Role of staphylococcal superantigens in upper airway disease

Pathophysiology of nasal congestion

Nasal congestion is a common symptom in rhinitis (both allergic and nonallergic), rhinosinusitis and nasal polyposis. Congestion can also be caused by physical obstruction of nasal passages and/or modulation of sensory perception. Mucosal inflammation underlies many of the specific and interrelated factors that contribute to nasal congestion, as well as other symptoms of both allergic rhinitis and rhinosinusitis. A wide range of biologically active agents (eg, histamine, tumor necrosis factor-α, interleukins, cell adhesion molecules) and cell types contribute to inflammation, which can manifest as venous engorgement, increased nasal secretions and tissue swelling/edema, ultimately leading to impaired airflow and the sensation of nasal congestion. Inflammation-induced changes in the properties of sensory afferents (eg, expression of peptides and receptors) that innervate the nose can also contribute to altered sensory perception, which may result in a subjective feeling of congestion. Increased understanding of the mechanisms underlying inflammation can facilitate improved treatment selection and the development of new therapies for congestion.

Screening for staphylococcal superantigen genes shows no correlation with the presence or the severity of chronic rhinosinusitis and nasal polyposis

BACKGROUND

Staphylococcus aureus secretes numerous exotoxins which may exhibit superantigenic properties. Whereas the virulence of several of them is well documented, their exact biological effects are not fully understood. Exotoxins may influence the immune and inflammatory state of various organs, including the sinonasal mucosa: their possible involvement in chronic rhinosinusitis has been suggested and is one of the main trends in current research. The aim of this study was to investigate whether the presence of any of the 22 currently known staphylococcal exotoxin genes could be correlated with chronic rhinosinusitis.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted a prospective, multi-centred European study, analysing 93 Staphylococcus aureus positive swabs taken from the middle meatus of patients suffering from chronic rhinosinusitis, with or without nasal polyposis, and controls. Strains were systematically tested for the presence of the 22 currently known exotoxin genes and genotyped according to their agr groups. No direct correlation was observed between chronic rhinosinusitis, with or without nasal polyposis, and either agr groups or the presence of the most studied exotoxins genes (egc, sea, seb, pvl, exfoliatins or tsst-1). However, genes for enterotoxins P and Q were frequently observed in nasal polyposis for the first time, but absent in the control group. The number of exotoxin genes detected was not statistically different among the 3 patient groups.

CONCLUSIONS/SIGNIFICANCE

Unlike many previous studies have been suggesting, we did not find any evident correlation between staphylococcal exotoxin genes and the presence or severity of chronic rhinosinusitis with or without nasal polyposis.

Toxins from bacteria

Bacterial toxins damage the host at the site of bacterial infection or distant from the site. Bacterial toxins can be single proteins or oligomeric protein complexes that are organized with distinct AB structure-function properties. The A domain encodes a catalytic activity. ADP ribosylation of host proteins is the earliest post-translational modification determined to be performed by bacterial toxins; other modifications include glucosylation and proteolysis. Bacterial toxins also catalyze the non-covalent modification of host protein function or can modify host cell properties through direct protein-protein interactions. The B domain includes two functional domains: a receptor-binding domain, which defines the tropism of a toxin for a cell and a translocation domain that delivers the A domain across a lipid bilayer, either on the plasma membrane or the endosome. Bacterial toxins are often characterized based upon the secretion mechanism that delivers the toxin out of the bacterium, termed types I-VII. This review summarizes the major families of bacterial toxins and also describes the specific structure-function properties of the botulinum neurotoxins.

[Bacteriological study of ethmoid specimens from patients with nasal polyposis after ethmoidal surgery]

OBJECTIVE

To compare the bacteriological and clinical findings in ethmoid specimens from patients with nasal polyposis after radical ethmoidal surgery.

PATIENTS AND METHODS

From June to November 2008, 60 patients were prospectively included. For each patient, two samples for each ethmoidal cavity were taken. Aerobic and anaerobic bacterial cultures and fungal cultures were processed and the antibiotic susceptibility was evaluated for each isolated bacterial strain.

RESULTS

Pathogenic bacteria were isolated in 48 patients (80%) including predominantly Staphylococcus aureus (60%) or a Gram-negative bacterium. The microorganisms were nearly all susceptible to antibiotics, including the aminoglycosides. No correlation between the presence of pathogenic bacteria and the clinical status of the patients was found.

CONCLUSION

In this study, a great number of patients was colonized with pathogenic bacteria. However, the presence of pathogenic bacteria was not correlated with the clinical status of the patients.

Detection of Staphylococcus aureus in nasal tissue with peptide nucleic acid-fluorescence in situ hybridization

BACKGROUND

Staphylococcus aureus (SA) in the nose can be a simple colonizer but also may create an intramucosal reservoir causing recurrent infections or can be a specific immune modulator through superantigenic mechanisms. Because the colonization rate of SA is high, but immunologic reactions causing chronic disease are less frequent, the purpose of this study was to identify the presence of intramucosal SA in healthy subjects and in patients with chronic rhinosinusitis (CRS) and to eventually relate those to the specific immunologic changes due to SA enterotoxins.

METHODS

Nasal tissue was collected in 40 subjects (9 controls, 21 CRS patients with [CRSwNP], and 10 CRS patients without nasal polyps [CRSsNP]). Tissues were homogenized, and mediators and specific IgE-antibodies against SA enterotoxins (SAE-IgE) were measured using the UniCAP system. The tissue was analyzed for the presence of SA by the peptide nucleic acid-fluorescence in situ hybridization (PNA-FISH) technique (AdvanDx), and a semiquantitative scoring system was applied. Mann-Whitney exact test was used for statistical analysis.

RESULTS

SA in the mucosal tissue was detected in a higher quantity among CRSwNP subjects with aspirin exacerbated respiratory disease (AERD) versus controls and CRSsNP (p=0.03). Among CRSwNP patients, Th2 markers (eosinophil cationic protein, p=0.006, and total IgE, p=0.004) were increased related to the SAE-IgE status but not related to the presence of SA in the tissue.

CONCLUSION

This study describes the detection of SA within nasal tissue using the PNA-FISH technique. The presence of SA in the submucosa did not correlate with the amplification of the Th2-related inflammation typically found in CRSwNP patients, but this reaction is dependent on the formation of SAE-IgE within mucosal tissue. We also show, for the first time, that submucosal SA is a prevalent finding in CRSwNP patients with AERD.

Diverse enterotoxin gene profiles among clonal complexes of Staphylococcus aureus isolates from the Bronx, New York

Staphylococcal enterotoxins (SE) can cause toxin-mediated disease, and those that function as superantigens are implicated in the pathogenesis of allergic diseases. The prevalence of 19 enterotoxin genes was determined by PCR in clinical S. aureus strains derived from wounds (108) and blood (99). We performed spa typing and multilocus sequence typing (MLST) to determine clonal origin, and for selected strains staphylococcal enterotoxin B (SEB) production was measured by enzyme-linked immunosorbent assay. Strains carried a median of five SE genes. For most SE genes, the prevalence rates among methicillin-resistant and methicillin-sensitive S. aureus isolates, as well as wound- and blood-derived isolates, did not differ. At least one SE gene was detected in all except two S. aureus isolates (>99%). Complete egc clusters were found in only 11% of S. aureus isolates, whereas the combination of sed, sej, and ser was detected in 24% of clinical strains. S. aureus strains exhibited distinct combinations of SE genes, even if their pulsed-field gel electrophoresis and MLST patterns demonstrated clonality. USA300 strains also showed considerable variability in SE content, although they contained a lower number of SE genes (mean, 3). By contrast, SE content was unchanged in five pairs of serial isolates. SEB production by individual strains varied up to 200-fold, and even up to 15-fold in a pair of serial isolates. In conclusion, our results illustrate the genetic diversity of S. aureus strains with respect to enterotoxin genes and suggest that horizontal transfer of mobile genetic elements encoding virulence genes occurs frequently.

Unmet needs in severe chronic upper airway disease (SCUAD)

Although the majority of patients with chronic upper airway diseases have controlled symptoms during treatment, many patients have severe chronic upper airway diseases (SCUADs). SCUAD defines those patients whose symptoms are inadequately controlled despite adequate (ie, effective, safe, and acceptable) pharmacologic treatment based on guidelines. These patients have impaired quality of life, social functioning, sleep, and school/work performance. Severe uncontrolled allergic rhinitis, nonallergic rhinitis, chronic rhinosinusitis, aspirin-exacerbated respiratory diseases, or occupational airway diseases are defined as SCUADs. Pediatric SCUADs are still unclear. In developing countries SCUADs exist, but risk factors can differ from those seen in developed countries. Comorbidities are common in patients with SCUADs and might increase their severity. The present document is the position of a group of experts considering that SCUADs should be considered differently from mild chronic upper airway diseases. It reviews the state of the art, highlighting gaps in our knowledge, and proposes several areas for a better understanding, prevention, and management of SCUADs. This document can also serve to optimize the pharmacoeconomic evaluation of SCUADs by means of comparison with mild chronic upper airway diseases.

Short-term antibiotics treatment in patients with nasal polyps and enterotoxins producing Staphylococcus aureus strains

Enterotoxins produced by Staphylococcus aureus (SA) can act as super-antigens and thus influence the course of chronic rhinosinusitis with nasal polyps (NP). The aim of this study was to determine if antibiotic treatment administered after endoscopic sinus surgery (ESS) for NP can positively influence the course of the disease compared to placebo. After ESS, 23 patients who tested positive, in a perioperative culture, for SA strains producing enterotoxins A-E and TSST-1, were randomized into two groups. Group A which in addition to standard treatment received oral anti-staphylococcal antibiotics for 3 weeks. Group B received a placebo. Both groups were compared preoperatively, and at 3 and 6 months after surgery using a symptom-specific score, an endoscopic score and the SNOT-22 quality of life questionnaire. Slightly better results were achieved in patients who received antibiotic therapy. However, the differences were not statistically significant. Regardless of post-operative treatment, approximately 30% of patients had a SA-negative culture 6 months after surgery.

Intrinsic asthma: not so different from allergic asthma but driven by superantigens?

The mechanisms of intrinsic or non-allergic asthma remain uncertain as allergens have no obvious role in driving the inflammatory process in the airways. However, IgE synthesis occurs in the airways, despite negative skin prick tests and serum-specific IgE. Furthermore, the inflammatory process in the airways is very similar between allergic and non-allergic asthma, with increased T-helper type 2 (Th2) cells, mast cell activation and infiltration of eosinophils. This pattern of inflammation is associated with a similar expression of inflammatory mediators, including Th2 cytokines and eosinophilotactic chemokines. There is increasing evidence that microbial superantigens, particularly Staphylococcal enterotoxins are important in amplifying inflammation in atopic dermatitis and chronic rhinosinusitis, in atopic and non-atopic patients. Superantigens may also be important in intrinsic asthma as airway epithelial cells may be colonized by Staphylococci and other superantigen-producing microbes. Superantigens produced locally in the airways may lead to class switching of local B cells, resulting in polyclonal IgE production in the airways and also specific IgE against the superantigen (which functions as a 'superallergen'). This leads to sensitization of mast cells, which can be activated by the usual asthma triggers, such as exercise. Superantigens also cause clonal expansion of T cells, resulting in increased Th2 cells and CD8(+) cells, while suppressing regulatory T cells. Superantigens may also reduce responsiveness to corticosteroids, resulting in more severe asthma. Finally, cytotoxic autoantibodies may also be implicated as IgG antibodies directed against epithelial proteins, such as cytokeratin-18, have been detected in intrinsic asthma, possibly as a result of epithelial damage and this may make epithelial cells more susceptible to microbial colonization. The therapeutic implications are that antibodies against local IgE and microbial superantigens or antibiotic therapy to eradicate the relevant superantigen-producing microorganisms may improve the efficacy of conventional therapy with corticosteroids.

Molecular requirements for MHC class II alpha-chain engagement and allelic discrimination by the bacterial superantigen streptococcal pyrogenic exotoxin C

Superantigens (SAgs) are microbial toxins that bind to both TCR beta-chain variable domains (Vbetas) and MHC class II molecules, resulting in the activation of T cells in a Vbeta-specific manner. It is now well established that different isoforms of MHC II molecules can play a significant role in the immune response to bacterial SAgs. In this work, using directed mutational studies in conjunction with functional analyses, we provide a complete functional map of the low-affinity MHC II alpha-chain binding interface of the SAg streptococcal pyrogenic exotoxin C (SpeC) and identify a functional epitope in the beta-barrel domain that is required for the activation of T cells. Using cell lines that exclusively express individual MHC II isoforms, our studies provide a molecular basis for the selectivity of SpeC-MHC II recognition, and provide one mechanism by how SAgs are capable of distinguishing between different MHC II alleles.

Human mast cell activation by Staphylococcus aureus: interleukin-8 and tumor necrosis factor alpha release and the role of Toll-like receptor 2 and CD48 molecules

The ability of Staphylococcus aureus to invade and survive within host cells is believed to contribute to its propensity to cause persistent and metastatic infections. In addition, S. aureus infections often are associated with atopic diseases such as dermatitis, rhinitis, and asthma. Mast cells, the key cells of allergic diseases, have a pivotal role in innate immunity and have the capacity of phagocytosis, and they can destroy some pathogenic bacteria. However, little is known about the ability of some other bacteria to survive and overcome mast cell phagocytosis. Therefore, we were interested in evaluating the interplay between mast cells and S. aureus. In this study, we show that human cord blood-derived mast cells (CBMC) can be infected by pathogenic S. aureus. S. aureus displayed a high adherence to mast cells as well as invasive and survival abilities within them. However, when infections were performed in the presence of cytochalasin D or when CBMC were preincubated with anti-Toll-like receptor 2 (TLR2) or anti-CD48 antibodies, the invasiveness and the inflammatory response were abrogated, respectively. Furthermore, we observed an increase of TLR2 and CD48 molecules on CBMC after S. aureus infection. The infection of CBMC with S. aureus also caused the release of tumor necrosis factor alpha (TNF-alpha) and interleukin-8 (IL-8). Both live and killed S. aureus organisms were found to trigger TNF-alpha and IL-8 release by CBMC in a time-dependent manner. Cumulatively, these findings suggest that S. aureus internalizes and survives in mast cells. This may play an important role in infections and in atopic diseases associated with S. aureus.