Murine macrophage activation by staphylococcal exotoxins

Progress of stimulus responsive nanosystems for targeting treatment of bacterial infectious diseases

In recent decades, due to insufficient concentration at the lesion site, low bioavailability and increasingly serious resistance, antibiotics have become less and less dominant in the treatment of bacterial infectious diseases. It promotes the development of efficient drug delivery systems, and is expected to achieve high absorption, targeted drug release and satisfactory therapy effects. A variety of endogenous stimulation-responsive nanosystems have been constructed by using special infection microenvironments (pH, enzymes, temperature, etc.). In this review, we firstly provide an extensive review of the current research progress in antibiotic treatment dilemmas and drug delivery systems. Then, the mechanism of microenvironment characteristics of bacterial infected lesions was elucidated to provide a strong theoretical basis for bacteria-targeting nanosystems design. In particular, the discussion focuses on the design principles of single-stimulus and dual-stimulus responsive nanosystems, as well as the use of endogenous stimulus-responsive nanosystems to deliver antimicrobial agents to target locations for combating bacterial infectious diseases. Finally, the challenges and prospects of endogenous stimulus-responsive nanosystems were summarized.

Calcium Peroxide Nanoparticles-Embedded Coatings on Anti-Inflammatory TiO2 Nanotubes for Bacteria Elimination and Inflammatory Environment Amelioration

Implant-associated bacterial infections significantly impair the integration between titanium and soft tissues. Traditional antibacterial modifications of titanium implants are able to eliminate bacteria, but the resulting pro-inflammatory reactions are usually ignored, which still poses potential risks to human bodies. Here, a dual drug-loading system on titanium has been developed via the adhesion of a catechol motif-modified methacrylated gelatin hydrogel onto TiO₂ nanotubes. Then synthesized CaO₂ nanoparticles (NPs) are embedded into the hydrogel, and interleukin-4 (IL-4) is loaded into the nanotubes to achieve both antibacterial and anti-inflammatory properties. The dual drug-loading system can eliminate Staphylococcus aureus (S. aureus) rapidly, attributed to the H₂ O₂ release from CaO₂ NPs. The potential cytotoxicity of CaO₂ NPs is also remarkably reduced after being embedded into the hydrogel. More importantly, with the gradual release of IL-4, the dual drug-loading system is capable of modulating pro-inflammatory reactions by inducing M2 phenotype polarization of macrophages. In a subcutaneous infection model, the S. aureus contamination is effectively resolved after 2 days, and the resulting pro-inflammatory reactions are also inhibited after 7 days. Finally, the damaged tissue is significantly recovered. Taken together, the dual drug-loading system exhibits great therapeutic potential in effectively killing pathogens and inhibiting the resulting pro-inflammatory reactions.

Exotoxins and endotoxins: Inducers of inflammatory cytokines

Endotoxins and exotoxins are among the most potent bacterial inducers of cytokines. During infectious processes, the production of inflammatory cytokines including tumor necrosis factor (TNF), interleukin-1β (IL-1β), gamma interferon (IFNγ) and chemokines orchestrates the anti-infectious innate immune response. However, an overzealous production, leading up to a cytokine storm, can be deleterious and contributes to mortality consecutive to sepsis or toxic shock syndrome. Endotoxins of Gram-negative bacteria (lipopolysaccharide, LPS) are particularly inflammatory because they generate auto-amplificatory loops after activation of monocytes/macrophages. LPS and numerous pore-forming exotoxins also activate the inflammasome, the molecular platform that allows the release of mature IL-1β and IL-18. Among exotoxins, some behave as superantigens, and as such activate the release of cytokines by T-lymphocytes. In most cases, pre-exposure to exotoxins enhances the cytokine production induced by LPS and its lethality, whereas pre-exposure to endotoxin usually results in tolerance. In this review we recall the various steps, which, from the very early discovery of pyrogenicity induced by bacterial products, ended to the discovery of the endogenous pyrogen. Furthermore, we compare the specific characteristics of endotoxins and exotoxins in their capacity to induce inflammatory cytokines.

Staphylococcal enterotoxin B induces hepatic injury and lethal shock in endotoxin-resistant C3H/HeJ mice despite a deficient macrophage response

Bacterial toxins, including endotoxin/LPS as well as superantigens, are major causative agents of multi-organ failure associated with sepsis and liver disease. However, the precise mechanisms initiating cell activation by the toxins have not been clarified. We compared lethal shock and cytokine production in response to LPS with responses to the superantigen staphylococcal enterotoxin B (SEB) in both LPS-responsive C3H/HeN mice and LPS-hyporesponsive C3H/HeJ mice treated with D-galactosamine (GalN). LPS was not lethal and did not induce production of TNF-α in C3H/HeJ mice. In contrast, SEB produced lethal shock associated with liver failure and induced cytokines such as TNF-α, IFN-γ, and IL-2 in both C3H/HeN and C3H/HeJ mice. Peritoneal macrophages from C3H/HeJ mice did not produce TNF-α in vitro in response to SEB or LPS. However, no significant difference was observed in production of TNF-α in response to stimulation in vitro by SEB between C3H/HeN and C3H/HeJ splenic lymphocytes. We have demonstrated that SEB causes lethal toxicity associated with liver injury in LPS-hyporesponsive C3H/HeJ mice and that as the underlying mechanism, the normal T-cell function in these mice still maintained the sensitivity to SEB since the genetic defect of C3H/HeJ mice unresponsive to LPS and SEB is restricted in macrophages/monocytes and does not extend to T cells.

Lipopolysaccharide is required for the lethal effects of enterotoxin B after D-galactosamine sensitization

We tested the D-galactosamine sensitization model with staphylococcal enterotoxin B (SEB). LPS was required for the lethal effects of SEB in D-galactosamine sensitized mice. Only two (2/62) among the C3HeB/FeJ (H-2k), Balb/c (H-2d) and C57BL/6J (H-2b) mice died in response to SEB in the absence of LPS whereas injection of SEB and minimally lethal concentrations of LPS became highly toxic. Similar to LPS, the lethal effect of SEB was dependent on the mouse strain used. Mouse strains more sensitive to the effects of LPS (Balb/c and C57BL/6J) were also more sensitive to the effects of SEB in comparison to C3H mice when equivalent doses of LPS and SEB were used. Among Balb/c and C3HeB/FeJ but not C57BL/6J mice, SEB (20 μg) potentiated the lethal effects of LPS at low doses (0.1 μg LPS), but had an apparent protective effect at high doses (1 μg LPS). Lastly, there was an inverse correlation between pathogenesis and serum IL-2 concentrations and splenic T cell activation in C3H mice. However, macrophage mobilization did correlate with lethality. Therefore, some questions remain about the mechanisms involved in the D-galactosamine/SEB pathogenesis model. We conclude that when sensitizing mice with D-galactosamine and assessing the lethal effects of SEB, endotoxin contamination must be assessed.

The retrovirus/superantigen hypothesis of multiple sclerosis

The pathogenesis of multiple sclerosis (MS) is as yet unknown. Commonly, MS is assumed to be due to an autoimmune inflammation of the central nervous system (CNS). Neurodegeneration is regarded to be a secondary reaction. This concept is increasingly being challenged. Human endogenous retroviruses (HERV) that could be locally activated in the CNS have been proposed as an alternative concept. HERV-encoded envelope proteins (env) can act as strong immune stimulators (superantigens). Thus, slow disease progression following neurodegeneration might be induced by re-activation of HERV expression directly, while relapses in parallel to inflammation might be secondary to the expression of HERV-encoded superantigens. It has been shown previously that T-cell superantigens are capable to induce a cellular inflammatory reaction in the CNS of experimental animals similar to that in MS. Furthermore, B-cell superantigens have been shown to activate blood leucocytes in vitro to produce immunoglobulin in an oligoclonal manner. It remains to be established, whether the outlined hypothesis accords with all known features of MS. Furthermore, anti-HERV agents may be taken into consideration to enrich and improve MS therapy.

Development and characterization of two porcine monocyte-derived macrophage cell lines

Cell lines CΔ2+ and CΔ2- were developed from monocytes obtained from a 10-month-old, crossbred, female pig. These cells morphologically resembled macrophages, stained positively for α-naphthyl esterase and negatively for peroxidase. The cell lines were bactericidal and highly phagocytic. Both cell lines expressed the porcine cell-surface molecules MHCI, CD11b, CD14, CD16, CD172, and small amounts of CD2; however, only minimal amounts of CD163 were measured. The lines were negative for the mouse marker H2K^k, bovine CD2 control, and secondary antibody control. Additionally, cells tested negative for Bovine Viral Diarrhea Virus and Porcine Circovirus Type 2. Therefore, these cells resembled porcine macrophages based on morphology, cell-surface marker phenotype, and function and will be useful tools for studying porcine macrophage biology.

TCA cycle inactivation in Staphylococcus aureus alters nitric oxide production in RAW 264.7 cells

Inactivation of the Staphylococcus aureus tricarboxylic acid (TCA) cycle delays the resolution of cutaneous ulcers in a mouse soft tissue infection model. In this study, it was observed that cutaneous lesions in mice infected with wild-type or isogenic aconitase mutant S. aureus strains contained comparable inflammatory infiltrates, suggesting the delayed resolution was independent of the recruitment of immune cells. These observations led us to hypothesize that staphylococcal metabolism can modulate the host immune response. Using an in vitro model system involving RAW 264.7 cells, the authors observed that cells cultured with S. aureus aconitase mutant strains produced significantly lower amounts of nitric oxide (NO(•)) and an inducible nitric oxide synthase as compared to those cells exposed to wild-type bacteria. Despite the decrease in NO(•) synthesis, the expression of antigen-presentation and costimulatory molecules was similar in cells cultured with wild-type and those cultured with aconitase mutant bacteria. The data suggest that staphylococci can evade innate immune responses and potentially enhance their ability to survive in infected hosts by altering their metabolism. This may also explain the occurrence of TCA cycle mutants in clinical S. aureus isolates.

Superantigens increase the survival of mice bearing T cell lymphomas by inducing apoptosis of neoplastic cells

Superantigens bind to major histocompatibility complex class II molecules and interact with T cells expressing a particular T cell receptor Vβ inducing a strong proliferation/deletion response of the superantigen-reactive T cells. However, there have been no attempts to investigate the ability of Sags to induce apoptosis in neoplastic T cells by signaling through the Vβ region of their TCR. In the present study we show that bacterial and MMTV-encoded superantigens induce the apoptosis of AKR/J cognate lymphoma T cells both in vitro and in vivo. The Fas-Fas-L pathway was shown to be involved in the apoptosis of lymphoma T cells induced by bacterial superantigens. In vivo exposure to bacterial superantigens was able to improve the survival of lymphoma bearing mice. Moreover, the permanent expression of a retroviral encoded superantigen induced the complete remission of an aggressive lymphoma in a high percentage of mice. The possibility of a therapeutic use of superantigens in lymphoma/leukemia T cell malignancies is discussed.

Defective nitric oxide production by alveolar macrophages during Pneumocystis pneumonia

The effect of nitric oxide (NO) on Pneumocystis (Pc) organisms, the role of NO in the defense against infection with Pc, and the production of NO by alveolar macrophages (AMs) during Pneumocystis pneumonia (PCP) were investigated. The results indicate that NO was toxic to Pc organisms and inhibited their proliferation in culture. When the production of NO was inhibited by intraperitoneal injection of rats with the nitric oxide synthase inhibitor L-N(5)-(1-iminoethyl) ornithine, progression of Pc infection in immunocompetent rats was enhanced. Concentrations of NO in bronchoalveolar lavage fluids from immunosuppressed, Pc-infected rats and mice were greatly reduced, compared with those from uninfected animals, and AMs from these animals were defective in NO production. However, inducible nitric oxide synthase (iNOS) mRNA and protein concentrations were high in AMs from Pc-infected rats and mice. Immunoblot analysis showed that iNOS in AMs from Pc-infected rats existed primarily as a monomer, but the homo-dimerization of iNOS monomers was required for the production of NO. When iNOS dimerization cofactors, including calmodulin, were added to macrophage lysates, iNOS dimerization increased, whereas incubation of the same lysates with all cofactors except calmodulin did not rescue iNOS dimer formation. These data suggest that NO is important in the defense against Pc infection, but that the production of NO in AMs during PCP is defective because of the reduced dimerization of iNOS.

Defining the immune response to Ehrlichia species using murine models

Pathogenic bacteria belonging to the family Anaplasmataceae include species of the genera Ehrlichia and Anaplasma. Ehrlichia chaffeensis, first known as the causative agent of human monocytic ehrlichiosis, also infects several vertebrate hosts including white-tailed deer, dogs, coyotes and goats. E. chaffeensis is transmitted from the bite of an infected hard tick, such as Amblyomma americanum. E. chaffeensis and other tick-transmitted pathogens have adapted to both the tick and vertebrate host cell environments. Although E. chaffeensis persists in both vertebrate and tick hosts for long periods of time, little is known about that process. Immunological studies will be valuable in assessing how the pathogen persists in nature in both vertebrate and invertebrate hosts. Understanding the host immune response to the pathogen originating from dual host backgrounds is also important to develop effective methods of diagnosis, control and treatment. In this paper, we provide our perspective of the current understanding of the immune response against E. chaffeensis in relation to other related Anaplasmataceae pathogens.

Quantitative aspects of lipopolysaccharide and cytokine requirements to generate nitric oxide in macrophages from LPS-hyporesponsive (Lps(d)) C3H/HeJ mice

Due to a gene defect (Lps(d)), C3H/HeJ mice are known to be hyporesponsive to the immunobiological potential of lipopolysaccharide (LPS). We studied dose requirements for LPS, IFN-gamma, and cytokines TNF-alpha and IL-10 to produce nitric oxide (NO) in peritoneal macrophages (Mphi) from these animals. In contrast to the Lps(n) C3H/HeN mice, high concentrations of LPS (up to 5 microg/mL) or IFN-gamma (up to 5 ng/mL) by themselves were unable to activate NO production in C3H/HeJ Mphi. The failure to produce NO could not be overcome by addition of L-arginine or tetrahydropterin. The high-output NO biosynthesis was dose-dependently stimulated by combined administration of varying concentrations of IFN-gamma (50-5000 pg/mL) and LPS (approximately 1 ng/mL) or to a lesser extent by IFN-gamma plus TNF-alpha or TNF-alpha/IL-10. Formation of NO in C3H/HeJ MCO triggered by high concentration of LPS (approximately 1 microg/mL) given together with IFN-gamma (0.2-5 ng/mL) reached the values typical for Lps(n) C3H/HeN mice. While Mphi from C3H/HeN mice secreted TNF-alpha, IL-10, and IL-10 upon contact with a low dose of LPS (1 ng/mL), C3H/HeJ Mphi required high concentration of LPS (5 microg/mL) to enhance the secretion of the cytokines. Yet, this dose remained ineffective to stimulate IFN-gamma in Mphi from C3H/HeJ mice. It can be presumed that one of the important factors influencing their deficient ability to form NO is a failure of Mphi to produce IFN-gamma upon LPS contact.

Understanding the mechanism of action of the exfoliative toxins of Staphylococcus aureus

The exfoliative toxins of Staphylococcus aureus are responsible for the staphylococcal scalded skin syndrome, a blistering skin disorder that particularly affects infants and young children, as well as adults with underlying disease. Their three-dimensional structure is similar to other glutamate-specific trypsin-like serine proteases with two substrate-binding domains and a serine-histidine-aspartate catalytic triad that forms the active site. However, unlike other serine proteases, the exfoliative toxins possess a highly charged N-terminal alpha-helix and a unique orientation of a critical peptide bond, which blocks the active site of the toxins so that, in their native state, they do not possess any significant enzymatic activity. The target for the toxins has recently been identified as desmoglein-1, a desmosomal glycoprotein which plays an important role in maintaining cell-to-cell adhesion in the superficial epidermis. It is speculated that binding of the N-terminal alpha-helix to desmoglein-1 results in a conformation change that opens the active site of the toxin to cleave the extracellular domain of desmoglein-1 between the third and fourth domains, resulting in disruption of intercellular adhesion and formation of superficial blisters. Elucidating the mechanism of action of the toxins and identifying desmoglein-1 as their specific epidermal substrate has not only given us an insight into the pathogenesis of the staphylococcal scalded skin syndrome, but also provided us with useful information on normal skin physiology and the pathogenesis of other toxin-mediated diseases. It is hoped that this knowledge will lead to development of rapid screening and diagnostic tests, and new antitoxin strategies for the treatment and prevention of the staphylococcal scalded skin syndrome in the near future.

Mycoplasma arthritidis superantigen (MAM)-induced macrophage nitric oxide release is MHC class II restricted, interferongamma dependent, and toll-like receptor 4 independent

Mycoplasma arthritidis causes arthritis in rodents that resembles human rheumatoid arthritis. It produces a superantigen (MAM) that stimulates production of cytokines by making a bridge between lymphocyte T-cell receptor with the appropriate Vbeta chain, and H-2 1-Ealpha MHC class II molecules. Here we studied MAM-induced nitric oxide (NO) production in mouse peritoneal macrophages and found that it was: (1) time and concentration dependent, (2) possibly derived from inducible NOS synthase since it was reduced significantly by amino guanidine pretreatment, (3) restricted to H-2(K) (C3H/HePas and C3H/HeJ) and H-2(d) strains (BALB/c), (4) independent of TLR4 signaling since the coisogenic strains C3H/HePas and C3H/HeJ (TLR4 deficient) produced similar levels of NO following MAM stimulation, (5) potentiated by lipopolysaccharide, and (6) dependent on the presence of nonadherent peritoneal cells. Neutralization of interferon-gamma (IFNgamma in the peritoneal cell cultures with monoclonal antibodies abolished MAM-induced NO production. Addition of rIFNgamma to the adherent cells substituted the nonadherent cells for MAM-induced NO production. A macrophage cell line, J774A.1 (H-2(d)), also produced NO upon MAM stimulation but only when BALB/c spleen lymphocytes were added. Thus, in murine macrophages, MAM induces NO production that is dependent on signaling through MHC class II molecules and IFNgamma but independent of TLR4 expression.

Persistent Ehrlichia chaffeensis infection occurs in the absence of functional major histocompatibility complex class II genes

Human monocytic ehrlichiosis is an emerging tick-borne disease caused by the rickettsia Ehrlichia chaffeensis. We investigated the impact of two genes that control macrophage and T-cell function on murine resistance to E. chaffeensis. Congenic pairs of wild-type and toll-like receptor 4 (tlr4)- or major histocompatibility complex class II (MHC-II)-deficient mice were used for these studies. Wild-type mice cleared the infection within 2 weeks, and the response included macrophage activation and the synthesis of E. chaffeensis-specific Th1-type immunoglobulin G response. The absence of a functional tlr4 gene depressed nitric oxide and interleukin 6 secretion by macrophages and resulted in short-term persistent infections for > or =30 days. In the absence of MHC-II alleles, E. chaffeensis infections persisted throughout the entire 3-month evaluation period. Together, these data suggest that macrophage activation and cell-mediated immunity, orchestrated by CD4(+) T cells, are critical for conferring resistance to E. chaffeensis.

Periapical lesion progression and cytokine expression in an LPS hyporesponsive model

AIM

The purpose of this study was to compare periapical lesion progression and the expression of the bone modulating cytokines IL-1alpha, TNF-alpha, IL-4, IL-6 and IL-11 in periapical lesions of normal and C3H/HeJ (LPS hyporesponsive) mice.

METHODOLOGY

Pulps of both mandibular first molars from C3H/HeJ and BALB/c (normal) mice were exposed and inoculated with normal mouse oral microorganisms for 2, 4, 6, and 8 weeks. After euthanasia, specimens were prepared for histological examination. A quantitative evaluation of the lesional area and immunohistochemical stain counts was performed.

RESULTS

There were no statistically significant differences in progression of periapical lesions for both mouse strains with time (two-factor ANOVA, P > 0.05). The immunohistochemical staining revealed no overall differences between the two strains in levels of expression of the cytokines (P > 0.05). IL-11 expression did not change from control levels in BALB/c mice, but correlated with the expression of IL-6 and IL-4 in C3H/HeJ mice.

CONCLUSION

Responsiveness to LPS may not be significant in the pathogenesis of periapical lesions and in cytokine expression within the lesions, when the lesions are induced by non-specific oral flora.

Recent developments in staphylococcal scalded skin syndrome

Staphylococcal scalded skin syndrome describes a spectrum of superficial blistering skin disorders caused by the exfoliative toxins of Staphylococcus aureus. In its severe form, the exfoliation can spread to cover the entire body surface area. Two S. aureus exfoliative toxin serotypes affecting humans have been identified, but their purpose and mechanism of action have remained elusive. Based on their interaction with human and mouse epidermis, their three-dimensional structure and site-directed mutagenesis studies, it is speculated that they act as atypical serine proteases, and desmoglein-1 has now been identified as the specific epidermal substrate. Recent studies also suggest that the toxins may have a unique superantigenic activity. Clinically, new rapid diagnostic tests have been developed, including one that is able to detect the toxins directly from serum. With early diagnosis and appropriate management, mortality in children remains low and long-term complications are rare because the lesions are superficial and heal rapidly without scarring. In adults, however, the condition carries a mortality of almost 60% despite aggressive treatment, usually because of serious underlying illness. The recent developments in our understanding of the exfoliative toxins should lead to new and improved diagnostic and therapeutic strategies, including the use of specific antixoxins to prevent exfoliation.

Microspheres containing neutralizing antibodies to tumor necrosis factor-alpha and interleukin-1 beta protect rats from Staphylococcus aureus-induced peritonitis

Previous studies using microencapsulated neutralizing antibodies (NA) to tumor necrosis factor (TNF) and interleukin-1 (IL-1) in combination with gentamicin have demonstrated improved survival in a peritonitis model of gram-negative septic shock. Microencapsulation has been shown to improve the effectiveness of NA by delivering them intracellularly, taking advantage of the natural phagocytic activity of the macrophage. It is the purpose of this study to see if microencapsulated NA to TNF and IL-1 in combination with vancomycin can improve survival compared with NA in solution in Staphlococcus aureus-induced septic shock. Groups of 10 rats received the following treatments: (1) S. aureus plus no treatment, (2) S. aureus plus blank microspheres, (3) S. aureus plus vancomycin, (4) S. aureus plus a microsphere form of NA and vancomycin, (5) S. aureus plus a solution form of NA and vancomycin, (6) S. aureus plus a microsphere form of NA, and (7) S. aureus plus a solution form of NA. Survival was monitored for 5 days, and plasma TNF and IL-1 levels were measured for 48 h after S. aureus administration. All (100%) animals that received the microsphere form of NA plus vancomycin, 20%-70% of the animals that received the microsphere form of NA alone, and 20% of the animals that received antibiotics alone survived for 5 days or more. None of the animals in the no treatment group or blank microsphere treatment group and only 10% of the animals in the solution form of NA plus or minus vancomycin group survived for more than 5 days. Plasma TNF and IL-1 levels were significantly increased after S. aureus treatment. Simultaneous and delayed treatment with the microsphere form of NA plus or minus vancomycin significantly reduced TNF and IL-1 levels, and the solution form of NA significantly reduced only TNF levels after immediate treatment. The survival rate was higher in animals with lower TNF levels and IL-1 levels. The results demonstrate that the microsphere form of cytokine NA is 100% effective in combination with vancomycin in protecting rats from S. aureus-induced peritonitis. The microsphere form was also more efficient in attenuating both TNF and IL-1 levels.

Depression of constitutive murine cytochromes P450 by staphylococcal enterotoxin B

Most in vivo studies demonstrating decreased activities of hepatic cytochromes P450 with inflammation have used Gram-negative bacterial lipopolysaccharide (LPS) as the inflammatory stimulant. But products of Gram-positive bacteria, such as staphylococcal enterotoxin B (SEB), also stimulate inflammatory mediators, albeit with a different pattern than LPS. Therefore, effects of SEB on the regulation of murine constitutive P450s were determined in this study and compared with those of LPS. LPS-responsive C3H/HeN and LPS-unresponsive C3H/HeJ mice were injected with either LPS (0.5 mg/kg) or SEB (0.66 to 6.6 mg/kg), and hepatic cytochromes P450 and serum tumor necrosis factor-alpha, interleukin-6, nitrate/nitrite, and serum amyloid A concentrations were determined up to 24 hr. HeJ mice were generally less responsive than HeN mice to both stimuli, with lower cytokine, nitrate/nitrite, and serum amyloid A responses. However, in both mouse strains SEB caused more prolonged cytokine, higher nitrate/nitrite, and lower serum amyloid A concentrations than LPS. Despite these differences, in HeN mice, after both SEB and LPS administration, total P450 concentrations were equally depressed by 40%. Both SEB and LPS depressed CYP1A1 and 1A2 microsomal protein concentrations by 45 and 30%, respectively; CYP2E1 by 64%; and CYP3A by 70%. There was comparable inhibition of enzymatic activities. In HeJ mice, SEB was only slightly more effective in depressing P450s than LPS, as might be expected. These data showed that the Gram-positive bacterial inflammatory stimulant SEB caused effects on murine hepatic cytochromes P450 similar to those of LPS, even though the pattern of inflammatory mediators induced after SEB exposure was different.

Interleukin-10 inhibits hepatic injury and tumor necrosis factor-alpha and interferon-gamma mRNA expression induced by staphylococcal enterotoxin B or lipopolysaccharide in galactosamine-sensitized mice

BACKGROUND/AIMS

Proinflammatory cytokines including tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) play a critical role in the pathogenesis of liver injury induced by lipopolysaccharide (LPS) or staphylococcal enterotoxin B (SEB) in D-galactosamine (GalN)-sensitized mice. The aim of this study was to examine the ability of interleukin-10 (IL-10), a recently characterized, highly potent anti-inflammatory mediator, to protect sensitized mice against hepatotoxicity induced by SEB or LPS.

METHODS

IL-10 was injected at various concentrations into BALB/c mice treated by GalN/SEB or GalN/LPS. Liver injury was assessed biochemically and histologically. Serum levels of TNF-alpha and IFN-gamma were measured and the expressions of TNF-alpha and IFN-gamma mRNA in the liver and spleen were determined by reverse-transcription polymerase chain reaction.

RESULTS

Treatment with IL-10 markedly reduced serum transaminase activities in a dose-dependent manner and reduced hemorrhagic liver damage in sensitized mice exposed to either toxin. IL-10 also inhibited increases in serum TNF-alpha and IFN-gamma concentrations with either toxin. Treatment with IL-10 significantly reduced TNF-alpha mRNA and IFN-gamma mRNA expression in the liver and spleen after administration of either toxin to sensitized mice.

CONCLUSIONS

These findings suggest that IL-10 is capable of regulating both T cell- and macrophage-mediated hepatic injury in vivo and that this cytokine might be useful in the treatment of acute liver failure.

Effects of spaceflight and PEG-IL-2 on rat physiological and immunological responses

Sprague-Dawley rats were subjected to two 8-day spaceflights on the space shuttle. Rats housed in the National Aeronautics and Space Administration's animal enclosure were injected (iv or sc) with pegylated interleukin-2 (PEG-IL-2) or a placebo. We tested the hypothesis that PEG-IL-2 would ameliorate some of the effects of spaceflight. We measured body and organ weights; blood cell differentials; plasma corticosterone; colony-forming units (macrophage and granulocyte macrophage); lymphocyte mitogenic, superantigenic, and interferon-gamma responses; bone marrow cell and peritoneal macrophage cytokine secretion; and bone strength and mass. Few immunological parameters were affected by spaceflight. However, some spaceflight effects were observed in each flight. Specifically, peritoneal macrophage spontaneous secretion of tumor necrosis factor-alpha occurred in the first but not in the second flight. A significant monocytopenia and lymphocytopenia were detected in the second but not in the first flight. The second mission produced bone changes more consistent with past spaceflight investigations. PEG-IL-2 did not appear to be beneficial; however, this was mostly due to the lack of spaceflight effects. These studies reflect the difficulty in reproducing experimental models by using current space shuttle conditions.

Clinical, microbial, and biochemical aspects of the exfoliative toxins causing staphylococcal scalded-skin syndrome

The exfoliative (epidermolytic) toxins of Staphylococcus aureus are the causative agents of the staphylococcal scalded-skin syndrome (SSSS), a blistering skin disorder that predominantly affects children. Clinical features of SSSS vary along a spectrum, ranging from a few localized blisters to generalized exfoliation covering almost the entire body. The toxins act specifically at the zona granulosa of the epidermis to produce the characteristic exfoliation, although the mechanism by which this is achieved is still poorly understood. Despite the availability of antibiotics, SSSS carries a significant mortality rate, particularly among neonates with secondary complications of epidermal loss and among adults with underlying diseases. The aim of this article is to provide a comprehensive review of the literature spanning more than a century and to cover all aspects of the disease. The epidemiology, clinical features, potential complications, risk factors, susceptibility, diagnosis, differential diagnoses, investigations currently available, treatment options, and preventive measures are all discussed in detail. Recent crystallographic data on the toxins has provided us with a clearer and more defined approach to studying the disease. Understanding their mode of action has important implications in future treatment and prevention of SSSS and other diseases, and knowledge of their specific site of action may provide a useful tool for physiologists, dermatologists, and pharmacologists.

Lymphocyte Activation Gene-3, a MHC Class II Ligand Expressed on Activated T Cells, Stimulates TNF-α and IL-12 Production by Monocytes and Dendritic Cells

Lymphocyte activation gene-3 (LAG-3) is an MHC class II ligand structurally and genetically related to CD4. Although its expression is restricted to activated T cells and NK cells, the functions of LAG-3 remain to be elucidated. Here, we report on the expression and function of LAG-3 on proinflammatory bystander T cells that are activated in the absence of TCR engagement. LAG-3 is expressed at high levels on human T cells cocultured with autologous monocytes and IL-2 and synergizes with the low levels of CD40 ligand (CD40L) expressed on these cells to trigger TNF-α and IL-12 production by monocytes. Indeed, anti-LAG-3 mAb inhibits both IL-12 and IFN-γ production in IL-2-stimulated cocultures of T cells and autologous monocytes. Soluble LAG-3Ig fusion protein markedly enhances IL-12 production by monocytes stimulated with infra-optimal concentrations of sCD40L, whereas it directly stimulates monocyte-derived dendritic cells (DC) for the production of TNF-α and IL-12, unravelling an enhanced responsiveness to MHC class II engagemenent in DC as compared with activated monocytes. Thus similar to CD40L, LAG-3 may be involved in the proinflammatory activity of cytokine-activated bystander T cells and most importantly it may directly activate DC.

Effects of space flight and IGF-1 on immune function

We tested the hypothesis that insulin-like growth factor-1 (IGF-1) would ameliorate space flight-induced effects on the immune system. Twelve male, Sprague-Dawley rats, surgically implanted with mini osmotic pumps, were subjected to space flight for 10 days on STS-77. Six rats received 10 mg/kg/day of IGF-1 and 6 rats received saline. Flight animals had a lymphocytopenia and granulocytosis which were reversed by IGF-1. Flight animals had significantly higher corticosterone levels than ground controls but IGF-1 did not impact this stress hormone. Therefore, the reversed granulocytosis did not correlate with serum corticosterone. Space flight and IGF-1 also combined to induce a monocytopenia that was not evident in ground control animals treated with IGF-1 or in animals subjected to space flight but given physiological saline. There was a significant increase in spleen weights in vivarium animals treated with IGF-1, however, this change did not occur in flight animals. We observed reduced agonist-induced lymph node cell proliferation by cells from flight animals compared to ground controls. The reduced proliferation was not augmented by IGF-1 treatment. There was enhanced secretion of TNF, IL-6 and NO by flight-animal peritoneal macrophages compared to vivarium controls, however, O2(-) secretion was not affected. These data suggest that IGF-1 can ameliorate some of the effects of space flight but that space flight can also impact the normal response to IGF-1. Grant Numbers: NAGW-1197, NAGW-2328.

Antitumor Response Elicited by a Superantigen- Transmembrane Sequence Fusion Protein Anchored onto Tumor Cells

Superantigens stimulate T cells bearing certain TCR β-chain variable regions when bound to MHC II molecules. We investigated whether the superantigen toxic shock syndrome toxin-1 (TSST1) could induce an antitumor immune response when anchored onto MHC II-negative tumor cells. Our approach was to facilitate association of TSST1 with cell membranes by fusing its coding region to the transmembrane region (TM) sequence of the proto-oncogene c-erb-B-2. TSST1-TM was expressed in bacteria with an N-terminal histidine tag and purified using nickel-agarose affinity chromatography. Purified TSST1-TM added to cultures of several different MHC II-negative tumor cells spontaneously associated with cell membranes, as detected by flow cytometry. Because superantigens can direct cell-mediated cytotoxicity against MHC II-positive cells, a TM fusion protein lacking the TSST1 MHC II binding domain (TSST88–194-TM) was also constructed. Tumor cells precoated with TSST1-TM or TSST88–194-TM stimulated proliferation of human peripheral blood lymphocytes in vitro whereas uncoated tumor cells did not. Mice preimmunized with TSST1-TM- or TSST88–194-TM-coated tumor cells mounted a systemic response that resulted in significant antitumor immunity as measured by regression of a parental tumor challenge. TSST1-TM and TSST88–194-TM fusion proteins represent a useful new strategy for attaching superantigens or potentially other proteins onto tumor cell surfaces without genetic manipulation.

Macrophage cell lines derived from major histocompatibility complex II-negative mice

Two bone-marrow-derived macrophage cell lines, C2D and C2Dt, were isolated from major histocompatibility class II negative knock-out mice. The C2D cell line was stabilized by continuous culture in colony-stimulating factor-1 and the C2Dt cell line was transformed with SV40 virus large T antigen. These cells exhibited phenotypic properties of macrophages including morphology and expression of Mac 1 and Mac 2 cell surface molecules. These cells also had comparable growth to the bone-marrow-derived macrophage cell line B6MP102. These new cell lines were not spontaneously cytotoxic and were only capable of modest killing of F5b tumor cells when stimulated with LPS and interferon-gamma, but not when stimulated with LPS alone or with staphylococcal exotoxin. C2D and C2Dt cells phagocytosed labeled Staphylococcus aureus similarly to B6MP102 cells but less well than C2D peritoneal macrophages. These cell lines secreted interleukin-6, but not tumor necrosis factor or nitric oxide in response to LPS or staphlococcal enterotoxins A or B C2D(t) cells were tumorigenic in C2D and C57BL/6J mice but C2D cells were not. These data suggest that macrophage cell lines can be established from bone marrow cells of major histocompatibility complex II-negative mice.

Endotoxin alters the systemic disposition of nitric oxide synthase inhibitors in the awake sheep

1. We evaluated the haemodynamic effects and systemic disposition of the nitric oxide synthase (NOS) inhibitor NL-nitro-L-arginine (NOLA) after intravenous (i.v.) administration of two different doses (5 and 20 mg/kg) in awake healthy sheep and awake sheep given a continuous i.v. infusion of endotoxin (lipopolysaccharide, 12 ng/kg per h, i.v., for 18 h). In addition, we determined the systemic disposition of another NOS inhibitor, NL-nitro-L-arginine methylester (L-NAME; 20 mg/kg, i.v.) in awake healthy sheep only. 2. NL-Nitro-L-arginine produced a dose-dependent decrease in heart rate (HR) and cardiac output (CO) together with a dose-dependent increase in mean arterial pressure (MAP) and peripheral vascular resistance (PVR) when compared to baseline. In endotoxic sheep NOLA produced a greater increase in MAP and mean pulmonary arterial pressure (MPAP). 3. In healthy sheep there was a dose-related increase in total body clearance (Cl) of NOLA. The Cl increased from 0.028 L/min after the lower dose to 0.032 L/min after the higher dose. The infusion of endotoxin caused an increase in Cl of NOLA to 0.040 and 0.047 L/min, respectively, and a decrease in plasma slow half-life (t1/2) from 825 to 546 min and from 780 to 453 min, respectively. 4. NL-Nitro-L-arginine methylester was rapidly cleared from the plasma with a slow half-life of approximately 7.5 min and there was a simultaneous appearance of NOLA in the plasma. 5. These results support the view that nitric oxide has a significant role in regulating vascular tone in healthy and endotoxic sheep and indicate that the increases in Cl of NOLA with an increase in its dose and the presence of endotoxin will be important in influencing appropriate dosage regimens in clinical studies.

Role of tumor necrosis factor and nitric oxide in the cytotoxic effects of Clostridium difficile toxin A and toxin B on macrophages

Clostridium difficile, the bacterium involved in antibiotic-associated colitis, produces two exotoxins, toxin A (TxA) and toxin B (TxB). Although these toxins are well recognized as being cytotoxic to several mammalian cell types, the mechanisms involved are not fully understood. The aim of the present investigation was to examine the cytotoxicity of TxA and TxB to peritoneal macrophages in culture and to investigate whether tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) are involved in the process. As a control, the effect of E. coli LPS was also investigated. TxA, TxB and LPS were dose-dependently cytotoxic to macrophage monolayers, with TxB being the most potent. All of the toxins stimulated the release of TNF-alpha from macrophages. TxB was again the most active in inducing this response. The TNF-alpha released appears to be involved in the action of LPS and TxA, but not of TxB, since a mAb against TNF-alpha inhibited the cytotoxicity of the former two but had no effect on the latter. NO is not involved in the effects of TxA and TxB since these toxins did not induce the production of this mediator in macrophages, even in the presence of IFN-gamma. In addition, L-imino-ethyl-L-ornithine (L-NIO), a NO synthase inhibitor, did not modify the macrophage death caused by TxA or TxB. Although LPS was able to induce the production of high amounts of NO, NO did not mediate the LPS cytotoxicity since L-NIO did not influence the degree of macrophage death caused by LPS. TxA and TxB therefore appear to exert cytotoxic effects on cultured macrophages by different mechanisms. TNF-alpha is involved in TxA and LPS-mediated cytotoxicity but not in the toxicity caused by TxB. NO is not involved in the killing action of any of these toxins.

Immunohistochemical localization of nitric oxide synthase in normal human skin: expression of endothelial-type and inducible-type nitric oxide synthase in keratinocytes

Nitric oxide (NO) is a critical mediator of various biological functions. NO is generated from L-arginine by nitric oxide synthase (NOS), which has three isoforms; endothelial-type NOS (eNOS) and brain-type NOS (bNOS) are constitutive enzymes, and inducible-type NOS (iNOS) is expressed after stimulation. We investigated the expression of NOS in normal human skin by an immunohistochemical technique and western blotting analysis. In human skin, epidermal keratinocytes and the outer root sheath were labeled with not only eNOS antibody but also with iNOS antibody. Both eNOS and iNOS protein in epidermal keratinocytes were confirmed by western blotting. eNOS immunoreactivity was observed in endothelial cells, fibroblasts, the arrector pili muscle, apocrine secretory gland, eccrine coiled duct, and eccrine secretory gland. bNOS immunoreactivity was observed in mast cells. No staining with anti-bNOS antibody was observed in any other cell type. Our present findings suggest that epidermal keratinocytes in normal human skin contain both eNOS and iNOS.

Effect of endotoxin on interleukin-6 secretion and messenger ribonucleic acid in porcine anterior pituitary cells

The pleiotropic cytokine interleukin-6 (IL-6) is produced in and secreted from anterior pituitary (AP) cells of a number of species. Bacterial endotoxin (END) may enhance the transcription of IL-6 and its secretion from the AP. In the studies presented here, we evaluated pig AP cells for the presence of IL-6 mRNA. In addition, because we had observed previously that END stimulated the secretion of prostaglandin E2 from cultured porcine AP cells, the effects of the inhibition of END-stimulated cyclooxygenase products on IL-6 mRNA abundance and the secretion of IL-6 were evaluated. In the first experiment, RNA was extracted from cultured pig AP cells that had been treated with END for 0.5 or 1 hr and subjected to reverse transcription followed by polymerase chain reaction and hybridization after Southern transfer. Bands of expected amplified product size, corresponding to IL-6, were observed only from cells treated with END, although specific hybridization was observed from both control and END-treated wells. In the next experiment, RNA was extracted from cultured AP cells treated with END or END in the presence of the cyclooxygenase inhibitor indomethacin (IND). Amplification of the expected product could be observed from all cultured cells except those treated with IND. However, hybridization data indicated that IND did not eliminate IL-6 mRNA entirely. Next, we measured IL-6 secretion from cultured AP cells exposed to END or END and IND. Treatment with END stimulated IL-6 secretion (P < 0.001) above controls, whereas IND blocked END stimulation of IL-6 secretion (P < 0.001). Finally, using immunostaining, we confirmed the presence of CD14, an END receptor, in cultured pig AP cells. These studies clearly establish the presence of IL-6 mRNA and secretion of the cytokine from cultured porcine AP cells. In addition, END stimulates the secretion of IL-6, perhaps through cells expressing CD14, and END-stimulated IL-6 secretion appears to be mediated by products of the cyclooxygenase pathway.

Staphylococcal enterotoxins bind H-2Db molecules on macrophages

We screened a panel of monoclonal antibodies against selected macrophage cell surface molecules for their ability to inhibit enterotoxin binding to major histocompatibility complex class II-negative C2D (H-2b) macrophages. Two monoclonal antibodies, HB36 and TIB126, that are specific for the alpha 2 domain of major histocompatibility complex class I, blocked staphylococcal enterotoxins A and B (SEA and SEB, respectively) binding to C2D macrophages in a specific and concentration-dependent manner. Inhibitory activities were haplotype-specific in that SEA and SEB binding to H-2k or H-2d macrophages was not inhibited by either monoclonal antibody. HB36, but not TIB126, inhibited enterotoxin-induced secretion of cytokines by H-2b macrophages. Lastly, passive protection of D-galactosamine-sensitized C2D mice by injection with HB36 antibody prevented SEB-induced death. Therefore, SEA and SEB binding to the alpha 2 domain of the H-2Db molecule induces biological activity and has physiological consequences.

A toxic shock syndrome toxin 1 mutant that defines a functional site critical for T-cell activation

Toxic shock syndrome toxin 1 (TSST-1), a superantigen produced by Staphylococcus aureus, is a causative agent of toxic shock syndrome (TSS). This superantigen is a potent stimulator of T cells and macrophages/monocytes, resulting in the release of cytokines that are implicated in the pathogenesis of TSS. This study characterizes a mutant TSST-1, derived by site-directed mutagenesis, that has an alanine substitution at histidine 135 (mutant 135). This single-amino-acid change results in a mutant toxin that has lost mitogenic activity for T cells. In contrast to wild-type TSST-1, this mutant does not induce T cells to express interleukin-2, gamma interferon, or tumor necrosis factor beta (TNF-beta). The inability of mutant 135 to activate T cells is not due to a lack of binding to the class II major histocompatibility complex receptor. In addition, the mutant TSST-1 does not induce expression of TNF-alpha, which plays a role in the development of lethal shock. The lack of TNF-alpha induction by mutant 135 is likely due to its inability to activate T cells. These data suggest that the mutation at histidine 135 in TSST-1 affects toxin interactions with the T-cell receptor rather than the class II major histocompatibility complex receptor.

Superantigens and pseudosuperantigens of gram-positive cocci

Superantigens use an elaborate and unique mechanism of T lymphocyte stimulation. Prototype superantigen are the pyrogenic exotoxins produced by Staphylococcus aureus and Streptococcus pyogenes. Many candidate proteins of bacterial, viral and protozoal origin have recently been reported to be superantigens. In most cases the evidence that these proteins are in fact superantigens is highly indirect. In this review the evidence that gram-positive cocci produce superantigens other than the pyrogenic exotoxins is critically discussed. Evidence in described demonstrating that the epidermolytic toxins of Staphylococcus aureus and the pyrogenic exotoxin B and M-proteins of Streptococcus pyrogenes are not superantigens. Criteria are described for acceptance of a candidate as a superantigen.

Staphylococcal glycocalyx activates macrophage prostaglandin E2 and interleukin 1 production and modulates tumor necrosis factor alpha and nitric oxide production

We have examined the effect of staphylococcal glycocalyces on the ability of murine peritoneal macrophages to produce prostaglandin E2 (PGE2) and the inflammatory cytokines interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) and to generate nitric oxide. Glycocalyx partially purified under endotoxin-free conditions from defined liquid medium cultures of Staphylococcus lugdunensis or Staphylococcus epidermidis was a strong stimulator of PGE2 and IL-1 production. The addition of 10 to 100 micrograms of glycocalyx per ml induced levels of IL-1 and PGE2 production similar to that induced by 0.1 to 1 micrograms of Escherichia coli lipopolysaccharide (LPS) per ml. In contrast, glycocalyx induced ninefold less TNF-alpha and three- to fourfold less nitrite than LPS. A modulatory effect was suggested by the observation that the amount of TNF-alpha and nitrite generated remained constant whether the macrophages were stimulated with 10 or 100 micrograms of glycocalyx per ml. A selective modulation of macrophage activation was confirmed by the demonstration that costimulation of macrophages with both glycocalyx and LPS resulted in a reduction in TNF-alpha and nitrite generation relative to stimulation with LPS alone even though costimulation had no effect on PGE2 production and increased IL-1 production. Involvement of PGE2 in this modulatory effect was suggested by the ability of indomethacin to augment glycocalyx-stimulated TNF-alpha production and to reverse the inhibitory effect of glycocalyx on LPS induction of TNF-alpha production. However, the inability of indomethacin to reverse the inhibitory effect of glycocalyx on LPS-induced nitric oxide generation suggests that the selective modulation of macrophage function by glycocalyx may be more complex than increased sensitivity to PGE2 feedback inhibition.

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.

Effects of extracellular matrix proteins on macrophage differentiation, growth, and function: comparison of liquid and agar culture systems

Both spaceflight and skeletal unloading suppress the haematopoietic differentiation of macrophages (Sonnenfeld et al., Aviat. Space Environ. Med., 61:648-653, 1990; Armstrong et al., J. Appl. Physiol., 75:2734-2739, 1993). The mechanism behind this reduction in haematopoiesis has yet to be elucidated. However, changes in bone marrow extracellular matrix (ECM) may be involved. To further understand the role of ECM products in macrophage differentiation, we have performed experiments evaluating the effects of fibronectin, laminin, collagen type I, and collagen type IV on macrophage development and function. Bone marrow-derived macrophages cultured on four different ECM substrates in liquid culture medium showed less growth than those cultured on plastic. Significant morphological differences were seen on each of the substrates used. Phenotypically and functionally, as measured by class II major histocompatibility molecule (MHCII) expression, MAC-2 expression, and the secretion of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), these macrophages were similar. In contrast, bone marrow-derived macrophages cultured in suspension, using agar, showed no difference in growth when exposed to ECM proteins. However, IL-6 and TNF-alpha secretion was affected by fibronectin, laminin, collagen type I, and collagen type IV in a concentration-dependent manner. We conclude that the ECM products fibronectin, laminin, collagen type I, and collagen type IV have profound effects on macrophage development and function. Additionally, we suggest that an ECM-supplemented agar culture system provides an environment more analogous to in vivo bone marrow than does a traditional liquid culture system.

Leukocytosis and resistance to septic shock in intercellular adhesion molecule 1-deficient mice

Intercellular adhesion molecule 1 (ICAM-1) is one of three immunoglobulin superfamily members that bind to the integrins lymphocyte function associated 1 (LFA-1) and Mac-1 on leukocytes. We have generated mice that are genetically and functionally deficient in ICAM-1. These mice have elevated numbers of circulating neutrophils and lymphocytes, as well as diminished allogeneic T cell responses and delayed type hypersensitivity. Mutant mice are resistant to lethal effects of high doses of endotoxin (lipopolysaccharide [LPS]), and this correlates with a significant decrease in neutrophil infiltration in the liver. Production of inflammatory cytokines such as tumor necrosis factor alpha or interleukin 1 is normal in ICAM-1-deficient mice, and thus protection appears to be related to a diminution in critical leukocyte-endothelial interactions. After sensitization with D-galactosamine (D-Gal), ICAM-1-deficient mice are resistant to the lethal effect of low doses of exotoxin (Staphylococcus aureus enterotoxin B [SEB]), which has been shown to mediate its toxic effects via the activation of specific T cells. In this model, ICAM-1-mediated protection against SEB lethality correlates with a decrease in the systemic release of inflammatory cytokines, as well as with prevention of extensive hepatocyte necrosis and hemorrhage. ICAM-1-deficient mice sensitized with D-Gal, however, are not protected from lethality when challenged with low doses of endotoxin (LPS). These studies show that the different contribution of ICAM-1 in the activation of either T cells or macrophages is decisive for the fatal outcome of the shock in these two models. This work suggests that anti-ICAM-1 therapy may be beneficial in both gram-positive and -negative septic shock, either by reducing T cell activation or by diminishing neutrophil infiltration.

Biological and kinetic characterization of recombinant human macrophage inflammatory peptides 2 alpha and beta and comparison with the neutrophil activating peptide 2 and interleukin 8

We examined the biological and kinetic characteristics of two new members of the intercrine family of cytokines. Human macrophage inflammatory peptides 2 alpha and beta (huMIP-2 alpha and beta) were compared to human interleukin 8 (huIL-8), neutrophil activating peptide 2 (huNAP-2), and N-formyl-L-methionyl-L-phenylalanine (fMLP). The huMIP-2 peptides were the least potent cytokine tested in triggering neutrophil degranulation. They were also less potent neutrophil chemotaxins than fMLP or huIL-8. However, they were more effective than NAP-2 in stimulating chemotaxis of neutrophils. The binding studies showed that huMIP-2 peptides could interact with specific receptors on human blood neutrophils. Moreover, huMIP-2 peptides competed for up to 60% of the huIL-8 binding sites on neutrophils whereas huIL-8 competed for almost 100% of either of the huMIP-2 peptide binding sites. These data suggest the huMIP-2 peptides have little or no affinity for 40% of the huIL-8 receptors. In addition, detectable amounts of mRNA for huMIP-2 alpha were found in samples from human alveolar macrophages stimulated with Staphylococcus aureus, toxic shock syndrome toxin-1 (TSST), but not in samples stimulated with S. aureus enterotoxin A (SEA) or Escherichia coli endotoxin (lipopolysaccharide = LPS). In conclusion, huMIP-2 alpha and beta are weak neutrophil stimulating agents, which may increase inflammation in diseases such as toxic shock syndrome.

Induction of cytokines in phagocytic mammalian cells infected with virulent and avirulent Listeria strains

The present paper analyzes the cytokine response of mouse macrophages during infection by Listeria monocytogenes. The use of different mutants of L. monocytogenes impaired in various steps of the infection process allowed us to dissect the cytokine response. Cytokine mRNA expression was detected by PCR-assisted amplification of RNA extracted from macrophages after infection with different Listeria strains. An increase in the amount of mRNA for tumor necrosis factor alpha (TNF-alpha), interleukin-1 alpha (IL-1 alpha), IL-1 beta, and IL-6 was detected in P388D1 macrophages infected with L. monocytogenes at 4 h postinfection. Interestingly, only hemolytic strains of L. monocytogenes were able to induce IL-1 alpha, IL-6, and TNF-alpha mRNA. This indicated that the induction of these cytokine mRNAs requires entry of the listeriae into the host cell cytoplasm. In contrast, IL-1 beta was also induced by infection with nonhemolytic mutants of L. monocytogenes which remain entrapped within the phagosome. The levels of TNF, IL-1 alpha, and IL-6 found in the supernatants of Listeria-infected P388D1 macrophages generally correlated well with the induction of the respective mRNAs, but it became obvious that cytokine activity is also regulated through posttranscriptional mechanisms. In vitro induction of the cytokines IL-1 alpha, IL-1 beta, IL-6, and TNF-alpha was also observed by infection of bone-marrow-derived macrophages with L. monocytogenes.

Production and action of cytokines in space

B6MP102 cells, a continuously cultured murine bone marrow macrophage cell line, were tested for secretion of tumor necrosis factor-alpha and Interleukin-1 during space flight. We found that B6MP102 cells secreted more tumor necrosis factor-alpha and interleukin-1 when stimulated in space with lipopolysaccharide than controls similarly stimulated on earth. This compared to increased secretion of interferon-beta and -gamma by lymphocytes that was measured on the same shuttle flights. Although space flight enhanced B6MP102 secretion of tumor necrosis factor-alpha, an experiment on a subsequent space flight (STS-50) found that cellular cytotoxicity, mediated by tumor necrosis factor-alpha, was inhibited.

Engagement of major histocompatibility complex class II molecules leads to nitrite production in bone marrow-derived macrophages

The present study was designed to examine whether engagement of major histocompatibility complex (MHC) class II molecules can lead to induction of NO synthase in bone marrow-derived macrophages. We treated the macrophages with toxic shock syndrome toxin 1 (TSST-1), a superantigen which activates T cells in an MHC class II-dependent manner. Upon addition of syngeneic spleen cells as a source of mature T cells to the TSST-1-treated macrophage culture. NO2- production was greatly increased. To test whether monoclonal antibodies (mAb) to MHC class II antigens also serve as an effective trigger signal for induction of NO synthase we incubated the cells with the anti-I-Ad/b mAb D3.137 and measured NO2- production in culture supernatants. The addition of the mAb D3.137 resulted in NO2- production which was completely suppressed by NG-monomethyl-L-arginine, a homologue of L-arginine, indicating that antibody-induced NO2- production was due to activation of NO synthase. The ability of anti-I-A antibodies, which may imitate the effects of T cells, to induce NO2- production suggests that MHC class II molecules act as transmembrane signal transducers finally leading to induction of NO synthase.

Staphylococcus-mediated T-cell activation and spontaneous natural killer cell activity in the absence of major histocompatibility complex class II molecules

We used major histocompatibility complex class II antigen-deficient transgenic mice to show that in vitro natural killer cell cytotoxicity and T-cell activation by staphylococcal exotoxins (superantigens) are not dependent upon the presence of major histocompatibility complex class II molecules. T cells can be activated by exotoxins in the presence of exogenously added interleukin 1 or 2 or in the presence of specific antibody without exogenously added cytokines.

Superantigenic exotoxin-secreting potential of staphylococci isolated from atopic eczematous skin

Although the deleterious effect of Staphylococcus aureus on atopic eczema is well recognized, the mechanism of this effect may be more complex than pyogenic infection alone. We have shown that the majority of S. aureus cultures isolated from atopic eczema produced exotoxins with superantigenic properties, although this was no more frequent than in a control group, and was not restricted to one particular superantigen. However, the widespread nature of staphylococcal infections in atopic eczema indicates that sufficient superantigen may be released to cause T-lymphocyte activation, cytokine release, and mast cell degranulation. These mechanisms could, in part, explain the exacerbations of atopic eczema associated with S. aureus infection.

Induction of macrophage parasiticidal activity by Staphylococcus aureus and exotoxins through the nitric oxide synthesis pathway

Murine peritoneal macrophages stimulated in vitro with killed Gram-positive bacteria Staphylococcus aureus or its membrane components in the presence of interferon-gamma (IFN-gamma) expressed high levels of nitric oxide (NO) synthase and produced large amounts of NO in a dose-dependent manner. This is not due to the contamination by Gram-negative endotoxin because the stimulatory activity was not affected by the addition of polymyxin B. The expression of the NO synthase and the synthesis of NO by macrophages stimulated with toxic shock syndrome toxin-1 (TSST), lipoteichoic acid (LTA) or killed whole S. aureus together with IFN-gamma was inhibited by the glucocorticoid, dexamethasone or by the specific inhibitor of NO synthesis, L-N-iminoethyl-ornithine (L-NIO). The exotoxins together with IFN-gamma also activated macrophages to kill the intracellular parasite Leishmania major. The leishmanicidal activity was completely inhibited by L-NIO.

Phenotypic characterization of xpr, a global regulator of extracellular virulence factors in Staphylococcus aureus

We recently described a Tn551 insertion in the chromosome of Staphylococcus aureus S6C that resulted in drastically reduced expression of extracellular lipase (M. S. Smeltzer, S. R. Gill, and J. J. Iandolo, J. Bacteriol. 174:4000-4006, 1992). The insertion was localized to a chromosomal site (designated omega 1058) distinct from the lipase structural gene (geh) and the accessory gene regulator (agr), both of which were structurally intact in the lipase-negative (Lip-) mutants. In this report, we describe a phenotypic comparison between strains S6C, a hyperproducer of enterotoxin B; KSI9051, a derivative of S6C carrying the Tn551 insertion at omega 1058; ISP546, an 8325-4 strain that carries a Tn551 insertion in the agr locus; and ISP479C, the parent strain of ISP546 cured of the Tn551 delivery plasmid pI258repA36. Compared with their respective parent strains, ISP546 and KSI9051 produced greatly reduced amounts of lipase, alpha-toxin, delta-toxin, protease, and nuclease. KSI9051 also produced reduced amounts of staphylococcal enterotoxin B. Coagulase production was increased in ISP546 but not in KSI9051. Using a mouse model, we also demonstrated that ISP546 and KSI9051 were far less virulent than ISP479C and S6C. We have designated the genetic element defined by the Tn551 insertion at omega 1058 xpr to denote its role as a regulator of extracellular protein synthesis. We conclude that xpr and agr are similar and possibly interactive regulatory genes that play an important role in pathogenesis of staphylococcal disease.

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.

Feedback suppression of staphylococcal enterotoxin-stimulated T-lymphocyte proliferation by macrophages through inductive nitric oxide synthesis

Staphylococcal enterotoxin A (SEA)- or SEB-stimulated T-lymphocyte proliferation was suppressed by the addition of high numbers of murine peritoneal macrophages or rat peritoneal or alveolar macrophages, whereas lower numbers of murine peritoneal macrophages enhanced the T-lymphocyte response. Suppression was associated with the increase of accumulation of nitrite, a product of nitric oxide, in the culture supernatants. This macrophage-mediated suppression was totally reversed by the addition of NG-monomethyl-L-arginine, a homolog of L-arginine, indicating that macrophage-mediated suppression of T-lymphocyte proliferation was mediated through the nitric oxide-synthesizing pathway activity. Macrophages in large numbers spontaneously produced nitric oxide in culture supernatant fluids. By the addition of autologous or allogeneic spleen cells but not thymocytes to SEA- or SEB-stimulated macrophage culture, nitric oxide production was greatly increased. When T lymphocytes in spleen cells were killed by antibody before addition to macrophage culture, nitric oxide production was diminished to the basal level. These results suggest that in addition to the action to support the process of T-lymphocyte activation by SEA or SEB, macrophages display a feedback regulatory action on the SEA- or SEB-stimulated T-cell proliferative response by releasing nitric oxide through interaction between macrophages and activated T lymphocytes.