The mechanism of superantigen-mediated toxic shock: not a simple Th1 cytokine storm

Investigation of genomic and pathogenicity characteristics of Streptococcus suis ST1 human strains from Guangxi Zhuang Autonomous Region (GX) between 2005 and 2020 in China

Streptococcus suis is a significant and emerging zoonotic pathogen. ST1 and ST7 strains are the primary agents responsible for S. suis human infections in China, including the Guangxi Zhuang Autonomous Region (GX). To enhance our understanding of S. suis ST1 population characteristics, we conducted an investigation into the phylogenetic structure, genomic features, and virulence levels of 73 S. suis ST1 human strains from GX between 2005 and 2020. The ST1 GX strains were categorized into three lineages in phylogenetic analysis. Sub-lineage 3-1a exhibited a closer phylogenetic relationship with the ST7 epidemic strain SC84. The strains from lineage 3 predominantly harboured 89K-like pathogenicity islands (PAIs) which were categorized into four clades based on sequence alignment. The acquirement of 89K-like PAIs increased the antibiotic resistance and pathogenicity of corresponding transconjugants. We observed significant diversity in virulence levels among the 37 representative ST1 GX strains, that were classified as follows: epidemic (E)/highly virulent (HV) (32.4%, 12/37), virulent plus (V+) (29.7%, 11/37), virulent (V) (18.9%, 7/37), and lowly virulent (LV) (18.9%, 7/37) strains based on survival curves and mortality rates at different time points in C57BL/6 mice following infection. The E/HV strains were characterized by the overproduction of tumour necrosis factor (TNF)-α in serum and promptly established infection at the early phase of infection. Our research offers novel insights into the population structure, evolution, genomic features, and pathogenicity of ST1 strains. Our data also indicates the importance of establishing a scheme for characterizing and subtyping the virulence levels of S. suis strains.

Novel insights into the immune response to bacterial T cell superantigens

Bacterial T cell superantigens (SAgs) are a family of microbial exotoxins that function to activate large numbers of T cells simultaneously. SAgs activate T cells by direct binding and crosslinking of the lateral regions of MHC class II molecules on antigen-presenting cells with T cell receptors (TCRs) on T cells; these interactions alter the normal TCR-peptide-MHC class II architecture to activate T cells in a manner that is independent of the antigen specificity of the TCR. SAgs have well-recognized, central roles in human diseases such as toxic shock syndrome and scarlet fever through their quantitative effects on the T cell response; in addition, numerous other consequences of SAg-driven T cell activation are now being recognized, including direct roles in the pathogenesis of endocarditis, bloodstream infections, skin disease and pharyngitis. In this Review, we summarize the expanding family of bacterial SAgs and how these toxins can engage highly diverse adaptive immune receptors. We highlight recent findings regarding how SAg-driven manipulation of the adaptive immune response may operate in multiple human diseases, as well as contributing to the biology and life cycle of SAg-producing bacterial pathogens.

De novo design of a protein binder against Staphylococcus enterotoxin B

Staphylococcus enterotoxin B (SEB) interacts with MHC-II molecules to overactivate immune cells and thereby to produce excessive pro-inflammatory cytokines. Disrupting the interactions between SEB and MHC-II helps eliminate the lethal threat posed by SEB. In this study, a de novo computational approach was used to design protein binders targeting SEB. The MHC-II binding domain of SEB was selected as the target, and the possible promising binding mode was broadly explored. The obtained original binder was folded into triple-helix bundles and contained 56 amino acids with molecular weight 5.9 kDa. The interface of SEB and the binder was highly hydrophobic. ProteinMPNN optimization further enlarged the hydrophobic region of the binder and improved the stability of the binder-SEB complex. In vitro study demonstrated that the optimized binder significantly inhibited the inflammatory response induced by SEB. Overall, our research demonstrated the applicability of this approach in de novo designing protein binders against SEB, and thereby providing potential therapeutics for SEB induced diseases.

Development of nanobodies against Staphylococcus enterotoxin B through yeast surface display

Staphylococcus enterotoxin B (SEB) is one of the primary virulence factors of Staphylococcus aureus but there is still a lack of targeted drugs. SEB activates immune cells via interacting with MHC-II on antigen-presenting cells, leading to the production of large amounts of pro-inflammatory cytokines. Blocking the interaction between SEB and MHC-II can avert the overactivation of immune cells. Nanobodies are the smallest functional antibodies that can bind stably to antigens. In this study, an ideal approach to obtain specific nanobodies without immunizing camelids was introduced. We constructed a library containing up to 5 × 108 nanobodies, and then screened those targeting SEB by using yeast surface display (YSD) technique and fluorescence-activated cell sorting (FACS). A total of 8 nanobodies with divergent complementarity-determining regions (CDRs) sequences were identified and one candidate Nb8 with high affinity to SEB was isolated. In vitro study demonstrated that Nb8 significantly inhibited SEB-induced inflammatory response. Molecular docking simulation indicated that the unique CDR3 sequence contributed to the binding of Nb8 to the MHC-II binding domain of SEB and accordingly cut off the connection between SEB and MHC-II. Our efforts contributed to the development of specific nanobodies for eliminating the threats of SEB.

Molecular Characteristics and Pathogenicity of Staphylococcus aureus Exotoxins

Staphylococcus aureus stands as one of the most pervasive pathogens given its morbidity and mortality worldwide due to its roles as an infectious agent that causes a wide variety of diseases ranging from moderately severe skin infections to fatal pneumonia and sepsis. S. aureus produces a variety of exotoxins that serve as important virulence factors in S. aureus-related infectious diseases and food poisoning in both humans and animals. For example, staphylococcal enterotoxins (SEs) produced by S. aureus induce staphylococcal foodborne poisoning; toxic shock syndrome toxin-1 (TSST-1), as a typical superantigen, induces toxic shock syndrome; hemolysins induce cell damage in erythrocytes and leukocytes; and exfoliative toxin induces staphylococcal skin scalded syndrome. Recently, Panton-Valentine leucocidin, a cytotoxin produced by community-associated methicillin-resistant S. aureus (CA-MRSA), has been reported, and new types of SEs and staphylococcal enterotoxin-like toxins (SEls) were discovered and reported successively. This review addresses the progress of and novel insights into the molecular structure, biological activities, and pathogenicity of both the classic and the newly identified exotoxins produced by S. aureus.

Severe COVID-19 versus multisystem inflammatory syndrome: comparing two critical outcomes of SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with diverse host response immunodynamics and variable inflammatory manifestations. Several immune-modulating risk factors can contribute to a more severe coronavirus disease 2019 (COVID-19) course with increased morbidity and mortality. The comparatively rare post-infectious multisystem inflammatory syndrome (MIS) can develop in formerly healthy individuals, with accelerated progression to life-threatening illness. A common trajectory of immune dysregulation forms a continuum of the COVID-19 spectrum and MIS; however, severity of COVID-19 or the development of MIS is dependent on distinct aetiological factors that produce variable host inflammatory responses to infection with different spatiotemporal manifestations, a comprehensive understanding of which is necessary to set better targeted therapeutic and preventative strategies for both.

T cell activation profiles can distinguish gram negative/positive bacterial sepsis and are associated with ICU discharge

Introduction

Sepsis is a life-threatening complication resulting from a dysregulated host response to a serious infection, of which bacteria are the most common cause. A rapid differentiation of the gram negative (G^-)/gram positive (G⁺) pathogens facilitates antibiotic treatment, which in turn improves patients' survival.

Methods

We performed a prospective, observational study of adult patients in intensive care unit (ICU) unit and underwent the analysis of peripheral blood lymphocyte subsets, cytokines and other clinical indexes. The enrolled 94 patients were divided into no infection group (n=28) and bacterial sepsis group (n=66), and the latter group was subdivided into G^- (n=46) and G⁺ (n=20) sepsis subgroups.

Results

The best immune biomarker which differentiated the diagnosis of G^- sepsis from G⁺ sepsis, included activation markers of CD69, human leukocyte antigen DR (HLA-DR) on CD3⁺CD8⁺T subset. The ratio of CD3⁺CD4⁺CD69⁺T/CD3⁺CD8⁺CD69⁺T (odds ratio (OR): 0.078(0.012,0.506), P = 0.008), PCT>0.53 ng/ml (OR: 9.31(1.36,63.58), P = 0.023), and CO₂CP<26.5 mmol/l (OR: 10.99(1.29, 93.36), P = 0.028) were predictive of G^- sepsis (versus G⁺ sepsis), and the area under the curve (AUC) was 0.947. Additionally, the ratio of CD3⁺CD4⁺CD69⁺T/CD3⁺CD8⁺CD69⁺T ≤ 0.2697 was an independent risk factor for poor ICU discharge in G^- sepsis patients (HR: 0.34 (0.13, 0.88), P=0.026).

Conclusion

We conclude that enhanced activation of T cells may regulate the excessive inflammatory response of G^- bacterial sepsis, and that T cell activation profiles can rapidly distinguish G^- sepsis from G⁺ sepsis and are associated with ICU discharge.

IFN- Is Protective in Cytokine Release Syndrome-associated Extrapulmonary Acute Lung Injury

The mechanisms by which excessive systemic activation of adaptive T lymphocytes, as in cytokine release syndrome (CRS), leads to innate immune cell-mediated acute lung injury (ALI) or acute respiratory distress syndrome, often in the absence of any infection, remains unknown. Here, we investigated the roles of IFN-γ and IL-17A, key T-cell cytokines significantly elevated in patients with CRS, in the immunopathogenesis of CRS-induced extrapulmonary ALI. CRS was induced in wild-type (WT), IL-17A- and IFN-γ knockout (KO) human leukocyte antigen-DR3 transgenic mice with 10 μg of the superantigen, staphylococcal enterotoxin B, given intraperitoneally. Several ALI parameters, including gene expression profiling in the lungs, were studied 4, 24, or 48 hours later. Systemic T-cell activation with staphylococcal enterotoxin B resulted in robust upregulation of several chemokines, S100A8/A9, matrix metalloproteases, and other molecules implicated in tissue damage, granulocyte as well as agranulocyte adhesion, and diapedesis in the lungs as early as 4 hours, which was accompanied by subsequent neutrophil/eosinophil lung infiltration and severe ALI in IFN-γ KO mice. These pathways were significantly underexpressed in IL-17A KO mice, which manifested mildest ALI and intermediate in WT mice. Neutralization of IFN-γ worsened ALI in WT and IL-17A KO mice, whereas neutralizing IL-17A did not mitigate lung injury in IFN-γ KO mice, suggesting a dominant protective role for IFN-γ in ALI and that IL-17A is dispensable. Ruxolitinib, a Janus kinase inhibitor, increased ALI severity in WT mice. Thus, our study identified novel mechanisms of ALI in CRS and its differential modulation by IFN-γ and IL-17A.

The Role of Staphylococcus aureus and Its Toxins in the Pathogenesis of Allergic Asthma

Bronchial asthma is one of the most common chronic diseases worldwide and affects more than 300 million patients. Allergic asthma affects the majority of asthmatic children as well as approximately 50% of adult asthmatics. It is characterized by a Th2-mediated immune response against aeroallergens. Many aspects of the overall pathophysiology are known, while the underlying mechanisms and predisposing factors remain largely elusive today. Over the last decade, respiratory colonization with Staphylococcus aureus (S. aureus), a Gram-positive facultative bacterial pathogen, came into focus as a risk factor for the development of atopic respiratory diseases. More than 30% of the world’s population is constantly colonized with S. aureus in their nasopharynx. This colonization is mostly asymptomatic, but in immunocompromised patients, it can lead to serious complications including pneumonia, sepsis, or even death. S. aureus is known for its ability to produce a wide range of proteins including toxins, serine-protease-like proteins, and protein A. In this review, we provide an overview of the current knowledge about the pathophysiology of allergic asthma and to what extent it can be affected by different toxins produced by S. aureus. Intensifying this knowledge might lead to new preventive strategies for atopic respiratory diseases.

Extracellular Vesicles in Inner Ear Therapies-Pathophysiological, Manufacturing, and Clinical Considerations

(1) Background: Sensorineural hearing loss is a common and debilitating condition. To date, comprehensive pharmacologic interventions are not available. The complex and diverse molecular pathology that underlies hearing loss may limit our ability to intervene with small molecules. The current review foccusses on the potential for the use of extracellular vesicles in neurotology. (2) Methods: Narrative literature review. (3) Results: Extracellular vesicles provide an opportunity to modulate a wide range of pathologic and physiologic pathways and can be manufactured under GMP conditions allowing for their application in the human inner ear. The role of inflammation in hearing loss with a focus on cochlear implantation is shown. How extracellular vesicles may provide a therapeutic option for complex inflammatory disorders of the inner ear is discussed. Additionally, manufacturing and regulatory issues that need to be addressed to develop EVs as advanced therapy medicinal product for use in the inner ear are outlined. (4) Conclusion: Given the complexities of inner ear injury, novel therapeutics such as extracellular vesicles could provide a means to modulate inflammation, stress pathways and apoptosis in the inner ear.

Peritoneal M2 macrophage-derived extracellular vesicles as natural multitarget nanotherapeutics to attenuate cytokine storms after severe infections

Cytokine storms are a primary cause of multiple organ damage and death after severe infections, such as SARS-CoV-2. However, current single cytokine-targeted strategies display limited therapeutic efficacy. Here, we report that peritoneal M2 macrophage-derived extracellular vesicles (M2-EVs) are multitarget nanotherapeutics that can be used to resolve cytokine storms. In detail, primary peritoneal M2 macrophages exhibited superior anti-inflammatory potential than immobilized cell lines. Systemically administered M2-EVs entered major organs and were taken up by phagocytes (e.g., macrophages). M2-EV treatment effectively reduced excessive cytokine (e.g., TNF-α and IL-6) release in vitro and in vivo, thereby attenuating oxidative stress and multiple organ (lung, liver, spleen and kidney) damage in endotoxin-induced cytokine storms. Moreover, M2-EVs simultaneously inhibited multiple key proinflammatory pathways (e.g., NF-κB, JAK-STAT and p38 MAPK) by regulating complex miRNA-gene and gene-gene networks, and this effect was collectively mediated by many functional cargos (miRNAs and proteins) in EVs. In addition to the direct anti-inflammatory role, human peritoneal M2-EVs expressed angiotensin-converting enzyme 2 (ACE2), a receptor of SARS-CoV-2 spike protein, and thus could serve as nanodecoys to prevent SARS-CoV-2 pseudovirus infection in vitro. As cell-derived nanomaterials, the therapeutic index of M2-EVs can be further improved by genetic/chemical modification or loading with specific drugs. This study highlights that peritoneal M2-EVs are promising multifunctional nanotherapeutics to attenuate infectious disease-related cytokine storms.

Functional and Immunological Studies Revealed a Second Superantigen Toxin in Staphylococcal Enterotoxin C Producing Staphylococcus aureus Strains

Staphylococcus aureus is a human and animal pathogen as well as a commensal bacterium. It can be a causative agent of severe, life-threatening infections with high mortality, e.g., toxic shock syndrome, septic shock, and multi-organ failure. S. aureus strains secrete a number of toxins. Exotoxins/enterotoxins are considered important in the pathogenesis of the above-mentioned conditions. Exotoxins, e.g., superantigen toxins, cause uncontrolled and polyclonal T cell activation and unregulated activation of inflammatory cytokines. Here we show the importance of genomic analysis of infectious strains in order to identify disease-causing exotoxins. Further, we show through functional analysis of superantigenic properties of staphylococcal exotoxins that even very small amounts of a putative superantigenic contaminant can have a significant mitogenic effect. The results show expression and production of two distinct staphylococcal exotoxins, SEC and SEL, in several strains from clinical isolates. Antibodies against both toxins are required to neutralise the superantigenic activity of staphylococcal supernatants and purified staphylococcal toxins.

COVID-19 and Progesterone: Part 2. Unraveling High Severity, Immunity Patterns, Immunity grading, Progesterone and its potential clinical use

Severely ill COVID–19 (Corona Virus Disease of 2019) patients have a hyperinflammatory condition with a high concentration of pro-inflammatory cytokines termed the cytokine storm. This milieu is reported to cause acute lung injury, oxygen deprivation, multiorgan damage, critical illness, and often death. Post SARS–CoV–2 (Severe Acute Respiratory Syndrome Coronavirus 2) infection, the fight between the invading virus and the host's immune system would either terminate in recovery, with eradication of the infection and regulation of the immune system; or there would be a continuation of immune attacks even after the virus has been cleared, leading to immune dysregulation and disease. This outcome is chiefly dependent on two factors: (1) the patient's immune response, and (2) sufficiency plus efficiency of the regulator(s). Concerning the first, the present research introduces a framework based on different types of immune responses to SARS–CoV–2 along with known disease examples, and how this relates to varying clinical outcomes and treatment needs for COVID–19 patients. About the second factor of ‘regulator(s)’, part 1 of the manuscript described in depth the regulatory role of progesterone in COVID–19. The present study investigates five immunity patterns and the status of the regulatory hormone progesterone with respect to the two established demographic risk factors for COVID–19 high-severity: male sex, and old age. The study evaluates the status of progesterone as a credible determinant of immune regulation and dysregulation. It duly relates the immunity patterns to clinical outcomes and evinces indications for clinical use of progesterone in COVID–19. It proposes a clear answer to the question: "why are males and old patients most likely to have critical illness due to COVID–19?" The study highlights clinical domains for the use of progesterone in COVID–19. Part 2 of this research introduces the concept of immunity patterns and immunity grading. These concepts herewith provided for the clinical course of COVID–19 also apply to other hyperinflammatory conditions. Possible clinical applications of progesterone to treat critically ill COVID–19 patients will open an avenue for hormonal treatments of infections and other immune-related diseases.

The role of influenza A virus-induced hypercytokinemia

Influenza viruses are one of the leading causes of respiratory tract infections in humans and their newly emerging and re-emerging virus strains are responsible for seasonal epidemics and occasional pandemics, leading to a serious threat to global public health systems. The poor clinical outcome and pathogenesis during influenza virus infection in humans and animal models are often associated with elevated proinflammatory cytokines and chemokines production, which is also known as hypercytokinemia or "cytokine storm", that precedes acute respiratory distress syndrome (ARDS) and often leads to death. Although we still do not fully understand the complex nature of cytokine storms, the use of immunomodulatory drugs is a promising approach for treating hypercytokinemia induced by an acute viral infection, including highly pathogenic avian influenza virus infection and Coronavirus Disease 2019 (COVID-19). This review aims to discuss the immune responses and cytokine storm pathology induced by influenza virus infection and also summarize alternative experimental strategies for treating hypercytokinemia caused by influenza virus.

Investigation of the Genomic and Pathogenic Features of the Potentially Zoonotic Streptococcus parasuis

Recently, Streptococcus suis reference strains of serotype 20, 22, and 26 were reclassified as Streptococcus parasuis. The public health significance of S. parasuis is underestimated due to the lack of clinical isolates. In the present study, we first reported two sporadic S. parasuis infections in humans, after using full-length 16S rRNA and housekeeping genes' phylogeny and ANI values of genome sequence comparisons to determine the species of their isolates BS26 and BS27. Compared to highly pathogenic S. suis strain P1/7, S. parasuis strains BS26 and BS27 possessed a delayed capacity to initiate lethal infection, which may attribute to the later production of higher level of pro-inflammatory cytokines. Differed to S. suis strain P1/7, S. parasuis strains did not induce significant inflammatory response in the brain of mice. Histopathological changes in liver and lungs were widely present in mice infected with S. parasuis strains. Our data indicated that the pathogenic mechanism of S. parasuis may be different from that of S. suis. Three lineages in the core-genome phylogenetic tree and ten types of cps gene cluster were found in 13 S. parasuis genomes, indicating high heterogeneity of this species. The similarity of CPS structure and antibiotic-resistant genes relative to S. suis indicated the evolutionary affinity between the two species. Our data suggested S. parasuis is a potential zoonotic pathogen and poses severe threat to health of susceptible people. Further study on the epidemiology and public health significance of S. parasuis is urgently necessary.

The 'cytokine storm': molecular mechanisms and therapeutic prospects

Cytokine storm syndrome (CSS) has generally been described as a collection of clinical manifestations resulting from an overactivated immune system. Cytokine storms (CSs) are associated with various pathologies, as observed in infectious diseases, certain acquired or inherited immunodeficiencies and autoinflammatory diseases, or following therapeutic interventions. Despite the role of CS in tissue damage and multiorgan failure, a systematic understanding of its underlying molecular mechanisms is lacking. Recent studies demonstrate a positive feedback loop between cytokine release and cell death pathways; certain cytokines, pathogen-associated molecular patterns (PAMPs), and damage-associated molecular patterns (DAMPs), can activate inflammatory cell death, leading to further cytokine secretion. Here, we discuss recent progress in innate immunity and inflammatory cell death, providing insights into the cellular and molecular mechanisms of CSs and therapeutics that might quell ensuing life-threatening effects.

Local Anesthetics and Recurrence after Cancer Surgery-What's New? A Narrative Review

The perioperative use of regional anesthesia and local anesthetics is part of almost every anesthesiologist’s daily clinical practice. Retrospective analyses and results from experimental studies pointed towards a potential beneficial effect of the local anesthetics regarding outcome—i.e., overall and/or recurrence-free survival—in patients undergoing cancer surgery. The perioperative period, where the anesthesiologist is responsible for the patients, might be crucial for the further course of the disease, as circulating tumor cells (shed from the primary tumor into the patient’s bloodstream) might form new micro-metastases independent of complete tumor removal. Due to their strong anti-inflammatory properties, local anesthetics might have a certain impact on these circulating tumor cells, either via direct or indirect measures, for example via blunting the inflammatory stress response as induced by the surgical stimulus. This narrative review highlights the foundation of these principles, features recent experimental and clinical data and provides an outlook regarding current and potential future research activities.

Different Modulatory Effects of Four Methicillin-Resistant Staphylococcus aureus Clones on MG-63 Osteoblast-Like Cells

Staphylococcus aureus is a Gram-positive bacterium responsible for a variety of mild to life-threatening infections including bone infections such as osteomyelitis. This bacterium is able to invade and persist within non-professional phagocytic cells such as osteoblasts. In the present study, four different S. aureus strains, namely, 2SA-ST239-III (ST239), 5SA-ST5-II (ST5), 10SA-ST228-I (ST228), and 14SA-ST22-IVh (ST22), were tested for their ability to modulate cell viability in MG-63 osteoblast-like cells following successful invasion and persistence. Methicillin-sensitive S. aureus (MSSA) ATCC-12598-ST30 (ST30) was used as control strain. Despite being proven that ST30, ST239, and ST22 have a similar ability to internalize and persist in MG-63 osteoblast-like cells under our experimental conditions, we demonstrated that the observed decrease in cell viability was due to the different behavior of the considered strains, rather than the number of intracellular bacteria. We focused our attention on different biochemical cell functions related to inflammation, cell metabolism, and oxidative stress during osteoblast infections. We were able to show the following: (1) ST30 and ST239 were the only two clones able to persist and maintain their number in the hostile environment of the cell during the entire period of infection; (2) ST239 was the only clone able to significantly increase gene expression (3 and 24 h post-infection (p.i.)) and protein secretion (24 h p.i.) of both interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) in MG-63 osteoblast-like cells; (3) the same clone determined a significant up-regulation of the transforming growth factorbeta 1 (TGF-β1) and of the metabolic marker glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNAs at 24 h p.i.; and (4) neither the MSSA nor the four methicillin-resistant S. aureus (MRSA) strains induced oxidative stress phenomena in MG-63 cells, although a high degree of variability was observed for the different clones with regard to the expression pattern of nuclear factor E2-related factor 2 (Nrf2) and its downstream gene heme oxygenase 1 (HO-1) activation. Our results may pave the way for an approach to S. aureus-induced damage, moving towards individualized therapeutic strategies that take into account the differences between MSSA and MRSA as well as the distinctive features of the different clones. This approach is based on a change of paradigm in antibiotic therapy involving a case-based use of molecules able to counteract pro-inflammatory cytokines activity such as selective cytokine signaling inhibitors (IL-6, TNF-α).

High Titer Persistent Neutralizing Antibodies Induced by TSST-1 Variant Vaccine Against Toxic Shock Cytokine Storm

Staphylococcal superantigen toxins lead to a devastating cytokine storm resulting in shock and multi-organ failure. We have previously assessed the safety and immunogenicity of a recombinant toxic shock syndrome toxin 1 variant vaccine (rTSST-1v) in clinical trials (NCT02971670 and NCT02340338). The current study assessed neutralizing antibody titers after repeated vaccination with escalating doses of rTSST-1v. At study entry, 23 out of 34 subjects (67.6%) had neutralizing antibody titers inhibiting T cell activation as determined by ³H-thymidine incorporation at a serum dilution of ≤1:100 with similar figures for inhibition of IL-2 activation (19 of 34 subjects, 55.9%) as assessed by quantitative PCR. After the first vaccination, numbers of subjects with neutralization titers inhibiting T cell activation (61.7% ≥ 1:1000) and inhibiting IL-2 gene induction (88.2% ≥ 1:1000) increased. The immune response was augmented after the second vaccination (inhibiting T cell activation: 78.8% ≥ 1:1000; inhibiting IL-2 induction: 93.9% ≥ 1:1000) corroborated with a third immunization months later in a small subgroup of subjects. Assessment of IFNγ, TNFα and IL-6 inhibition revealed similar results, whereas neutralization titers did not change in placebo participants. Antibody titer studies show that vaccination with rTSST-1v in subjects with no/low neutralizing antibodies can rapidly induce high titer neutralizing antibodies persisting over months.

Contribution of Staphylococcal Enterotoxin B to Staphylococcus aureus Systemic Infection

Staphylococcal enterotoxin B (SEB), which is produced by the major human pathogen, Staphylococcus aureus, represents a powerful superantigenic toxin and is considered a bioweapon. However, the contribution of SEB to S. aureus pathogenesis has never been directly demonstrated with genetically defined mutants in clinically relevant strains. Many isolates of the predominant Asian community-associated methicillin-resistant S. aureus lineage sequence type (ST) 59 harbor seb, implying a significant role of SEB in the observed hypervirulence of this lineage. We created an isogenic seb mutant in a representative ST59 isolate and assessed its virulence potential in mouse infection models. We detected a significant contribution of seb to systemic ST59 infection that was associated with a cytokine storm. Our results directly demonstrate that seb contributes to S. aureus pathogenesis, suggesting the value of including SEB as a target in multipronged antistaphylococcal drug development strategies. Furthermore, they indicate that seb contributes to fatal exacerbation of community-associated methicillin-resistant S. aureus infection.

Integrative Analysis of lncRNAs in Kidney Cancer to Discover A New lncRNA (LINC00847) as A Therapeutic Target for Staphylococcal Enterotoxin tst Gene

OBJECTIVE

Bacterial toxin can cause cell death through induction of apoptosis in cancer cell lines as well as changes in the expression patterns of long non-coding RNAs (lncRNAs) and genes. In the present study, the effect of tst gene on ACHN cell lines was reported along with proposing a novel pathway of apoptosis in kidney cancer.

MATERIALS AND METHODS

In this experimental study, effective lncRNAs and genes were predicted from different criteria for renal cell carcinoma (RCC) by bioinformatics methods and lncRNA-miRNA-mRNA interaction was constructed; then the effect of Staphylococcus aureus tst gene on induction of apoptosis pathways on ACHN and HDF cell lines was investigated.

RESULTS

After creation of lncRNA-miRNA-mRNA interaction, changes in expression levels of lncRNA LINC00847 (P=0.0024) and PTEN gene (P=0.0027) were identified, as potential apoptosis biomarkers for kidney cancer, after treating ACHN cell line by pCDNA3.1 (+)-tst compared to the empty vector. In contrast, there was no statistically significant difference in DICER1 expression levels in ACHN-tst cell (P≥0.05). In addition, transfection by pcDNA3.1 (+)-tst could increase ACHN cell apoptosis level (P<0.0001) compared to the pcDNA3.1 (+) group; but no significant effect was observed on normal cells.

CONCLUSION

It is suggested that lncRNA LINC00847, discovered in this study, could provide a new landscape for researches aimed to determine relationship between functional lncRNA and RCC pathways. pcDNA3.1 (+)-tst was found to increase apoptosis in the transfected cells.

SpeS: A Novel Superantigen and Its Potential as a Vaccine Adjuvant against Strangles

Bacterial superantigens (sAgs) are powerful activators of the immune response that trigger unspecific T cell responses accompanied by the release of proinflammatory cytokines. Streptococcus equi (S. equi) and Streptococcus zooepidemicus (S. zooepidemicus) produce sAgs that play an important role in their ability to cause disease. Strangles, caused by S. equi, is one of the most common infectious diseases of horses worldwide. Here, we report the identification of a new sAg of S. zooepidemicus, SpeS, and show that mutation of the putative T cell receptor (TCR)-binding motif (YAY to IAY) abrogated TCR-binding, whilst maintaining interaction with major histocompatibility complex (MHC) class II molecules. The fusion of SpeS and SpeS^Y39I to six S. equi surface proteins using two different peptide linkers was conducted to determine if MHC class II-binding properties were maintained. Proliferation assays, qPCR and flow cytometry analysis showed that SpeS^Y39I and its fusion proteins induced less mitogenic activity and interferon gamma expression when compared to SpeS, whilst retaining Antigen-Presenting Cell (APC)-binding properties. Our data suggest that SpeS^Y39I-surface protein fusions could be used to direct vaccine antigens towards antigen-presenting cells in vivo with the potential to enhance antigen presentation and improve immune responses.

Correction of arginine metabolism with sepiapterin-the precursor of nitric oxide synthase cofactor BH4-induces immunostimulatory-shift of breast cancer

Immunotherapy is a first-line treatment for many tumor types. However, most breast tumors are immuno-suppressive and only modestly respond to immunotherapy. We hypothesized that correcting arginine metabolism might improve the immunogenicity of breast tumors. We tested whether supplementing sepiapterin, the precursor of tetrahydrobiopterin (BH4)-the nitric oxide synthase (NOS) cofactor-redirects arginine metabolism from the pathway synthesizing polyamines to that of synthesizing nitric oxide (NO) and make breast tumors more immunogenic. We showed that sepiapterin elevated NO but lowered polyamine levels in tumor cells, as well as in tumor-associated macrophages (TAMs). This not only suppressed tumor cell proliferation, but also induced the conversion of TAMs from the immuno-suppressive M2-type to immuno-stimulatory M1-type. Furthermore, sepiapterin abrogated the expression of a checkpoint ligand, PD-L1, in tumors in a STAT3-dependent manner. This is the first study which reveals that supplementing sepiapterin normalizes arginine metabolism, improves the immunogenicity and inhibits the growth of breast tumor cells.

Kawasaki disease: pathophysiology and insights from mouse models

Kawasaki disease is an acute febrile illness and systemic vasculitis of unknown aetiology that predominantly afflicts young children, causes coronary artery aneurysms and can result in long-term cardiovascular sequelae. Kawasaki disease is the leading cause of acquired heart disease among children in the USA. Coronary artery aneurysms develop in some untreated children with Kawasaki disease, leading to ischaemic heart disease and myocardial infarction. Although intravenous immunoglobulin (IVIG) treatment reduces the risk of development of coronary artery aneurysms, some children have IVIG-resistant Kawasaki disease and are at increased risk of developing coronary artery damage. In addition, the lack of specific diagnostic tests and biomarkers for Kawasaki disease make early diagnosis and treatment challenging. The use of experimental mouse models of Kawasaki disease vasculitis has considerably improved our understanding of the pathology of the disease and helped characterize the cellular and molecular immune mechanisms contributing to cardiovascular complications, in turn leading to the development of innovative therapeutic approaches. Here, we outline the pathophysiology of Kawasaki disease and summarize and discuss the progress gained from experimental mouse models and their potential therapeutic translation to human disease.

This Review outlines the pathophysiology of Kawasaki disease and discusses the progress gained from experimental mouse models and their potential therapeutic translation to human disease.

Kawasaki disease is a childhood systemic vasculitis leading to the development of coronary artery aneurysms; it is the leading cause of acquired heart disease in children in developed countries.

The cause of Kawasaki disease is unknown, although it is suspected to be triggered by an unidentified infectious pathogen in genetically predisposed children.

Kawasaki disease might not be a normal immune response to an unusual environmental stimulus, but rather a genetically determined unusual and uncontrolled immune response to a common stimulus.

Although the aetiological agent in humans is unknown, mouse models of Kawasaki disease vasculitis demonstrate similar pathological features and have substantially accelerated discoveries in the field.

Genetic and transcriptomic analysis of blood samples from patients with Kawasaki disease and experimental evidence generated using mouse models have demonstrated the critical role of IL-1β in the pathogenesis of this disease and the therapeutic potential of targeting this pathway (currently under investigation in clinical trials).

Staphylococcus aureus Isolated from Skin from Atopic-Dermatitis Patients Produces Staphylococcal Enterotoxin Y, Which Predominantly Induces T-Cell Receptor Vα-Specific Expansion of T Cells

While investigating the virulence traits of Staphylococcus aureus adhering to the skin of atopic-dermatitis (AD) patients, we identified a novel open reading frame (ORF) with structural similarity to a superantigen from genome sequence data of an isolate from AD skin. Concurrently, the same ORF was identified in a bovine isolate of S. aureus and designated SElY (H. K. Ono, Y. Sato'o, K. Narita, I. Naito, et al., Appl Environ Microbiol 81:7034-7040, 2015, https://doi.org/10.1128/AEM.01873-15). Recombinant SElY_bov had superantigen activity in human peripheral blood mononuclear cells. It further demonstrated emetic activity in a primate animal model, and it was proposed that SElY be renamed SEY (H. K. Ono, S. Hirose, K. Narita, M. Sugiyama, et al., PLoS Pathog 15:e1007803, 2019, https://doi.org/10.1371/journal.ppat.1007803). Here, we investigated the prevalence of the sey gene in 270 human clinical isolates of various origins in Japan. Forty-two strains were positive for the sey gene, and the positive isolates were from patients with the skin diseases atopic dermatitis and impetigo/staphylococcal scalded skin syndrome (SSSS), with a detection rate of ∼17 to 22%. There were three variants of SEY (SEY₁, SEY₂, and SEY₃), and isolates producing SEY variants formed three distinct clusters corresponding to clonal complexes (CCs) 121, 59, and 20, respectively. Most sey ⁺ isolates produced SEY in broth culture. Unlike SEY_bov, the three recombinant SEY variants exhibited stability against heat treatment. SEY predominantly activated human T cells with a particular T-cell receptor (TCR) Vα profile, a unique observation since most staphylococcal enterotoxins exert their superantigenic activities through activating T cells with specific TCR Vβ profiles. SEY may act to induce localized inflammation via skin-resident T-cell activation, facilitating the pathogenesis of S. aureus infection in disrupted epithelial barriers.

MAIT Cells Are Major Contributors to the Cytokine Response in Group A Streptococcal Toxic Shock Syndrome

Streptococcal toxic shock syndrome (STSS) is a rapidly progressing, life-threatening, systemic reaction to invasive infection caused by group A streptococci (GAS). GAS superantigens are key mediators of STSS through their potent activation of T cells leading to a cytokine storm and consequently vascular leakage, shock, and multiorgan failure. Mucosal-associated invariant T (MAIT) cells recognize MR1-presented antigens derived from microbial riboflavin biosynthesis and mount protective innate-like immune responses against the microbes producing such metabolites. GAS lack de novo riboflavin synthesis, and the role of MAIT cells in STSS has therefore so far been overlooked. Here we have conducted a comprehensive analysis of human MAIT cell responses to GAS, aiming to understand the contribution of MAIT cells to the pathogenesis of STSS. We show that MAIT cells are strongly activated and represent the major T cell source of IFNγ and TNF in the early stages of response to GAS. MAIT cell activation is biphasic with a rapid TCR Vβ2-specific, TNF-dominated response to superantigens and a later IL-12- and IL-18-dependent, IFNγ-dominated response to both bacterial cells and secreted factors. Depletion of MAIT cells from PBMC resulted in decreased total production of IFNγ, IL-1β, IL-2, and TNFβ. Peripheral blood MAIT cells in patients with STSS expressed elevated levels of the activation markers CD69, CD25, CD38, and HLA-DR during the acute compared with the convalescent phase. Our data demonstrate that MAIT cells are major contributors to the early cytokine response to GAS, and are therefore likely to contribute to the pathological cytokine storm underlying STSS.

Toxic Shock Syndrome Toxin 1 Evaluation and Antibiotic Impact in a Transgenic Model of Staphylococcal Soft Tissue Infection

Staphylococcal toxic shock syndrome (TSS) is a life-threatening illness causing fever, rash, and shock, attributed to toxins produced by the bacterium Staphylococcus aureus, mainly toxic shock syndrome toxin 1 (TSST-1). TSS was in the past commonly linked with menstruation and high-absorbency tampons; now, TSS is more frequently triggered by other staphylococcal infections, particularly of skin and soft tissue. Investigating the progress and treatment of TSS in patients is challenging, as TSS is rare; animal models do not mimic TSS adequately, as toxins interact best with human immune cells. We developed a new model of staphylococcal soft tissue infection in mice producing human immune cell proteins, rendering them TSST-1 sensitive, to investigate TSS. The significance of our research was that TSST-1 was found in soft tissues and immune organs of mice and that early treatment of mice with the antibiotic clindamycin altered TSST-1 production. Therefore, the early treatment of patients suspected of having TSS with clindamycin may influence their response to treatment.

Nonmenstrual toxic shock syndrome (nmTSS), linked to TSST-1-producing CC30 Staphylococcus aureus, is the leading manifestation of toxic shock syndrome (TSS). Due to case rarity and a lack of tractable animal models, TSS pathogenesis is poorly understood. We developed an S. aureus abscess model in HLA class II transgenic mice to investigate pathogenesis and treatment. TSST-1 sensitivity was established using murine spleen cell proliferation assays and cytokine assays following TSST-1 injection in vivo. HLA-DQ8 mice were infected subcutaneously with a tst-positive CC30 methicillin-sensitive S. aureus clinical TSS-associated isolate. Mice received intraperitoneal flucloxacillin, clindamycin, flucloxacillin and clindamycin, or a control reagent. Abscess size, bacterial counts, TSST-1 expression, and TSST-1 bioactivity were measured in tissues. Antibiotic effects were compared with the effects of control reagent. Purified TSST-1 expanded HLA-DQ8 T-cell Vβ subsets 3 and 13 in vitro and instigated cytokine release in vivo, confirming TSST-1 sensitivity. TSST-1 was detected in abscesses (0 to 8.0 μg/ml) and draining lymph nodes (0 to 0.2 μg/ml) of infected mice. Interleukin 6 (IL-6), gamma interferon (IFN-γ), KC (CXCL1), and MCP-1 were consistent markers of inflammation during infection. Clindamycin-containing antibiotic regimens reduced abscess size and TSST-1 production. Infection led to detectable TSST-1 in soft tissues, and TSST-1 was detected in draining lymph nodes, events which may be pivotal to TSS pathogenesis. The reduction in TSST-1 production and lesion size after a single dose of clindamycin underscores a potential role for adjunctive clindamycin at the start of treatment of patients suspected of having TSS to alter disease progression.

IMPORTANCE Staphylococcal toxic shock syndrome (TSS) is a life-threatening illness causing fever, rash, and shock, attributed to toxins produced by the bacterium Staphylococcus aureus, mainly toxic shock syndrome toxin 1 (TSST-1). TSS was in the past commonly linked with menstruation and high-absorbency tampons; now, TSS is more frequently triggered by other staphylococcal infections, particularly of skin and soft tissue. Investigating the progress and treatment of TSS in patients is challenging, as TSS is rare; animal models do not mimic TSS adequately, as toxins interact best with human immune cells. We developed a new model of staphylococcal soft tissue infection in mice producing human immune cell proteins, rendering them TSST-1 sensitive, to investigate TSS. The significance of our research was that TSST-1 was found in soft tissues and immune organs of mice and that early treatment of mice with the antibiotic clindamycin altered TSST-1 production. Therefore, the early treatment of patients suspected of having TSS with clindamycin may influence their response to treatment.

Staphylococcal Superantigens: Pyrogenic Toxins Induce Toxic Shock

Staphylococcal enterotoxin B (SEB) and related superantigenic toxins produced by Staphylococcus aureus are potent activators of the immune system. These protein toxins bind to major histocompatibility complex (MHC) class II molecules and specific Vβ regions of T-cell receptors (TCRs), resulting in the activation of both monocytes/macrophages and T lymphocytes. The bridging of TCRs with MHC class II molecules by superantigens triggers an early “cytokine storm” and massive polyclonal T-cell proliferation. Proinflammatory cytokines, tumor necrosis factor α, interleukin 1 (IL-1), IL-2, interferon γ (IFNγ), and macrophage chemoattractant protein 1 elicit fever, inflammation, multiple organ injury, hypotension, and lethal shock. Upon MHC/TCR ligation, superantigens induce signaling pathways, including mitogen-activated protein kinase cascades and cytokine receptor signaling, which results in NFκB activation and the phosphoinositide 3-kinase/mammalian target of rapamycin pathways. In addition, gene profiling studies have revealed the essential roles of innate antimicrobial defense genes in the pathogenesis of SEB. The genes expressed in a murine model of SEB-induced shock include intracellular DNA/RNA sensors, apoptosis/DNA damage-related molecules, endoplasmic reticulum/mitochondrial stress responses, immunoproteasome components, and IFN-stimulated genes. This review focuses on the signaling pathways induced by superantigens that lead to the activation of inflammation and damage response genes. The induction of these damage response genes provides evidence that SEB induces danger signals in host cells, resulting in multiorgan injury and toxic shock. Therapeutics targeting both host inflammatory and cell death pathways can potentially mitigate the toxic effects of staphylococcal superantigens.

Streptococcal superantigen-induced expansion of human tonsil T cells leads to altered T follicular helper cell phenotype, B cell death and reduced immunoglobulin release

Streptococcal pyrogenic exotoxin (Spe) A expression is epidemiologically linked to streptococcal tonsillo‐pharyngitis and outbreaks of scarlet fever, although the mechanisms by which superantigens confer advantage to Streptococcus pyogenes are unclear. S. pyogenes is an exclusively human pathogen. As the leucocyte profile of tonsil is unique, the impact of SpeA production on human tonsil cell function was investigated. Human tonsil cells from routine tonsillectomy were co‐incubated with purified streptococcal superantigens or culture supernatants from isogenic streptococcal isolates, differing only in superantigen production. Tonsil cell proliferation was quantified by tritiated thymidine incorporation, and cell surface characteristics assessed by flow cytometry. Soluble mediators including immunoglobulin were measured using enzyme‐linked immunosorbent assay. Tonsil T cells proliferated in response to SpeA and demonstrated typical release of proinflammatory cytokines. When cultured in the absence of superantigen, tonsil preparations released large quantities of immunoglobulin over 7 days. In contrast, marked B cell apoptosis and abrogation of total immunoglobulin (Ig)A, IgM, and IgG production occurred in the presence of SpeA and other superantigens. In SpeA‐stimulated cultures, T follicular helper (Tfh) cells showed a reduction in C‐X‐C chemokine receptor (CXCR)5 (CD185) expression, but up‐regulation of OX40 (CD134) and inducible T cell co‐stimulator (ICOS) (CD278) expression. The phenotypical change in the Tfh population was associated with impaired chemotactic response to CXCL13. SpeA and other superantigens cause dysregulated tonsil immune function, driving T cells from Tfh to a proliferating phenotype, with resultant loss of B cells and immunoglobulin production, providing superantigen‐producing bacteria with a probable survival advantage.

Aetiological Significance of Infectious Stimuli in Kawasaki Disease

Kawasaki disease (KD) is a pediatric vasculitis syndrome that is often involves coronary artery lesions (e. g., coronary artery aneurysms). Although its causal factors and entire pathogenesis remain elusive, the available evidence indicates that the pathogenesis of KD is closely associated with dysregulation of immune responses to various viruses or microbes. In this short review, we address several essential aspects of the etiology of KD with respect to the immune response to infectious stimuli: 1) the role of viral infections, 2) the role of bacterial infections and the superantigen hypothesis, 3) involvement of innate immune response including pathogens/microbe-associated molecular patterns and complement pathways, and 4) the influence of genetic background on the response to infectious stimuli. Based on the clinical and experimental evidence, we discuss the possibility that a wide range of microbes and viruses could cause KD through common and distinct immune processes.

Growth-inhibitory effects of TGFαL3-SEB chimeric protein on colon cancer cell line

BACKGROUND

TGFαL3-SEB chimeric protein is a synthetic protein, which is produced by combining the third loop (L3) of transforming growth factor-α (TGF-α) with staphylococcal enterotoxin type B. To the best of our knowledge, anti-cancer activity of this chimeric protein against colon cancer that overexpresses epidermal growth factor receptor (EGFR) has not yet been studied. Thus, in the present study, the anti-tumor effects of TGFαL3-SEB chimeric protein on HT-29 colon cancer cells were evaluated.

MATERIALS AND METHODS

The TGFαL3-SEB chimeric protein was previously designed and cloned in Escherichia coli (E. coli) [1,2]. The level of expression and the purity of this novel protein were examined for further analysis. For this purpose, the cells were treated with different concentrations (25, 50 and 75 μg/ml) of TGFαL3-SEB and then the proliferation was detected using the MTT assay. The apoptosis-inducing potential of TGFαL3-SEB in HT-29 and HEK-293 cells was evaluated by flow cytometry using Annexin V/PI double staining method; in addition, bax/bcl2 mRNA ratio, caspase-3 and caspase-9 activity were also assessed.

RESULTS

In the present study, TGFαL3-SEB chimeric protein was produced in E. coli. After effective purification, its growth inhibitory effect was evaluated. Our results indicated that the incubation of HT-29 colon cancer cell with 25, 50 and 75 μg/ml of TGFαL3-SEB for 24 h leads to significant reduction of proliferation in a dose-dependent manner (P < 0.05). Further analysis indicated that exposure of EGFR expressing HT-29 cells to TGFαL3-SEB leads to significant increase of the caspase-3 and caspase-9 activity in a concentration-dependent manner (P < 0.05). Bax/bcl-2 ratio also confirmed that TGFαL3-SEB has the pro-apoptotic effect. Flow cytometry analysis of TGFαL3-SEB treated cells showed that in addition to apoptotic cells, necrotic cells were also increased significantly at the concentration of 25, 50 and 75 μg/ml (P < 0.05).

CONCLUSION

In conclusion, our results demonstrated that TGFαL3-SEB chimeric protein induced cell death through both mechanisms of apoptosis and necrosis in HT-29 colon cancer cells. This paper has highlighted that TGFαL3-SEB has the potential to target EGFR expressing cancer cell.

Historical links between toxinology and immunology

Research on bacterial toxins is closely linked to the birth of immunology. Our understanding of the interaction of bacterial protein toxins with immune cells has helped to decipher immunopathology, develop preventive and curative treatments for infections, and propose anti-cancer immunotherapies. The link started when Behring and Kitasato demonstrated that serotherapy was effective against 'the strangling angel', namely diphtheria, and its dreadful toxin discovered by Roux and Yersin. The antitoxin treatment helped to save thousands of children. Glenny demonstrated the efficacy of the secondary immune response compared to the primary one. Ramon described anatoxins that allowed the elaboration of effective vaccines and discovered the use of adjuvant to boost the antibody response. Similar approaches were later made for the tetanus toxin. Studying antitoxin antibodies Ehrlich demonstrated, for the first time, the transfer of immunity from mother to newborns. In 1989 Marrack and Kappler coined the concept of 'superantigens' to characterize protein toxins that induce T-lymphocyte proliferation, and cytokine release by both T-lymphocytes and antigen presenting cells. More recently, immunotoxins have been designed to kill cancer cells targeted by either specific antibodies or cytokines. Finally, the action of IgE antibodies against toxins may explain their persistence through evolution despite their side effect in allergy.

Sexual dimorphism in bacterial infections

Background

Sex differences are important epidemiological factors that impact in the frequency and severity of infectious diseases. A clear sexual dimorphism in bacterial infections has been reported in both humans and animal models. Nevertheless, the molecular mechanisms involved in this gender bias are just starting to be elucidated. In the present article, we aim to review the available data in the literature that report bacterial infections presenting a clear sexual dimorphism, without considering behavioral and social factors.

Main body

The sexual dimorphism in bacterial infections has been mainly attributed to the differential levels of sex hormones between males and females, as well as to genetic factors. In general, males are more susceptible to gastrointestinal and respiratory bacterial diseases and sepsis, while females are more susceptible to genitourinary tract bacterial infections. However, these incidences depend on the population evaluated, animal model and the bacterial species. Female protection against bacterial infections and the associated complications is assumed to be due to the pro-inflammatory effect of estradiol, while male susceptibility to those infections is associated with the testosterone-mediated immune suppression, probably via their specific receptors. Recent studies indicate that the protective effect of estradiol depends on the estrogen receptor subtype and the specific tissue compartment involved in the bacterial insult, suggesting that tissue-specific expression of particular sex steroid receptors contributes to the susceptibility to bacterial infections. Furthermore, this gender bias also depends on the effects of sex hormones on specific bacterial species. Finally, since a large number of genes related to immune functions are located on the X chromosome, X-linked mosaicism confers a highly polymorphic gene expression program that allows women to respond with a more expanded immune repertoire as compared with men.

Conclusion

Notwithstanding there is increasing evidence that confirms the sexual dimorphism in certain bacterial infections and the molecular mechanisms associated, further studies are required to clarify conflicting data and to determine the role of specific hormone receptors involved in the gender bias of bacterial infections, as well as their potential as therapeutic targets.

Manipulation of Innate and Adaptive Immunity by Staphylococcal Superantigens

Staphylococcal superantigens (SAgs) constitute a family of potent exotoxins secreted by Staphylococcus aureus and other select staphylococcal species. SAgs function to cross-link major histocompatibility complex (MHC) class II molecules with T cell receptors (TCRs) to stimulate the uncontrolled activation of T lymphocytes, potentially leading to severe human illnesses such as toxic shock syndrome. The ubiquity of SAgs in clinical S. aureus isolates suggests that they likely make an important contribution to the evolutionary fitness of S. aureus. Although the apparent redundancy of SAgs in S. aureus has not been explained, the high level of sequence diversity within this toxin family may allow for SAgs to recognize an assorted range of TCR and MHC class II molecules, as well as aid in the avoidance of humoral immunity. Herein, we outline the major diseases associated with the staphylococcal SAgs and how a dysregulated immune system may contribute to pathology. We then highlight recent research that considers the importance of SAgs in the pathogenesis of S. aureus infections, demonstrating that SAgs are more than simply an immunological diversion. We suggest that SAgs can act as targeted modulators that drive the immune response away from an effective response, and thus aid in S. aureus persistence.

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

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

Systemic cytokine and chemokine responses in immunized mice challenged with staphylococcal enterotoxin B

The cytokine storm induced by staphylococcal enterotoxin B (SEB) describes the rapid and dramatic induction of mediators which are likely responsible for the toxin's deleterious effects. However despite the use of numerous animal models for investigating SEB related illness in humans, mechanisms of toxicity and correlates of protection remain unclear. In the present study, we used an LPS-potentiated model of SEB lethality to investigate the toxin-induced cytokine and chemokine responses in untreated and immunized mice. Of 30 separate mediators analyzed, serum levels for 28 or 27 of these cytokines and chemokines were elevated following administration of dosages of 3 or 30 LD50 of native SEB, respectively. Mice immunized with a non-toxic SEB vaccine candidate expressed in either E. coli or transgenic soy expression systems were protected from lethality when challenged with potentiated SEB. The majority of SEB-induced cytokines and chemokines (21 of 28 or 23 of 27 following challenge with dosages of 3 or 30 LD50 of native SEB, respectively) were significantly decreased in mice immunized with an SEB vaccine candidate when compared to control animals. Together, these studies provide the most comprehensive evaluation of the cytokine storm induced in this LPS-potentiated model of SEB lethality to date. As with other animal models, the identification of those mediators which are necessary and sufficient for SEB-induced toxicity remains unclear.

Rapid and Rigorous IL-17A Production by a Distinct Subpopulation of Effector Memory T Lymphocytes Constitutes a Novel Mechanism of Toxic Shock Syndrome Immunopathology

Toxic shock syndrome (TSS) is caused by staphylococcal and streptococcal superantigens (SAgs) that provoke a swift hyperinflammatory response typified by a cytokine storm. The precipitous decline in the host's clinical status and the lack of targeted therapies for TSS emphasize the need to identify key players of the storm's initial wave. Using a humanized mouse model of TSS and human cells, we herein demonstrate that SAgs elicit in vitro and in vivo IL-17A responses within hours. SAg-triggered human IL-17A production was characterized by remarkably high mRNA stability for this cytokine. A distinct subpopulation of CD4+ effector memory T (TEM) cells that secrete IL-17A, but not IFN-γ, was responsible for early IL-17A production. We found mouse "TEM-17" cells to be enriched within the intestinal epithelium and among lamina propria lymphocytes. Furthermore, interfering with IL-17A receptor signaling in human PBMCs attenuated the expression of numerous inflammatory mediators implicated in the TSS-associated cytokine storm. IL-17A receptor blockade also abrogated the secondary effect of SAg-stimulated PBMCs on human dermal fibroblasts as judged by C/EBP δ expression. Finally, the early IL-17A response to SAgs was pathogenic because in vivo neutralization of IL-17A in humanized mice ameliorated hepatic and intestinal damage and reduced mortality. Together, our findings identify CD4+ TEM cells as a key effector of TSS and reveal a novel role for IL-17A in TSS immunopathogenesis. Our work thus elucidates a pathogenic, as opposed to protective, role for IL-17A during Gram-positive bacterial infections. Accordingly, the IL-17-IL-17R axis may provide an attractive target for the management of SAg-mediated illnesses.

Contralateral compartment syndrome inoculated by invasive group A streptococcus

Compartment syndrome is a rare but a well-documented complication in patients with trauma-induced group A streptococcus infection. Here, we present a case of a male who developed compartment syndrome on the left lower extremity after an injury inoculated by group A streptococcus on the right lower extremity. The patient was resuscitated with antibiotics, urgent fasciotomy, and immunoglobulin. The patient was eventually transferred to a burn center for further care.

A Sublethal Swine Model for Defining In Vivo Superantigen-Induced Responses Following Exposure to Staphylococcal Enterotoxin B

In vivo responses to bacterially derived superantigen-like toxins have been difficult to define due to the inherent limitations with rodent models and the relevance that the results obtained from such models may, or may not, have for human pathophysiology. Further the use of challenge doses of superantigen toxins that are lethal or supra-lethal complicates analogies to human exposures which are rarely fatal. Here, we utilize the superantigen, staphylococcal enterotoxin B, at doses that are sublethal in a swine model of toxin-induced incapacitation. Relevant dosing using an animal species for which this toxin is a true superantigen distinguishes this model.

Bacterial Toxins-Staphylococcal Enterotoxin B

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

Stress-caused anergy of leukocytes towards Staphylococcal enterotoxin B and exposure transcriptome signatures

Leucocytes from soldiers exposed to battlefield-like stress (RASP: Rangers Assessment and Selection Program) were exposed in vitro to Staphylococcal enterotoxin B (SEB). We assayed SEB-induced regulation of gene expression, both in the presence and absence of severe stress, to generate two sets of gene profiles. One set of transcripts and microRNAs were specific to post-RASP SEB exposure, and another set were signatures of SEB exposure common to both the pre- and post-RASP leucocytes. Pathways and upstream regulatory analyses indicated that the post-RASP SEB-signature transcripts were manifestation of the anergic state of post-RASP leucocytes. These were further verified using expression-based predictions of cellular processes and literature searches. Specificity of the second set of transcripts to SEB exposure was verified using machine-learning algorithms on our and four other (Gene Expression Omnibus) data sets. Cell adhesion, coagulation, hypoxia and vascular endothelial growth factor-mediated vascular leakage were SEB-specific pathways even under the background of severe stress. Hsa-miR-155-3p was the top SEB exposure predictor in our data set, and C-X-C motif chemokine ligand 9 was SEB specific in all the analyzed data sets. The SEB-signature transcripts (which also showed distinct expression signatures from Yersinia pestis and dengue virus) may serve as potential biomarkers of SEB exposure even under the background of stress.

Review of studies that have used knockout mice to assess normal function of prion protein under immunological or pathophysiological stress

Deletion of cellular isoform of prion protein (PrP(C)) increases neuronal predisposition to damage by modulating apoptosis and the negative consequences of oxidative stress. In vivo studies have demonstrated that PrP(C)-deficient mice are more prone to seizure, depression, and induction of epilepsy and experience extensive cerebral damage following ischemic challenge or viral infection. In addition, adenovirus-mediated overexpression of PrP(C) reduces brain damage in rat models of cerebral ischemia. In experimental autoimmune encephalomyelitis, PrP(C)-deficient mice reportedly have a more aggressive disease onset and less clinical improvement during the chronic phase than wild-type mice mice. In mice given oral dextran sulfate, PrP(C) has a potential protective role against inflammatory bowel disease. PrP(C)-deficient mice demonstrate significantly greater increases in blood glucose concentrations after intraperitoneal injection of glucose than wild-type mice. Further in vivo challenges to PrP gene-deficient models and conditional knockout models with siRNA and in vivo administration of PrP-ligating agents may assist in refining knowledge of the lymphoid function of PrP(C) and predicting the effects of anti-PrP treatment on the immune system. Together, these findings indicate that PrP(C) may have multiple neuroprotective and anti-inflammatory roles, which explains why this protein is so widely expressed.

Δ(9) Tetrahydrocannabinol attenuates Staphylococcal enterotoxin B-induced inflammatory lung injury and prevents mortality in mice by modulation of miR-17-92 cluster and induction of T-regulatory cells

BACKGROUND AND PURPOSE

Staphylococcal enterotoxin B (SEB) is a potent activator of Vβ8+T-cells resulting in the clonal expansion of ∼30% of the T-cell pool. Consequently, this leads to the release of inflammatory cytokines, toxic shock, and eventually death. In the current study, we investigated if Δ(9) tetrahydrocannabinol (THC), a cannabinoid known for its anti-inflammatory properties, could prevent SEB-induced mortality and alleviate symptoms of toxic shock.

EXPERIMENTAL APPROACH

We investigated the efficacy of THC against the dual administration (intranasal and i.p.) of SEB into C3H/HeJ mice based on the measurement of SEB-mediated clinical parameters, including cytokine production, cellular infiltration, vascular leak, and airway resistance. In addition, the molecular mechanism of action was elucidated in vitro by the activation of splenocytes with SEB.

KEY RESULTS

Exposure to SEB resulted in acute mortality, while THC treatment led to 100% survival of mice. SEB induced the miRNA-17-92 cluster, specifically miRNA-18a, which targeted Pten (phosphatase and tensin homologue), an inhibitor of the PI3K/Akt signalling pathway, thereby suppressing T-regulatory cells. In contrast, THC treatment inhibited the individual miRNAs in the cluster, reversing the effects of SEB.

CONCLUSIONS AND IMPLICATIONS

We report, for the first time a role for the miRNA 17-92 cluster in SEB-mediated inflammation. Furthermore, our results suggest that THC is a potent anti-inflammatory compound that may serve as a novel therapeutic to suppress SEB-induced pulmonary inflammation by modulating critical miRNA involved in SEB-induced toxicity and death.

Role of miRNA in the regulation of inflammatory genes in staphylococcal enterotoxin B-induced acute inflammatory lung injury and mortality

Exposure to Staphylococcal enterotoxin B (SEB) causes food poisoning, acute inflammatory lung injury, toxic shock syndrome, and often death. In this study, we investigated whether microRNA (miRNA) play a role in regulating SEB-driven inflammation in the lungs. Exposure to SEB caused immune cell infiltration, robust cytokine and chemokine production, compromised lung function, and 100% mortality in mice. We assessed miRNA and mRNA expression in lung infiltrating mononuclear cells following exposure to SEB and found 89 miRNA that were dysregulated (>2-fold) compared with vehicle controls. In silico analysis revealed that the miRNA exhibited biological functions pertaining to cell death and survival, cellular proliferation, and cell cycle progression. Through the use of q-RT PCR, we validated 9 specific miRNA (miR-155, miR-132, miR-31, miR-222, miR-20b, miR-34a, miR-192, miR-193*, and let-7e) and observed that they were predicted to bind the 3'-UTR of a number of genes that were either involved in the stringent regulation of inflammation (Smad3, Tgfb, Runx1, and Foxo3) or those that contributed to its exacerbation (Stat3, Ptgs2, Ccnd1, Ccne1, NfκB, and Tbx21). Further, by increasing or decreasing the levels of miR-132 (a miRNA highly induced by SEB), we noted the corresponding decrease or increase in the levels of its predicted target FOXO3. As a result of FOXO3 suppression by miR-132, we saw increase in Ifn-γ, Ccnd, and Ccne1. Taken together, our data support the role for miRNA in actively participating and orchestrating SEB-mediated inflammation in the lungs and provide several therapeutic targets for the treatment of SEB-driven toxicity via the modulation of miRNA.

Staphylococcal enterotoxin H induced apoptosis of bovine mammary epithelial cells in vitro

Staphylococcal enterotoxins (SEs) are powerful superantigenic toxins produced by Staphylococcus aureus (S. aureus). They can cause food poisoning and toxic shock. However, their impact on bovine mammary epithelial cells (bMECs) is still unknown. In this study, the distribution of SE genes was evaluated in 116 S. aureus isolates from bovine mastitis, and the most prevalent genes were seh (36.2%), followed by sei (12.1%), seg (11.2%), ser (4.3%), sec (3.4%), sea (2.6%) and sed (1.7%). To better understand the effect of staphylococcal enterotoxin H (SEH) on bMECs, the seh gene was cloned and inserted into the prokaryotic expression vector, pET28a, and transformed into Escherichia coli BL21 (DE3). The recombinant staphylococcal enterotoxin H (rSEH) was expressed and purified as soluble protein. Bioactivity analysis showed that rSEH possessed the activity of stimulating lymphocytes proliferation. The XTT assay showed that 100 μg/mL of rSEH produced the cytotoxic effect on bMECs, and fluorescence microscopy and flow cytometry analysis revealed that a certain dose of rSEH is effective at inducing bMECs apoptosis in vitro. This indicates that SEs can directly lead to cellular apoptosis of bMECs in bovine mastitis associated with S. aureus.

Structural basis for the neutralization and specificity of Staphylococcal enterotoxin B against its MHC Class II binding site

Staphylococcal enterotoxin (SE) B is among the potent toxins produced by Staphylococcus aureus that cause toxic shock syndrome (TSS), which can result in multi-organ failure and death. Currently, neutralizing antibodies have been shown to be effective immunotherapeutic agents against this toxin, but the structural basis of the neutralizing mechanism is still unknown. In this study, we generated a neutralizing monoclonal antibody, 3E2, against SEB, and analyzed the crystal structure of the SEB-3E2 Fab complex. Crystallographic analysis suggested that the neutralizing epitope overlapped with the MHC II molecule binding site on SEB, and thus 3E2 could inhibit SEB function by preventing interaction with the MHC II molecule. Mutagenesis studies were done on SEB, as well as the related Staphylococcus aureus toxins SEA and SEC. These studies revealed that tyrosine (Y)46 and lysine (K)71 residues of SEB are essential to specific antibody-antigen recognition and neutralization. Substitution of Y at SEA glutamine (Q)49, which corresponds to SEB Y46, increased both 3E2's binding to SEA in vitro and the neutralization of SEA in vivo. These results suggested that SEB Y46 is responsible for distinguishing SEB from SEA. These findings may be helpful for the development of antibody-based therapy for SEB-induced TSS.