 also did not inhibit enhancement of LPS-induced serum TNF-alpha by TSST-1 but inhibited the enhancement effect of TSST-1 on LPS-induced serum IFN-gamma by 50%. These experiments support the theory that TSST-1-induced hypersensitivity to LPS is mediated primarily by IFN-gamma derived from superantigen-activated T cells.

Biochemical and biological properties of Staphylococcal enterotoxin K

Staphylococcus aureus is an important human pathogen which is implicated in a wide variety of diseases. Major determinants of the virulence of this organism include extracellular virulence factors. Staphylococcal enterotoxins (SEs) are important causative agents in staphylococcal toxic shock syndrome and food poisoning. Our study identified a novel enterotoxin, SEK, and examined its biochemical and biological properties. SEK had a molecular weight of 26,000 and an experimentally determined pI of between 7.0 and 7.5. SEK was secreted by clinical isolates of S. aureus. We demonstrated that SEK had many of the biological activities associated with the SEs, including superantigenicity, pyrogenicity, the ability to enhance the lethal effect of endotoxin, and lethality in a rabbit model when administered by subcutaneous miniosmotic pump. Recombinant SEK was shown to stimulate human CD4(+) and CD8(+) T cells in a Vbeta-specific manner; T-cells bearing Vbeta 5.1, 5.2, and 6.7 were significantly stimulated to proliferate.

Toxoids of streptococcal pyrogenic exotoxin A are protective in rabbit models of streptococcal toxic shock syndrome

Streptococcal pyrogenic exotoxins (SPEs) are superantigens that have been implicated in causing streptococcal toxic shock syndrome (STSS). Most notably, SPE serotype A is made by nearly all M-protein serotype 1 and 3 streptococci, the M types most associated with the illness (these strains contain one or more other SPEs, and those proteins are likely also to contribute to disease). We have prepared double-, triple-, and hexa-amino-acid mutants of SPE A by PCR and other mutagenesis procedures. The sites chosen for mutation were solvent-exposed residues thought to be important for T-cell receptor (TCR) or major histocompatibility complex (MHC) class II interaction. These mutants were nonsuperantigenic for human peripheral blood mononuclear cells and rabbit and mouse splenocytes and were nonlethal in two rabbit models of STSS. In addition, these mutants stimulated protective antibody responses. Interestingly, mutants that altered toxin binding to MHC class II were more immunogenic than mutants altering TCR binding. Collectively, these studies indicate that multiple-site mutants of SPE A are toxoids that may have use in protecting against the toxin's effects in STSS.

Pyrogenic toxin superantigen site specificity in toxic shock syndrome and food poisoning in animals

Staphylococcus aureus and Streptococcus pyogenes express pyrogenic toxin superantigens (PTSAgs) that are associated with toxic shock syndrome (TSS) and staphylococcal food poisoning (SFP). Most PTSAgs cause TSS in deep-tissue infections, whereas only TSS toxin 1 (TSST-1) is associated with menstrual, vaginal TSS. In contrast, SFP has been linked only with staphylococcal enterotoxins (SEs). Because of the differential abilities of PTSAgs to cause systemic or localized symptoms in a site-dependent manner, the present study was undertaken to assess the toxins' abilities to cross mucosal barriers. The activity of three PTSAgs when delivered orally, vaginally, or intravenously to rabbits and orally to monkeys was investigated. TSST-1 induced shock via all three routes in rabbits. Although active when administered intravenously, SEC1 and streptococcal pyrogenic exotoxin A (SPEA) did not cause symptoms when administered orally or vaginally. Only SEC1 induced emesis in the monkey feeding assay. TSST-1, albeit less stable than SEC1 and SPEA to pepsin, induced diarrhea in monkeys. Our results may explain the unique association of TSST-1 with menstrual TSS and why SPEA is only rarely associated with TSS after pharyngitis, despite being highly associated with TSS after subcutaneous infections. Finally, our studies indicate that enterotoxicity in SFP is not the result of superantigenicity.

Toxic shock syndrome

Toxic shock syndrome (TSS) is an acute febrile illness accompanied by watery diarrhea, sunburn rash, vomiting, hypotension, and multiple organ involvement. When it was initially recognized 20 years ago, TSS was primarily associated with menstruation. Since then, the frequency of menstrual TSS has decreased dramatically. Staphylococcus aureus is the cause of menstrual TSS and is also responsible for about half of all cases of nonmenstrual TSS. Since the late 1980s, Streptococcus pyogenes has been shown to cause a nonmenstrual TSS-like illness, with a higher mortality rate. The mechanism of TSS is attributable to bacterial endotoxins that impede the body's immune system and cause the release of cytokines, which are responsible for the clinical manifestations of the disease. Early recognition and treatment of TSS are important factors in improving patient survival. Patients should be treated with parenteral antibiotics that are highly effective against staphylococci and streptococci. They should also receive fluid resuscitation and vasopressors. Some patients require intubation, dialysis, or immunoglobulin therapy.

Cytokine secretion by stimulated monocytes depends on the growth phase and heat treatment of bacteria: a comparative study between lactic acid bacteria and invasive pathogens

The consumption of food containing lactic acid bacteria (LAB) has been shown to exert immunomodulatory effects in humans. The specific cellular interaction of these bacteria with immuno-competent cells has not yet been fully understood. Since the TNF-alpha secretion of stimulated monocytes is an important initial response to a bacterial challenge, we investigated the potential of LAB originating from the human intestine or fermented food in comparison to the effect of invasive pathogens. The challenge of monocytes with three LAB strains, Listeria monocytogenes or enterohaemorrhagic Escherichia coli (EHEC) elicited a strain specific, dose-dependent biphasic TNF-alpha secretion. The concentration (EDmax) of bacteria or bacterial cell wall components necessary to induce maximal TNF-alpha secretion (TNFmax) by monocytes was mathematically approximated. It was shown for exponentially growing LAB strains that the maximal TNF-alpha secretion (TNFmax) was stronger (57 to 78%) upon stimulation with living bacteria than with heat killed cells. In contrast to log-phase bacteria, the maximal TNF-alpha secretion of monocytes (TNFmax) was higher (15 to 55%) after the stimulation with heat killed, stationary-phase bacteria when compared to that of live LAB. Thus, monocyte stimulation was clearly affected by the growth phase of bacteria. Purified cell walls of LAB strains revealed only a limited potential for monocyte stimulation. LPS exhibited a higher capacity to stimulate monocytes than purified gram positive cell walls or muramyldipeptide. In comparison to pathogenic bacteria, the maximal secretory TNF-alpha response (TNFmax) was up to 2 fold higher with LAB strains. In general, the amount of bacteria (EDmax) necessary to induce maximal TNF-alpha secretion (TNFmax) was approximately 1 to 3 log higher for heat killed bacteria when compared to live bacterial cells illustrating the significant lower potential of heat killed bacteria to activate monocytes.

Exotoxins of Staphylococcus aureus

This article reviews the literature regarding the structure and function of two types of exotoxins expressed by Staphylococcus aureus, pyrogenic toxin superantigens (PTSAgs) and hemolysins. The molecular basis of PTSAg toxicity is presented in the context of two diseases known to be caused by these exotoxins: toxic shock syndrome and staphylococcal food poisoning. The family of staphylococcal PTSAgs presently includes toxic shock syndrome toxin-1 (TSST-1) and most of the staphylococcal enterotoxins (SEs) (SEA, SEB, SEC, SED, SEE, SEG, and SEH). As the name implies, the PTSAgs are multifunctional proteins that invariably exhibit lethal activity, pyrogenicity, superantigenicity, and the capacity to induce lethal hypersensitivity to endotoxin. Other properties exhibited by one or more staphylococcal PTSAgs include emetic activity (SEs) and penetration across mucosal barriers (TSST-1). A detailed review of the molecular mechanisms underlying the toxicity of the staphylococcal hemolysins is also presented.

Exotoxins of Staphylococcus aureus

This article reviews the literature regarding the structure and function of two types of exotoxins expressed by Staphylococcus aureus, pyrogenic toxin superantigens (PTSAgs) and hemolysins. The molecular basis of PTSAg toxicity is presented in the context of two diseases known to be caused by these exotoxins: toxic shock syndrome and staphylococcal food poisoning. The family of staphylococcal PTSAgs presently includes toxic shock syndrome toxin-1 (TSST-1) and most of the staphylococcal enterotoxins (SEs) (SEA, SEB, SEC, SED, SEE, SEG, and SEH). As the name implies, the PTSAgs are multifunctional proteins that invariably exhibit lethal activity, pyrogenicity, superantigenicity, and the capacity to induce lethal hypersensitivity to endotoxin. Other properties exhibited by one or more staphylococcal PTSAgs include emetic activity (SEs) and penetration across mucosal barriers (TSST-1). A detailed review of the molecular mechanisms underlying the toxicity of the staphylococcal hemolysins is also presented.

Gram-positive sepsis. Mechanisms and differences from gram-negative sepsis

This article has reviewed the mechanisms by which gram-positive bacteria lead to septic shock, with regard to bacterial structure and toxicology and the host responses elicited both in animal models and in the clinical setting. Gram-positive organisms are better suited to invade host tissues and elicit, in general, a brisker phagocytic response than gram-negative organisms. The lack of endotoxin in the outer cell wall is compensated for by the presence of exposed peptidoglycan and a range of other toxic secreted products. It appears that cell wall components of gram-positive bacteria may signal via the same receptor as gram-negative endotoxin, although the type of signal and coreceptor may differ. Both animal and clinical data suggest that, unlike endotoxin-mediated shock, gram-positive infection produces a modest TNF response only and does not respond well to anti-TNF therapies. This leads one to conclude that the mechanisms leading to shock in gram-positive infection may be multifactorial and perhaps more difficult to treat. A thorough review of gram-positive mechanisms of sepsis is hampered by a lack of basic research in this field. Understanding of gram-negative bacterial structure and the regulation of virulence genes is at an advanced stage, yet the molecular tools to analyse virulence factors in the gram-positive genome have only recently become available. There is a paucity of good animal models of gram-positive infection and a lack of microbiologic data from some of the major trials in sepsis that might have given greater insight into the mechanisms leading to shock in various infections.

Correlation of temperature and toxicity in murine studies of staphylococcal enterotoxins and toxic shock syndrome toxin 1

This study describes a quick (<12 h) assay for detecting temperature decreases in BALB/c and C57BL/6 mice injected intraperitoneally (i.p. ) with staphylococcal enterotoxin A (SEA), SEB, or SEC3 or toxic shock syndrome toxin 1 and a potentiating dose of lipopolysaccharide (LPS). Toxin-specific antisera effectively neutralized the temperature fluctuations in this model. Orally administered SEA or SEB (50 microg/animal), with or without LPS, did not have an effect on temperature or lethality. Versus wild-type mice, transgenic knockout mice lacking the p55 receptor for tumor necrosis factor (TNF) or gamma interferon were protected against an i.p. challenge of SEA plus LPS. The p75 receptor for TNF and intercellular adhesion molecule 1 have a negligible role in this toxic shock model.

Host damage from bacterial toxins

Bacterial infection often involves toxin-mediated damage to the host. This can occur at mucosal epithelial surfaces, in subepithelial tissues (involving connective tissue, blood vessels and host defence cells), or at organ or tissue sites distant from the focus of infection. This paper deals with host damage at each of these levels and examples have been selected of toxins that have a well defined role in pathogenesis and for which evidence is less clear cut. Current views of mechanisms of host damage are presented along with summaries of mode of action at the molecular level where this is known. Certain unifying features of mechanisms of toxin action on host cells are emphasised. Modern genetic methods and gene cloning techniques should help in the assessment of the role of individual toxic factors where pathogenesis is multifactorial, and preliminary examples of this approach are mentioned. The search for new toxins continues and this is illustrated with reference to the toxins involved in the staphylococcal scalded skin syndrome and staphylococcal toxic shock syndrome. This overview is intended to convey an impression of the rapid development that has taken place in knowledge of the role of toxins in pathogenesis.

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

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

Investigation of the role of the disulphide bond in the activity and structure of staphylococcal enterotoxin C1

The goal of this study was to investigate the role of the disulphide bond of staphylococcal enterotoxin C1 (SEC1) in the structure and activity of the toxin. Mutants unable to form a disulphide bond were generated by substituting alanine or serine for cysteine at positions 93 and/or 110. Although we did not directly investigate the residues between the disulphide linkage, tryptic lability showed that significant native structure in the cystine loop is preserved in the absence of covalent bonding between residues 93 and 110. Since no correlation was observed between the behaviour of these mutants with regard to toxin stability, emesis and T cell proliferation we conclude that SEC1-induced emesis and T cell proliferation are dependent on separate regions of the molecule. The disulphide bond itself is not an absolute requirement for either activity. However, conformation within or adjacent to the loop is important for emesis. Although mutants with alanine substitutions were not emetic, those with serine substitutions retained this activity, suggesting that the disulphide linkage stabilizes a crucial conformation but can be replaced by residues which hydrogen bond.

Treatment of sepsis by extracorporeal elimination of endotoxin using polymyxin B-immobilized fiber

Despite the use of potent antibiotics and intensive supportive care, mortality remains high among septic shock patients, especially those with endotoxemia. To remove endotoxin directly from the blood, a material consisting of polymyxin B that is immobilized on fibers (PMX-F) and that can selectively detoxify endotoxin was developed. In a preliminary clinical study, 16 patients with septic multiple organ failure were treated with direct hemoperfusion using a PMX-F column. This therapy significantly decreased the endotoxin level from 76 pg/mL to 21 pg/mL after 2 hours of direct hemoperfusion. The hyperdynamic state of the cardiac index, which is a characteristic of endotoxic shock, returned to normal levels after treatment. In septic shock patients with a systolic pressure of less than 100 mm Hg, the systolic arterial pressure increased significantly from the pretreatment level. The alleviation of fever caused by this therapy continued until the day after treatment. Of the 16 patients who underwent this therapy, 9 were alive 2 weeks after this therapy and 7 patients were discharged from the hospital alive. Hemoperfusion with PMX may be an effective treatment for sepsis and septic shock.

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

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

Early diagnosis of staphylococcal toxaemia in burned children

The features of toxic shock syndrome in burned children have been described in a review of seven patients (J. D. Frame et al., Burns 1985; 11, 234). These include a 'prodromal' 24-48 h period with diarrhoea, vomiting, general malaise, pyrexia, tachycardia and tachypnoea. The white cell count and haemoglobin concentration fall prior to the 'shock' phase, which occurs 3-4 days postburn. Once 'shock' has occurred the mortality of the condition is approximately 50 per cent; in the absence of 'shock' it is much reduced. We have undertaken a retrospective review of six burned children who were admitted in a 2-year period to the Mount Vernon NHS Trust Burns Unit with a clinical diagnosis of toxic shock syndrome. The evidence from our patients suggests that reliable early diagnostic signs are a rapidly developing severe pyrexia of 39.5 degrees C or above, and a simultaneously increasing tachycardia and tachypnoea to high levels. There is a sudden profound fall in the white cell count and haemoglobin concentration over a period of hours between 1 and 3 days from injury. Specific treatment should be instituted before the onset of 'shock'. The name staphylococcal toxaemia might promote earlier diagnosis and treatment of this condition and so reduce its mortality.

Immune cell lethality induced by streptococcal pyrogenic exotoxin A and endotoxin

Streptococcal pyrogenic exotoxin (SPE) A has many effects on the immune system, including immunolethality, which is characterized by a significant decrease in circulating immune cells as well as depletion of the spleen and lymph nodes prior to death of experimental animals. In this report, characterization of the mechanism of immunolethality has been undertaken. Synergistic induction of immunolethality was observed in vitro when human lymphocytes were treated with both SPE A and lipopolysaccharide (LPS). The same effect was demonstrated in the absence of a mitogenic response with the murine T-cell receptor, as well as in the absence of antigen-presenting cells and their secreted cytokines. The addition of antigen-presenting cells did not significantly affect lethality. SPE A directly interacted with LPS through interaction with ketodeoxyoctonate as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and iodinated exotoxin overlays. This interaction was demonstrated to be important for immunolethality, since simultaneous addition of SPE A and LPS was required, whereas sequential addition of SPE A and LPS did not result in lethality. LPS appeared to be acting, in part, to enhance the cell-binding ability of SPE A, since SPE A could only be detected in A.E7 cell membrane preparations after simultaneous incubation with SPE A and LPS.

Possibility of separating toxins from bacteria associated with sudden infant death syndrome using anion exchange chromatography

AIMS

To develop techniques for the characterisation of toxins elaborated by a strain of Escherichia coli associated with sudden infant death syndrome (SIDS).

METHODS

E coli SIDS 04, isolated from the nasopharynx of a case of SIDS, was studied. Cell-free toxin preparations were standardised, their protein measured, and analytical separation of proteins achieved using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Acetone precipitation of proteins was required prior to Coomassie blue staining of bands. Preparative separation was achieved on an anion exchange column using a programmed concentration gradient of NaCl in TRIS buffer. Fractions were tested individually or pooled for presence of lethal toxin including endotoxin. Lethal toxin was detected with the chick embryo test system. Endotoxin was measured using a chromogenic modification of the Limulus amoebocyte assay.

RESULTS

Twenty one peaks were detected by chromatography. Ten individual, or pooled, fractions were assayed for endotoxin which ranged from 27-33 pg/ml. Much greater variation was found when the same fractions were assayed in chick embryos. E coli fractions varied considerably in lethal toxicity, from 0/10 to 10/10 chick embryos killed/tested. Certain E coli fractions tested individually (lethality four out of 10 to eight out of 10) proved more lethal (10 out of 10) if pooled prior to testing.

CONCLUSIONS

In E coli infection associated with SIDS relatively low concentrations of extracellular protein are lethally toxigenic for the chick embryo model of SIDS. These proteins can be separated analytically by SDS-PAGE and preparatively by anion exchange chromatography. Toxicity of individual fractions is not correlated with endotoxin concentrations in samples tested.

Induction of nitric oxide synthase activity by toxic shock syndrome toxin 1 in a macrophage-monocyte cell line

Toxic shock syndrome toxin 1 (TSST-1) is a Mr 22,000 protein produced by Staphylococcus aureus. It is thought to be the cause of toxic shock syndrome. We investigated the hypothesis that TSST-1 induces nitric oxide (NO) synthase and that the NO formed may be involved in the pathogenesis of toxic shock syndrome. We used the murine monocyte-macrophage cell line J744.2 that responds to TSST-1 and also expresses NO synthase activity upon immunological stimulation. J774.2 macrophages stimulated with TSST-1 (10-100 nM) generated nitrite, a breakdown product of NO, and induced concentration-dependent elevations of cGMP in the pig kidney epithelial cell line (LLC-PK1). This latter effect was due to the generation of L-arginine-derived NO for it was (i) abolished by oxyhemoglobin (10 microM), a scavenger of NO, or by methylene blue (10 microM), an inhibitor of NO-activated guanylate cyclase; (ii) potentiated by superoxide dismutase (100 units/ml), which prolongs the life of NO; (iii) inhibited by NG-monomethyl-L-arginine (0.3 mM), an inhibitor of NO synthase; (iv) significantly decreased when L-arginine (0.4 mM) in the medium was replaced by D-arginine (0.4 mM). Moreover, TSST-1 (100 nM) enhanced the activity of cytosolic NO synthase in J774.2 cells. Hydrocortisone (1 microM) but not indomethacin (5 micrograms/ml) or salicylic acid (5 micrograms/ml) prevented the generation of NO2- and the increases in cGMP levels in LLC-PK1 cells induced by J774.2 cells stimulated with TSST-1. The effects of hydrocortisone were partially reversed by coincubation with RU 486 (1 microM), an antagonist of glucocorticoid receptors. Thus, TSST-1 and perhaps other exotoxins produced by Gram-positive bacteria induce NO synthase and the increased NO formation may contribute to toxic shock syndrome and possibly to changes in the immune responses that accompany infection.

Toxic shock syndrome toxin 1 enhances synthesis of endotoxin-induced tumor necrosis factor in mice

Toxic shock syndrome toxin 1 (TSST-1) was tested for its ability to enhance the production of endotoxin-induced tumor necrosis factor (TNF) in C3H/HeN mice. The TNF level in serum was quantified by a sandwich enzyme-linked immunosorbent assay (ELISA). It was found that when mice were injected with 20 micrograms of TSST-1 12 h before exposure to 1 micrograms of endotoxin, the serum endotoxin-induced TNF was 20 times as high as that found in mice exposed to endotoxin alone. Although 20 micrograms of TSST-1 did induce a maximum level of near 1 ng of TNF per ml of serum 1.5 h after exposure, the TNF concentration was greatly diminished after 5 to 6 h and was no longer detectable after 12 h. Pretreatment of mice with 20 micrograms of TSST-1 or 1 micrograms of endotoxin did not influence TNF induction by TSST-1 12 h later. Also, pretreatment of mice with 1 micrograms of endotoxin did not enhance TNF induction by endotoxin 12 h later. Enhancement was achieved only when mice were exposed to TSST-1 more than 4 h and less than 24 h before injection of endotoxin. Despite the relatively high serum TNF levels (30 to 50 ng/ml), no mortality was observed in the mice treated with both TSST and endotoxin.

Staphylococcal and streptococcal pyrogenic toxins involved in toxic shock syndrome and related illnesses

Toxic-shock syndrome (TSS) is an acute onset, multiorgan illness which resembles severe scarlet fever. The illness is caused by Staphylococcus aureus strains that express TSS toxin-1 (TSST-1), enterotoxin B, or enterotoxin C. TSST-1 is associated with menstrual TSS and approximately one-half of nonmenstrual cases; the other two toxins cause nonmenstrual cases, 47% and 3%, respectively. The three toxins are expressed in culture media under similar environmental conditions. These conditions may explain the association of certain tampons with menstrual TSS. Biochemically, the toxins are all relatively low molecular weight and fairly heat and protease stable. Enterotoxins B and C, share nearly 50% sequence homology with streptococcal scarlet fever toxin A; they share no homology with TSST-1 despite sharing numerous biological properties. Numerous animal models for development of TSS have suggested mechanisms of toxin action, though the exact molecular action is not known. The toxins are all potent pyrogens, induce T lymphocyte proliferation, requiring interleukin 1 release from macrophages, suppress immunoglobulin production, enhance endotoxin shock, and enhance hypersensitivity skin reactions. The genetic control of the toxins has been studied and suggests the exotoxins are variable traits. Some additional properties of TSS S. aureus which facilitate disease causation have been clarified.

Treatment of toxic shock syndrome with endotoxin-neutralizing antibody

The enhancement of host susceptibility to endotoxin (lipopolysaccharide, LPS) by toxic shock syndrome toxin-1 (TSST-1) is an important mechanism in the pathogenesis of toxic shock syndrome. In these studies, we sought to determine whether an endotoxin-neutralizing monoclonal antibody could be useful in the treatment of toxic shock syndrome. We isolated a murine monoclonal hybridoma (3-H3) which secreted monoclonal antibody (mAb) specific for Escherichia coli 0111:B4 LPS. Spleen cells cocultured with E. coli 0111:B4 LPS demonstrated up to a 60% decrease in mitogenic activity in the presence of 3-H3 mAb, but not control mAb, demonstrating that this antibody neutralized endotoxin in vitro. Rabbits pretreated with 3-H3 mAb or control mAb were injected intradermally with E. coli 0111:B4 LPS. One day later rabbits received E. coli 0111:B4 LPS intravenously to elicit the dermal Shwartzman reaction. Rabbits pretreated with 3-H3 mAb did not develop this reaction (0/6) compared to animals pretreated with control mAb (5/6), demonstrating that this antibody neutralized endotoxin in vivo (P less than 0.05). When this antibody was evaluated in a rabbit model of lethal toxic shock syndrome, rabbits pretreated with antibody demonstrated greater survival (8/14) than saline control animals (1/10) after challenge with TSST-1 and E. coli 0111:B4 LPS (P less than 0.05). Since the suspicion exists that low levels of endogenous LPS may potentiate TSST-1 activity during clinical toxic shock syndrome, we hypothesized that endotoxin-neutralizing antibodies could be useful in the treatment of this lethal disease process.

Levels of toxic shock syndrome toxin-1 production among Staphylococcus aureus strains and clinical implications

Among 250 S. aureus clinical isolates, the incidence of TSST-1 production was 18.0%. S. aureus var. hominis strains were predominant (95.6%), producing high levels of toxin in vitro, within the range of 0.6 to 4.3 micrograms/ml and exhibiting crystal violet binding with C/D pattern. No correlation was found between the level of TSST-1 production in vitro and the clinical course. Two (3.4%) of the var. bovis strains produced toxin in amounts less than 0.6 micrograms/ml and did not bind crystal violet. None of the 24 var. canis isolates produced TSST-1. Fifty five per cent of the isolates of phage group I produced TSST-1 and corresponded to 57.8% of the toxigenic strains. Two of the 250 patients developed toxic shock syndrome.

The toxic shock syndrome in a burn victim

A case of toxic shock syndrome (TSS) in a 6-year-old boy with a 5 per cent body surface area partial thickness scald burn is reported. Biobrane was the wound dressing used initially. The clinical and laboratory characteristics of the syndrome are listed. The syndrome is caused by an exotoxin of Staph. aureus and can occur in the absence of invasive infection. The syndrome, first described in menstruating women who used tampons, has occurred in patients with a variety of wounds. Reports of the TSS syndrome in burn victims are limited to children whose wounds were covered. Children are most vulnerable to the development of TSS because of their limited prior exposure to the toxin.

Neutralization of toxic shock syndrome toxin-1 by monoclonal antibodies in vitro and in vivo

Sixteen monoclonal antibodies (MAbs) directed against toxic shock syndrome toxin-1 (TSST-1) were generated by immunization of mice with purified TSST-1 and subsequent fusion of spleen cells with myeloma cells. Antibody-producing clones, identified by an enzyme-linked immunosorbent assay, were maintained as ascites tumors, and MAbs were purified by protein A chromatography. High-titered clones were further characterized and tested for the ability to neutralize several biological activities of TSST-1. The MAbs, which are of several immunoglobulin subtypes, reacted specifically with purified TSST-1 and TSST-1 present in Staphylococcus aureus culture supernatants. Three MAbs neutralized TSST-1-induced mitogenesis in a dose-dependent manner. Three of eight MAbs tested were able to neutralize induction by TSST-1 of interleukin-1 production by human monocytes. One neutralizing MAb, 8-5-7, was tested for the ability to protect rabbits from a constant infusion of TSST-1. Rabbits given the MAb had an attenuated clinical illness and were protected from the hypocalcemia, lipemia, and hepatic and renal insufficiency seen in control rabbits. Six of seven control rabbits died, compared with only one of seven rabbits treated with MAb 8-5-7. These experiments suggest that MAb 8-5-7 is directed against an antigenic determinant critical to the toxicity of TSST-1 and that the MAbs should be useful as probes in structure-function analyses of the TSST-1 molecule.

Synergistic induction of interleukin-1 by endotoxin and toxic shock syndrome toxin-1 using rat macrophages

We studied interleukin-1 (IL-1) secretion by rat peritoneal exudate macrophages stimulated with purified toxic shock syndrome toxin-1 (TSST-1). TSST-1 was observed to be a more potent inducer of IL-1 than was endotoxin. The induction of IL-1 secretion by TSST-1 was not blocked by polymyxin B but could be blocked by monoclonal antibodies directed against TSST-1. Synergistic induction of IL-1 was observed when the cells were stimulated with TSST-1 and endotoxin. The sequence of addition was found to be important for the synergistic response. Enhanced IL-1 production was observed only when macrophages were exposed to endotoxin before or simultaneously with TSST-1. Prior exposure of macrophages to TSST-1 had no enhancing effect on endotoxin-induced IL-1 secretion. We conclude that stimulation of the macrophage by endotoxin enhances the responsiveness of the cells to TSST-1 and may thereby play a role in the pathogenesis of toxic shock syndrome.

Lethal challenge of gnotobiotic weanling rats with bacterial isolates from cases of sudden infant death syndrome (SIDS)

An attempt was made to produce an animal model of sudden infant death syndrome (SIDS). The experimental animals (germ free weanling rats) were exposed to nasopharyngeal isolates from cases of SIDS to test the hypothesis that common bacteria may have an aetiological role in the disease. Negative results were obtained when the strains were tested in isolation, but certain combinations of organisms (specifically some Staphylococcus aureus and Escherichia coli) killed the animals rapidly (less than 18 hours) without prolonged terminal illness. Post mortem histological findings were consistent with those of SIDS. The lethal toxigenic potential of nasopharyngeal bacteria, which are regarded as harmless in adults, should be reconsidered in respect of the aetiology of SIDS.

A rabbit model of toxic shock syndrome that uses a constant, subcutaneous infusion of toxic shock syndrome toxin 1

We have developed a rabbit model of toxic shock syndrome that uses a subcutaneous infusion pump to administer toxic shock syndrome toxin 1 (TSST-1). A dose of 150 micrograms, infused at a constant rate over a period of 7 days, resulted in a characteristic illness highlighted by fever, conjunctival hyperemia, cachexia, and lethargy. The illness was uniformly fatal, with a mean interval until death of 3.2 +/- 0.4 days. Serial determinations of serum chemistries confirmed the multisystem nature of this illness. Rabbits developed profound hypocalcemia, with levels falling from 15.5 +/- 0.2 to 7.6 +/- 0.4 mg/dl under the influence of TSST-1. Blood urea nitrogen and creatinine rose dramatically, in the setting of oliguria or anuria. Serum glutamicpyruvic transaminase was the most reliable indicator of hepatic dysfunction, with the mean rising from 48 U/liter before administration of TSST-1 to 546 U/liter among rabbits surviving 2 days of the infusion. Creatine phosphokinase also rose dramatically in 10 of 16 rabbits. Rabbits demonstrated relative neutrophilia and lymphopenia as well as an increase in the partial thromboplastin time. Histopathologic examination demonstrated disease of multiple organs, particularly the liver, spleen, and lymph nodes, all of which demonstrated inflammation, thrombosis, hemorrhage, and erythrophagocytosis. The concurrent administration of prednisolone with TSST-1 prevented death in four of four rabbits and greatly lessened the morbidity. Rabbits were not protected from morbidity or mortality by the concurrent administration of polymyxin B. We believe that a constant, subcutaneous infusion of TSST-1 in rabbits provides a reproducible model for studying the pathogenesis of TSS.

Hormonal influence on experimental infections by a toxic shock strain of Staphylococcus aureus

Subcutaneous infection chambers in rabbits were infected with a strain of Staphylococcus aureus isolated from a patient with toxic shock syndrome. Estrogens (mestranol and 17-beta-estradiol) protected male rabbits and prolonged survival. Neither androgens (testosterone and dihydrotestosterone) nor progesterone affected the susceptibility of intact or ovarihysterectomized female rabbits.

Affinity purification of staphylococcal toxic shock syndrome toxin 1 and its pathologic effects in rabbits

Toxic shock syndrome toxin 1 (TSST-1) was purified to apparent homogeneity by chromatofocusing and affinity chromatography. The amino acid composition of the toxin was very similar to that reported for TSST-1 by other investigators. The amino-terminal amino acid was serine. A partial specific volume of 0.73 ml/g was calculated for the toxin from the amino acid data, and a molecular weight of 19,200 +/- 1,300 was determined by hydrodynamic methods. New Zealand white rabbits of both sexes were equally susceptible to the lethal effects of the toxin; however, older rabbits (greater than 12 months) were far more susceptible than young adults or weanlings. The 50% lethal dose of TSST-1 in older rabbits was 50 to 60 micrograms/kg when injected subcutaneously and 20 to 30 micrograms/kg when injected intravenously. Enhancement of lethal endotoxin shock by TSST-1 could not be demonstrated when both toxins were injected subcutaneously; however, lethal shock did occur when endotoxin (10 micrograms/kg) was injected intravenously after TSST-1 had been injected by either the subcutaneous (50 to 60 micrograms/kg) or the intravenous (20 to 30 micrograms/kg) route. Endotoxin alone was not lethal at a dose of 500 micrograms/kg of body weight when injected subcutaneously. When injected intravenously, endotoxin at a dose of 500 micrograms/kg was not lethal in weanling males or in females in any age group; however, young (6 to 7 months) and adult (greater than 12 months) males were killed by endotoxin doses as low as 45 to 50 micrograms/kg. Histopathologic studies of rabbits by both sexes which died as a result of TSST-1 alone or in combination with endotoxin showed extensive damage to organs rich in lymphoid and mononuclear phagocytic cells such as the thymus, mesenteric lymph nodes, liver, and spleen. Severe congestion of these organs as well as erythrophagocytosis and lymphoid depletion in the spleen and mesenteric lymph nodes were noted. Congestion and hemorrhage were also found in the heart, lungs, trachea, and thymus. The systemic pathology produced by TSST-1 was strikingly similar to that seen in humans who had died of toxic shock syndrome and in rabbits with subcutaneous chamber inoculated with toxic shock case strains of Staphylococcus aureus. Rabbits that were not killed by the toxin suffered a very rapid and severe leukopenia followed by leukocytosis with a left shift. Lymphopenia was also noted as was a mild but persistent anemia. With the exception of the early leukopenia, very similar hematologic findings have been noted in humans with toxic shock syndrome.

Resolution of highly purified toxic-shock syndrome toxin 1 into two distinct proteins by isoelectric focusing

Highly purified toxic-shock syndrome toxin 1 (TSST-1) was prepared by differential precipitation with ethanol and resolubilization in water followed by successive electrofocusing in pH gradients of 3-10, 6-8, and 6.5-7.5. TSST-1, thus isolated, migrated as two distinct protein bands with isoelectric points of 7.08 (TSST-1a) and 7.22 (TSST-1b). When tested by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, both toxins migrated as homogeneous bands with molecular weights of 22 000. The gel bands were visualized by silver staining. The two toxins have nearly identical amino acid compositions and are immunologically identical as shown by Ouchterlony reactivity against TSST-1 hyperimmune serum. TSST-1a and TSST-1b have the same biological activities as TSST-1: the capacity to induce fever, enhancement of host susceptibility to lethal endotoxin shock, nonspecific T lymphocyte mitogenicity, and suppression of immunoglobulin M synthesis against sheep erythrocytes. These two proteins have been isolated from several different TSS-associated Staphylococcus aureus strains. The data suggest that the differences in isoelectric point result either from the presence of a cofactor or from alternative conformations. Since only two bands appear, microheterogeneity as a result of deamination or acetylation is unlikely.