Effects of staphylococcal enterotoxin B on rodent mast cells

Effects of Growth Stage on the Characterization of Enterotoxin A-Producing Staphylococcus aureus‐Derived Membrane vesicles

Virulence factors, such as staphylococcal enterotoxin A (SEA), are contained within membrane vesicles (MVs) in the cell membrane of Staphylococcus aureus. In this study, the effects of the growth stage on quantitative and qualitative changes in the components contained in the MVs of S. aureus SEA-producing strains were examined. Changes in the expression levels of S. aureus genes were examined at each growth stage; phenol-soluble modulin (PSM) gene reached a maximum after 8 h, and the expression of cell membrane-related genes was decreased after 6 h. Based on these gene expression patterns, MVs were prepared at 6, 17, and 24 h. The particle size of MVs did not change depending on the growth stage. MVs prepared after culture for 17 h maintained their particle size when stored at 23 °C. The amount of SEA in the culture supernatant and MVs were not correlated. Bifunctional autolysin, a protein involved in cell wall biosynthesis/degradation, was increased in MVs at 17 h. The expression pattern of inflammation-related genes in human adult low calcium high temperature (HaCaT) cells induced by MVs was different for each growth stage. The inclusion components of S. aureus-derived MVs are selective, depend on the stage of growth, and may play an important role in toxicity.

Allergy-A New Role for T Cell Superantigens of Staphylococcus aureus?

Staphylococcus aureus superantigens (SAgs) are among the most potent T cell mitogens known. They stimulate large fractions of T cells by cross-linking their T cell receptor with major histocompatibility complex class-II molecules on antigen presenting cells, resulting in T cell proliferation and massive cytokine release. To date, 26 different SAgs have been described in the species S. aureus; they comprise the toxic shock syndrome toxin (TSST-1), as well as 25 staphylococcal enterotoxins (SEs) or enterotoxin-like proteins (SEls). SAgs can cause staphylococcal food poisoning and toxic shock syndrome and contribute to the clinical symptoms of staphylococcal infection. In addition, there is growing evidence that SAgs are involved in allergic diseases. This review provides an overview on recent epidemiological data on the involvement of S. aureus SAgs and anti-SAg-IgE in allergy, demonstrating that being sensitized to SEs—in contrast to inhalant allergens—is associated with a severe disease course in patients with chronic airway inflammation. The mechanisms by which SAgs trigger or amplify allergic immune responses, however, are not yet fully understood. Here, we discuss known and hypothetical pathways by which SAgs can drive an atopic disease.

Mast Cell Responses to Viruses and Pathogen Products

Mast cells are well accepted as important sentinel cells for host defence against selected pathogens. Their location at mucosal surfaces and ability to mobilize multiple aspects of early immune responses makes them critical contributors to effective immunity in several experimental settings. However, the interactions of mast cells with viruses and pathogen products are complex and can have both detrimental and positive impacts. There is substantial evidence for mast cell mobilization and activation of effector cells and mobilization of dendritic cells following viral challenge. These cells are a major and under-appreciated local source of type I and III interferons following viral challenge. However, mast cells have also been implicated in inappropriate inflammatory responses, long term fibrosis, and vascular leakage associated with viral infections. Progress in combating infection and boosting effective immunity requires a better understanding of mast cell responses to viral infection and the pathogen products and receptors we can employ to modify such responses. In this review, we outline some of the key known responses of mast cells to viral infection and their major responses to pathogen products. We have placed an emphasis on data obtained from human mast cells and aim to provide a framework for considering the complex interactions between mast cells and pathogens with a view to exploiting this knowledge therapeutically. Long-lived resident mast cells and their responses to viruses and pathogen products provide excellent opportunities to modify local immune responses that remain to be fully exploited in cancer immunotherapy, vaccination, and treatment of infectious diseases.

Submucosal mast cells in the gastrointestinal tract are a target of staphylococcal enterotoxin type A

Staphylococcal enterotoxin A (SEA) is a leading causative toxin of staphylococcal food poisoning. However, it remains unclear how this toxin induces emesis in humans, primates, and certain experimental animals. To understand the mechanism of SEA-induced emesis, we investigated the behavior of SEA in the gastrointestinal (GI) tract in vivo using the house musk shrew (Suncus murinus). Immunofluorescence of GI sections showed that perorally administered SEA translocated from the lumen to the interior tissues of the GI tract and rapidly accumulated in certain submucosa cells. These SEA-binding cells in the submucosa were both tryptase- and FcεRIα-positive, suggesting these SEA-binding cells were mast cells. These SEA-binding mast cells were 5-hydroxytryptamine (5-HT)-positive, but the intensity of the 5-HT signal decreased over time compared to that of mast cells in the negative control. Furthermore, toluidine blue staining showed the number of metachromatic mast cells was decreased in the duodenal submucosa, suggesting that SEA binding induced degranulation and release of 5-HT from submucosal mast cells. These observations suggest that the target cells of SEA are submucosal mast cells in the GI tract and that 5-HT released from submucosal mast cells plays an important role in SEA-induced emesis.

The mast cell in innate and adaptive immunity

Mast cells (MCs) were once considered only as effector cells in pathogenic IgE- and IgG-mediated responses such as allergy. However, developments over the last 15 years have suggested that MCs have evolved in vertebrates as beneficial effector cells that are involved in the very first inflammatory responses generated during infection. This pro-inflammatory environment has been demonstrated to be important for initiating innate responses in many different models of infection and more recently, in the development of adaptive immunity as well. Interestingly this latter finding has led to the discovery that small MC-activating compounds can behave as adjuvants in vaccine formulations. Thus, our continued understanding of the MC in the context of infectious disease is likely to not only expand our scope of the MC in the normal processes of immunity, but provide new therapeutic targets to combat disease.

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.

Lipoteichoic acids selectively stimulate rat mast cells to cysteinyl leukotriene generation and affect mast cell migration after tumor necrosis factor (TNF)-priming

It is well established that mast cells play a critical role in the host defense against bacteria. Upon stimulation with bacteria and their antigens, mast cells release various mediators and cytokines that promote the development of inflammation at the site of infection. In the present study, we examined the ability of lipoteichoic acids (LTAs), some of the major components of cell walls of most gram-positive bacteria, to stimulate mast cell degranulation and histamine release as well as to generate of cysteinyl leukotrienes (LTs). We also studied the influence of LTAs on mast cell migration. Experiments were done on rat peritoneal mast cells and LTA from Staphyloccocus aureus and LTA from Bacillus subtilis were used. We have stated that neither S. aureus LTA nor B. subtilis LTA used at a wide range of concentrations (from 10(-4) to 10(5)ng/mL) induced mast cell degranulation and histamine release. However, stimulation of mast cells with both LTAs resulted in generation and release of significant levels of LTs. We have also documented that none of the LTAs stimulated rat mast cell migration, even in the presence of laminin. IL-6 priming did not influence mast cell migration towards LTAs, whereas, pretreatment of mast cells with TNF caused time-dependent mast cell migration in response to LTAs stimulation. Pretreatment of mast cells with anti-TNFR1 antibodies completely inhibited LTA-induced migratory response of TNF-primed mast cells. Our results showed that LTAs might be among important bacterial antigens involved in mast cell activation during bacterial infections.

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.

The 5-HT3 receptor antagonist tropisetron inhibits T cell activation by targeting the calcineurin pathway

Tropisetron, an antagonist of serotonin type 3 receptor, has been investigated in chronic inflammatory joint process. Since T cells play a key role in the onset of several inflammatory diseases, we have evaluated the immunosuppressive activity of tropisetron in human T cells, discovering that this compound is a potent inhibitor of early and late events in TCR-mediated T cell activation. Moreover, we found that tropisetron specifically inhibited both IL-2 gene transcription and IL-2 synthesis in stimulated T cells. To further characterize the inhibitory mechanisms of tropisetron at the transcriptional level, we examined the DNA binding and transcriptional activities of NF-(kappa)B, NFAT and AP-1 transcription factors in Jurkat T cells. We found that tropisetron inhibited both the binding to DNA and the transcriptional activity of NFAT and AP-1. We also observed that tropisetron is a potent inhibitor of PMA plus ionomycin-induced NF-(kappa)B activation but in contrast TNF(alpha)-mediated NF-(kappa)B activation was not affected by this antagonist. Finally, overexpression of a constitutively active form of calcineurin indicated that this phosphatase may represent one of the main targets for the inhibitory activity of tropisetron. These findings provide new mechanistic insights into the anti-inflammatory activities of tropisetron, which are probably independent of serotonin receptor signalling and highlight their potential to design novel therapeutic strategies to manage inflammatory diseases.

Murine lethal toxic shock caused by intranasal administration of staphylococcal enterotoxin B

Currently available murine staphylococcal enterotoxin B (SEB) shock models require pretreatment with various agents to increase mouse sensitivity to SEB. This study was performed to show that C3H/HeJ mice are highly susceptible to intranasal SEB inoculation, which caused toxic shock without using pretreatment agents. For this purpose, mice were injected intranasally with different doses of SEB and observed for up to 1 month. The median lethal dose of SEB was determined using the probit procedure. Tissue samples were taken at different time points for histopathological examination. The LD(50) was found at 1.6 microg/g (95% fiducial limit (f.l.) 0.7 to 2.2), the LD(80) at 2.7 microg/g (95% f.l. 1.9 to 4.0) and the LD(90) at 3.6 microg/g (95% f.l. 2.7 to 6.4). Histopathologic examination revealed pulmonary edema and bronchopneumonia. Mucosal-associated lymphoid tissue first became activated, followed by increasing lymphocyte apoptosis and depletion. In the liver there were intralobular and portal inflammatory foci with increasing lymphocyte apoptosis and degenerative necrosis. The splenic white pulp was characterized by early activation and subsequent depletion of lymphoid follicle germinal centers. The thymus initially was activated, followed by increasing apoptosis and migration of lymphoid cells from the cortex to the medulla. The pathological features detected in the mice were similar to those of rhesus monkeys treated with SEB aerosol challenge.

Vaginal bacterial flora activates rat peritoneal mast cells

Sixteen strains of physiological and pathological vaginal bacteria were tested for their ability to secrete histamine from rat peritoneal mast cells in vitro. We noticed that Mycoplasma hominis-induced histamine release was very high (up to 53.6%). The stimulation of rat mast cells with Staphylococccus cohnii, Staphylococcus coagulase(-) (two strains), Ureaplasma urealyticum, Peptostreptococcus spp., Bacteroides capillosus, Staphylococcus aureus and Streptococcus agalactiae resulted in lower but significant histamine secretion (11.2%-17.5%). Other bacteria strains (Staphylococcus epidermidids, Enterococcus faecalis, Escherichia coli, Actinomyces naeslundii (two strains) and Lactobacillus fermentum (two strains) caused very low (4.2% - 8.8%) histamine 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.

Mast cells as sentinels of innate immunity

Mast cells are widely regarded as important effector cells in immune responses associated with Th2 cells and IgE. Recent work shows that they can also contribute significantly to the expression of innate immunity; furthermore, survival in a model of acute bacterial infection that is dependent on complement and mast cells can be greatly enhanced by long-term treatment of mice with the kit ligand (stem cell factor) at least in part because of the effects of such treatment on mast cell numbers and/or function. These findings not only indicate that mast cells can represent a critical component of host defense in natural immunity but also suggest that mast cell function in this setting can be manipulated for therapeutic ends.

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.

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.

Localization of binding sites of staphylococcal enterotoxin B (SEB), a superantigen, for HLA-DR by inhibition with synthetic peptides of SEB

Staphylococcal enterotoxins are major causes of food poisoning and toxic shock syndrome. Their ability to bind to major histocompatibility complex (MHC) class II molecules has been suggested to be the first step in the mechanism whereby they cause illness. By flow cytometric analysis, the sites of interaction of staphylococcal enterotoxin B (SEB) with HLA-DR molecules were probed in the present study by inhibiting the binding of biotinylated SEB to a human T-cell line (HUT-78) with synthetic peptides of SEB. Five peptides of SEB gave significant inhibition of binding: a peptide containing amino acids 9 to 20 [SEB(9-20)], SEB(30-38), SEB(61-70), SEB(90-114), and SEB(169-181). One peptide, SEB(39-51), enhanced binding. Among the inhibitory peptides, SEB(90-114), a peptide spanning the entire disulfide loop, showed the most efficient inhibition of binding. Peptides SEB(9-20) and SEB(39-51) include amino acid residues that have been identified by previous mutation studies (J.W. Kappler, A. Herman, J. Clements, and P. Marrack, J. Exp. Med. 175:387-396, 1992) as being important in binding to MHC class II. Amino acids lining the alpha 5 groove of SEB have also been postulated to be involved in binding to MHC class II molecules. However, only two of the residues that line the alpha 5 groove of SEB, His-12 and Tyr-17, are on peptide SEB(9-20) that inhibits binding. These results confirm previous studies that implicated the amino-terminal portion of the molecule in binding to MHC class II molecules and further indicate an important role for residues in other regions, particularly the disulfide loop.

Increased susceptibility to staphylococcal enterotoxin B intoxication in mice primed with actinomycin D

Mice (BALB/cJ, C3H/HeN, and C3H/HeJ) primed with actinomycin D became highly susceptible to lethal intoxication with staphylococcal enterotoxin B (SEB). The mice underwent toxicosis and toxic shock and died. Actinomycin D-primed C3H/HeN and C3H/HeJ mice showed equal sensitivity to SEB, suggesting that bacterial lipopolysaccharide derived from gram-negative bacteria in the gut may not be an important cofactor in intoxication. In a time course study of the illness, prominent pathological changes characterized by blood congestion and thickening of alveolar septa were seen in the lung, while blood congestion, inflammation, epithelial cell flattening, and villous blunting were seen in the small intestine. In lymphoid tissues, such as the spleen, congestion, inflammation, and lymphoid cell depletion were the major reactions. The pathological features of the mice had many similarities to those of rhesus monkeys intoxicated with intravenous SEB. The actinomycin D-primed C3H/HeJ mice are thus an ideal mouse model for studying SEB toxicosis and toxic shock.

Binding and activation of major histocompatibility complex class II-deficient macrophages by staphylococcal exotoxins

Macrophages from C2D transgenic mice deficient in the expression of major histocompatibility complex (MHC) class II proteins were used to identify binding sites for superantigens distinct from the MHC class II molecule. Iodinated staphylococcal enterotoxins A and B (SEA and SEB) and exfoliative toxins A and B (ETA and ETB) bound to C2D macrophages in a concentration-dependent and competitive manner. All four toxins increased F-actin concentration within 30 s of their addition to C2D macrophages, indicating that signal transduction occurred in response to toxin in the absence of class II MHC. Furthermore, ETA, ETB, SEA, and, to a lesser extent, SEB induced C2D macrophages to produce interleukin 6. Several molecular species on C2D macrophages with molecular masses of 140, 97, 61, 52, 43, and 37 kDa bound SEA in immunoprecipitation experiments. These data indicate the presence of novel, functionally active toxin binding sites on murine macrophages distinct from MHC class II molecules.

Immunopharmacology of the superantigen staphylococcal enterotoxin A in T-cell receptor V beta 3 transgenic mice

The response of mouse T cells to the superantigen staphylococcal enterotoxin A (SEA) requires 1000-fold higher concentrations compared to human T cells. In order to develop a sensitive model for SEA studies in mice, the immunopharmacology has been studied in T-cell receptor (TcR) V beta 3 transgenic (TGV beta 3) and non-transgenic (non-TG) C57Bl/6 mice. The frequency of SEA-responsive T cells in the TGV beta 3 mice exceeded 90%, whereas a 10-fold lower frequency was seen in normal C57Bl/6 mice. Nanograms of SEA injected intravenously into TGV beta 3 mice induced strong cytolytic T lymphocyte (CTL) activity against SEA-coated major histocompatibility complex (MHC) class II+ B-lymphoma cells, whereas administration of 1000-fold higher amounts of SEA to non-TG littermates or normal C57Bl/6 mice induced only a moderate response. Kinetic analysis demonstrated that the CTL activity was more rapidly detectable in TG mice, but substantial levels were seen 2 days after SEA injection in both TGV beta 3 and non-TG mice. The cytotoxic T-cell response induced by SEA in TGV beta 3 and non-TG mice was completely MHC class II dependent, as SEA-coated MHC class II-transfected syngeneic B16 melanoma cells but not untransfected B16 cells were sensitive to lysis. Large amounts of tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) accumulated in serum of TGV beta 3 mice after injection of 10 ng SEA, whereas only marginal amounts were recorded in non-TG even after injection of 100 micrograms SEA. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrated that SEA-induced TNF-alpha and IFN-gamma mRNA reached maximal levels 1 hr after SEA administration in TGV beta 3 mice, whereas peak serum levels of TNF-alpha and IFN-gamma proteins were recorded after 2 hr. Comparison of the mRNA levels of a panel of cytokines in the TGV beta 3 and non-TG mice revealed that almost similar amounts of interleukin-1 (IL-1) were induced in both strains, whereas IL-4 was only detected at significant levels in the TGV beta 3 mouse. The results suggest that TGV beta 3 mice are suitable for studying in vivo immune responses to superantigens at concentrations comparable to the potent effects elicited in humans. Moreover, this model is useful for detailed studies on the dynamic regulation of T-cell activation and anergy induced by superantigens.

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.

Dual roles for class II major histocompatibility complex molecules in staphylococcal enterotoxin-induced cytokine production and in vivo toxicity

The staphylococcal enterotoxins (SE) specifically bind to class II major histocompatibility complex (MHC) proteins, resulting in activation of monocytes and T cells. The SE cause weight loss in mice, which is dependent on T-cell stimulation and tumor necrosis factor alpha (TNF-alpha) production. Here we use a mutant of staphylococcal enterotoxin A that binds class II MHC molecules and activates monocytes but not T cells to evaluate the relative contributions of monocyte- and T-cell-stimulatory activities to in vivo toxicity. The mutant toxin did not cause weight loss in B10. BR mice but did stimulate monocyte TNF-alpha production in vitro, as did the wild-type toxin. Addition of a supernatant from toxin-activated T cells enhanced monocyte-stimulatory activity of both mutant and wild-type toxins fivefold. The effect of the supernatant could be mimicked by recombinant gamma interferon (IFN-gamma) and was inhibited by antibody to IFN-gamma. These results suggest that toxin-induced monocyte TNF-alpha production is upregulated by IFN-gamma, which likely represents the T-cell requirement in SE-mediated weight loss. Our studies thus implicate two distinct class II MHC-dependent signaling pathways for SE, the first involving direct signal transduction through class II MHC molecules mediated by either mutant or wild-type toxin and the second requiring T-cell stimulation by toxin-class II MHC complexes with consequent production of IFN-gamma. We suggest that both pathways are required for optimal monocyte TNF-alpha production in vitro and SE-induced toxicity in vivo.