Role of substance P in immediate-type skin reactions induced by staphylococcal enterotoxin B in unsensitized monkeys

Exploring the Role of Staphylococcus aureus in Inflammatory Diseases

Staphylococcus aureus is a very common Gram-positive bacterium, and S. aureus infections play an extremely important role in a variety of diseases. This paper describes the types of virulence factors involved, the inflammatory cells activated, the process of host cell death, and the associated diseases caused by S. aureus. S. aureus can secrete a variety of enterotoxins and other toxins to trigger inflammatory responses and activate inflammatory cells, such as keratinocytes, helper T cells, innate lymphoid cells, macrophages, dendritic cells, mast cells, neutrophils, eosinophils, and basophils. Activated inflammatory cells can express various cytokines and induce an inflammatory response. S. aureus can also induce host cell death through pyroptosis, apoptosis, necroptosis, autophagy, etc. This article discusses S. aureus and MRSA (methicillin-resistant S. aureus) in atopic dermatitis, psoriasis, pulmonary cystic fibrosis, allergic asthma, food poisoning, sarcoidosis, multiple sclerosis, and osteomyelitis. Summarizing the pathogenic mechanism of Staphylococcus aureus provides a basis for the targeted treatment of Staphylococcus aureus infection.

Basis of Virulence in Enterotoxin-Mediated Staphylococcal Food Poisoning

The Staphylococcus aureus enterotoxins are a superfamily of secreted virulence factors that share structural and functional similarities and possess potent superantigenic activity causing disruptions in adaptive immunity. The enterotoxins can be separated into two groups; the classical (SEA-SEE) and the newer (SEG-SElY and counting) enterotoxin groups. Many members from both these groups contribute to the pathogenesis of several serious human diseases, including toxic shock syndrome, pneumonia, and sepsis-related infections. Additionally, many members demonstrate emetic activity and are frequently responsible for food poisoning outbreaks. Due to their robust tolerance to denaturing, the enterotoxins retain activity in food contaminated previously with S. aureus. The genes encoding the enterotoxins are found mostly on a variety of different mobile genetic elements. Therefore, the presence of enterotoxins can vary widely among different S. aureus isolates. Additionally, the enterotoxins are regulated by multiple, and often overlapping, regulatory pathways, which are influenced by environmental factors. In this review, we also will focus on the newer enterotoxins (SEG-SElY), which matter for the role of S. aureus as an enteropathogen, and summarize our current knowledge on their prevalence in recent food poisoning outbreaks. Finally, we will review the current literature regarding the key elements that govern the complex regulation of enterotoxins, the molecular mechanisms underlying their enterotoxigenic, superantigenic, and immunomodulatory functions, and discuss how these activities may collectively contribute to the overall manifestation of staphylococcal food poisoning.

Monkey Feeding Assay for Testing Emetic Activity of Staphylococcal Enterotoxin

Staphylococcal enterotoxins (SEs) are unique bacterial toxins that cause gastrointestinal toxicity as well as superantigenic activity. Since systemic administration of SEs induces superantigenic activity leading to toxic shock syndrome that may mimic enterotoxic activity of SEs such as vomiting and diarrhea, oral administration of SEs in the monkey feeding assay is considered as a standard method to evaluate emetic activity of SEs. This chapter summarizes and discusses practical considerations of the monkey feeding assay used in studies characterizing classical and newly identified SEs.

Staphylococcal Superantigens Spark Host-Mediated Danger Signals

Staphylococcal enterotoxin B (SEB) of Staphylococcus aureus, and related superantigenic toxins produced by myriad microbes, are potent stimulators of the immune system causing a variety of human diseases from transient food poisoning to lethal toxic shock. These protein toxins bind directly to specific Vβ regions of T-cell receptors (TCR) and major histocompatibility complex (MHC) class II on antigen-presenting cells, resulting in hyperactivation of T lymphocytes and monocytes/macrophages. Activated host cells produce excessive amounts of proinflammatory cytokines and chemokines, especially tumor necrosis factor α, interleukin 1 (IL-1), IL-2, interferon γ (IFNγ), and macrophage chemoattractant protein 1 causing clinical symptoms of fever, hypotension, and shock. Because of superantigen-induced T cells skewed toward TH1 helper cells, and the induction of proinflammatory cytokines, superantigens can exacerbate autoimmune diseases. Upon TCR/MHC ligation, pathways induced by superantigens include the mitogen-activated protein kinase cascades and cytokine receptor signaling, resulting in activation of NFκB and the phosphoinositide 3-kinase/mammalian target of rapamycin pathways. Various mouse models exist to study SEB-induced shock including those with potentiating agents, transgenic mice and an “SEB-only” model. However, therapeutics to treat toxic shock remain elusive as host response genes central to pathogenesis of superantigens have only been identified recently. Gene profiling of a murine model for SEB-induced shock reveals novel molecules upregulated in multiple organs not previously associated with SEB-induced responses. The pivotal genes include intracellular DNA/RNA sensors, apoptosis/DNA damage-related molecules, immunoproteasome components, as well as antiviral and IFN-stimulated genes. The host-wide induction of these, and other, antimicrobial defense genes provide evidence that SEB elicits danger signals resulting in multi-organ damage and toxic shock. Ultimately, these discoveries might lead to novel therapeutics for various superantigen-based diseases.

Bacterial Toxins-Staphylococcal Enterotoxin B

Staphylococcal enterotoxin B is one of the most potent bacterial superantigens that exerts profound toxic effects upon the immune system, leading to stimulation of cytokine release and inflammation. It is associated with food poisoning, nonmenstrual toxic shock, atopic dermatitis, asthma, and nasal polyps in humans. Currently, there is no treatment or vaccine available. Passive immunotherapy using monoclonal antibodies made in several different species has shown significant inhibition in in vitro studies and reduction in staphylococcal enterotoxin B-induced lethal shock in in vivo studies. This should encourage future endeavors to develop these antibodies as therapeutic reagents.

Multifaceted interactions of bacterial toxins with the gastrointestinal mucosa

The digestive tract is one of the ecosystems that harbors the largest number and greatest variety of bacteria. Among them, certain bacteria have developed various strategies, including the synthesis of virulence factors such as toxins, to interact with the intestinal mucosa, and are responsible for various pathologies. A large variety of bacterial toxins of different sizes, structures and modes of action are able to interact with the gastrointestinal mucosa. Some toxins, termed enterotoxins, directly stimulate fluid secretion in enterocytes or cause their death, whereas other toxins pass through the intestinal barrier and disseminate by the general circulation to remote organs or tissues, where they are active. After recognition of a membrane receptor on target cells, toxins can act at the cell membrane by transducing a signal across the membrane in a hormone-like manner, by pore formation or by damaging membrane compounds. Other toxins can enter the cells and modify an intracellular target leading to a disregulation of certain physiological processes or disorganization of some structural architectures and cell death. Toxins are fascinating molecules, which mimic or interfere with eukaryotic physiological processes. Thereby, they have permitted the identification and characterization of new natural hormones or regulatory pathways. Besides use as protective antigens in vaccines, toxins offer multiple possibilities in pharmacology, such as immune modulation or specific delivery of a protein of interest into target cells.

Therapeutic down-modulators of staphylococcal superantigen-induced inflammation and toxic shock

Staphylococcal enterotoxin B (SEB) and related superantigenic toxins are potent stimulators of the immune system and cause a variety of diseases in humans, ranging from food poisoning to toxic shock. These toxins bind directly to major histocompatibility complex (MHC) class II molecules on antigen-presenting cells and specific Vβ regions of T-cell receptors (TCR), resulting in hyperactivation of both monocytes/macrophages and T lymphocytes. Activated host cells produce massive amounts of proinflammatory cytokines and chemokines, activating inflammation and coagulation, causing clinical symptoms that include fever, hypotension, and shock. This review summarizes the in vitro and in vivo effects of staphylococcal superantigens, the role of pivotal mediators induced by these toxins in the pathogenic mechanisms of tissue injury, and the therapeutic agents to mitigate the toxic effects of superantigens.

Food poisoning and Staphylococcus aureus enterotoxins

Staphylococcus aureus produces a wide variety of toxins including staphylococcal enterotoxins (SEs; SEA to SEE, SEG to SEI, SER to SET) with demonstrated emetic activity, and staphylococcal-like (SEl) proteins, which are not emetic in a primate model (SElL and SElQ) or have yet to be tested (SElJ, SElK, SElM to SElP, SElU, SElU2 and SElV). SEs and SEls have been traditionally subdivided into classical (SEA to SEE) and new (SEG to SElU2) types. All possess superantigenic activity and are encoded by accessory genetic elements, including plasmids, prophages, pathogenicity islands, vSa genomic islands, or by genes located next to the staphylococcal cassette chromosome (SCC) implicated in methicillin resistance. SEs are a major cause of food poisoning, which typically occurs after ingestion of different foods, particularly processed meat and dairy products, contaminated with S. aureus by improper handling and subsequent storage at elevated temperatures. Symptoms are of rapid onset and include nausea and violent vomiting, with or without diarrhea. The illness is usually self-limiting and only occasionally it is severe enough to warrant hospitalization. SEA is the most common cause of staphylococcal food poisoning worldwide, but the involvement of other classical SEs has been also demonstrated. Of the new SE/SEls, only SEH have clearly been associated with food poisoning. However, genes encoding novel SEs as well as SEls with untested emetic activity are widely represented in S. aureus, and their role in pathogenesis may be underestimated.

Bacterial toxins and the nervous system: neurotoxins and multipotential toxins interacting with neuronal cells

Toxins are potent molecules used by various bacteria to interact with a host organism. Some of them specifically act on neuronal cells (clostridial neurotoxins) leading to characteristics neurological affections. But many other toxins are multifunctional and recognize a wider range of cell types including neuronal cells. Various enterotoxins interact with the enteric nervous system, for example by stimulating afferent neurons or inducing neurotransmitter release from enterochromaffin cells which result either in vomiting, in amplification of the diarrhea, or in intestinal inflammation process. Other toxins can pass the blood brain barrier and directly act on specific neurons.

Pre-exposure to Staphylococcal enterotoxin A exacerbates the pulmonary allergic eosinophil recruitment in rats

Gram-positive Staphylococcus aureus releases classical enterotoxins which aggravates allergic airway diseases. However, little is known about the mechanisms underlying the cell influx exacerbation in asthmatic individuals under exposure to Staphylococcal enterotoxins. We therefore aimed to investigate the effects of airways exposure to Staphylococcal enterotoxin A (SEA) to pulmonary leukocyte recruitment in rats sensitized and challenged with ovalbumin (OVA). Rats were exposed to SEA at 4h prior to OVA challenge or at 4h post-OVA challenge. Bronchoalveolar lavage (BAL) fluid, bone marrow and lung tissue were obtained at 24h after OVA challenge. Pre-exposure to SEA markedly enhanced the eosinophil counts in both BAL fluid and pulmonary tissue in OVA-challenged rats, whereas neutrophil and mononuclear cell counts remained unchanged. In bone marrow, pre-exposure to SEA alone significantly increased the number of eosinophils, and that was further increased in OVA-challenged rats. Exposure to SEA post-OVA challenge did not affect the number of eosinophils, neutrophils and mononuclear cells in BAL fluid. Pre-exposure to the endotoxin lipopolyssacharide (LPS) in OVA-challenged animals rather enhanced the neutrophil number in BAL fluid. In rats pre-exposed to SEA and OVA-challenged, a marked elevation in the levels of TNF-alpha and eotaxin (but not of IL-10) in BAL fluid was observed. The eotaxin levels increased by about of 3-fold in alveolar macrophages treated with SEA in vitro. In conclusion, airways pre-exposure to SEA causes a selective increase in eosinophil number in BAL fluid and bone marrow of OVA-challenged rats by mechanisms involving enhancement of TNF-alpha and eotaxin synthesis.

Involvement of tumour necrosis factor-alpha in Clostridium perfringens beta-toxin-induced plasma extravasation in mice

BACKGROUND AND PURPOSE

Clostridium perfringens beta-toxin, an important agent of necrotic enteritis, causes plasma extravasation due to the release of a tachykinin NK(1) receptor agonist in mouse skin. In this study, we investigated the role of cytokines in beta-toxin-induced plasma extravasation.

EXPERIMENTAL APPROACH

Male Balb/c, C3H/HeN and C3H/HeJ mice were anaesthetized with pentobarbitone and beta-toxin was injected i.d. into shaved dorsal skin. SR140333, capsaicin, chlorpromazine and pentoxifylline were given as pretreatment when required before the injection of the toxin. Cytokines in the dorsal skin were measured by ELISA.

KEY RESULTS

Injection (i.d.) of beta-toxin induced a dose-dependent increase in dermal TNF-alpha and interleukin (IL)-1beta levels with a concomitant increase in plasma extravasation, but not the release of IL-6. SR140333 and capsaicin significantly inhibited the toxin-induced release of TNF-alpha and IL-1beta. The plasma extravasation and the release of TNF-alpha induced by beta-toxin were significantly inhibited by chlorpromazine and pentoxifylline which inhibit the release of TNF-alpha. The toxin-induced plasma extravasation in mouse skin was attenuated by pretreatment with a monoclonal antibody against TNF-alpha, but not anti-IL-1beta. Furthermore, the toxin caused an increase in plasma extravasation in both C3H/HeN (TLR4-intact) and C3H/HeJ (TLR4-deficient) mice. In C3H/HeN mice, the toxin-induced leakage was not inhibited by pretreatment with anti-TLR4/MD-2 antibody.

CONCLUSIONS AND IMPLICATIONS

These observations show that beta-toxin-induced plasma extravasation in mouse skin is related to the release of TNF-alpha via the mechanism involving tachykinin NK(1) receptors, but not via TLR4.

A polymorphism of MS4A2 (- 109T > C) encoding the beta-chain of the high-affinity immunoglobulin E receptor (FcepsilonR1beta) is associated with a susceptibility to aspirin-intolerant asthma

BACKGROUND AND OBJECTIVE

The MS4A2 gene, the beta chain of the high-affinity receptor for immunoglobulin (Ig)E, has previously been linked to atopy and asthma. The beta-chain of FcepsilonR1 enhances receptor maturation and signal transduction capacity, leading to the release of proinflammatory mediators and cytokines that can exacerbate the symptom of asthma. This study was performed to evaluate whether two genetic polymorphisms of the FcepsilonR1beta gene (FcepsilonR1beta-109T > C and FcepsilonR1beta E237G) are associated with aspirin-intolerant asthma (AIA). The MS4A2 gene polymorphisms (FcepsilonR1beta-109T > C and FcepsilonR1beta E237G) were determined by SNP-IT assays in patients with AIA (N = 164), aspirin-tolerant asthma (ATA, N = 144) and normal controls (NC, N = 264) recruited from a Korean population.

RESULTS

The genotype frequencies of FcepsilonR1beta-109T > C and E237G polymorphisms were not significantly associated with the pathogenesis of AIA. However, FcepsilonR1beta-109T > C polymorphism was significantly associated with the presence of specific IgE to Staphylococcal enterotoxin B (SEB); the number of subjects carrying both homozygous TT genotype of FcepsilonR1beta-109T > C and specific IgE to SEB was significantly higher in the AIA group when compared with the other control groups (P = 0.01, odds ratio (OR) = 7.723, 95% confidence interval (CI) = 1.327-39.860 for AIA vs. ATA; P = 0.02, OR = 6.364, 95% CI = 1.149 approximately 35.229 for AIA vs. NC). In addition, luciferase reporter assays also showed that the FcepsilonR1beta-109T allele was associated with higher promoter activity of MS4A2 in both RBL-2H3 and A549 cell lines.

CONCLUSION

FcepsilonR1beta-109T > C polymorphism may increase expression of MS4A2 by mast cells, leading to enhanced release of proinflammatory mediators in the asthmatic airway, contributing to increased susceptibility to AIA.

Involvement of tachykinin receptors in Clostridium perfringens beta-toxin-induced plasma extravasation

1 Clostridium perfringens beta-toxin causes dermonecrosis and oedema in the dorsal skin of animals. In the present study, we investigated the mechanisms of oedema induced by the toxin. 2 The toxin induced plasma extravasation in the dorsal skin of Balb/c mice. 3 The extravasation was significantly inhibited by diphenhydramine, a histamine 1 receptor antagonist. However, the toxin did not cause the release of histamine from mouse mastocytoma cells. 4 Tachykinin NK(1) receptor antagonists, [D-Pro(2), D-Trp(7,9)]-SP, [D-Pro(4), D-Trp(7,9)]-SP and spantide, inhibited the toxin-induced leakage in a dose-dependent manner. Furthermore, the non-peptide tachykinin NK(1) receptor antagonist, SR140333, markedly inhibited the toxin-induced leakage. 5 The leakage induced by the toxin was markedly reduced in capsaicin-pretreated mouse skin but the leakage was not affected by systemic pretreatment with a calcitonin gene-related peptide receptor antagonist (CGRP(8-37)). 6 The toxin-induced leakage was significantly inhibited by the N-type Ca(2+) channel blocker, omega-conotoxin MVIIA, and the bradykinin B(2) receptor antagonist, HOE140 (D-Arg-[Hyp(3), Thi(5), D-Tic(7), Oic(8)]-bradykinin), but was not affected by the selective L-type Ca(2+) channel blocker, verapamil, the P-type Ca(2+) channel blocker, omega-agatoxin IVA, tetrodotoxin (TTX), the TTX-resistant Na(+) channel blocker, carbamazepine, or the sensory nerve conduction blocker, lignocaine. 7 These results suggest that plasma extravasation induced by beta-toxin in mouse skin is mediated via a mechanism involving tachykinin NK(1) receptors.

Evidence for the involvement of a macrophage-derived chemotactic mediator in the neutrophil recruitment induced by staphylococcal enterotoxin B in mice

Staphylococcus aureus secretes enterotoxins which are superantigens and the major cause of food poisoning in man. Staphylococcal enterotoxins types A and B can induce neutrophil migration into the peritoneal cavity of mice through sensory C-fiber neuropeptides, lipoxygenase or cyclooxygenase metabolites, nitric oxide, histamine, platelet-activating factor and resident macrophages. In this work, we examined the influence of macrophage-derived products on neutrophil migration during peritonitis induced by staphylococcal enterotoxin type B (SEB) in mice. Macrophages stimulated with SEB released a thermolabile neutrophil chemotactic protein with a molecular weight of 1,000-3,000 (by ultrafiltration). This release was inhibited 30% by dexamethasone (an inhibitor of cytokine synthesis and phospholipase A(2) activity), but not by indomethacin (a cyclooxygenase inhibitor) or BW755C (a dual cyclo- and lipoxygenase inhibitor). Dexamethasone also inhibited (100%) the neutrophil migration induced by the chemotactic protein. Similar inhibition occurred in mice pretreated with BWA4C (lipoxygenase inhibitor; 90%), BW755C (99%), BN52021 (platelet-activating factor-acether receptor antagonist; 93%), cimetidine (histamine H(2) receptor antagonist; 76%), capsaicin (a depletor of sensory C-fiber neuropeptides; 82%) and the neurokinin-1 receptor antagonist SR140333 (71%), but not by indomethacin or the neurokinin(2) receptor antagonist SR48968. These results confirm that macrophages are involved in the neutrophil recruitment induced by SEB, and that the chemotactic protein apparently induces neutrophil migration by a mechanism mediated by platelet-activating factor, histamine H(2) receptors, lipoxygenase products and substance P.

Lack of muco-cutaneous signs of toxic shock syndrome when T cells are absent: S. aureus shock in immunodeficient adults with multiple myeloma

Staphylococcal toxic shock syndrome (TSS) is an acute life threatening disease. The diagnosis can be made clinically based on diagnostic criteria. The clinical manifestations are caused in large part by there lease of high levels of T-cell-derived cytokines as a result of potent toxins, also called superantigens (SAg), produced by Staphylococcus aureus, but it is not clear which clinical symptoms/signs are strictly T-cell dependent. Here, we report on three adults with multiple myeloma (MM) presenting with S.aureus sepsis/shock, and two patients with typical TSS. The MM patients had compromised humoral immunity because of depression of normal immunoglobulin (Ig) levels at the expense of the M protein. In addition, their T cells were absent due to high dose chemotherapy initiated for bone marrow trans-plantation. The MM cases lacked mucosal hyperemia, erythroderma and desquamation, but were otherwise indistinguishable from the TSS cases. All patients grew S. aureus and in each case, SAg genes were detected by PCR. In several cases, the plasma contained biological SAg activity resulting in VP specific proliferation of indicator T cells in vitro. The same specific activity was observed with the supernatant fluids of S. aureus broth cultures from the respective bacterial isolates. This confirms the presence of bio-active toxins in the plasma but did not lead to full blown TSS when T cells were lacking.Thus, S. aureus sepsis/shock can be clinically distinguished from typical TSS, and we suggest that mucocutaneous manifestations of TSS are the most telling signs of massive T-cell-dependent cytokine release.

Involvement of kinins, mast cells and sensory neurons in the plasma exudation and paw oedema induced by staphylococcal enterotoxin B in the mouse

Intraplantar injection of staphylococcal enterotoxin B induces long-lasting oedema mediated by both cyclooxygenase and lipoxygenase products as well as by neuropeptides from sensory nerves. This study was undertaken to further clarify the role of peripheral primary afferent sensory nerves in staphylococcal enterotoxin B (25 microg/paw)-induced plasma extravasation and oedema formation. The tachykinin NK(1) receptor antagonist (S)-1-[2-[3-(3, 4-dichlorophenyl)-1 (3-isopropoxyphenylacetyl)piperidin-3-yl] ethyl]-4-phenyl-1 azoniabicyclo [2.2.2]octane cloride (SR140333; 120 nmol/kg, s.c.+120 nmol/kg, i.v.) significantly inhibited plasma exudation and paw oedema evoked by staphylococcal enterotoxin B. The tachykinin NK(2) receptor antagonist (S)-N-methyl-N[4-(4-acetylamino-4-phenyl piperidino)-2-(3, 4-dichlorophenyl)butyl]-benzamide (SR48968) had no effect on the staphylococcal enterotoxin B-induced responses. The bradykinin B(2) receptor antagonist D-Arg-[Hyp(3),Thi(5),D-Tic(7),Oic(8)]bradykinin (Hoe 140; 400 nmol/kg, i.v.) significantly reduced staphylococcal enterotoxin B-induced responses. The magnitude of the inhibition observed with Hoe 140 alone was similar to that caused by concomitant treatment of animals with SR140333 and Hoe 140, suggesting that there is a final common pathway. Additionally, SR140333 given alone reduced bradykinin (3 nmol/paw)-induced paw oedema. The vanilloid receptor antagonist N-[2-(4-chlorophenyl) ethyl]-1,3,4,5-tetrahydro-7, 8-dihydroxy-2H-2-benzazepine-2-carbothioamide (capsazepine; 100 micromol/kg) significantly reduced staphylococcal enterotoxin B-induced responses. The 5-HT receptor antagonist methysergide (10 mg/kg, i.v.) and the histamine H(1) receptor antagonist mepyramine (10 mg/kg, i.v.) produced a significant reduction in paw oedema whereas plasma exudation was reduced only by methysergide. In diabetic mice, exudation and oedema evoked by staphylococcal enterotoxin B were markedly reduced. Acute administration of insulin (20 UI/kg, s.c., 30 min before) did not restore the increased permeability induced by staphylococcal enterotoxin B. We conclude that plasma exudation and paw oedema in response to staphylococcal enterotoxin B are a consequence of a complex neurogenic response involving direct activation of vanilloid receptors on sensory nerves, release of kinins and subsequent activation of bradykinin B(2) receptors at a prejunctional level, and direct or indirect degranulation of mast cells.

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.

Potential effect of the administration of substance P and allergen therapy on immunoglobulin E-mediated allergic reactions in human subjects

Previously we observed and reported that immunoglobulin E-mediated (IgE-mediated) allergy in rhesus monkeys was decreased by the administration of substance P (SP) and an allergen. We extended these studies to human subjects, giving SP and 1 allergen to subjects with reactivity to more than 1 allergen, using reactivity to a second allergen as a control. SP and an allergen were initially given by aerosol delivery but subsequently were given by injection. The administration of SP and 1 allergen by aerosol delivery or injection resulted in decreased IgE-mediated reactivity to the allergen administered and also to the control allergen. This result occurred in 7 of 8 human subjects. The 2 initial subjects receiving 8 SP and allergen injections had a sharp reduction in their symptoms of ragweed hay fever lasting for 3 years to date. No significant reactions to the injection of SP occurred. Further controlled human research is necessary on the administration of SP and allergen and the mechanisms of action. Unexpected and serendipitous results first observed in rhesus monkeys and reproduced in allergic human subjects provide a new and potential mechanism for control and perhaps obliteration of common IgE-mediated allergies and even more-serious allergic problems.

Neutrophil migration induced by staphylococcal enterotoxin type A in mice: a pharmacological analysis

Staphylococcal enterotoxin type A induced marked neutrophil migration into the mouse peritoneal cavity and was dependent on the number of resident macrophages. This migratory response was dose- (16-64 microg of staphylococcal enterotoxin type A/cavity) and time-dependent, peaking at 12 h and disappearing after 72 h. Dexamethasone (0.5 mg/kg) inhibited the neutrophil migration induced by staphylococcal enterotoxin type A (32 microg; 42% inhibition). A similar response was observed with the platelet-activating factor-acether receptor antagonist, BN 52021 (ginkgolide B, 3-(1,1-dimethylethyl)-hexahydro-1,4-7b-trihydroxy-8-methyl-9H-1,7alph a (epoxymethano-1H,6alphaH-cyclopenta (c) furo (2,3-b) furo (3', 2': 3,4) cyclopenta (1,2-d) furan-5, 9, 12 (4H)-trione); 10 mg/kg; 57% inhibition), the histamine H2 receptor antagonist, cimetidine (2 mg/kg; 31% inhibition), the lipoxygenase inhibitor, BWA4C (N-(3-phenoxycinnamyl) acetohydroxamic acid); 10 mg/kg; 73% inhibition), and capsaicin (trans-8-methyl-N-vanillyl-6-nonamide), a sensory C-fiber neuropeptide depletor. In contrast, indomethacin (5 mg/kg) had no effect on staphylococcal enterotoxin type A-induced chemotaxis. We conclude that the peritonitis induced by staphylococcal enterotoxin type A in mice is macrophage-dependent. The mechanism whereby staphylococcal enterotoxin type A stimulates macrophages to induce neutrophil recruitment remains to be elucidated.

Staphylococcal enterotoxin B inhibits the production of interleukin-4 in a human mast-cell line HMC-1

Staphylococcal enterotoxins belong to the recently characterized group of immunocytotropic bacterial superantigens that are potent mitogens for human T cells. Superantigens are presented, but without intracellular processing, to T cells by monocyte/macrophages, Langerhans' cells and keratinocytes via the class II major histocompatibility complex (MHC) molecules. Superantigens have been demonstrated to act as potent inducers of several proinflammatory cytokines in the antigen-presenting cells such as interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha). As mast cells participate in the pathogenesis of several inflammatory skin disorders such as atopic dermatitis (AD), which is often aggravated by staphylococcal infections, we studied the effect of staphylococcal enterotoxin B (SEB) superantigen on the histamine release and IL-4 expression in a human mast-cell line (HMC-1). Incubation of SEB (50 micrograms/ml) with HMC-1 cells for 45 min, could not induce any histamine release. The HMC-1 cells were also stimulated with various concentrations of SEB (0, 1, 10, 20, 50 micrograms/ml) for 1, 2, 3 and 4 days. Clear dose-dependent inhibition of IL-4 protein production and release was observed on day 4 without any observed effect on cell viability. Compared with unstimulated HMC-1 cells, after 50 micrograms/ml SEB stimulation, the IL-4 mRNA levels decreased steadily in the 2, 6, 18 and 24 hr samples in repeated experiments as measured with the reverse transcription polymerase chain reaction (RT-PCR) method. In comparison, a biphasic decrease in TNF-alpha expression was found. Our results show that an human leukaemic mast cells, superantigen stimulation downregulates the production of IL-4.

Involvement of substance P as a mediator in capsaicin-induced mouse ear oedema

We examined the involvement of substance P (SP) in mouse ear oedema induced by topical application of capsaicin (250 micrograms/ear). Reapplication of capsaicin at 4 h, 24 h, and 48 h after initial treatment did not induce a second oedema response. Oedema induced after the second application was significantly (p < 0.01 or p < 0.001) suppressed for up to 30 days but was observed when capsaicin was applied 40 days after initial treatment. Topical pretreatment of ears with capsaicin at 4 h, 24 h and 48 h before i.v. injection of SP (5 micrograms/kg) did not cause a significant inhibition of plasma extravasation in ear skin. NK1 receptor antagonists such as RP 67580 (ED50:0.19 mg/kg, i.v.), spantide II (ED50:0.33 mg/kg, i.v.), and GR 82334 (ED50:0.26 mg/kg, i.v.), inhibited capsaicin-induced ear oedema, whereas SR 48968 (2.0 mg/kg, i.v.), a NK2 receptor antagonist, had no effect. Furthermore, RP 67580 (0.5 kg/mg, i.v.) inhibited the oedema response induced by reapplication of capsaicin at 50 days after initial treatment. These results indicate that tachyphylaxis of capsaicin-induced oedema is reversible and suggest that this response may be due mainly to a reduction of SP in sensory neurones but not to any loss of responsiveness of NK1 receptors. We also conclude that SP and NK1 receptors are involved predominantly in the development of capsaicin-induced mouse ear oedema.

Humoral immunity to aerosolized staphylococcal enterotoxin B (SEB), a superantigen, in monkeys vaccinated with SEB toxoid-containing microspheres

Staphylococcal enterotoxin B (SEB) toxoid-containing microspheres were tested for efficacy in rhesus monkeys as a vaccine candidate for respiratory SEB toxicosis and toxic shock. Forty monkeys were randomly separated into 10 groups of four monkeys each: 9 groups were vaccinated with the microspheres via combinations of mucosal and nonmucosal routes, and 1 group served as nonvaccinated controls. Both vaccinated and nonvaccinated monkeys were then challenged with a high lethal dose of SEB aerosol. Monkeys primed with an intramuscular dose of the microspheres followed by an intratracheal booster all survived the SEB challenge. Overall, monkeys with an intratracheal booster generally had the highest antibody levels, which is consistent with their high survival rate and lower rate of illness. Protective immunity was correlated with antibody levels in both the circulation and the respiratory tract. The protection was not due to the depletion or anergy of SEB-reactive T cells, since SEB-induced proliferation in cultures of circulating lymphocytes was not significantly reduced after the microsphere vaccination. It is evident that the nonsurvivors did not die of systemic anaphylaxis or hypersensitivity because the monkeys did not die immediately after SEB challenge and there were no significant differences in histamine levels between the vaccinated and control monkeys before and after SEB challenge. The antibodies seemed to neutralize the SEB that got into the airway and the circulation.

Superantigenic staphylococcal exotoxins induce T-cell proliferation in the presence of Langerhans cells or class II-bearing keratinocytes and stimulate keratinocytes to produce T-cell-activating cytokines

Several staphylococcal toxins are among a growing number of immunostimulatory molecules called "superantigens" because of their ability, when presented by appropriate major histocompatibility complex class II+ accessory cells, to activate essentially all T cells bearing particular T-cell receptor V beta gene segments. We have examined the ability of murine epidermal Langerhans cells and/or keratinocytes to act as accessory cells in the T-cell response to the superantigens staphylococcal enterotoxin B and exfoliative toxin, also known as epidermolysin. Purified murine splenic T cells were stimulated with staphylococcal enterotoxin B or exfoliative toxin in the presence of Langerhans cells--enriched epidermal cells from normal mice or epidermal cells isolated from mice pretreated with recombinant interferon-gamma, a procedure that induces the expression of major histocompatibility complex class II molecules on keratinocytes. The data show that both Langerhans cells and class II-bearing keratinocytes can act as accessory cells in the T-cell response to staphylococcal enterotoxin B and exfoliative toxin. We also observed that both human and murine keratinocytes cultured in the presence of staphylococcal enterotoxin B or exfoliative toxin produce increased amounts of cytokine(s) capable of stimulating thymocytes and D10 cells, and that this toxin activity is independent of the level of expression of class II on keratinocytes. Studies by enzyme-linked immunosorbent assay showed that staphylococcal enterotoxin B stimulates keratinocytes to produce tumor necrosis factor-alpha but not interleukin-1, suggesting tumor necrosis factor-alpha and perhaps other cytokines are responsible for the T-cell proliferative activity. These results demonstrate that two distinct epidermal constituents (i.e. Langerhans cells and keratinocytes) can serve as accessory cells in the responses of T cells to superantigenic bacterial toxins. It is possible that such toxins contribute to the pathogenesis of a variety of skin diseases by either locally activating T cells bearing particular V beta genes and/or enhancing keratinocyte production of immunomodulatory cytokines.

Superantigens

"Superantigens" is the term for a group of molecules that have in common an extremely potent stimulatory activity for T lymphocytes of several species. They stimulate CD4+, CD8+ and gamma delta + T cells by a unique mechanism: they cross-link variable parts of the T-cell receptor (TCR) with MHC class II molecules on accessory or target cells. The interaction site on the class II molecule and on the TCR is different from the peptide binding site; on the TCR it is the variable part of the beta chain (V beta). The prototype superantigen is the staphylococcal enterotoxin B (SEB), member of a family of genetically related proteins produced by Staphylococcus aureus and Streptococcus pyogenes. These are soluble exotoxins of approximately 27 kd molecular mass. It is intriguing that this molecular mechanism of T-cell stimulation has been independently produced at least three times in evolution. Other pathogens producing superantigens are retroviruses (the Mouse Mammary Tumor Viruses) and a mycoplasma (Mycoplasma arthritidis). Many additional candidate superantigens have been proposed, but in most cases unequivocal evidence for superantigen activity is still missing. There are several reasons why these molecules have aroused such tremendous interest in recent years. First, they have provided key information on tolerance mechanisms, both on the deletion of T cells in the thymus and on the induction of peripheral tolerance by anergy and apoptosis. Second, of all polyclonal T-cell stimulators they are the ones that most closely mimic the recognition of specific antigen. Finally, they have been recognized as important factors in the pathogenicity of the producing pathogens, inducing shock and immunosuppression. Whilst there is evidence that superantigens could be involved in the pathogenesis of certain human diseases, in most cases this is still very preliminary and indirect.

Activation of mucosal V beta 3+ T cells and tissue damage in human small intestine by the bacterial superantigen, Staphylococcus aureus enterotoxin B

Staphylococcus aureus enterotoxin B (SEB) was added to explants of fetal human intestine in organ culture or administered into the lumen of fetal small intestine prior to culture. Both routes produced a massive increase in lamina propria T cells expressing V beta 3, and to a lesser extent, those expressing V beta 5 and V beta 12. SEB-activated lamina propria T cells produced interleukin-2 and interferon-gamma and T cell activation was accompanied by tissue damage, which was inhibited by FK506.

Immunity and responses of circulating leukocytes and lymphocytes in monkeys to aerosolized staphylococcal enterotoxin B

Rhesus monkeys immunized intramuscularly or orally with staphylococcal enterotoxin B (SEB) toxoid or SEB toxoid incorporated in microspheres made of poly(DL-lactide-co-glycolide) were challenged with a lethal dose of aerosolized SEB to study their immunity and cellular responses in the circulation. It was found that circulating antibodies play a critical role in preventing SEB from triggering toxicosis. Monkeys with high levels of antibodies survived, while those with low levels underwent 2 to 3 days of toxicosis and died. Intramuscular immunization induced high levels and oral immunization induced low levels of antibodies. The circulating antibodies in surviving monkeys decreased dramatically within 20 min and started to rebound at 90 min after SEB challenge. At 90 min, the dying monkeys showed in the circulation a dramatic increase of polymorphonuclear leukocytes and decreases of NK cells and monocytes (CD16 and CD56 markers) as well as of lymphocytes with HLA-DR, CD2, CD8, and IL2R alpha (CD25) markers. The number of polymorphonuclear leukocytes showed an inverse correlation with the numbers of monocytes and various lymphocyte subpopulations which, except for IL-2R, CD16, and CD56(+) cells, showed a direct correlation with one another. The changes in the populations of leukocytes, monocytes, NK cells, and lymphocytes seem to be an indication of initial toxicosis; however, the roles of these cells in toxicosis and death remain to be defined.

Stimulation of human T cells by microbial 'superantigens'

The enterotoxins and the TSST of S. aureus, the erythrogenic toxins A and C of S. pyogenes and a still uncharacterized exoprotein of M. arthritidis belong to a family of exotoxins that have in common a potent mitogenic activity for T lymphocytes of several species. These proteins stimulate CD4+ and C8+ T cells, as well as a fraction of gamma delta TCR-bearing T cells by cross-linking variable parts of the T cell antigen receptor with MHC class II molecules on accessory or target cells. They are functionally bivalent molecules having distinct interaction sites for variable parts of the TCR and for nonpolymorphic parts of the MHC class II molecule. For alpha beta TCR-bearing T cells the V beta is the dominant site of interaction with the toxins. However, there is only a preferential but not exclusive stimulation of T cells carrying a certain V beta, because T cell clones carrying e.g. V beta 5 or V beta 8 can respond also to those toxins that do not stimulate V beta 5+ and V beta 8+ T cells in bulk cultures. Therefore, different TCR bind to these toxins with different affinities and the specificity of the TCR-toxin interaction is quantitative rather than qualitative in nature. Murine T cells respond to the mitogen of M. arthritidis that is a natural pathogen for mice and rats much better than to the toxins of the human pathogenic bacteria, whereas the opposite is true for human T cells. This could indicate that the toxins have been adapted to the host's immune system in evolution. The T cell-stimulating activity contributes to the pathogenesis of the respective diseases.

T lymphocyte-stimulating microbial toxins as "superantigens"

Infectious pathogens generally have to cope with the host's adaptive immune system, i.e., T and B lymphocytes. Common evasion mechanisms in this complex interaction are antigenic variations, the escape to immunologically priviledged sites or the use of immunosuppressive mechanisms. Many bacteria and other microorganisms eleborate soluble factors or toxins that act suppressively on cells of the immune system, such as pore-forming molecules or proteins that interfere with the function of G proteins. Gram-positive cocci and a mycoplasma have developed an extremely potent mechanism of T cell stimulation by closely mimicking recognition of specific antigen. From the functional similarity to antigen recognition and the multiclonal activation of T cells the designation "superantigens" has been suggested for these molecules.