Superantigens and their potential role in human disease

Chemoattraction of human T cells by IL-18

Cell locomotion is crucial to the induction of an effective immune response. We report here the chemoattraction of CD4(+) T cells by IL-18, a member of the IL-1 cytokine family. Recombinant IL-18 increased the proportion of T cells in polarized morphology in vitro and stimulated their subsequent invasion into collagen gels in an IL-18 concentration gradient-dependent manner. Immunofluorescent microscopy studies determined that the major cell type responding to IL-18 was IL-18R(+)CD4(+). Importantly, synovial CD4(+) T cells from patients with rheumatoid arthritis responded to IL-18, adopting polarized morphology and gel invasion without further activation ex vivo, indicating the physiologic relevance of our observations. Finally, injection of rIL-18 into the footpad of DBA/1 mice led to local accumulation of inflammatory cells. These data therefore demonstrate for the first time lymphocyte chemoattractant properties of a member of the IL-1 cytokine family and its relevance in inflammatory diseases.

Update on glucocorticoid action and resistance

Glucocorticoids (GCs) are the most common group of medications used in the treatment of allergic and autoimmune disorders. They produce potent anti-inflammatory effects by inducing or repressing the expression of target genes. Although most patients with allergic diseases and autoimmune disorders respond to GC therapy, a small subset of patients demonstrate persistent tissue inflammation despite treatment with high doses of GCs. This condition results from an interaction between susceptibility genes, the host's environment, and immunologic factors. The treatment of these patients requires a systematic approach to rule out underlying conditions that lead to steroid resistance or treatment failure, as well as the use of alternative strategies to inhibit tissue inflammation.

Comparative molecular analysis of community- or hospital-acquired methicillin-resistant Staphylococcus aureus

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a growing public health concern that has been associated with pediatric fatalities. It is hypothesized that the evolution of CA-MRSA is a recent event due to the acquisition of mec DNA by previously methicillin-susceptible strains that circulated in the community. This study investigated the genetic relatedness between CA-MRSA, hospital-associated MRSA (HA-MRSA), and nonmenstrual toxic shock syndrome (nmTSS) isolates. Thirty-one of 32 CA-MRSA isolates were highly related as determined by pulsed-field gel electrophoresis and spa typing yet were distinguishable from 32 HA-MRSA strains. The 31 related CA-MRSA isolates produced either staphylococcal enterotoxin B (n = 5) or C (n = 26), and none made TSS toxin 1. All CA-MRSA isolates tested contained a type IV staphylococcal cassette chromosome mec (SCCmec) element. In comparison, none of the HA-MRSA isolates (n = 32) expressed the three superantigens. Antibiotic susceptibility patterns were different between the CA-MRSA and HA-MRSA isolates; CA-MRSA was typically resistant only to beta-lactam antibiotics. Six of twenty-one nmTSS isolates were indistinguishable or highly related to the CA-MRSA isolates. MnCop, an nmTSS isolate obtained in Alabama in 1986, was highly related to the CA-MRSA isolates except that it did not contain an SCCmec element. These data suggest that CA-MRSA strains may represent a new acquisition of SCCmec DNA in a previously susceptible genetic background that was capable of causing nmTSS. CA-MRSA poses a serious health risk not only because it is resistant to the antibiotics of choice for community-acquired staphylococcal infections but also because of its ability to cause nmTSS via superantigen production.

TSST-1 induces Th1 or Th2 differentiation in naïve CD4+ T cells in a dose- and APC-dependent manner

Superantigens are potent activators of the immune system, causing a variety of diseases, ranging from food poisoning to septic shock. Here, we examined the effects of different toxic shock syndrome toxin 1 (TSST-1) concentrations on the activation, proliferation and synthesis of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) in purified naïve human CD4+ T cells in a serum-free in vitro system. TSST-1 given in low doses (1-10 pg/ml) generates a pronounced T helper 2 (Th2)-like cytokine profile, characterized by elevated IL-4-expressing T-cell populations and reduced IFN-gamma-producing populations, whereas higher doses (100 pg/ml) induce a Th1-like profile, with increased expression of IFN-gamma and reduced expression of IL-4. These patterns were even more pronounced by adding exogenous cytokines like IL-12 and IL-4 and by the type of antigen-presenting cells (APCs). Thus, B cells induced Th2 shifts, whereas monocytes favoured Th1 induction. Moreover, IL-12 in conditions with B cells counteracted their Th2 bias. Interestingly, in purified naïve T-cell cultures, containing a small population of HLA-DR+ T cells, Th1/Th2 differentiation can be induced by TSST-1 too. There, Th-cell polarization is strongly dependent on TSST-1 concentration, indicating that this is a key parameter in regulating the differentiation of T cells. In conclusion, our data show that Th1/Th2 differentiation of TSST-1-stimulated naïve T cells is controlled by the type of APCs, and in APC-depleted cultures, it depends on the presence of HLA-DR+ cells and TSST-1 concentration.

The Three-dimensional structure of a superantigen-like protein, SET3, from a pathogenicity island of the Staphylococcus aureus genome

The staphylococcal enterotoxin-like toxins (SETs) are a family of proteins encoded within the Staphylococcus aureus genome that were identified by their similarity to the well described bacterial superantigens. The first crystal structure of a member of the SET family, SET3, has been determined to 1.9 A (R = 0.205, R(free) = 0.240) and reveals a fold characteristic of the superantigen family but with significant differences. The SET proteins are secreted at varying levels by staphylococcal isolates, and seroconversion studies of normal individuals indicate that they are strongly antigenic to humans. Recombinant SETs do not exhibit any of the properties expected of superantigens such as major histocompatibility complex class II binding or broad T-cell activation, suggesting they have an entirely different function. The fact that the whole gene family is clustered within the pathogenicity island SaIn2 of the S. aureus genome suggests that they are involved in host/pathogen interactions.

Expression and function of transgenic HLA-DQ molecules and lymphocyte development in mice lacking invariant chain

Invariant chain (Ii) is a non-MHC-encoded molecule, which plays an accessory role in the proper assembly/expression of functional MHC class II molecules and there by plays an important role in Ag processing/presentation. The phenotype of mice lacking Ii depends on the allotype of the MHC class II molecule. In some mice strains, Ii deficiency results in reduction in expression of class II molecules accompanied by defective CD4(+) T cell development. Responses to conventional Ags/superantigens are also compromised. In this study, we describe for the first time the functionality of human class II molecules, HLA-DQ6 and HLA-DQ8, in transgenic mice lacking Ii. HLA transgenic Ii(-/-) mice expressed very low levels of surface DQ6 and DQ8 accompanied by severe reduction in CD4(+) T cells both in the thymus and periphery. In vitro proliferation and cytokine production to an exogenous superantigen, staphylococcal enterotoxin B (SEB) was diminished in HLA-transgenic Ii(-/-) mice. However, SEB-induced in vivo expansion of CD8(+) T cells expressing TCR Vbeta8 family in DQ8.Ii(-/-) mice was comparable with that of DQ8.Ii(+/+) mice. Systemic IFN-gamma production following in vivo challenge with SEB was reduced in DQ8.Ii(-/-) mice and were also protected from SEB-induced toxic shock. Although the T cell response to a known peptide Ag was diminished in DQ8.Ii(-/-) mice, DQ8.Ii(-/-) APCs were capable of presenting that peptide to primed T cells from wild-type DQ8 mice as well as to a specific T cell hybridoma. Differentiation of mature B cells was also affected to a certain extent in DQ8.Ii(-/-) mice.

Simultaneous analysis of T cell clonality and cytokine production in rheumatoid arthritis using three-colour flow cytometry

In this study we examined the cytokine production by T cells and TCRVbeta subsets in peripheral blood (PB) and synovial fluid (SF) from six RA patients and PB from 10 normal subjects, using three-colour flow cytometry. In two RA subjects we assessed T cell clonality by RT PCR using TCRBV family-specific primers and analysed the CDR3 (complementarity determining region 3) length by GeneScan analysis. A high percentage of IFN-gamma- and IL-2- producing cells was observed among the PB T cells in both the RA patients and normal controls and among the SF T cells in RA patients. In contrast, the percentage of T cells producing IL-4 and IL-5 was small among PB T cells in both RA patients and normal controls and among SF T cells in RA patients. There was no significant difference in the production of IFN-gamma, IL-2 and IL-5 between the two compartments (PB and SF); however, there were significantly more IL-4-producing cells in SF. Molecular analysis revealed clonal expansions of four TCRBV families in SF of two of the RA patients studied: TCRBV6.7, TCRBV13.1 and TCRBV22 in one and TCRBV6.7, TCRBV21.3 and TCRBV22 in the second. These expansions demonstrated cytokine expression profiles that differed from total CD3+ cells, implying that T cell subsets bearing various TCR-Vbeta families may have the potential to modulate the immune response in RA patients.

Structural and thermodynamic correlates of T cell signaling

The first crystal structures of intact T cell receptors (TCRs) bound to class I peptide-MHC (pMHCs) antigens were determined in 1996. Since then, further structures of class I TCR/pMHC complexes have explored the degree of structural variability in the TCR-pMHC system and the structural basis for positive and negative selection. The recent determination of class II and allogeneic class I TCR/pMHC structures, as well as those of accessory molecules (e.g., CD3), has pushed our knowledge of TCR/pMHC interactions into new realms, shedding light on clinical pathologies, such as graft rejection and graft-versus-host disease. Furthermore, the determination of coreceptor structures lays the foundation for a more comprehensive structural description of the supramolecular TCR signaling events and those assemblies that arise in the immunological synapse. While these telling photodocumentaries of the TCR/pMHC interaction are composed mainly from static crystal structures, a full description of the biological snapshots in T cell signaling requires additional analytical methods that record the dynamics of the process. To this end, surface plasmon resonance (SPR), isothermal titration calorimetry (ITC), and ultracentrifugation (UC) have furnished both affinities and kinetics of the TCR/pMHC association. In the past year, structural, biochemical, and molecular biological data describing TCR/pMHC interactions have sublimely coalesced into a burgeoning well of understanding that promises to deliver further insights into T cell recognition. The coming years will, through a more intimate union of structural and kinetic data, allow many pressing questions to be addressed, such as how TCR/pMHC ligation is affected by coreceptor binding and what is the mechanism of TCR signaling in both early and late stages of T cell engagement with antigen-presenting cells.

Immunopathogenesis of acute transverse myelitis

Acute transverse myelitis is a group of disorders characterized by focal inflammation of the spinal cord and resultant neural injury. Acute transverse myelitis may be an isolated entity or may occur in the context of multifocal or even multisystemic disease. It is clear that the pathological substrate--injury and dysfunction of neural cells within the spinal cord--may be caused by a variety of immunological mechanisms. For example, in acute transverse myelitis associated with systemic disease (i.e. systemic lupus erythematosus or sarcoidosis), a vasculitic or granulomatous process can often be identified. In idiopathic acute transverse myelitis, there is an intraparenchymal or perivascular cellular influx into the spinal cord, resulting in the breakdown of the blood-brain barrier and variable demyelination and neuronal injury. There are several critical questions that must be answered before we truly understand acute transverse myelitis: (1) What are the various triggers for the inflammatory process that induces neural injury in the spinal cord? (2) What are the cellular and humoral factors that induce this neural injury? and (3) Is there a way to modulate the inflammatory response in order to improve patient outcome? Although much remains to be elucidated about the causes of acute transverse myelitis, tantalizing clues as to the potential immunopathogenic mechanisms in acute transverse myelitis and related inflammatory disorders of the spinal cord have recently emerged. It is the purpose of this review to illustrate recent discoveries that shed light on this topic, relying when necessary on data from related diseases such as acute disseminated encephalomyelitis, Guillain-Barré syndrome and neuromyelitis optica. Developing a further understanding of how the immune system induces neural injury will depend upon confirmation and extension of these findings and will require multicenter collaborative efforts.

Prevalence of superantigen-secreting bacteria in patients with Kawasaki disease

OBJECTIVES

To assess the prevalence of superantigen secreting bacteria in children with acute Kawasaki disease (KD) relative to control patients.

STUDY DESIGN

Bacterial cultures were obtained in a blinded fashion from the throat, rectum, and groin of 45 patients with untreated acute KD and 37 febrile control patients from 6 centers in the United States. Cultures were processed for the presence of superantigen-producing bacteria at a central laboratory.

RESULTS

Staphylococci or streptococci that produced superantigens (TSST-1, SEB, SEC, SPEB, SPEC) were isolated from 25 of 45 patients with KD (56%) as compared with 13 of 37 (35%) control patients (P =.078). Because SEB- and SEC-producing Staphylococcus aureus have not been associated with KD and because they do not induce a Vbeta2+ T-lymphocyte response, we analyzed the difference between groups relative to superantigens TSST-1 or SPEB/SPEC production. TSST-1 secreting S aureus or SPEB/SPEC producing group A streptococci were isolated from 20 of 45 (44%) patients with KD compared with 7 of 37 (19%) control patients (P =.019).

CONCLUSIONS

The overall isolation rates of superantigen (TSST-1, SPEB, SPEC, SEB, SEC) producing bacteria between patients with KD and febrile control patients were not statistically significant. However, future studies should further examine the potential role of Vbeta2-stimulatory superantigens (TSST-1 and SPEB/SPEC) in KD.

Influence of histidine beta81 of HLA-DR101 on peptide binding and presentation to T-cell receptor

HA(306-318) is an immunodominant peptide of the hemagglutinin of influenza virus that binds to most human leukocyte antigen (HLA-DR) alleles, while p18(73-85) is a HIV peptide characterized as a DR101 binding peptide. Our results demonstrate that crystal relaxation leads to the loss of a hydrogen bond between the beta81 histidine and the HA(306-318) peptide. This histidine is also involved in the binding of superantigens like SEA via a coordination of a zinc atom. To monitor the interaction of these peptides with this histidine of HLA-DR molecules, chemical modification, peptide binding on HLA-DR101 wild type and mutated molecules, and proliferation experiments were conducted, together with molecular simulation of HLA-DR/peptide molecular complexes. Our data suggest a different binding peptide pattern, depending of whether the peptide is HLA-DR101 allele specific or a shared one. Furthermore, tyrosine substitution at position beta81 does not affect either peptide binding or HA(306-318) clone-specific T-cell proliferation. On the contrary, the alanine substitution at position HLA-DR101 beta81 abrogated both peptide binding and T-cell proliferation. These results suggest that the histidine 81 on the DRbeta chain plays an important role in the HLA-DR peptide binding, more likely by polar interactions of the amino acid side chain ring with the peptide.

TCR usage and cytokine expression in peripheral blood and BAL T cells

T cells are thought to play an important regulatory role in atopic asthma. We hypothesized that human blood and BAL T cell subsets bearing various TCR-Vbeta genes might show selective differences in their cytokine profile. Peripheral blood (PB) and bronchoalveolar lavage (BAL) T cells from seven atopic asthmatic and six non-atopic non-asthmatic subjects were stimulated with PMA and ionomycin in the presence of monensin and analysed for TCR-Vbeta expression and production of cytokines at the single cell level. The percentage of IFN-gamma- and IL-2-producing BAL T cells was elevated compared with PB T cells from both the asthmatic subjects and the non-atopic, non-asthmatic controls. A small percentage of PB and BAL T cells produced IL-4 and IL-5, in asthmatic and normal subjects. In peripheral blood, the percentage of T cells expressing each cytokine was similar in the various TCR-Vbeta subsets and in total CD3+ T cells in all normal and six of seven asthmatic subjects. However, there was a substantial degree of heterogeneity in the cytokine profile of BAL TCR-Vbeta subsets compared with the total CD3+ T cells. This was more obvious in the asthmatic subjects with a reduction in the percentage of IFN-gamma- and IL-2-expressing T cells (five of seven asthmatic subjects) and an increase in the percentage of IL-4- and IL-5-expressing T cells (two of seven asthmatic subjects). These data confirm previous findings of an elevated proportion of IFN-gamma- and IL-2-producing BAL T cells while only a small proportion of PB and BAL T cells produce IL-4 and IL-5. Moreover, subsets of BAL T cells, defined by their TCR-Vbeta usage, may differ in their cytokine profile compared with the total CD3+ T cells, implying that T cells expressing different Vbeta elements may play different roles in regulating the airway inflammation in asthma.

Continuous exposure of mice to superantigenic toxins induces a high-level protracted expansion and an immunological memory in the toxin-reactive CD4+ T cells

We analyzed the responses of several T cell fractions reactive with superantigenic toxins (SAGTs), staphylococcal enterotoxin A (SEA), or Yersinia pseudotuberculosis-derived mitogen (YPM) in mice implanted with mini-osmotic pumps filled with SEA or YPM. In mice implanted with the SEA pump, SEA-reactive Vbeta3(+)CD4(+) T cells exhibited a high-level protracted expansion for 30 days, and SEA-reactive Vbeta11(+)CD4(+) T cells exhibited a low-level protracted expansion. SEA-reactive CD8(+) counterparts exhibited only a transient expansion. A similar difference in T cell expansion was also observed in YPM-reactive T cell fractions in mice implanted with the YPM pump. Vbeta3(+)CD4(+) and Vbeta11(+)CD4(+) T cells from mice implanted with the SEA pump exhibited cell divisions upon in vitro restimulation with SEA and expressed surface phenotypes as memory T cells. CD4(+) T cells from mice implanted with the SEA pump exhibited high IL-4 production upon in vitro restimulation with SEA, which was due to the enhanced capacity of the SEA-reactive CD4(+) T cells to produce IL-4. The findings in the present study indicate that, in mice implanted with a specific SAGT, the level of expansion of the SAGT-reactive CD4(+) T cell fractions varies widely depending on the TCR Vbeta elements expressed and that the reactive CD4(+) T cells acquire a capacity to raise a memory response. CD8(+) T cells are low responders to SAGTs.

Virus-induced autoimmunity: potential role of viruses in initiation, perpetuation, and progression of T-cell-mediated autoimmune disease

Virus infections have been implicated in the initiation of multiple human autoimmune diseases. This article focuses on reviewing the role of viruses in initiation, progression, and perpetuation of autoimmune diseases. Various mechanisms by which virus infections can induce autoimmune responses including molecular mimicry, epitope spreading, direct bystander activation, and release of cryptic epitopes are discussed. Evidence implicating virus infections in the pathogenesis of various human autoimmune diseases is reviewed. Last, the characteristics of animal models that have been developed for the study of the potential role of viruses in the initiation and progression of autoimmune disease are reviewed.

Viruses and autoimmunity: an affair but not a marriage contract

Viruses are considered as causative agents and contributors to lesion expression in autoimmune disease, notions best supported by studies in animal model systems. This review discusses relationships between virus infection and autoimmunity focusing on mechanisms by which they could induce autoreactivity. The popular idea of molecular mimicry is viewed skeptically with the reviewers taking the viewpoint that viruses contribute to autoimmunity mainly by inducing several nonspecific inflammatory events that together are sufficient to trigger autoreactivity in genetically receptive hosts.

The polyphenol chlorogenic acid inhibits staphylococcal exotoxin-induced inflammatory cytokines and chemokines

Proinflammatory cytokines mediate the toxic effect of staphylococcal exotoxins (SE). Chlorogenic acid, a plant polyphenol, inhibited SE-induced T-cell proliferation (by 98%) and production of interleukin 1beta, tumor necrosis factor, interleukin 6, interferon gamma, monocyte chemotactic protein I (MCP-l), macrophage inflammatory protein (MIP)-lalpha, and MIP-lbeta by human peripheral blood mononuclear cells. These data indicate that chlorogenic acid may be therapeutically useful for mitigating the pathogenic effects of SE. Naturally occurring polyphenolic compounds such as chlorogenic acid may serve as a potent anti-inflammatory agent alternative to conventional chemotherapeutics.

Stimulant-dependent modulation of cytokines and chemokines by airway epithelial cells: cross talk between pulmonary epithelial and peripheral blood mononuclear cells

Staphylococcal exotoxins (SE) and lipopolysaccharide (LPS) stimulate cells of the immune system to produce proinflammatory cytokines and chemokines which mediate septic shock and acute lung inflammation. A coculture of human peripheral blood mononuclear cells (PBMC) and pulmonary A549 epithelial cells was used to investigate inflammatory responses triggered by staphylococcal enterotoxin B (SEB), toxic shock syndrome toxin 1, and LPS. The levels of interleukin 1beta (IL-1beta), IL-6, gamma interferon-inducible protein 10, monocyte chemotactic protein 1 (MCP-1), macrophage inflammatory protein 1alpha, and RANTES were enhanced by 3.8-, 4.2-, 3.1-, 8.9-, 2-, and 2.9-fold, respectively, in cocultures of SEB-stimulated cells compared to in SEB-stimulated PBMC. In LPS-stimulated cocultures, only MCP-1 and RANTES levels were increased. These data suggest that the modulation of specific cytokines and chemokines is dependent on the stimulus and that there is bidirectional interaction between PBMC and lung epithelial cells to influence the immune response to these different stimuli.

Participation of Vbeta13(+) and Vbeta1(+) T cells in transfer thyroiditis after activation of mouse thyroglobulin-primed T cells by superantigen staphylococcal enterotoxin A

Murine experimental autoimmune thyroiditis (EAT) is a T-cell-mediated disease, but the T cell receptor (TCR) Vbeta gene usage in pathogenesis has not been well delineated. One approach is to utilize bacterial superantigens, such as staphylococcal enterotoxin (SE) A and B, to stimulate known sets of TCR Vbeta families in mouse thyroglobulin (mTg)-primed cells for thyroiditis transfer. Our previous use of SEB to activate mTg-primed cells led to no thyroiditis transfer, despite a major increase in Vbeta8(+) T cells. Unlike SEB, SEA activation did transfer thyroiditis. To determine which thyroiditogenic Vbeta(+) T cells were involved, SEA-activated T cells have now been analyzed. After repeated SEA activation in vitro, both mTg-reactive and thyroiditogenic cells persisted. FACS analysis indicated that most Vbeta13(+) cells were "large" cells (IL-2R(+)) and expressed the activation marker, transferrin receptor (CD71). RT-PCR analysis also showed the presence of both Vbeta13(+) and SEA-reactive Vbeta1(+) cells. Since our previous analyses by RT-PCR of the thyroid infiltrate after either induction or adoptive transfer have implicated both Vbeta13(+) and Vbeta1(+) cells, their activation by SEA to transfer thyroiditis further supports their role.

Zap-70-independent Ca(2+) mobilization and Erk activation in Jurkat T cells in response to T-cell antigen receptor ligation

The tyrosine kinase ZAP-70 has been implicated as a critical intermediary between T-cell antigen receptor (TCR) stimulation and Erk activation on the basis of the ability of dominant negative ZAP-70 to inhibit TCR-stimulated Erk activation, and the reported inability of anti-CD3 antibodies to activate Erk in ZAP-70-negative Jurkat cells. However, Erk is activated in T cells receiving a partial agonist signal, despite failing to activate ZAP-70. This discrepancy led us to reanalyze the ZAP-70-negative Jurkat T-cell line P116 for its ability to support Erk activation in response to TCR/CD3 stimulation. Erk was activated by CD3 cross-linking in P116 cells. However, this response required a higher concentration of anti-CD3 antibody and was delayed and transient compared to that in Jurkat T cells. Activation of Raf-1 and MEK-1 was coincident with Erk activation. Remarkably, the time course of Ras activation was comparable in the two cell lines, despite proceeding in the absence of LAT tyrosine phosphorylation in the P116 cells. CD3 stimulation of P116 cells also induced tyrosine phosphorylation of phospholipase C-gamma1 (PLCgamma1) and increased the intracellular Ca(2+) concentration. Protein kinase C (PKC) inhibitors blocked CD3-stimulated Erk activation in P116 cells, while parental Jurkat cells were refractory to PKC inhibition. The physiologic relevance of these signaling events is further supported by the finding of PLCgamma1 tyrosine phosphorylation, Erk activation, and CD69 upregulation in P116 cells on stimulation with superantigen and antigen-presenting cells. These results demonstrate the existence of two pathways leading to TCR-stimulated Erk activation in Jurkat T cells: a ZAP-70-independent pathway requiring PKC and a ZAP-70-dependent pathway that is PKC independent.

Infectious disease update

Many newly described or "re-emerging" infectious diseases may present to the dermatologist, often with potentially life-threatening implications. Prompt recognition and early intervention can greatly diminish the morbidity and mortality associated with these diseases.

Allergies in children

Allergic diseases in children have increased significantly in recent years and now affect up to 35% of children. They are a major cause of morbidity in children. Although there is a genetic predisposition, it is the exposure to environmental allergens, irritants and infections that will determine the sensitization to different dietary and inhalant allergens. As the genetic and environmental factors that act on an immature cellular immune system are better elucidated and their roles established, the implementation of more enduring preventive efforts will be developed. However, at present, the best approach to the child at high risk for the development of allergies is to institute dietary and environmental control measures early to decrease sensitization, and to recognize and appropriately treat the evolving signs and symptoms of allergic disease.

Immunotherapy of sepsis

Sepsis is a clinical syndrome that results from a systemic host response to an infection. The outcome of sepsis is poor, and mortality rates are as high as 30-40%. Sepsis is associated with the activation of multiple inflammatory pathways, including the cytokine network and the coagulation system. Sepsis can also result in an immunodepressed state that could leave patients more susceptible to secondary nosocomial infections. Modulation of the host response to infection has been studied as an adjunctive therapeutic approach in many preclinical investigations and clinical trials in the past 20 years. As a result of these studies our knowledge of the pathogenesis of sepsis has increased considerably. This review focuses on immunomodulatory strategies that have reached the phase of clinical evaluation in patients with sepsis.

Role of cyclin kinase inhibitor p21 in systemic autoimmunity

The cyclin kinase inhibitor protein p21 affects multiple processes relevant to the immune system, including cell cycle progression, replicative senescence, hemopoietic stem cell quiescence, and apoptosis. Therefore, malfunction of this protein may be a contributor to the pathogenesis of systemic autoimmunity. Here, we report that mixed background p21-deficient 129/Sv x C57BL/6 mice showed increased in vitro and in vivo T cell cycling and activation, moderate hypergammaglobulinemia and, at low penetrance, anti-chromatin autoantibodies. Homeostatic anti-self MHC/peptide ligand-induced proliferation of p21-deficient T cells was also enhanced. However, lymphoid organ enlargement was very mild, presumably due to increased apoptosis of the rapidly dividing cells. Moreover, the older p21-deficient mice had kidney pathology representing a similar, but slightly more advanced, state than that seen in the control mice. The timing and severity of the above serologic, cellular, and histologic manifestations in p21-deficient mice were unaffected by gender. Thus, p21 deficiency significantly enhances T cell activation and homeostatic proliferation, and can induce mild autoimmune manifestations at a low incidence without gender bias, but does not in itself generate the full spectrum of lupus-like disease.

A superantigen hypothesis for the pathogenesis of chronic hypertrophic rhinosinusitis, allergic fungal sinusitis, and related disorders

BACKGROUND

Chronic eosinophilic-lymphocytic respiratory mucosal inflammatory disorders include hypertrophic sinus disease, allergic fungal sinusitis, allergic bronchopulmonary aspergillosis, and chronic severe asthma. They have many analogous or shared aspects of pathology at molecular, cellular, and clinical levels of analysis.

OBJECTIVE

To propose a theory, and supporting data through comprehensive literature review, that unifies these diseases' pathogenesis. METHODS AND DATA SOURCES: Current medical literature was used as supportive background information. Reinterpretation of existing studies and reasoned speculation were used when necessary and identified where used. English language MEDLINE articles that referenced sinusitis, rhinosinusitis, allergic fungal sinusitis, asthma, allergic bronchopulmonary aspergillosis, nasal polyp, superantigen, and T cell receptor from 1983 to present were potentially used as background or supportive information. Additional referenced articles, published abstracts, and National Center for Biotechnology Information Entrez protein database searches were used. Case reports, studies, review articles, and textbooks were included.

RESULTS

Multiple lines of evidence support the proposed hypothesis that microbial T cell superantigen production, persistence, and host-responsiveness are the fundamental components that unify the pathogenesis of all common chronic eosinophilic-lymphocytic respiratory mucosal inflammatory disorders. Superantigen amplification of preexisting immunopathology is the proposed mechanism for disease induction and maintenance. Preexisting immunopathology is created in the individual by a potential heterogeneity of immunopathologic signals that can include type I immediate hypersensitivity, other antigen-specific immune responses, cytokine dysregulation, eicosanoid dysregulation, various genetic mutations, and other molecular pathology. Although the ability to develop chronic severe inflammatory disease is dependent upon this immunopathology, host T cell receptor V beta genetics and persistent superantigen production/exposure at the respiratory mucosa by relevant superantigen-producing extra- or intracellular microbes are postulated to be required. This mechanism for disease pathogenesis may also apply to other disorders. Approaches to prove this theory and its predictions are presented.

CONCLUSIONS

The pathogenesis of all the disorders discussed can be unified through the superantigen hypothesis proposed. Multiple lines of evidence support this hypothesis. How we view these common conditions will change, and new research into pathogenesis and treatment will occur if this proves true.

Immunological and biochemical characterization of streptococcal pyrogenic exotoxins I and J (SPE-I and SPE-J) from Streptococcus pyogenes

Recently, we described the identification of novel streptococcal superantigens (SAgs) by mining the Streptococcus pyogenes M1 genome database at Oklahoma University. Here, we report the cloning, expression, and functional analysis of streptococcal pyrogenic exotoxin (SPE)-J and another novel SAg (SPE-I). SPE-I is most closely related to SPE-H and staphylococcal enterotoxin I, whereas SPE-J is most closely related to SPE-C. Recombinant forms of SPE-I and SPE-J were mitogenic for PBL, both reaching half maximum responses at 0.1 pg/ml. Evidence from binding studies and cell aggregation assays using a human B-lymphoblastoid cell line (LG-2) suggests that both toxins exclusively bind to the polymorphic MHC class II beta-chain in a zinc-dependent mode but not to the generic MHC class II alpha-chain. The results from analysis by light scattering indicate that SPE-J exists as a dimer in solution above concentrations of 4.0 mg/ml. Moreover, SPE-J induced a rapid homotypic aggregation of LG-2 cells, suggesting that this toxin might cross-link MHC class II molecules on the cell surface by building tetramers of the type HLA-DRbeta-SPE-J-SPE-J-HLA-DRbeta. SPE-I preferably stimulates T cells bearing the Vbeta18.1 TCR, which is not targeted by any other known SAG: SPE-J almost exclusively stimulates Vbeta2.1 T cells, a Vbeta that is targeted by several other streptococcal SAgs, suggesting a specific role for this T cell subpopulation in immune defense. Despite a primary sequence diversity of 51%, SPE-J is functionally indistinguishable from SPE-C and might play a role in streptococcal disease, which has previously been addressed to SPE-C.

Children with atopic dermatitis who carry toxin-positive Staphylococcus aureus strains have an expansion of blood CD5- B lymphocytes without an increase in disease severity

Toxin-positive strains of Staphylococcus aureus (T + S. aureus) are present on the skin of some but not all patients with atopic dermatitis. Many staphylococcal toxins are superantigens, which can stimulate the immune response and thus may potentially lead to the very high levels of IgE characteristic of this condition, as well as exacerbating the clinical disease. The aim of this study was to determine whether the presence of T + S. aureus on the skin of children with atopic dermatitis was associated with in vivo evidence of a heightened humoral immune response, higher IgE levels and more severe clinical disease. Toxin gene expression in S. aureus isolated from the eczematous lesions of 28 children with atopic dermatitis was assessed by PCR. Clinical and immune data were also collected from this cohort. Thirteen of the 28 children (46%) were colonized with T + S. aureus strains. The presence of T + S. aureus was associated with a significant expansion in peripheral blood CD5- B cells (P = 0.01), and the more toxin types identified the greater the B-cell expansion (P = 0.002). However, in this cohort of children with atopic dermatitis, despite th in vivo expansion of B cells in children harbouring T + S. aureus, there was no associated increase in IgE levels or in clinical disease severity scores.

Preferential binding of Staphylococcus aureus to skin sites of Th2-mediated inflammation in a murine model

Staphylococcus aureus is found on over 90% of atopic dermatitis skin lesions and is thought to contribute to skin inflammation via the production of potent exotoxins. In contrast, less than 5% of normal subjects harbor S. aureus. This suggests that an atopic immune response itself may play a role in preferential binding of S. aureus to the skin. To examine this issue more directly, we analyzed the S. aureus binding characteristics of skin in mice undergoing different T helper type 1 cell versus T helper type 2 cell inflammatory responses using a novel in vitro bacterial binding assay. BALB/C female mice were first sensitized to ovalbumin with alum or ovalbumin with complete Freund's adjuvant to induce T helper type 2 or T helper type 1 responses, respectively. Mice were then challenged intradermally with either saline (control) or ovalbumin. Forty-eight hours later, skin specimens were obtained from the challenge sites, and the number of S. aureus binding to each skin section was quantitated. Bacterial binding was found to be significantly greater at skin sites of BALB/C mice that had been ovalbumin/alum sensitized compared with ovalbumin/complete Freund's adjuvant sensitized (p < or = 0.01). When compared to the ovalbumin sensitized/challenged skin of wild type BALB/C mice or interferon-gamma gene knockout mice, interleukin-4, but not interferon-gamma, gene knockout mice had significantly less S. aureus binding at their ovalbumin sensitized/challenged skin sites. Mutant S. aureus strains that lacked either fibronectin- or fibrinogen-binding protein expression showed significantly reduced S. aureus binding compared with the parent wild type strain (p < 0.005). Moreover, preincubation of the wild type bacteria with fibronectin or fibrinogen, but not collagen, resulted in significantly less skin binding of S. aureus (p < 0.01). Incubation of skin with interleukin-4, and less so with interferon-gamma, led to more binding of wild type S. aureus but not of an S. aureus mutant deficient in fibronectin binding protein expression. After interleukin-4 incubation, but not interferon-gamma, epidermal immunoreactivity for fibronectin was observed in murine skin explants. These results show that a T helper type 2 inflammatory environment can promote skin binding by S. aureus and that this binding is mediated by fibronectin and fibrinogen.

The Crohn's disease-associated bacterial protein I2 is a novel enteric t cell superantigen

An aberrant T cell response to enteric bacteria is important in inflammatory bowel disease. However, the identity of relevant microbial antigens is unknown. Here, we report the presence of I2, a Crohn's disease-associated microbial gene, in the murine intestine. The I2 protein induced a proliferative and IL-10 response by CD4(+) T cells from unimmunized mice. The I2 response was dependent on MHC class II-mediated recognition but did not require antigen processing. Selective activation was observed for the TCR-Vbeta5 subpopulation. These findings indicate that the I2 protein is a new class of T cell superantigen and suggest that colonization by the I2 microorganism in susceptible hosts may provide a superantigenic stimulus pertinent to Crohn's disease pathogenesis.

Disturbances in the peripheral T-cell repertoire of patients with motor neuron disease: high levels of activation and indirect evidence of superantigen

Our data on peripheral blood T cells from Motor neuron disease (MND) patients indicate major immunological disturbances linked to this disease. Both CD4+ and CD8+ T-cell subsets display an increased fraction of cells showing activation markers compared to controls, indicating an unusually high level of activity in both populations. Likewise, an increased number of T-cell expansions were noted in MND patients compared to controls, most dramatically observed in the CD4+ T-cell subset, where 5/144 T-cell V genes analyzed in eight subjects turned out to be expanded in the peripheral blood. In the CD8+ T-cell subset, four out of eight MND patients had peripheral BV gene expansions, 9/144 V genes analyzed. However, the most interesting result was the observation that in three out eight MND patients, expansions concerning the same BV gene were present in both CD4+ and CD8+ subsets (BV8S1 in two and BV12S1 in one patient). Parallel expansions of BV-gene restricted populations in both CD4+ and CD8+ subsets in the same individual, in an major histocompatibility complex (MHC)-unrestricted manner, are normally limited to situations where superantigens are involved. No known superantigen has to date been described with the capacity to simultaneously stimulate both BV8S1 and BV12S1, suggesting that the postulated 'MND-associated' superantigen is a hitherto undefined molecule.

Functional heterogeneity of cytokines and cytolytic effector molecules in human CD8+ T lymphocytes

CD8(+) T cells use a number of effector mechanisms to protect the host against infection. We have studied human CD8(+) T cells specific for CMV pp65(495-503) epitope, or for staphylococcal enterotoxin B, for the expression patterns of five cytokines and cytolytic effector molecules before and after antigenic stimulation. Ex vivo, the cytolytic molecule granzyme B was detected in a majority of circulating CMV-specific CD8(+) T cells, whereas perforin was rarely expressed. Both were highly expressed after Ag-specific activation accompanied by CD45RO up-regulation. TNF-alpha, IFN gamma, and IL-2 were sequentially acquired on recognition of Ag, but surprisingly, only around half of the CMV-specific CD8(+) T cells responded to antigenic stimuli with production of any cytokine measured. A dominant population coexpressed TNF-alpha and IFN-gamma, and cells expressing TNF-alpha only, IFN-gamma only, or all three cytokines together also occurred at lower but clearly detectable frequencies. Interestingly, perforin expression and production of IFN-gamma and TNF-alpha in CD8(+) T cells responding to staphylococcal enterotoxin B appeared to be largely segregated, and no IL-2 was detected in perforin-positive cells. Together, these data indicate that human CD8(+) T cells can be functionally segregated in vivo and have implications for the understanding of human CD8(+) T cell differentiation and specialization and regulation of effector mechanisms.

The flavonoid baicalin inhibits superantigen-induced inflammatory cytokines and chemokines

Excessive release of proinflammatory cytokines mediates the toxic effect of superantigenic staphylococcal exotoxins (SE). Baicalin, a flavone isolated from the Chinese herb Scutellaria baicalensis Georgi and used in China to treat infectious diseases, inhibited SE-stimulated T-cell proliferation (by 98%) and production of interleukin 1beta, interleukin 6, tumor necrosis factor, interferon gamma, monocyte chemotactic protein 1, macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta mRNA and protein by human peripheral blood mononuclear cells. These data suggest that baicalin may be therapeutically useful for mitigating the pathogenic effects of SE by inhibiting the signaling pathways activated by superantigens.

Quantitative relationship between MHC class II-superantigen complexes and the balance of T cell activation versus death

The binding of bacterial superantigens (SAgs) is profoundly affected by the nature of the MHC class II-associated antigenic peptide. It was proposed that this limitation in the density of SAgs displayed at the surface of APCs is important for efficient TCR serial triggering as well as for preventing apoptosis of the responding T lymphocytes. Here, we have addressed quantitatively the size of this SAg-receptive pool of HLA-DR molecules that are available to bind and present staphylococcal enterotoxin A (SEA) at the surface of B lymphocytes. Our binding curves, depletion experiments, and quantitative immunoprecipitations show that about half the HLA-DR class II molecules on B cells are refractory to SEA binding. Yet, as compared with typical nominal Ags, an unusually high amount of class II-SAg complexes can be presented to T cells. This characteristic appears to be necessary for SAg-induced T cell apoptosis. When <0.3% of the total cell surface MHC class II molecules are occupied by SEA, T cells undergo a normal sequence of early activation events. However, presentation of a ligand density beyond this threshold results in T cell activation that is readily aborted by apoptosis but only after a few cell divisions. Thus, we confirm the existence of MHC class II subsets that are structurally unable to present SEA and provide a quantitative framework to account for the ability of bacterial SAgs to induce peripheral activation vs tolerance in the host.

Cellular and cytokine responses in the circulation and tissue reactions in the lung of rhesus monkeys (Macaca mulatta) pretreated with cyclosporin A and challenged with staphylococcal enterotoxin B

Cyclosporin A (CsA), an inhibitor of T cell cytokine production, protects mice against staphylococcal enterotoxin B (SEB) intoxication. To determine whether CsA treatment would work in a species closer to humans. 4 rhesus monkeys were given 50 mg/kg CsA followed by an intratracheal challenge with approximately 6 LD50 of SEB. The CsA was not protective: one of the monkeys died and the other three had to be euthanised when they became moribund. All monkeys made IL-2, TNF, and IFN-gamma in response to SEB. In addition, there was about a 10-fold increase in ACTH levels 2 hr after SEB challenge. CsA significantly suppressed in vitro proliferation of lymphocytes from treated monkeys. Both CsA-treated monkeys and monkeys that had been challenged in a previous experiment with a lethal dose of SEB but had received no cyclosporin had pathologic changes in several organs. The most prominent changes were marked edema and leukocytic infiltration of the bronchial and bronchiolar mucosa. The CsA treatment appeared to reduce the intensity of lung inflammation, but this effect was not sufficient to protect the monkeys. The results suggest that CsA alone may not be an effective therapeutic agent for humans suffering from SEB intoxication or gram-positive septic shock.

High affinity T cell receptors from yeast display libraries block T cell activation by superantigens

The alphabeta T cell receptor (TCR) can be triggered by a class of ligands called superantigens. Enterotoxins secreted by bacteria act as superantigens by simultaneously binding to an MHC class II molecule on an antigen- presenting cell and to a TCR beta-chain, thereby causing activation of the T cell. The cross-reactivity of enterotoxins with different Vbeta regions can lead to stimulation of a large fraction of T cells. To understand the molecular details of TCR-enterotoxin interactions and to generate potential antagonists of these serious hyperimmune reactions, we engineered soluble TCR mutants with improved affinity for staphylococcal enterotoxin C3 (SEC3). A library of randomly mutated, single-chain TCRs (Vbeta-linker-Valpha) were expressed as fusions to the Aga2p protein on the surface of yeast cells. Mutants were selected by flow cytometric cell sorting with a fluorescent-labeled SEC3. Various mutations were identified, primarily in Vbeta residues that are located at the TCR:SEC3 interface. The combined mutations created a remodeled SEC3-binding surface and yielded a Vbeta domain with an affinity that was increased by 1000-fold (K(D)=7 nM). A soluble form of this Vbeta mutant was a potent inhibitor of SEC3-mediated T cell activity, suggesting that these engineered proteins may be useful as antagonists.

Suppression of endotoxin- and staphylococcal exotoxin-induced cytokines and chemokines by a phospholipase C inhibitor in human peripheral blood mononuclear cells

Excessive release of proinflammatory cytokines from cells stimulated with lipopolysaccharide (LPS) or staphylococcal exotoxin (SE) mediates the pathophysiologic manifestations of septic shock. Tricyclodecan-9-yl (D609), an inhibitor of phosphatidylcholine-specific phospholipase C, suppressed LPS- or SE-induced cytokines and chemokines in human peripheral blood mononuclear cells. These data suggest a potential role for D609 in the treatment of septic shock.

Crystal structure of a superantigen bound to the high-affinity, zinc-dependent site on MHC class II

MHC class II molecules possess two binding sites for bacterial superantigens (SAGs): a low-affinity site on the alpha chain and a high-affinity, zinc-dependent site on the beta chain. Only the former has been defined crystallographically. We report the structure of streptococcal pyrogenic exotoxin C (SPE-C) complexed with HLA-DR2a (DRA*0101, DRB5*0101) bearing a self-peptide from myelin basic protein (MBP). SPE-C binds the beta chain through a zinc bridge that links the SAG and class II molecules. Surprisingly, SPE-C also makes extensive contacts with the MBP peptide, such that peptide accounts for one third of the surface area of the MHC molecule buried in the complex, similar to TCR-peptide/MHC complexes. Thus, SPE-C may optimize T cell responses by mimicking the peptide dependence of conventional antigen presentation and recognition.

Prevention of murine acute graft-versus-host disease by staphylococcal enterotoxin B treatment

Retroviral superantigens such as minor lymphocyte stimulating (Mls) antigen play an important role in the pathogenesis of acute graft-versus-host disease (GVHD). However, it remains unclear how exogenous bacterial superantigens modulate acute GVHD. In this study, we tested the effects of staphylococcal enterotoxin B (SEB) on the development of acute GVHD in a model involving the systemic transfer of parental C57Bl/6 spleen cells into BDF1 mice. SEB treatment suppressed the expansion of donor-derived T cells and blocked the decrease in the number of host cells. Impaired haematopoiesis was actually rescued by treatment with SEB. In SEB-treated mice, both spontaneous proliferation and IL-2 production in T cells were suppressed on day 2 after parental cell infusion. On day 21, the number of donor-derived CD4+ Vbeta8+ T cells markedly decreased in the spleen of SEB-treated mice. Donor-derived CD4+ T cells failed to proliferate in response to host alloantigens, and both donor- and host-derived T cells were unable to produce IL-2 in response to concanavalin A stimulation, suggesting that SEB treatment induced a general immunosuppressive state. Our results indicate that SEB treatment prevents the development of acute GVHD by leading to unresponsiveness of donor-derived T cells against host alloantigens in a Vbeta-restricted and unrestricted manner.

Altered superantigenic ligands demonstrate the quantitative nature of T-cell activation

In a recent study, a superantigen mutated in the TCR binding site (staphylococcal enterotoxin B (SEB)delta61Y) was described, which behaved as a partial agonist for a Vbeta17-expressing T-cell clone. Evidence is now presented to demonstrate that there is distinct heterogeneity in the response of primary T cells to this protein. Some Vbeta17 T cells responded to SEBdelta61Y by modulating surface receptor expression consistent with activation, and by proliferating. Other Vbeta17 T cells did not proliferate, nor did they display a receptor expression phenotype consistent with activation. However, when repeatedly exposed to the altered superantigen, some of these non-responders entered cell cycle. This pattern of responses was not recapitulated by providing additional costimulation via CD28, although such treatment did induce some of the 'unresponsive' Vbeta17 T cells to upregulate the IL-2 receptor, indicative of partial activation. It was also found that the heterogeneous pattern could be replicated using very low doses of native SEB. The data are discussed in the context of models of T-cell activation in which differences in TCR ligand affinity and dose determine qualitatively different response phenotypes.

Superantigen-induced CD4 T cell tolerance mediated by myeloid cells and IFN-gamma

We have previously shown that systemic staphylococcal enterotoxin A (SEA) injections cause CD4 T cells in TCR-transgenic mice to become tolerant to subsequent ex vivo restimulation. An active IFN-gamma-dependent mechanism of suppression was responsible for the apparent unresponsiveness of the CD4 T cells. In this study, we analyze the response of CD4 T cells isolated throughout the first 10 days of the in vivo response to injected SEA. We show that CD4 T cells isolated at the peak of the in vivo response undergo very little activation-induced cell death after sterile FACS sorting or restimulation in the presence of neutralizing Abs to IFN-gamma. We also show that the IFN-gamma-dependent tolerance develops soon after SEA injection in the spleens of both normal and TCR-transgenic mice. This suppression is dependent upon myeloid cells from the SEA-treated mice and is optimal when inducible NO synthase activity and reactive oxygen intermediates are both present. The data indicate that IFN-gamma, myeloid cells, and a combination of NO and reactive oxygen intermediates all contribute to a common pathway of T cell death that targets activated or responding CD4 T cells. Sorted Gr-1(+) cells from SEA-treated mice also directly suppress the response of naive CD4 T cells in mixed cultures, indicating that this tolerance mechanism may play a role in down-regulating other vigorous immune responses.

Immunopathophysiological aspects of an emerging neonatal infectious disease induced by a bacterial superantigen

We recently discovered an emerging neonatal infectious disease, neonatal toxic shock syndrome-like (TSS-like) exanthematous disease (NTED), which is induced by a superantigen, TSS toxin-1 (TSST-1), produced by methicillin-resistant Staphylococcus aureus (MRSA). Here, we analyzed the activation and the response of TSST-1-reactive Vss2(+) T cells in NTED patients during the acute and recovery phases and in asymptomatic infants exposed to MRSA. In the acute phase, Vss2(+) T cells were anergic to stimulation with TSST-1 and underwent marked expansion, but by 2 months after disease onset, their numbers had declined to about 10% of the control level. Although the percentage of Vss2(+) T cells in the ten asymptomatic neonatal MRSA carriers was within the control range, these individuals could be divided into two groups on the basis of Vss2(+) T-cell activation. Vss2(+)CD4(+) T cells from three of these infants (Group 1) highly expressed CD45RO and were anergic to TSST-1, whereas in the other seven asymptomatic neonatal MRSA carriers (Group 2), these cells expressed CD45RO at the control level and were highly responsive to stimulation with TSST-1. The serum anti-TSST-1 IgG Ab titer was negligible in the four NTED patients in the acute phase and the three asymptomatic neonatal MRSA carriers in Group 1, but it was high in the seven asymptomatic carriers in Group 2. We suggest that maternally derived anti-TSST-1 IgGs helps to suppress T-cell activation by TSST-1 and protects infants from developing NTED.

Relative neutralizing activity in polyspecific IgM, IgA, and IgG preparations against group A streptococcal superantigens

In this study we compared the ability of different immunoglobulin (Ig) preparations containing IgG, IgM, and/or IgA to neutralize the activity of streptococcal pyrogenic exotoxin A (SpeA) or culture supernatant from a clinical group A streptococcal isolate. All Ig preparations markedly inhibited the mitogenic and cytokine-inducing activity of SpeA and culture supernatant at concentrations of 0.05-0.5 mg/mL, and at 0.5 mg/mL, most caused 95-100% inhibition of both stimuli. A significantly higher (P< or =.05) inhibition of SpeA was achieved by Pentaglobin (IgG, IgM, and IgA) and IgAbulin (IgA and IgG), as compared with pure IgG preparations. IgM- and IgA-enriched preparations had significantly higher inhibitory activity against SpeA than against culture supernatant, whereas the reverse was true for the IgG preparations (P< or =.05). The data show that IgM and IgA are potent inhibitors of specific streptococcal superantigens. These findings may have implications for the optimization of immunotherapy in invasive streptococcal infections.

Host variation in cytokine responses to superantigens determine the severity of invasive group A streptococcal infection

Cytokines elicited by superantigens have been suggested to play a central role in severe systemic clinical manifestations of gram-positive sepsis. Here we provide evidence for a potent inflammatory cytokine response in acute invasive group A streptococcal infections, and show a direct correlation between the magnitude of this response and the severity of systemic manifestations of the disease. Severe invasive cases suffering from toxic shock and/or necrotizing fasciitis had significantly higher frequencies of IL-2-, IL-6-, and TNF-alpha-producing cells in their circulation as compared to non-severe invasive cases (p=0.05-0.01). This difference was even more accentuated when severe and non-severe cases infected with a clonal M1T1 strain were compared (p=0.03-0. 004). To determine whether host factors were responsible for this difference in magnitude of cytokine responses, paired age- and gender-matched severe and non-severe M1T1 cases (n=8) were tested in vitro during their convalescent phase for immune response to superantigens produced by their infecting isolate. The results showed persistent and inherent differences in the magnitude of proliferative and cytokine responses of severe and non-severe patients to the streptococcal superantigens to which they had been exposed during infection. Thus, the study provides evidence that patients with a propensity to produce higher levels of inflammatory cytokines in response to streptococcal superantigens develop significantly more severe systemic manifestations than patients who have a propensity to produce lower levels of inflammatory cytokines to the same superantigens. We therefore conclude that host factors influence the magnitude of cytokine responses to superantigens and consequently the clinical outcome of the infection.

Prevotella intermedia stimulates expansion of Vbeta-specific CD4(+) T cells

Recent evidence suggests that certain periodontal pathogens preferentially stimulate T cells expressing specific variable regions on the beta chain (Vbeta) of the T-cell receptor, which may indicate the presence of a superantigen. Superantigens are microbial proteins that activate large numbers of CD4(+) T cells in a Vbeta-specific manner. The purpose of this study was to determine whether Prevotella intermedia, a putative periodontal pathogen, activates populations of specific Vbeta on CD4(+) T cells. Among the bacterial strains tested, P. intermedia strain 17, a clinical isolate, induced the strongest proliferative response in peripheral blood mononuclear cells. Antibodies raised against whole cells of this organism blocked the proliferative activity. P. intermedia-induced proliferation was T-cell specific and required the presence of antigen-presenting cells. Flow cytometric analysis showed that CD4(+) T-cell subsets expressing Vbeta8, Vbeta12, and Vbeta17 expanded in response to P. intermedia strain 17. The ability of P. intermedia to stimulate CD4(+)-T-cell proliferation was further supported by the production profiles of key T-cell cytokines, gamma interferon and interleukin-2. The data collectively suggest that certain strains of P. intermedia can activate Vbeta-specific T cells in a manner similar to that of other known microbial superantigens.

Effect of Staphylococcus enterotoxin B on the concurrent CD8(+) T cell response to influenza virus infection

Bacterial superantigens have potent in vivo effects. Respiratory viral infections are often associated with secondary bacterial infections, raising the likelihood of exposure to bacterial superantigens after the initiation of the anti-viral immune response. In this study, the general and V beta-specific effects of exposure to Staphylococcal enterotoxin B (SEB) during influenza virus infection on both the ongoing acute and the subsequent recall CD8(+) T cell responses were analyzed, using the well-characterized murine influenza model system and tetrameric MHC/peptide reagents to directly identify virus-specific T cells. The results show that although superantigen exposure during the primary viral infection caused delayed viral clearance, there was remarkably little effect of SEB on the magnitude or TCR repertoire of the ongoing cytolytic T cell response or on the recall response elicited by secondary viral infection. Thus, despite the well-characterized immunomodulatory effects of SEB, there was surprisingly little interference with concurrent anti-viral immunity.

Characterization and distribution of a new enterotoxin-related superantigen produced by Staphylococcus aureus

Staphylococcal enterotoxins (SEs) are a family of structurally related pyrogenic exotoxins consisting of the five prototypic SEs (types A to E) and three newly characterized SEs (types G to I) produced by Staphylococcus aureus (S. aureus). They also work as superantigens and cause food poisoning and shock symptoms in humans. In this study, we cloned a new variant gene of the seg and characterized its superantigenic properties and distribution among the clinical isolates of S. aureus. The gene encodes a 233 amino acid protein which is highly homologous to SEG (97.7%). The variant SEG (SEGv) expressed by the cloned gene exerted mitogenic activity on human peripheral blood mononuclear cells at the concentration of 100 pg/ml. T cells bearing Vbeta3, 12, 13.1, 13.2, 14 and 15 were preferentially expanded after stimulation with the recombinant protein. The mRNA of the variant seg gene was detected in the total RNA of the organisms bearing this gene. By PCR, 27 out of 48 clinical isolates of S. aureus (56%) possessed either the seg or variant seg gene. These findings suggest that SEG, or SEGv, is one of the most frequently produced superantigen exotoxins by S. aureus and may participate in the inflammatory process of the host by activating a distinct set of Vbeta families of T cells.

[Viral superantigens]

Viral superantigens bind several alleles and isotypes belonging to the MHC class II and subsequently activate particular T cell families via the variable portion of the beta chain of TCR. As a result, a superantigen bridges MHC and TCR molecules, leading to activation of T and B cells. The T expansion of various TCR V beta subsets is triggered on the basis of their V beta specificity, but not on their antigenic specificity. The best known superantigens are bacterial endotoxins produced by Staphylococcus aureus. However, viruses such as mouse mammary tumor or rabies viruses encode superantigens too. The ability of superantigens to break the barriers of MHC restriction and to activate large numbers of T and B cells has led to the hypothesis that superantigens may activate autoreactive T and B cells to initiate or worsen autoimmune diseases such as diabetes, multiple sclerosis, or psoriasis.