Regulatory T cells modulate staphylococcal enterotoxin B-induced effector T-cell activation and acceleration of colitis

IL-35 is critical in suppressing superantigenic Staphylococcus aureus-driven inflammatory Th17 responses in human nasopharynx-associated lymphoid tissue

The human nasopharynx is frequently exposed to microbial pathogens, including superantigen-producing Staphylococcus aureus (SAg-Sau), which activates potent pro-inflammatory T cell responses. However, cellular mechanisms that control SAg-Sau-driven T cell activation are poorly understood. Using human nasopharynx-associated lymphoid tissue (NALT), we show that SAg-Sau drove a strong Th17 activation, which was associated with an impaired CD4⁺ T cell-mediated immune regulation. This impairment of immune control correlated with a significant downregulation of interleukin-35 (IL-35) expression in tonsillar CD4⁺ T cells by SAg-Sau. Supplementing recombinant IL-35 suppressed SAg-Sau-activated Th17 responses, and this IL-35-mediated suppression positively correlated with the level of Th17 activation. Interestingly, SAg-Sau stimulation induced Foxp3⁺ Treg expansion and interleukin-10 (IL-10) production, which effectively suppressed the Th1 response, but failed to control the activation of Th17 cells. Overall, our results reveal an aberrant T cell regulation on SAg-Sau-driven Th17 activation and identify IL-35 as a critical cytokine to control superantigenic S.aureus-activated Th17 responses.

Staphylococcal enterotoxin B administration in pregnant rats alters the splenic lymphocyte response in adult offspring rats

Background

Our previous study suggested that SEB exposure in pregnant rats could lead to the change of T cells subpopulation in both peripheral blood and thymus of the offspring rats. However, rarely is known about the influence of SEB exposure in pregnant rats on T cell subpopulation in the spleens of offspring rats.

Results

SEB was intravenously administered to the pregnant rats at gestational day 16 in this study. The percentages, in vivo and in vitro responses of CD4 and CD8 T cells were investigated with flow cytometry. The prenatal SEB exposure obviously increased splenic CD4 T cell percentages of both neonates and adult offspring rats, and obviously reduced splenic CD8 T cell percentages of both the fifth day neonates and adult offspring rats. After spleens in the adult offspring rats were re-stimulated with SEB in vivo or in vitro, in vivo SEB stimulation could lead to the marked decrease of splenic CD4 T cell percentage and the marked increase of splenic CD8 T cell percentage. While in vitro SEB stimulation to the cultured splenocytes markedly decreased the proliferation of the splenic lymphocytes and the CD4 T cell percentage, and had no influence on CD8 T cell percentage.

Conclusion

The prenatal SEB exposure could alter the percentages of CD4/CD8 T cell subpopulation and the response of CD4 and CD8 T cells to the in vivo and in vitro secondary SEB stimulation in the splenocytes of adult offspring rats.

Staphylococcal Enterotoxin B (SEB) Induces Memory CD4 T Cell Anergy in vivo and Impairs Recall Immunity to Unrelated Antigens

INTRODUCTION

Naïve and memory T cells can utilize unique regulatory pathways to promote protection but prevent self-reactivity. A bacterial superantigen SEB exploits unique TCR proximal signaling processes in memory CD4 T cells to induce clonal anergy. The aim of this study was to determine if SEB could antagonize memory CD4 T cells in vivo and whether there would be consequences on recall immune responses. We evaluated Ab responses to a T-dependent antigen as a measurement of memory T cell helper function.

METHOD

BALB/c mice were primed with TNP-RGG to elicit memory B cells and also immunized with an ovalbumin peptide to elicit memory helper T cells. Another group of TNP-RGG immunized mice were used as adoptive transfer recipients of exogenous DO11.10 memory T cells. Mice were challenged with TNP-OVA with or without prior administration of SEB. B cells secreting IgM or IgG TNP-specific Ab were enumerated by ELISPOT as indicators of primary versus secondary humoral immunity.

RESULTS

Comparing the SEB and non-SEB-treated groups, the SEB-treated group failed to produce TNP-specific IgG in response to challenge with TNP-OVA, even if they were previously immunized with OVA. All groups produced IgM, indicating that the primary Ab responses and naïve helper T cells were not impacted by SEB. SEB had no negative impact when DO11.10 × Fyn^-/- memory T cells were used as donor cells.

CONCLUSION

The present study indicated that SEB selectively targeted memory CD4 T cells in vivo and prevented helper function. Consequently, recall humoral immunity was lost. The data are most consistent with in vivo T cell anergy as opposed to indirect suppression as elimination of Fyn kinase restored helper function. These data suggest that bacterial superantigens can impair post-vaccination memory cell responses to unrelated antigens via their ability to target Vb families and antagonize memory cell activation.

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.

Role of staphylococcal superantigens in airway disease

Staphylococcus aureus is a common human pathogen, which is regularly part of the normal microflora found in the nose and skin. It represents a significant threat to human health, not in the least because of its capability to produce exotoxins, which have superantigenic properties. These exotoxins, in particular the staphylococcal enterotoxins (SEs), are known to be involved in the modulation and aggravation of airway inflammation. Indeed, recent studies show an important impact of SEs on the natural course of allergic rhinitis, nasal polyposis, asthma and COPD. This review outlines the current knowledge on the influence of SEs on airway inflammation. We highlight, in particular, the recent evidence on their role in asthma.

Murine immune response to a chronic Staphylococcus aureus biofilm infection

Staphylococcus aureus has reemerged as an important human pathogen in recent decades. Although many infections caused by this microbial species persist through a biofilm mode of growth, little is known about how the host's adaptive immune system responds to these biofilm infections. In this study, S. aureus cells adhered to pins in culture and were subsequently inserted into the tibiae of C57BL/6 mice, with an infecting dose of 2 × 10⁵ CFU. This model was utilized to determine local cytokine levels, antibody (Ab) function, and T cell populations at multiple time points throughout infection. Like human hosts, S. aureus implant infection was chronic and remained localized in 100% of C57BL/6 mice at a consistent level of approximately 10(7) CFU/gram bone tissue after day 7. This infection persisted locally for >49 days and was recalcitrant to clearance by the host immune response and antimicrobial therapy. Local inflammatory cytokines of the Th1 (interleukin-2 [IL-2], IL-12 p70, tumor necrosis factor alpha [TNF-α], and IL-1β) and Th17 (IL-6 and IL-17) responses were upregulated throughout the infection, except IL-12 p70, which dwindled late in the infection. In addition, Th1 Ab subtypes against a biofilm antigen (SA0486) were upregulated early in the infection, while Th2 Abs and anti-inflammatory regulatory T cells (Tregs) were not upregulated until later. These results indicate that early Th1 and Th17 inflammatory responses and downregulated Th2 and Treg responses occur during the development of a chronic biofilm implant infection. This unrestrained inflammatory response may cause tissue damage, thereby enabling S. aureus to attach and thrive in a biofilm mode of growth.

The systemic and pulmonary immune response to staphylococcal enterotoxins

In response to environmental cues the human pathogen Staphylococcus aureus synthesizes and releases proteinaceous enterotoxins. These enterotoxins are natural etiologic entities of severe food poisoning, toxic shock syndrome, and acute diseases. Staphylococcal enterotoxins are currently listed as Category B Bioterrorism Agents by the Center for Disease Control and Prevention. They are associated with respiratory illnesses, and may contribute to exacerbation of pulmonary disease. This likely stems from the ability of Staphylococcal enterotoxins to elicit powerful episodes of T cell stimulation resulting in release of pro-inflammatory cytokines. Here, we discuss the role of the immune system and potential mechanisms of disease initiation and progression.

Concurrent exposure to microbial products and food antigens triggers initiation of food allergy

It is estimated that as much as 6-8% population suffers from food allergy or food antigen-related disorders. The prevalence keeps rising. So far we do not have identified remedy to treat food allergy. Avoidance of the offending food is the only effective method currently. Skewed T helper 2 polarization is one of the major feature in the pathogenesis of food allergy. However, the causative mechanism in the initiation of food allergy remains to be further understood. Research in food allergy has got giant advance in recent years. Several animal models have been established and used in food allergy study. One of the common features of these food allergy animal models is that most of them require using microbial products as adjuvant to sensitize animals. This review documents the recent advance in the mechanistic study on concurrent use of microbial products and food antigens to study food allergy.