One-way synergistic effect of low superantigen concentrations on lipopolysaccharide-induced cytokine production

COVID-19-Associated Acute Brain Dysfunction Related to Sepsis

In global term, as of November 30, 2020, over 30 million people has been infected by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and more than 10,000,000 of them died of acute organ failure. Our reviews have shown that coronavirus disease 2019 (COVID-19) patients with pneumonia and acute respiratory distress syndrome (ARDS) have life-threatening acute brain dysfunction (ABD), ranging from altered mental status/delirium to stupor/coma. Altered mental status/delirium was the most common manifestation of ABD caused by severe COVID-19. The prevalence of altered mental status and/or delirium was up to 66-79.5%, and prevalence of coma was 10%. The most common clinical type of COVID-19-associated ABD was COVID-19-associated acute stroke including ischemic and hemorrhagic stroke (n > 350 cases), followed by COVID-19-associated encephalopathy (n > 200 cases), and COVID-19-associated central nervous system (CNS) infection (n > 70 cases). According to the Sepsis-3 criteria, we confess that severe COVID-19-associated ABD with ARDS and altered mental status is related to sepsis. Moreover, we also review the diagnosis and treatment of COVID-19-associated ABD with sepsis. In view of the fact that COVID-19 is at the peak of epidemic worldwide, we hope that this review will provide evidence of COVID-19 sepsis threating to the brain dysunction. Thus, recognizing the COVID-19-associated ABD related to sepsis is very important for early empirical combination therapy to survive severe COVID-19.

Toxic Shock Syndrome Toxin 1 Induces Immune Response via the Activation of NLRP3 Inflammasome

Staphylococcus aureus is a Gram-positive opportunistic pathogen which causes infections in a variety of vertebrates. Virulence factors are the main pathogenesis of S. aureus as a pathogen, which induce the host’s innate and adaptive immune responses. Toxic shock syndrome toxin 1 (TSST-1) is one of the most important virulence factors of S. aureus. However, the role of nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) in TSST-1-induced innate immune response is still unclear. Here, purified recombinant TSST-1 (rTSST-1) was prepared and used to stimulate mouse peritoneal macrophages. The results showed that under the action of adenosine-triphosphate (ATP), rTSST-1 significantly induced interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) production in mouse macrophages and the production was dose-dependent. In addition, rTSST-1+ATP-stimulated cytokine production in macrophage depends on the activation of toll like receptor 4 (TLR4), but not TLR2 on the cells. Furthermore, the macrophages of NLRP3^−/− mice stimulated with rTSST-1+ATP showed significantly low levels of IL-1β production compared to that of wild-type mice. These results demonstrated that TSST-1 can induce the expression of inflammatory cytokines in macrophages via the activation of the TLR4 and NLRP3 signaling pathways. Our study provides new information about the mechanism of the TSST-1-inducing host’s innate immune responses.

Staphylococcal enterotoxin B- and lipopolysaccharide-induced toxic shock syndrome in a burn patient

Toxic shock syndrome (TSS) is caused by toxic shock syndrome toxin 1 or enterotoxins secreted by Staphylococcus aureus. Lipopolysaccharide (LPS) has also been shown to play a major role in the development of sepsis. Staphylococcal superantigens and LPS operate synergistically in conditioning cytokine release and lethal shock in mice. An 80-year-old woman was admitted because of a 20% mixed-depth flame burn. Despite two excisions and grafts, necrotic ulcers with methicillin-resistant Staphylococcus aureus (MRSA) colonization remained. On the 7th day after the operation, she developed shock with an erythematous rash. Blood examination revealed evidence of disseminated intravascular coagulation, and liver and renal dysfunction. A blood culture revealed a staphylococcal enterotoxin B (SEB)-producing strain of MRSA and Klebsiella pneumoniae. The septic symptoms were prolonged, but the condition gradually improved with extensive treatment. T-cell receptor analysis demonstrated a marked accumulation of SEB-mediated Vβ T cells. Stimulation of peripheral blood mononuclear cells in the recovery phase with SEB and LPS induced additive effects on tumor necrosis factor-α, interferon-γ, and interleukin-6 production. Although the present case did not fulfill the clinical criteria for TSS, the additive effects of SEB and LPS might have caused the severe septic shock.

The Superantigen Toxic Shock Syndrome Toxin 1 Alters Human Aortic Endothelial Cell Function

Staphylococcus aureus infective endocarditis (IE) is a fast-progressing and tissue-destructive infection of the cardiac endothelium. The superantigens (SAgs) toxic shock syndrome toxin 1 (TSST-1), staphylococcal enterotoxin C (SEC), and the toxins encoded by the enterotoxin gene cluster (egc) play a novel and essential role in the etiology of S. aureus IE. Recent studies indicate that SAgs act at the infection site to cause tissue pathology and promote vegetation growth. The underlying mechanism of SAg involvement has not been clearly defined. In SAg-mediated responses, immune cell priming is considered a primary triggering event leading to endothelial cell activation and altered function. Utilizing immortalized human aortic endothelial cells (iHAECs), we demonstrated that TSST-1 directly activates iHAECs, as documented by upregulation of vascular and intercellular adhesion molecules (VCAM-1 and ICAM-1). TSST-1-mediated activation results in increased monolayer permeability and defects in vascular reendothelialization. Yet stimulation of iHAECs with TSST-1 fails to induce interleukin-8 (IL-8) and IL-6 production. Furthermore, simultaneous stimulation of iHAECs with TSST-1 and lipopolysaccharide (LPS) inhibits LPS-mediated IL-8 and IL-6 secretion, even after pretreatment with either of the proinflammatory cytokines tumor necrosis factor alpha (TNF-α) and IL-1β. IL-8 suppression is not mediated by TSST-1 binding to its canonical receptor major histocompatibility complex class II (MHC-II), supporting current evidence for a nonhematopoietic interacting site on SAgs. Together, the data suggest that TSST-1 differentially regulates cell-bound and secreted markers of endothelial cell activation that may result in dysregulated innate immune responses during S. aureus IE. Endothelial changes resulting from the action of SAgs can therefore directly contribute to the aggressive nature of S. aureus IE and development of life-threatening complications.

Staphylococcal toxic shock syndrome: superantigen-mediated enhancement of endotoxin shock and adaptive immune suppression

Infectious diseases caused by Staphylococcus aureus present a significant clinical and public health problem. S. aureus causes some of the most severe hospital-associated and community-acquired illnesses. Specifically, it is the leading cause of infective endocarditis and osteomyelitis, and the second leading cause of sepsis in the USA. While pathogenesis of S. aureus infections is at the center of current research, many questions remain about the mechanisms underlying staphylococcal toxic shock syndrome (TSS) and associated adaptive immune suppression. Both conditions are mediated by staphylococcal superantigens (SAgs)-secreted staphylococcal toxins that are major S. aureus virulence factors. Toxic shock syndrome toxin-1 (TSST-1) is the SAg responsible for almost all menstrual TSS cases in the USA. TSST-1, staphylococcal enterotoxin B and C are also responsible for most cases of non-menstrual TSS. While SAgs mediate all of the hallmark features of TSS, such as fever, rash, hypotension, and multi-organ dysfunction, they are also capable of enhancing the toxic effects of endogenous endotoxin. This interaction appears to be critical in mediating the severity of TSS and related mortality. In addition, interaction between SAgs and the host immune system has been recognized to result in a unique form of adaptive immune suppression, contributing to poor outcomes of S. aureus infections. Utilizing rabbit models of S. aureus infective endocarditis, pneumonia and sepsis, and molecular genetics techniques, we aim to elucidate the mechanisms of SAg and endotoxin synergism in the pathogenesis of TSS, and examine the cellular and molecular mechanisms underlying SAg-mediated immune dysfunction.

Beta-(1-->3)-D-glucan modulates DNA binding of nuclear factors kappaB, AT and IL-6 leading to an anti-inflammatory shift of the IL-1beta/IL-1 receptor antagonist ratio

BACKGROUND

Beta-1-->3-D-glucans represent a pathogen-associated molecular pattern and are able to modify biological responses. Employing a comprehensive methodological approach, the aim of our in vitro study was to elucidate novel molecular and cellular mechanisms of human peripheral blood immune cells mediated by a fungal beta-1-->3-D-glucan, i.e. glucan phosphate, in the presence of lipopolysaccharide (LPS) or toxic shock syndrome toxin 1 (TSST-1).

RESULTS

Despite an activation of nuclear factor (NF) kappaB, NFinterleukin(IL)-6 and NFAT similar to LPS or TSST-1, we observed no significant production of IL-1beta, IL-6, tumor necrosis factor alpha or interferon gamma induced by glucan phosphate. Glucan phosphate-treated leukocytes induced a substantial amount of IL-8 (peak at 18 h: 5000 pg/ml), likely due to binding of NFkappaB to a consensus site in the IL-8 promoter. An increase in IL-1receptor antagonist (RA) production (peak at 24 h: 12000 pg/ml) by glucan phosphate-treated cells positively correlated with IL-8 levels. Glucan phosphate induced significant binding to a known NFIL-6 site and a new NFAT site within the IL-1RA promoter, which was confirmed by inhibition experiments. When applied in combination with either LPS or TSST-1 at the same time points, we detected that glucan phosphate elevated the LPS- and the TSST-1-induced DNA binding of NFkappaB, NFIL-6 and NFAT, leading to a synergistic increase of IL-1RA. Further, glucan phosphate modulated the TSST-1-induced inflammatory response via reduction of IL-1beta and IL-6. As a consequence, glucan phosphate shifted the TSST-1-induced IL-1beta/IL-1RA ratio towards an anti-inflammatory phenotype. Subsequently, glucan phosphate decreased the TSST-1-induced, IL-1-dependent production of IL-2.

CONCLUSION

Thus, beta-1-->3-D-glucans may induce beneficial effects in the presence of pro-inflammatory responses, downstream of receptor binding and signaling by switching a pro- to an anti-inflammatory IL-1RA-mediated reaction. Our results also offer new insights into the complex regulation of the IL-1RA gene, which can be modulated by a beta-1-->3-D-glucan.

Mixed bacterial infection model of sepsis in rabbits and its application to evaluate superantigen-adsorbing device

BACKGROUND

Superantigens are suspected to be the potent and lethal pathogens of gram-positive sepsis, and a new therapy that targeted to superantigens are required.

METHODS

A mixed infection model was developed in rabbits by the cecal ligation and puncture associated with the intraperitoneal injection of Staphylococcus aureus, which produces toxic shock syndrome toxin 1 (TSST-1). Animals were also hemoperfused with a superantigen-adsorbing device (SAAD), or a control column.

RESULTS

The model animals revealed multiple organ failure and died 6-12 h after the injection of S. aureus. The plasma levels of TSST-1, but not of lipopolysaccharide (LPS), significantly (p < 0.01) and inversely correlated with mean arterial pressure (r = -0.63). Plasma TSST-1 level was significantly reduced and shock-onset time was significantly retarded in the SAAD treated group, although the survival time was not significantly affected.

CONCLUSIONS

The animal model developed could serve as a model for sepsis. It is suggested that there is the potential application of SAAD in treating superantigen-related sepsis.

Chronic Staphylococcal enterotoxin B and lipopolysaccharide induce a bimodal pattern of hepatic dysfunction and injury

OBJECTIVE

To determine the effect of chronic exposure to endotoxin (lipopolysaccharide) and Staphylococcal enterotoxin B on hepatic injury and function.

DESIGN

Prospective, controlled trial.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Male Sprague-Dawley rats weighing 325-350 g with chronic vascular and bile catheters.

INTERVENTIONS

Chronically catheterized rats were treated daily with saline, 50 microg/kg Staphylococcal enterotoxin B alone, 1000 microg/kg lipopolysaccharide alone, 1000 microg/kg lipopolysaccharide with 50 microg/kg Staphylococcal enterotoxin B, or 100 microg/kg lipopolysaccharide with 50 microg/kg Staphylococcal enterotoxin B for 10 days. Serum and biliary measures of hepatic injury and dysfunction were measured before and then 6 hrs and 1, 2, 3, 7, and 10 days after the start of treatment. The animals were killed at 10 days and the livers examined histologically.

MEASUREMENTS AND MAIN RESULTS

Mean rates of bile flow, biliary indocyanine green excretion, and bile acid flux were significantly decreased immediately after treatment (6 hr, 1 and 2 days) and then at 10 days. Increases in biliary and serum gamma-glutamyltransferase and serum bile acids also occurred in a similar bimodal pattern. Animals treated with lipopolysaccharide or Staphylococcal enterotoxin B alone became tolerant and did not develop the bimodal pattern of hepatic dysfunction. Histologic examination of the liver at 10 days revealed periportal inflammation and fibrosis.

CONCLUSIONS

The combination of lipopolysaccharide and Staphylococcal enterotoxin B leads to late liver injury, whereas either toxin alone does not. These data may explain the frequent development of liver dysfunction in patients exposed to multiple bacterial toxins such as in sepsis, multiple-system organ failure, and other diseases with altered intestinal permeability.

Differential induction of hepatic dysfunction after intraportal and intravenous challenge with endotoxin and Staphylococcal enterotoxin B

We have previously shown that systemic infusion of the bacterial toxins Staphylococcal enterotoxin B (SEB) and endotoxin (LPS) induces hepatic dysfunction as measured by decreased biliary indocyanine green (ICG) excretion. In this study, we compare the effects of these bacterial toxins after infusion into the portal and systemic circulation and directly measure biliary bile acid excretion as a measure of cholestasis. We hypothesized that bacterial toxins infused into the portal vein would induce greater hepatic dysfunction than toxins infused into the systemic circulation. Using a chronically catheterized rat model, biliary bile acid excretion was directly measured after infusion of LPS at 10 and 100 microg/kg with and without 50 microg/kg SEB into the portal vein (IPV) or inferior vena cava (IV) at baseline, and at 6 and 24 h. We found that when LPS was infused alone, only IPV administration caused a significant decrease in bile acid excretion at 6 h. There was no change in bile acid excretion after IV administration of LPS. In contrast, when the combination of LPS and SEB was infused, both IV and IPV administration significantly decreased bile acid excretion at 6 and 24 h. At 6 h post-LPS and -SEB administration, the decrease in bile acid excretion was significantly greater after IPV than IV administration. There was no site-specific difference in IFN-gamma release after infusion of toxins. However, peak TNFalpha release was decreased in IPV-infused rats [10 microg/kg (P < 0.05) or 100 microg/kg (P = ns) LPS with SEB] compared with the same doses in IV-infused rats. These data question the role of systemic TNF-alpha and IFN-gamma in regulating hepatic dysfunction and suggest a differential functional response of the liver to systemic and gut-derived septic events. This study also further explains the frequent development of liver dysfunction in patients with sepsis, multisystem organ failure, and other diseases with altered intestinal permeability.

Mycobacterium bovis BCG-infected mice are more susceptible to staphylococcal enterotoxin B-mediated toxic shock than uninfected mice despite reduced in vitro splenocyte responses to superantigens

Type 1 T-cell responses against intracellular pathogens play a crucial role in mediating protection. We examined whether the induction of a strong type 1 T-cell response during a chronic bacterial infection influences responses to superantigens capable of inducing acute shock. Intravenous infection of mice with Mycobacterium bovis BCG appeared to induce a progressive anergy towards staphylococcal enterotoxin B (SEB) and towards antigen preparation of BCG (BCG-Ag) itself, based on diminished gamma interferon (IFN-gamma) production by SEB- and BCG-Ag-stimulated splenocytes from infected mice. In contrast to these in vitro results, injection of SEB into BCG-infected mice led to a dramatic increase in the serum IFN-gamma levels and the death of infected but not of control mice. In vitro hyporesponsiveness towards SEB and BCG-Ag occurred only with unfractionated splenocyte cultures, as purified T cells from infected mice produced higher levels of IFN-gamma. Hyporesponsiveness towards SEB and BCG-Ag in unfractionated splenocyte cultures was not due to suppressive antigen-presenting cells (APCs), as APCs from infected mice stimulated higher levels of IFN-gamma from purified T cells. The diminished IFN-gamma levels observed with bulk splenocytes appear to be due to changes in the T-cell-to-APC ratio that result in a decreased proportion of T cells, coupled to reduced proliferative responses and an increased susceptibility of effector T cells to activation-induced cell death in vitro. Our results indicate that the reported phenomena of T-cell anergy during mycobacterial infection may be an in vitro consequence of the development of a strong type 1 response in vivo.

Staphylococcal enterotoxin B potentiates LPS-induced hepatic dysfunction in chronically catheterized rats

Most models of liver dysfunction in sepsis use endotoxin (lipopolysaccharide; LPS) to induce a pathophysiological response. In our study published in this issue (Beno DWA, Uhing MR, Goto M, Chen Y, Jiyamapa-Serna VA, and Kimura RE. Am J Physiol Gastrointest Liver Physiol 280: G858-G865, 2001), the adverse effect of LPS on hepatic function in vivo was only significant at relatively high LPS doses despite high tumor necrosis factor-alpha concentrations. However, many patients with sepsis are exposed to multiple bacterial toxins that may augment the immune response, resulting in increased hepatic dysfunction. We have developed a model of polymicrobial sepsis by parentally administering a combination of staphylococcal enterotoxin B (SEB) and LPS. Using this model, we demonstrate that SEB (50 microg/kg) potentiates the effect of LPS-induced hepatic dysfunction as measured by decreased rates of biliary indocyanine green clearance and bile flow. These increases were most pronounced with doses of 10 and 100 microg/kg LPS, doses that by themselves do not induce hepatic dysfunction. This may explain the seemingly increased incidence and severity of liver dysfunction in sepsis, and it suggests that the exclusive use of LPS for replicating septic shock may not be relevant for studies of hepatic dysfunction.

Pentoxifylline inhibits superantigen-induced toxic shock and cytokine release

Tumor necrosis factor alpha (TNF-alpha) is a critical cytokine that mediates the toxic effects of bacterial superantigens like staphylococcal enterotoxin B (SEB) and toxic shock syndrome toxin 1 (TSST-1). Pentoxifylline, an anti-inflammatory agent that inhibits endotoxemia and lipopolysaccharide (LPS)-induced release of TNF-alpha, was tested for its ability to inhibit SEB- and TSST-1-induced activation of human peripheral blood mononuclear cells (PBMCs) in vitro and toxin-mediated shock in mice. Stimulation of PBMCs by SEB or TSST-1 was effectively blocked by pentoxifylline (10 mM), as evidenced by the inhibition of TNF-alpha, interleukin 1beta (IL-1beta), gamma interferon (IFN-gamma), and T-cell proliferation. The levels of TNF-alpha, IL-1alpha, and IFN-gamma in serum after an SEB or TSST-1 injection were significantly lower in mice given pentoxifylline (5.5 mg/animal) versus control mice. Additionally, pentoxifylline diminished the lethal effects and temperature fluctuations elicited by SEB and TSST-1. Thus, in addition to treating endotoxemias, the cumulative in vitro and in vivo data suggest that pentoxifylline may also be useful in abrogating the ill effects of staphylococcal enterotoxins and TSST-1.

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

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

Expression of cytokine mRNA during immuno-modulation of murine suppressor macrophages

In order to analyze the mechanism of immuno-modulation by LPS on murine peritoneal suppressor macrophages, we have, using RNase protection assay, checked the changes of mRNA expression pattern of several cytokine genes during the immuno-modulation. It has been found that, after treating peritoneal suppressor macrophages with LPS, mRNAs of IL-12 p35, IL-12 p40, IL-6 and IFN-gamma are newly appeared, while those of IL-1 alpha, IL-1 beta and IL-1Ra are increased and those of other cytokines, like TGF-beta 1 and MIF are not changed at all. It seems certain that those cytokines, whose expression is increased by LPS stimulation, may be responsible for the functional changes of suppressor macrophages during immuno-modulation. Among these changes, the appearance of IL-12 mRNA may play a critical role, and, in this regard, the synergetic effect between IFN-gamma and LPS on the increase of IL-12 p35 and Il-12 p40 mRNA expression is an interesting finding.

Sperm as infection-potentiating cofactors in HIV transmission

In this paper I will discuss the possible role of sperm as cofactors in the genital-mucosal transmission of HIV. The ideas involved arose from my laboratory's discovery that sperm bind to HLA-DR molecules expressed on somatic cells, and from our subsequent findings that lymphocytes are activated by these interactions. Sperm binding to HLA-DR mimics one of the two ligand binding characteristics of superantigens, which also bind to T-cell receptors in a V-beta-specific fashion. This property of sperm may be significant in HIV transmission because: (a) HLA-DR plays a central role in immune recognition and response; and (b) cell interactions involving HLA-DR are involved in HIV infection and disease development. After sexual contact, sperm elicit a transient leukocytic infiltration of the mammalian cervix (Thompson, L.A., Barratt, C.L., Bolton, A.E., Cooke, I.D., 1992. The leukocytic reaction of the human cervix. Am. J. Reprod. Immunol. 28, 85; Pandya, I.J., Cohen, J., 1985. The leukocytic reaction of the human uterine cervix to sperm. Fertil. Steril. 43, 417), and human cervical cells are bound and penetrated by sperm at this time (Sievers-Altermann, R., Engelbrecht, D.V., 1990. Entry of spermatozoa into the cervical mucosa and transmission of the AIDS virus. S. Afr. Med. J. 77, 319). At present, little is known about these in vivo events, but sperm-somatic cell interactions in vitro are also followed by sperm entry into the target cell cytoplasm and target cell activation. When the target cells are leukocytes, sperm interactions increase their susceptibility to HIV infection. If similar interactions occur in the cervicovaginal environment after sexual contact, they are likely to enhance the genital-mucosal transfer of HIV from semen.