A broad-spectrum inhibitory peptide against staphylococcal enterotoxin superantigen SEA, SEB and SEC

Identification of a novel protective human monoclonal antibody, LXY8, that targets the key neutralizing epitopes of staphylococcal enterotoxin B

Staphylococcal enterotoxin B (SEB), one of the exotoxins produced by Staphylococcus aureus, is the key toxin that causes poisoning reactions and toxic shock syndrome. In the current research work, a novel human antibody named LXY8 was screened from a human phage display antibody library, and LXY8 blocked the interaction between SEB and the T cell receptor (TCR). The binding activity between LXY8 and SEB was 0.525 nM. Furthermore, LXY8 could effectively inhibit the SEB-induced activation of peripheral blood mononuclear cells and release of cytokines. In the BALB/c mouse model, LXY8 effectively neutralized SEB toxicity in vivo. Finally, based on computer-guided molecular modeling, we designed a series of SEB mutation sites; these sites facilitated the determination of the key residues (i.e.176EFNN179) of SEB recognized by LXY8. The research revealed that the 176EFNN179 residues of SEB are important for specific antibody-antigen recognition. The results may be helpful for the development of antibody-based therapy for SEB-induced toxic shock syndrome.

Transcutaneous immunization of recombinant Staphylococcal enterotoxin B protein using a dissolving microneedle provides potent protection against lethal enterotoxin challenge

Staphylococcal enterotoxin B (SEB) produced by the Staphylococcus aureus bacteriumis most commonly associated with food poisoning and is known to also cause toxic shock syndrome. Currently, no approved vaccine or specific drug is available to treat SEB intoxication. In this study, we fabricated dissolving microneedles (MNs) loaded with recombinant SEB (rSEB) protein, and evaluated its characteristics, including dissolution profile, protein particle size, insertion depth, antigen retention time in vivo, and skin irritation. Our results showed that rSEB protein-loaded dissolving MNs made of chondroitin sulfate (2%) and trehalose (0.8%) could easily penetrate into the mouse skin within 5 min. The rSEB particle size was unchanged before and after MN fabrication. The skin penetration depth of the MNs was 260 µm. Moreover, the MNs also significantly extended the antigen retention time in vivo. rSEB protein-loaded dissolving MNs also triggered slight erythema at the beginning of administration, but this erythema disappeared within a few hours. More importantly, we investigated the immunogenicity and protective efficacy of rSEB protein-loaded dissolving MNs. Challenge studies in mice revealed that mice in full-dose MN group had a high level of SEB specific antibody response thatprovided100% protection against a lethal SEB toxin challenge. However, there was only 60% protection observed in mice that were in the half-dose MN (dose sparing) group. We also determined the pathological alterations in the tissues of the immunized mice. Taken together, these dissolving MNs may present a promising transcutaneous immunization strategy for treating SEB intoxication.

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.

Addressing bioterrorism concerns: options for investigating the mechanism of action of Staphylococcus aureus enterotoxin B

Staphylococcal enterotoxin B (SEB) is of concern to military and civilian populations as a bioterrorism threat agent. It is a highly potent toxin produced by Staphylococcus aureus and is stable in storage and under aerosolisation; it is able to produce prolonged highly incapacitating illness at very low-inhaled doses and death at elevated doses. Concerns regarding SEB are compounded by the lack of effective medical countermeasures for mass treatment of affected populations. This article considers the mechanism of action of SEB, the availability of appropriate experimental models for evaluating the efficacy of candidate medical countermeasures with particular reference to the need to realistically model SEB responses in man and the availability of candidate countermeasures (with an emphasis on commercial off-the-shelf options). The proposed in vitro approaches would be in keeping with Dstl’s commitment to reduction, refinement and replacement of animal models in biomedical research, particularly in relation to identifying valid alternatives to the use of nonhuman primates in experimental studies.

The staphylococcal enterotoxin (SE) family: SEB and siblings

Staphylococcus aureus plays an important role in numerous human cases of food poisoning, soft tissue, and bone infections, as well as potentially lethal toxic shock. This common bacterium synthesizes various virulence factors that include staphylococcal enterotoxins (SEs). These protein toxins bind directly to major histocompatibility complex class II on antigen-presenting cells and specific Vβ regions of T-cell receptors, resulting in potentially life-threatening stimulation of the immune system. Picomolar concentrations of SEs ultimately elicit proinflammatory cytokines that can induce fever, hypotension, multi-organ failure, and lethal shock. Various in vitro and in vivo models have provided important tools for studying the biological effects of, as well as potential vaccines/therapeutics against, the SEs. This review succinctly presents known physical and biological properties of the SEs, including various intervention strategies. In particular, SEB will often be portrayed as per biodefense concerns dating back to the 1960s.

The olive compound 4-hydroxytyrosol inactivates Staphylococcus aureus bacteria and Staphylococcal Enterotoxin A (SEA)

The foodborne pathogen Staphylococcus aureus produces the virulent staphylococcal enterotoxin A (SEA), a single chain protein which consists of 233 amino acid residues with a molecular weight of 27078 Da. SEA is a superantigen that is reported to contribute to animal (mastitis) and human (emesis, diarrhea, atopic dermatitis, arthritis, and toxic shock) syndromes. Changes in the native structural integrity may inactivate the toxin by preventing molecular interaction with cell membrane receptor sites of their host cells. In the present study, we evaluated the ability of the pure olive compound 4-hydroxytyrosol and a commercial olive powder called Hidrox-12, prepared by freeze-drying olive juice, to inhibit S. aureus bacteria and SEA's biological activity. Dilutions of both test substances inactivated the pathogens. Two independent cell assays (BrdU incorporation into newly synthesized DNA and glycyl-phenylalanyl-aminofluorocoumarin proteolysis) demonstrated that the olive compound 4-hydroxytyrosol also inactivated the biological activity of SEA at concentrations that were not toxic to the spleen cells. However, efforts to determine inhibition of the toxin by Hidrox-12 were not successful because the olive powder was cytotoxic to the spleen cells at concentrations found to be effective against the bacteria. The results suggest that food-compatible and safe antitoxin olive compounds can be used to inactivate both pathogens and toxins produced by the pathogens. Practical Application:  The results of this study suggest that food-compatible and safe antitoxin olive compounds can be used to reduce both pathogens and toxins produced by the pathogens in foods.

Generation and characterization of high affinity human monoclonal antibodies that neutralize staphylococcal enterotoxin B

Background

Staphylococcal enterotoxins are considered potential biowarfare agents that can be spread through ingestion or inhalation. Staphylococcal enterotoxin B (SEB) is a widely studied superantigen that can directly stimulate T-cells to release a massive amount of proinflammatory cytokines by bridging the MHC II molecules on an antigen presenting cell (APC) and the Vβ chains of the T-cell receptor (TCR). This potentially can lead to toxic, debilitating and lethal effects. Currently, there are no preventative measures for SEB exposure, only supportive therapies.

Methods

To develop a potential therapeutic candidate to combat SEB exposure, we have generated three human B-cell hybridomas that produce human monoclonal antibodies (HuMAbs) to SEB. These HuMAbs were screened for specificity, affinity and the ability to block SEB activity in vitro as well as its lethal effect in vivo.

Results

The high-affinity HuMAbs, as determined by BiaCore analysis, were specific to SEB with minimal crossreactivity to related toxins by ELISA. In an immunoblotting experiment, our HuMAbs bound SEB mixed in a cell lysate and did not bind any of the lysate proteins. In an in vitro cell-based assay, these HuMAbs could inhibit SEB-induced secretion of the proinflammatory cytokines (INF-γ and TNF-α) by primary human lymphocytes with high potency. In an in vivo LPS-potentiated mouse model, our lead antibody, HuMAb-154, was capable of neutralizing up to 100 μg of SEB challenge equivalent to 500 times over the reported LD₅₀ (0.2 μg) , protecting mice from death. Extended survival was also observed when HuMAb-154 was administered after SEB challenge.

Conclusion

We have generated high-affinity SEB-specific antibodies capable of neutralizing SEB in vitro as well as in vivo in a mouse model. Taken together, these results suggest that our antibodies hold the potential as passive immunotherapies for both prophylactic and therapeutic countermeasures of SEB exposure.

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

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