Broad-spectrum immunity against superantigens is elicited in mice protected from lethal shock by a superantigen antagonist peptide

New drugs for acute kidney injury

PURPOSE OF REVIEW

To describe recent advances in the development of therapeutic agents for acute kidney injury (AKI).

RECENT FINDINGS

Traditional care for AKI is mostly supportive. At present, no specific therapy has been developed to prevent or treat AKI. However, based on a better understanding of the pathophysiology of AKI, various potential compounds have been recently identified and tested. A variety of pathways has been targeted, including oxidative and mitochondrial stress, cellular metabolism and repair, inflammation, apoptosis and hemodynamics. Many of these potential agents are currently ongoing early-phase clinical trials, and the purpose of this review is to provide a summary of those with the most potential.

SUMMARY

Despite the lack of therapies specifically approved for AKI, many interesting potential agents are entering clinical trials, with the potential to transform the care of patients with AKI.

Drugs in Development for Acute Kidney Injury

The care of patients with acute kidney injury (AKI) has been limited due to the lack of effective therapeutics that can either prevent AKI during high-risk situations or treat AKI once established. A revolution in the scientific understanding of the pathogenesis of AKI has led to the identification of potential therapeutic targets. These targets include pathways involved in inflammation, cellular repair and fibrosis, cellular metabolism and mitochondrial function, oxidative stress, apoptosis, and hemodynamics and oxygen delivery. Many compounds are entering early-phase clinical trials. In addition, efforts to better describe sub-categories of AKI (through endo-phenotyping) hold promise to target therapies more effectively based upon pathways that are operative in the pathogenesis. These advances bring optimism that the care of patients with AKI will be transformed with the hope of better outcomes.

Staphylococcal and Streptococcal Superantigens Trigger B7/CD28 Costimulatory Receptor Engagement to Hyperinduce Inflammatory Cytokines

Staphylococcal and streptococcal superantigens are virulence factors that cause toxic shock by hyperinducing inflammatory cytokines. Effective T-cell activation requires interaction between the principal costimulatory receptor CD28 and its two coligands, B7-1 (CD80) and B7-2 (CD86). To elicit an inflammatory cytokine storm, bacterial superantigens must bind directly into the homodimer interfaces of CD28 and B7-2. Recent evidence revealed that by engaging CD28 and B7-2 directly at their dimer interface, staphylococcal enterotoxin B (SEB) potently enhances intercellular synapse formation mediated by B7-2 and CD28, resulting in T-cell hyperactivation. Here, we addressed the question, whether diverse bacterial superantigens share the property of triggering B7-2/CD28 receptor engagement and if so, whether they are capable of enhancing also the interaction between B7-1 and CD28, which occurs with an order-of-magnitude higher affinity. To this end, we compared the ability of distinct staphylococcal and streptococcal superantigens to enhance intercellular B7-2/CD28 engagement. Each of these diverse superantigens promoted B7-2/CD28 engagement to a comparable extent. Moreover, they were capable of triggering the intercellular B7-1/CD28 interaction, analyzed by flow cytometry of co-cultured cell populations transfected separately to express human CD28 or B7-1. Streptococcal mitogenic exotoxin Z (SMEZ), the most potent superantigen known, was as sensitive as SEB, SEA and toxic shock syndrome toxin-1 (TSST-1) to inhibition of inflammatory cytokine induction by CD28 and B7-2 dimer interface mimetic peptides. Thus, superantigens act not only by mediating unconventional interaction between MHC-II molecule and T-cell receptor but especially, by strongly promoting engagement of CD28 by its B7-2 and B7-1 coligands, a critical immune checkpoint, forcing the principal costimulatory axis to signal excessively. Our results show that the diverse superantigens use a common mechanism to subvert the inflammatory response, strongly enhancing B7-1/CD28 and B7-2/CD28 costimulatory receptor engagement.

Potent Neutralization of Staphylococcal Enterotoxin B In Vivo by Antibodies that Block Binding to the T-Cell Receptor

To develop an antibody (Ab) therapeutic against staphylococcal enterotoxin B (SEB), a potential incapacitating bioterrorism agent and a major cause of food poisoning, we developed a "class T" anti-SEB neutralizing Ab (GC132) targeting an epitope on SEB distinct from that of previously developed "class M" Abs. A systematic engineering approach was applied to affinity-mature Ab GC132 to yield an optimized therapeutic candidate (GC132a) with sub-nanomolar binding affinity. Mapping of the binding interface by hydrogen-deuterium exchange coupled to mass spectrometry revealed that the class T epitope on SEB overlapped with the T-cell receptor binding site, whereas other evidence suggested that the class M epitope overlapped with the binding site for the major histocompatibility complex. In the IgG format, GC132a showed ∼50-fold more potent toxin-neutralizing efficacy than the best class M Ab in vitro, and fully protected mice from lethal challenge in a toxic shock post-exposure model. We also engineered bispecific Abs (bsAbs) that bound tetravalently by utilizing two class M binding sites and two class T binding sites. The bsAbs displayed enhanced toxin neutralization efficacy compared with the respective monospecific Ab subunits as well as a mixture of the two, indicating that enhanced efficacy was due to heterotypic tetravalent binding to two non-overlapping epitopes on SEB. Together, these results suggest that class T anti-SEB Ab GC132a is an excellent candidate for clinical development and for bsAb engineering.

S101, an Inhibitor of Proliferating T Cells, Rescues Mice From Superantigen-Induced Shock

Superantigens (SAgs) are extremely potent bacterial toxins, which evoke a virulent immune response, inducing nonspecific T-cell proliferation, rapid cytokine release, and lethal toxic shock, for which there is no effective treatment. We previously developed a small molecule, S101, which potently inhibits proliferating T cells. In a severe mouse model of toxic shock, a single injection of S101 given together with superantigen challenge rescued 100% of the mice. Even when given 2 hours after challenge, S101 rescued 40% of the mice. S101 targets the T-cell receptor, inflammatory response, and actin cytoskeleton pathways. S101 inhibits the aryl hydrocarbon receptor, a ligand-activated transcription factor that is involved in the differentiation of T-helper cells, especially Th17, and regulatory T cells. Our results provide the rationale for developing S101 to treat superantigen-induced toxic shock and other pathologies characterized by T-cell activation and proliferation.

Validation of a clinical trial composite endpoint for patients with necrotizing soft tissue infections

OBJECTIVE

Our objective was to develop and validate a composite endpoint for patients with necrotizing soft tissue infections that incorporates: local tissue injury, systemic organ dysfunction, and mortality.

METHODS

The Necrotizing Infection Clinical Composite Endpoint (NICCE) was defined as follows:(i) alive at day 28, (ii) three or less debridements before day 14, (iii) no amputation beyond first debridement, (iv) modified sequential organ failure assessment score score (mSOFA) at day 14 ≤ 1. To be considered a success, all individual criteria must be met. Several data sets were used to assess validity: (i) a retrospective data set of 198 patients treated during 2013 at 12 US trauma centers; (ii) a subset with high disease acuity, admission mSOFA score of 3 or higher (n = 69); and (iii) 40 patients from a multicenter, phase 2 randomized trial of a CD28 immunomodulator (AB103). Clinical success based on each parameter and the composite score was assessed.

RESULTS

Using the retrospective data set for all patients and those with high disease severity (respectively), survival rates were 92% and 84%; day 14 mSOFA 1 or lower score was 69% and 51%; three or less debridements was 84% and 77%; and no subsequent amputations were 96% and 94%. Overall, the percent meeting all success criteria for NICCE was 58% (all patients) and 33% (mSOFA > 3). NICCE success was also associated with reduced utilization of health care resources, intensive care unit-free days were median (interquartile range) of 25.3 (21.9-28) and 19.6 (4.3-25.1) days (one-sided Wilcoxon p < 0.001) and ventilator-free days were 28 (26-28) versus 25 (14-28) (p < 0.001) for NICCE success versus failure, respectively. Using the phase 2 data set, the treated group (0.5 mg/kg, n = 15) demonstrated a NICCE success rate of 73.3% versus 40% for placebo (n = 10).

CONCLUSION

These data demonstrate internal consistency of the components and face and criterion validity of the NICCE endpoint. NICCE offers an opportunity to demonstrate a clinically relevant treatment effect for patients enrolled in clinical trials for necrotizing soft tissue infection.

LEVEL OF EVIDENCE

Prognostic/Epidemiological, level III; Therapeutic, level IV.

CD28 homodimer interface mimetic peptide acts as a preventive and therapeutic agent in models of severe bacterial sepsis and gram-negative bacterial peritonitis

BACKGROUND

Severe gram-negative bacterial infections and sepsis are major causes of morbidity and mortality. Dysregulated, excessive proinflammatory cytokine expression contributes to the pathogenesis of sepsis. A CD28 mimetic peptide (AB103; previously known as p2TA) that attenuates CD28 signaling and T-helper type 1 cytokine responses was tested for its ability to increase survival in models of polymicrobial infection and gram-negative sepsis.

METHODS

Mice received AB103, followed by an injection of Escherichia coli 0111:B4 lipopolysaccharide (LPS); underwent induction E. coli 018:K1 peritonitis induction, followed by treatment with AB103; or underwent cecal ligation and puncture (CLP), followed by treatment with AB103. The effects of AB103 on factors associated with and the lethality of challenge infections were analyzed.

RESULTS

AB103 strongly attenuated induction of tumor necrosis factor α and interleukin 6 (IL-6) by LPS in human peripheral blood mononuclear cells. Receipt of AB103 following intraperitoneal injection of LPS resulted in survival among 73% of CD1 mice (11 of 15), compared with 20% of controls (3 of 15). Suboptimal doses of antibiotic alone protected 20% of mice (1 of 5) from E. coli peritonitis, whereas 100% (15 of 15) survived when AB103 was added 4 hours following infection. Survival among mice treated with AB103 12 hours after CLP was 100% (8 of 8), compared with 17% among untreated mice (1 of 6). In addition, receipt of AB103 12 hours after CLP attenuated inflammatory cytokine responses and neutrophil influx into tissues and promoted bacterial clearance. Receipt of AB103 24 hours after CLP still protected 63% of mice (5 of 8).

CONCLUSIONS

Single-dose AB103 reduces mortality in experimental models of polymicrobial and gram-negative bacterial infection and sepsis, warranting further studies of this agent in clinical trials.

CD28: direct and critical receptor for superantigen toxins

Every adaptive immune response requires costimulation through the B7/CD28 axis, with CD28 on T-cells functioning as principal costimulatory receptor. Staphylococcal and streptococcal superantigen toxins hyperstimulate the T-cell-mediated immune response by orders of magnitude, inducing a lethal cytokine storm. We show that to elicit an inflammatory cytokine storm and lethality, superantigens must bind directly to CD28. Blocking access of the superantigen to its CD28 receptor with peptides mimicking the contact domains in either toxin or CD28 suffices to protect mice effectively from lethal shock. Our finding that CD28 is a direct receptor of superantigen toxins broadens the scope of microbial pathogen recognition mechanisms.

A peptide antagonist of CD28 signaling attenuates toxic shock and necrotizing soft-tissue infection induced by Streptococcus pyogenes

Staphylococcus aureus and group A Streptococcus pyogenes (GAS) express superantigen (SAg) exotoxin proteins capable of inducing lethal shock. To induce toxicity, SAgs must bind not only to the major histocompatibility complex II molecule of antigen-presenting cells and the variable β chain of the T-cell receptor but also to the dimer interface of the T-cell costimulatory receptor CD28. Here, we show that the CD28-mimetic peptide AB103 (originally designated "p2TA") protects mice from lethal challenge with streptococcal exotoxin A, as well as from lethal GAS bacterial infection in a murine model of necrotizing soft-tissue infection. Administration of a single dose of AB103 increased survival when given up to 5 hours after infection, reduced inflammatory cytokine expression and bacterial burden at the site of infection, and improved muscle inflammation in a dose-dependent manner, without compromising cellular and humoral immunity. Thus, AB103 merits further investigation as a potential therapeutic in SAg-mediated necrotizing soft-tissue infection.

Chimeric anti-staphylococcal enterotoxin B antibodies and lovastatin act synergistically to provide in vivo protection against lethal doses of SEB

Staphylococcal enterotoxin B (SEB) is one of a family of toxins secreted by Staphylococcus aureus that act as superantigens, activating a large fraction of the T-cell population and inducing production of high levels of inflammatory cytokines that can cause toxic shock syndrome (TSS) and death. Extracellular engagement of the TCR of T-cells and class II MHC of antigen presenting cells by SEB triggers the activation of many intracellular signaling processes. We engineered chimeric antibodies to block the extracellular engagement of cellular receptors by SEB and used a statin to inhibit intracellular signaling. Chimeric human-mouse antibodies directed against different neutralizing epitopes of SEB synergistically inhibited its activation of human T-cells in vitro. In the in vivo model of lethal toxic shock syndrome (TSS) in HLA-DR3 transgenic mice, two of these antibodies conferred significant partial protection when administered individually, but offered complete protection in a synergistic manner when given together. Similarly, in vivo, lovastatin alone conferred only partial protection from TSS similar to single anti-SEB antibodies. However, used in combination with one chimeric neutralizing anti-SEB antibody, lovastatin provided complete protection against lethal TSS in HLA-DR3 transgenic mice. These experiments demonstrate that in vivo protection against lethal doses of SEB can be achieved by a statin of proven clinical safety and chimeric human-mouse antibodies, agents now widely used and known to be of low immunogenicity in human hosts.

Binding of superantigen toxins into the CD28 homodimer interface is essential for induction of cytokine genes that mediate lethal shock

Bacterial superantigens, a diverse family of toxins, induce an inflammatory cytokine storm that can lead to lethal shock. CD28 is a homodimer expressed on T cells that functions as the principal costimulatory ligand in the immune response through an interaction with its B7 coligands, yet we show here that to elicit inflammatory cytokine gene expression and toxicity, superantigens must bind directly into the dimer interface of CD28. Preventing access of the superantigen to CD28 suffices to block its lethality. Mice were protected from lethal superantigen challenge by short peptide mimetics of the CD28 dimer interface and by peptides selected to compete with the superantigen for its binding site in CD28. Superantigens use a conserved β-strand/hinge/α-helix domain of hitherto unknown function to engage CD28. Mutation of this superantigen domain abolished inflammatory cytokine gene induction and lethality. Structural analysis showed that when a superantigen binds to the T cell receptor on the T cell and major histocompatibility class II molecule on the antigen-presenting cell, CD28 can be accommodated readily as third superantigen receptor in the quaternary complex, with the CD28 dimer interface oriented towards the β-strand/hinge/α-helix domain in the superantigen. Our findings identify the CD28 homodimer interface as a critical receptor target for superantigens. The novel role of CD28 as receptor for a class of microbial pathogens, the superantigen toxins, broadens the scope of pathogen recognition mechanisms.

Gram-positive bacterial superantigen outside-in signaling causes toxic shock syndrome

Staphylococcus aureus and Streptococcus pyogenes (group A streptococci) are Gram-positive pathogens capable of producing a variety of bacterial exotoxins known as superantigens. Superantigens interact with antigen-presenting cells (APCs) and T cells to induce T cell proliferation and massive cytokine production, which leads to fever, rash, capillary leak and subsequent hypotension, the major symptoms of toxic shock syndrome. Both S. aureus and group A streptococci colonize mucosal surfaces, including the anterior nares and vagina for S. aureus, and the oropharynx and less commonly the vagina for group A streptococci. However, due to their abilities to secrete a variety of virulence factors, the organisms can also cause illnesses from the mucosa. This review provides an updated discussion of the biochemical and structural features of one group of secreted virulence factors, the staphylococcal and group A streptococcal superantigens, and their abilities to cause toxic shock syndrome from a mucosal surface. The main focus of this review, however, is the abilities of superantigens to induce cytokines and chemokines from epithelial cells, which has been linked to a dodecapeptide region that is relatively conserved among all superantigens and is distinct from the binding sites required for interactions with APCs and T cells. This phenomenon, termed outside-in signaling, acts to recruit adaptive immune cells to the submucosa, where the superantigens can then interact with those cells to initiate the final cytokine cascades that lead to toxic shock syndrome.

Generation, characterization, and epitope mapping of neutralizing and protective monoclonal antibodies against staphylococcal enterotoxin B-induced lethal shock

T-cell stimulating activity of Staphylococcal enterotoxin B (SEB) is an important factor in the pathogenesis of certain staphylococcal diseases including SEB mediated shock. SEB is one of the most potent superantigens known and treatment of SEB induced shock remains a challenge. We generated and characterized murine monoclonal antibodies (mAbs) to SEB in mice. We tested mAbs neutralize mitogenic effects of SEB in vitro and in vivo with T-cell proliferation assays and 2 murine models for SEB induced lethal shock (SEBILS). Epitope mapping suggests that all these mAbs recognize conformational epitopes that are destroyed by deleting the C terminus of the protein. Further site-directed mutagenesis identified potential residues involved in binding to SEB that differ between Methicillin resistant and sensitive Staphylococcus aureus strains. Only mAb 20B1 was effective as a monotherapy in treating SEBILS in HLA DR3 transgenic mice, which exhibit enhanced sensitivity to SEB. It is noteworthy that mAbs, 14G8 and 6D3 were not protective when given alone in the HLA DR3 mice but their efficacy of protection could be greatly enhanced when mAbs were co-administered simultaneously. Our data suggest combinations of defined mAbs may constitute a better treatment strategy and provide a new insight for the development of passive immunotherapy.

Potent neutralization of staphylococcal enterotoxin B by synergistic action of chimeric antibodies

Staphylococcal enterotoxin B (SEB), a shock-inducing exotoxin synthesized by Staphylococcus aureus, is an important cause of food poisoning and is a class B bioterrorism agent. SEB mediates antigen-independent activation of a major subset of the T-cell population by cross-linking T-cell receptors (TCRs) with class II major histocompatibility complex (MHC-II) molecules of antigen-presenting cells, resulting in the induction of antigen independent proliferation and cytokine secretion by a significant fraction of the T-cell population. Neutralizing antibodies inhibit SEB-mediated T-cell activation by blocking the toxin's interaction with the TCR or MHC-II and provide protection against the debilitating effects of this superantigen. We derived and searched a set of monoclonal mouse anti-SEB antibodies to identify neutralizing anti-SEB antibodies that bind to different sites on the toxin. A pair of non-cross-reactive, neutralizing anti-SEB monoclonal antibodies (MAbs) was found, and a combination of these antibodies inhibited SEB-induced T-cell proliferation in a synergistic rather than merely additive manner. In order to engineer antibodies more suitable than mouse MAbs for use in humans, the genes encoding the VL and VH gene segments of a synergistically acting pair of mouse MAbs were grafted, respectively, onto genes encoding the constant regions of human Igkappa and human IgG1, transfected into mammalian cells, and used to generate chimeric versions of these antibodies that had affinity and neutralization profiles essentially identical to their mouse counterparts. When tested in cultures of human peripheral blood mononuclear cells or splenocytes derived from HLA-DR3 transgenic mice, the chimeric human-mouse antibodies synergistically neutralized SEB-induced T-cell activation and cytokine production.

Contribution of each of four Superantigens to Streptococcus equi-induced mitogenicity, gamma interferon synthesis, and immunity

Streptococcus equi is the causative agent of strangles, the most frequently diagnosed infectious disease of horses worldwide. The disease is characterized by abscessation and swelling of the lymph nodes of the head and neck, which can literally strangle the horse to death. S. equi produces four recently acquired phage-associated bacterial superantigens (sAgs; SeeH, SeeI, SeeL, and SeeM) that share homology with the mitogenic toxins of Streptococcus pyogenes. The aim of this study was to characterize the contribution of each of these S. equi sAgs to mitogenic activity in vitro and quantify the sAg-neutralizing capacity of sera from naturally infected horses in order to better understand their role in pathogenicity. Each of the sAgs was successfully cloned, and soluble proteins were produced in Escherichia coli. SeeI, SeeL, and SeeM induced a dose-dependent proliferative response in equine CD4 T lymphocytes and synthesis of gamma interferon (IFN-gamma). SeeH did not stimulate equine peripheral blood mononuclear cells (PBMC) but induced proliferation of asinine PBMC. Allelic replacement mutants of S. equi strain 4047 with sequential deletion of the superantigen genes were generated. Deletion of seeI, seeL, and seeM completely abrogated the mitogenic activity and synthesis of IFN-gamma, in equine PBMC, of the strain 4047 culture supernatant. Sera from naturally infected convalescent horses had only limited sAg-neutralizing activities. We propose that S. equi sAgs play an important role in S. equi pathogenicity by stimulating an overzealous and inappropriate Th1 response that may interfere with the development of an effective immune response.

A probiotic strain of Escherichia coli, Nissle 1917, given orally exerts local and systemic anti-inflammatory effects in lipopolysaccharide-induced sepsis in mice

BACKGROUND AND PURPOSE

Escherichia coli Nissle 1917 is a probiotic strain used in the treatment of intestinal immune diseases, including ulcerative colitis. The aim of the present study was to test if this probiotic bacterium can also show systemic immunomodulatory properties after oral administration.

EXPERIMENTAL APPROACH

The probiotic strain was administered to rats or mice for 2 weeks before its assay in two experimental models of altered immune response, the trinitrobenzenesulphonic acid (TNBS) model of rat colitis, localized in the colon, and the lipopolysaccharide (LPS) model of systemic septic shock in mice. Inflammatory status was evaluated both macroscopically and biochemically after 1 week in the TNBS model or after 24 h in the LPS shock model. In addition, splenocytes were obtained from mice and stimulated, ex vivo, with concanavalin A or LPS to activate T or B cells, respectively, and cytokine production (IL-2, IL-5 and IL-10) by T cells and IgG secretion by B cells measured.

KEY RESULTS

E. coli Nissle 1917 was anti-inflammatory in both models of altered immune response. This included a reduction in the pro-inflammatory cytokine tumour necrosis factor-alpha both in the intestine from colitic rats, and in plasma and lungs in mice treated with LPS. The systemic beneficial effect was associated with inhibited production of the T cell cytokines and by down-regulation of IgG release from splenocyte-derived B cells.

CONCLUSIONS AND IMPLICATIONS

The anti-inflammatory effects of E. coli Nissle 1917 given orally were not restricted to the gastrointestinal tract.

Novel toxic shock syndrome toxin-1 amino acids required for biological activity

Superantigens interact with T lymphocytes and macrophages to cause T lymphocyte proliferation and overwhelming cytokine production, which lead to toxic shock syndrome. Staphylococcus aureus superantigen toxic shock syndrome toxin-1 is a major cause of menstrual toxic shock syndrome. In general, superantigen-secreting S. aureus remains localized at the vaginal surface, and the superantigen must therefore penetrate the vaginal mucosa to interact with underlying immune cells to cause toxic shock syndrome. A dodecapeptide region (toxic shock syndrome toxin-1 amino acids F119-D130), relatively conserved among superantigens, has been implicated in superantigen penetration of the epithelium. The purpose of this study was to determine amino acids within this dodecapeptide region that are required for interaction with vaginal epithelium. Alanine mutations were constructed in S. aureus toxic shock syndrome toxin-1 amino acids D120 to D130. All mutants maintained superantigenicity, and selected mutants were lethal when given intravenously to rabbits. Toxic shock syndrome toxin-1 induces interleukin-8 from immortalized human vaginal epithelial cells; however, three toxin mutants (S127A, T128A, and D130A) induced low levels of interleukin-8 compared to wild type toxin. When carboxy-terminal mutants (S127A to D130A) were administered vaginally to rabbits, D130A was nonlethal, while S127A and T128A demonstrated delayed lethality compared to wild type toxin. In a porcine ex vivo permeability model, mutant D130A penetrated the vaginal mucosa more quickly than wild type toxin. Toxic shock syndrome toxin-1 residue D130 may contribute to binding an epithelial receptor, which allows it to penetrate the vaginal mucosa, induce interleukin-8, and cause toxic shock syndrome.

Staphylococcal enterotoxin B in vivo modulates both gamma interferon receptor expression and ligand-induced activation of signal transducer and activator of transcription 1 in T cells

Superantigens (SAg) are bacterial exotoxins that provoke extreme responses in the immune system; for example, the acute hyperactivation of SAg-reactive T cells that leads to toxic shock syndrome is followed within days by strong immunosuppression. The gamma interferon (IFN-gamma) response is deeply affected in both extremes. The implication of IFN-gamma in the pathophysiology of lethal shock induced in mice after a secondary challenge with the SAg staphylococcal enterotoxin B (SEB) prompted us to study the regulation of IFN-gamma secretion and the intracellular response. We demonstrate in this study that a rechallenge with SEB becomes lethal only when given inside a critical time window after SEB priming and is associated with an increase of IFN-gamma serum release 72 h after priming. However, at this time, a selective blockade of IFN-gamma/STAT1 signaling develops in spleen cells, correlating with a lack of expression of the IFN-gamma receptor beta subunit and STAT1 in the T-cell population. Selective blockade of the STAT1 signaling pathway--while simultaneously maintaining STAT3 signaling and expression--may be a protective mechanism that shortens IFN-gamma production during the Th1 effector response. This blockade may also have consequences on switching towards a suppressor phenotype with chronic exposure to the superantigen.

Dynamics of the immune response against extracellular products of group A streptococci during infection

The immune response against the infecting group A streptococcus (GAS) extracellular products (EP) was determined in acute- and convalescent-phase sera from 75 patients with different clinical manifestations of GAS infection. All EP elicited a high proliferative response in human peripheral blood mononuclear cells. In patients with bacteremia, low neutralization in acute-phase sera was associated with development of streptococcal toxic shock syndrome. Lack of neutralization in acute-phase sera was more common in patients infected with the T1emm1 serotype. The majority of patients did not develop the ability to neutralize the mitogenic activity of their infecting isolate despite a significant increase in enzyme-linked immunosorbent assay titer in early convalescent-phase sera. In patients with the ability to neutralize GAS EP, the immune response remained high over at least 3 years. In contrast, the neutralization capacity conferred by intravenous immunoglobulin and/or plasma treatment disappeared within 3 months.

Therapies for necrotising fasciitis

Necrotising fasciitis is a rare but life-threatening infectious disease emergency. Delays in diagnosis and treatment are common, and mortality rates often exceed 30%. Successful management of this disease requires high clinical suspicion and aggressive action. The mainstays of therapy include early and wide surgical debridement, antibiotics and supportive care, with prompt surgical intervention. Adjunctive modalities, such as protein synthesis inhibitors, hyperbaric oxygen and intravenous immunoglobulin, may have a role, but their effectiveness remains unproven. New rapid diagnostic tools are emerging that promise to revolutionize early detection of necrotising fasciitis. Research into the molecular microbiology, especially regarding group A streptococcus, are providing novel insights into the pathogenesis of necrotising soft tissue infections and identifying future targets for rationally designed interventions.

Necrotizing fasciitis: pathogenesis and treatment

Necrotizing fasciitis is a rapidly progressive, life-threatening infection and a true infectious disease emergency. Despite much clinical experience, the management of this disease remains suboptimal, with mortality rates remaining approximately 30%. Necrotizing fasciitis rarely presents with obvious signs and symptoms and delays in diagnosis enhance mortality. Therefore, successful patient care depends on the physician's acumen and index of suspicion. Prompt surgical debridement, intravenous antibiotics, fluid and electrolyte management, and analgesia are mainstays of therapy. Adjunctive clindamycin, hyperbaric oxygen therapy and intravenous immunoglobulin are frequently employed in the treatment of necrotizing fasciitis, but their efficacy has not been rigorously established. Improved understanding of the pathogenesis of necrotizing fasciitis has revealed new targets for rationally designed therapies to improve morbidity and mortality.

In vitro and in vivo evaluation of staphylococcal superantigen peptide antagonists

Superantigen peptide antagonists failed to block T-cell activation and cytokine production as well as toxic shock induced by staphylococcal enterotoxin B (SEB) in HLA class II transgenic mice. They also failed to inhibit the binding of SEB to HLA class II molecules as well as activation of human T lymphocytes in vitro.