Relative abilities of distinct isotypes of human major histocompatibility complex class II molecules to bind streptococcal pyrogenic exotoxin types A and B

Elevated risk of invasive group A streptococcal disease and host genetic variation in the human leucocyte antigen locus

Invasive group A streptococcal (GAS) disease is uncommon but carries a high case-fatality rate relative to other infectious diseases. Given the ubiquity of mild GAS infections, it remains unclear why healthy individuals will occasionally develop life-threatening infections, raising the possibility of host genetic predisposition. Here, we present the results of a case–control study including 43 invasive GAS cases and 1540 controls. Using HLA imputation and linear mixed models, we find each copy of the HLA-DQA1*01:03 allele associates with a twofold increased risk of disease (odds ratio 2.3, 95% confidence interval 1.3–4.4, P = 0.009), an association which persists with classical HLA typing of a subset of cases and analysis with an alternative large control dataset with validated HLA data. Moreover, we propose the association is driven by the allele itself rather than the background haplotype. Overall this finding provides impetus for further investigation of the immunogenetic basis of this devastating bacterial disease.

Tracing the evolutionary history of the pandemic group A streptococcal M1T1 clone

The past 50 years has witnessed the emergence of new viral and bacterial pathogens with global effect on human health. The hyperinvasive group A Streptococcus (GAS) M1T1 clone, first detected in the mid-1980s in the United States, has since disseminated worldwide and remains a major cause of severe invasive human infections. Although much is understood regarding the capacity of this pathogen to cause disease, much less is known of the precise evolutionary events selecting for its emergence. We used high-throughput technologies to sequence a World Health Organization strain collection of serotype M1 GAS and reconstructed its phylogeny based on the analysis of core genome single-nucleotide polymorphisms. We demonstrate that acquisition of a 36-kb genome segment from serotype M12 GAS and the bacteriophage-encoded DNase Sda1 led to increased virulence of the M1T1 precursor and occurred relatively early in the molecular evolutionary history of this strain. The more recent acquisition of the phage-encoded superantigen SpeA is likely to have provided selection advantage for the global dissemination of the M1T1 clone. This study provides an exemplar for the evolution and emergence of virulent clones from microbial populations existing commensally or causing only superficial infection.

Individual genetic variations directly effect polarization of cytokine responses to superantigens associated with streptococcal sepsis: implications for customized patient care

Host immunogenetic variations strongly influence the severity of group A streptococcus sepsis by modulating responses to streptococcal superantigens (Strep-SAgs). Although HLA-II-DR15/DQ6 alleles strongly protect against severe sepsis, HLA-II-DR14/DR7/DQ5 alleles significantly increase the risk for toxic shock syndrome. We found that, regardless of individual variations in TCR-Vβ repertoires, the presentation of Strep-SAgs by the protective HLA-II-DR15/DQ6 alleles significantly attenuated proliferative responses to Strep-SAgs, whereas their presentation by the high-risk alleles augmented it. Importantly, HLA-II variations differentially polarized cytokine responses to Strep-SAgs: the presentation of Strep-SAgs by HLA-II-DR15/DQ6 alleles elicited significantly higher ratios of anti-inflammatory cytokines (e.g., IL-10) to proinflammatory cytokines (e.g., IFN-γ) than did their presentation by the high-risk HLA-II alleles. Adding exogenous rIL-10 significantly attenuated responses to Strep-SAgs presented by the high-risk HLA-II alleles but did not completely block the response; instead, it reduced it to a level comparable to that seen when these superantigens were presented by the protective HLA-II alleles. Furthermore, adding neutralizing anti-IL-10 Abs augmented Strep-SAg responses in the presence of protective HLA-II alleles to the same level as (but no higher than) that seen when the superantigens were presented by the high-risk alleles. Our findings provide a molecular basis for the role of HLA-II allelic variations in modulating streptococcal sepsis outcomes and suggest the presence of an internal control mechanism that maintains superantigen responses within a defined range, which helps to eradicate the infection while attenuating pathological inflammatory responses that can inflict more harm than the infection itself.

Characterization of novel staphylococcal enterotoxin-like toxin type P

We investigated the biological properties of a novel staphylococcal enterotoxin (SE)-like toxin type P (SElP). SElP induced a substantial proliferative response and the production of cytokines interleukin-2, gamma interferon, tumor necrosis factor alpha, and interleukin-4 from human T cells when administered at a concentration of 0.4 pM (0.01 ng/ml) or more. The expression of major histocompatibility complex class II molecules on accessory cells was required for T-cell stimulation by SElP. SElP selectively stimulated a vast number of human T cells bearing receptors Vbeta 5.1, 6, 8, 16, 18, and 21.3. These results indicated that SElP acts as a superantigen. SElP proved to be emetic in the house musk shrew emetic assay, although at a relatively high dose (50 to 150 mug/animal). A quantitative assay of SElP production with 30 Staphylococcus aureus strains harboring selp showed that 60% of these strains produced significant amounts of SElP in vitro. All 10 strains carrying seb and selp produced SEB but not SElP, suggesting the inactivation of the selp locus in S. aureus strains with a particular se gene constitution.

HLA class II polymorphisms determine responses to bacterial superantigens

The excessive immunological response triggered by microbial superantigens has been implicated in the etiology of a wide range of human diseases but has been most clearly defined for the staphylococcal and streptococcal toxic shock syndromes. Because MHC class II presentation of superantigens to T cells is not MHC-restricted, the possibility that HLA polymorphisms could influence superantigenicity, and thus clinical susceptibility to the toxicity of individual superantigens, has received little attention. In this study, we demonstrate that binding of streptococcal and staphylococcal superantigens to HLA class II is influenced by allelic differences in class II. For the superantigen streptococcal pyrogenic exotoxin A, class II binding is dependent on DQ alpha-chain polymorphisms such that HLA-DQA1*01 alpha-chains show greater binding than DQA1*03/05 alpha-chains. The functional implications of differential binding on T cell activation were investigated in various experimental systems using human T cells and murine Vbeta8.2 transgenic cells as responders. These studies showed quantitative and qualitative differences resulting from differential HLA-DQ binding. We observed changes in T cell proliferation and cytokine production, and in the Vbeta specific changes in T cell repertoire that have hitherto been regarded as a defining feature of an individual superantigen. Our observations reveal a mechanism for the different outcomes seen following infection by toxigenic bacteria.

Comparison of pathogenic factors expressed by group A Streptococci isolated from patients with streptococcal toxic shock syndrome and scarlet fever

Streptococcal toxic shock syndrome (STSS) is an illness with high mortality. To obtain clues to understanding the pathogenesis of STSS, we investigated the expression of several pathogenic factors in ten group A streptococcus (GAS) isolates from ten patients with STSS in Japan, in comparison with ten GAS isolates from children with scarlet fever. The ten scarlet fever-derived GAS isolates were equally low in lethality and anti-phagocytic activity in mice and in the production of streptolysin O (SLO), and equally high in production of superantigenic exotoxins (SAGTs) and cysteine proteinase. By comparison, the ten STSS-derived GAS isolates were heterogeneous in the expression of the above pathogenic factors, which ranged from low to high values. Most of the ten STSS-derived isolates were higher in lethality and anti-phagocytic activity and production of SLO, and lower in the production of SAGTs and cysteine proteinase than the ten scarlet fever-derived isolates. The results suggest that the lethality and anti-phagocytic activity examined in mice and SLO may be involved mainly in the development of most of the ten STSS cases.

The superantigenic activity of streptococcal pyrogenic exotoxin B is independent of the protease activity

The nature of the mitogenic activity of pyrogenic streptococcal exotoxin B, also known as streptococcal cysteine protease, has been debated in the literature. Streptococcal exotoxin B has been shown to cleave interleukin-1beta precursor and create biologically active interleukin-1beta, a major cytokine mediating inflammation and shock. This activity could mimic the mitogenicity and cytokine release induced by superantigens in lymphocyte stimulating experiments. In this study, the protease activity of streptococcal exotoxin B was irreversibly inhibited by covalent binding of a tripeptide and the superantigenic properties of streptococcal exotoxin B were found not to be influenced by this inactivation. Native as well as protease-inactivated streptococcal exotoxin B was shown to stimulate T-cell proliferation without a need of metabolically active antigen presenting cells. Furthermore, streptococcal exotoxin B-induced T-cell proliferation was shown to require HLA-DQ since addition of HLA-DQ monoclonal antibodies totally inhibited the mitogenic activity of streptococcal exotoxin B, indicating that streptococcal exotoxin B, as other superantigens, makes direct contact with the T-cell receptor via HLA class II. The aim of this study was to characterize the relationship between the proteolytic and superantigenic properties of streptococcal exotoxin B.

Identification of domains involved in superantigenicity of streptococcal pyrogenic exotoxin F (SpeF)

A series of 11 synthetic peptides of 30 amino acids, each with 10 amino acids overlap which spanned the entire sequence of streptococcal pyrogenic exotoxin F (SpeF), were employed in proliferation studies on human peripheral blood mononuclear cells (PBMCs). Regions 41-70, 141-170 and 181-210 were identified as important for SpeF-induced lymphocyte activation. Secondary structure predictions of these peptides showed similarities to regions in other superantigens known to be important for T cell mitogenicity. Furthermore, antisera specific to peptides covering amino acids 1-70 and 181-228 were able to inhibit SpeF-induced mitogenicity by 25% when pre-incubated with SpeF prior to PBMC activation.

Superantigens of gram-positive bacteria: structure-function analyses and their implications for biological activity

Just as we thought that we know everything about superantigens, new molecular and structural studies indicate that we have only just begun to unravel the secrets of these fascinating molecules. Recent structure-function analysis of superantigens from Gram-positive bacteria, with emphasis on their interaction with major histocompatibility complex molecules, could help us decipher the role of superantigens in disease, identify host factors that potentiate their effects and design drugs that specifically block their activity.

Exclusion of bioactive contaminations in Streptococcus pyogenes erythrogenic toxin A preparations by recombinant expression in Escherichia coli

The streptococcal erythrogenic exotoxin A (SPEA) belongs to the family of bacterial superantigens and has been implicated in the pathogenesis of a toxic shock-like syndrome and scarlet fever. Concerning its biological activity, mainly T-cell-stimulatory properties, conflicting data exist. In this study, we show that most of the SPEA preparations used so far contain biologically active contaminations. Natural SPEA from the culture supernatant of Streptococcus pyogenes NY-5 and recombinant SPEA purified from the culture filtrate of S. sanguis are strongly contaminated with DNases. We show that natural SPEA induces more tumor necrosis factor alpha (TNF-alpha) than recombinant SPEA, but we also show that DNases are able to induce TNF-alpha. In commercial SPEA preparations, we identified a highly active protease, which was shown not to be SPEB. To exclude these contaminations, we overexpressed SPEA cloned in the effective high-level expression vector pIN-III-ompA2 in Escherichia coli. The expressed SPEA shows the same amino acid composition as natural SPEA, whereas functional studies reported so far were carried out with toxins containing an incorrect amino terminus. We describe the rapid purification of lipopolysaccharide-, DNase-, and protease-free SPEA in two steps from the host's periplasm and its structural characterization by circular dichroism. Our results represent for the first time the production in E. coli of recombinant SPEA with the authentic N-terminal sequence and a proven superantigenic activity. Collectively, our results indicate that immunological studies of superantigens require highly purified substances free of biologically active contaminations.

Streptococcal pyrogenic exotoxin A (SPE A) superantigen induced production of hematopoietic cytokines, IL-12 and IL-13 by human peripheral blood mononuclear cells

A quantitative and kinetic study of the release of the hematopoietic cytokines IL-3, IL-5 and GM-CSF, the immunoregulatory cytokine IL-12 heterodimer (and its p40 subunit) and IL-13 by human peripheral blood mononuclear cells (PBMC) stimulated in vitro with the superantigen streptococcal pyrogenic (erythrogenic) exotoxin A (SPE A) from Streptococcus pyogenes is reported. PBMC were stimulated in parallel with heat-killed group A streptococcal cells, E. coli lipopolysaccharide (LPS) and with concanavalin A (Con A) in certain experiments for comparative purposes. The cytokines were assayed in the supernatant fluids by ELISA. IL-13 expression was also determined by a quantitative competitive PCR. IL-3, IL-5, GM-CSF, IL-12 p40, IL-12 heterodimer and IL-13 expression was induced by SPE A in a time- and dose-dependent manner in rather substantial amounts except the IL-12 heterodimer, which was released in small quantities. In contrast to SPE A, IL-3, IL-5 and IL-13 were not or poorly elicited by streptococcal cells or LPS whereas these two stimulants induced relatively high amounts of GM-CSF. Interestingly, both IL-12 p40 and IL-12 heterodimer were released in much higher amounts by streptococcal cells. Con A induced IL-3, IL-5, GM-CSF and IL-13 production in amounts comparable to those elicited by SPE A. The possible pathophysiological relevance of the elicitation by SPE A and streptococcal cells of these cytokines is discussed.

Allelic polymorphisms at the H-2A and HLA-DQ loci influence the response of murine lymphocytes to the Mycoplasma arthritidis superantigen MAM

Mycoplasma arthritidis, an agent of rodent arthritis, produces a potent superantigen (SAg), MAM. Previous work established that MAM is presented to T cells by murine H-2E or the homologous human HLA-DR molecules and that lymphocytes lacking a functional H-2E molecule fail to respond to MAM. Recently, more potent and purified preparations of MAM of known protein content have become available. This enabled us to more effectively compare the response of MAM with that of other SAgs by using lymphocytes from mice whose cells express different H-2A and HLA-DQ molecules. Here we demonstrate that cells from some H-2E-negative mouse strains respond to higher concentrations of MAM. By use of inbred, congenic, and recombinant mice, we show that these differences are, in fact, exercised at the level of the major histocompatibility complex (MHC) and that allelic polymorphisms at H-2A influence reactivity to MAM. In addition, polymorphisms at HLA-DQ, the human homolog of H-2A, also influence responsiveness to MAM. Cells expressing DQw6 (HLA-DQA1*0103 and DQBI*0601 chains) gave much higher responses to MAM than did cells expressing DQw8 (DQA1*0301 and DQB1*0302 chains). In fact, responses of lymphocytes expressing DQB1*0601 chains homozygously were as high as those observed for cells expressing a functional H-2E molecule. Murine lymphocytes responded less well to staphylococcal enterotoxin B (SEB) and SEA, but mouse cells expressing human MHC molecules gave much higher responses. The patterns of reactivity observed with cells expressing the various murine and human alleles differed for MAM, SEB, and SEA, suggesting that each of these SAgs interacts with different regions or residues on MHC molecules. It has been hypothesized that SAgs might play a role in susceptibility to autoimmune disease. Allelic polymorphisms at MHC loci might therefore influence susceptibility to autoimmune disease by affecting immunoreactivity to specific superantigens.

Analysis of the superantigenic activity of mutant and allelic forms of streptococcal pyrogenic exotoxin A

Infections with Streptococcus pyogenes (group A streptococcus) can result in the recently described streptococcal toxic shock syndrome (STSS), which is characterized by rashes, hypotension, multiorgan failure, and a high mortality rate. S. pyogenes isolates associated with STSS usually produce streptococcal pyrogenic exotoxin A (SpeA), a bacterial superantigen capable of stimulating host immune cells. Most of the symptoms of STSS are believed to result from cytokine release by the stimulated cells. To better understand the pathogenesis of STSS, we began studies on the SpeA-immune cell interaction. We generated 20 mutant forms of SpeA1 (SpeA encoded by allele 1), and the mutant toxins were analyzed for mitogenic stimulation of human peripheral blood mononuclear cells, affinity for class II major histocompatibility complex molecules (DQ), and disulfide bond formation. Residues necessary for each of these functions were identified. There are four alleles of speA, and STSS strains usually contain either allele 2 or allele 3. The product of allele 2, SpeA2, had slightly higher affinity for the class II MHC molecule compared with SpeA1 but not significantly greater mitogenic activity. SpeA3, however, was significantly increased in mitogenic activity and affinity for class II MHC compared with SpeA1. Thus, we have evidence that the toxin encoded by some of the highly virulent S. pyogenes STSS-associated isolates is a more active form of SpeA.

Tumor necrosis factor production by human T-cells stimulated with bacterial superantigens

Tumor necrosis factor (TNF) production from T-cells stimulated with superantigenic exotoxins, staphylococcal enterotoxin B and streptococcal pyrogenic exotoxin A was investigated in the presence of cells bearing distinct isotypes of HLA class II molecules. The main T-cell subset for TNF production was investigated in parallel. Similarly high levels of TNF production were induced upon stimulation with the toxins in the presence of DR+ or DQ+ cells, but only marginal levels of TNF production were induced in the presence of DP+ cells. Although both CD4+ T-cells and CD8+ T-cells produced TNF-alpha and TNF-beta in response to toxin stimulation in the presence of HLA class II+ cells, the former T-cell subset was the major source of producers of TNF-alpha and TNF-beta.

Bacterial pyrogenic exotoxins as superantigens

The recent discovery of the mode of interaction between a group of microbial proteins known as superantigens and the immune system has opened a wide area of investigation into the possible role of these molecules in human diseases. Superantigens produced by certain viruses and bacteria, including Mycoplasma species, are either secreted or membrane-bound proteins. A unique feature of these proteins is that they can interact simultaneously with distinct receptors on different types of cells, resulting in enhanced cell-cell interaction and triggering a series of biochemical reactions that can lead to excessive cell proliferation and the release of inflammatory cytokines. However, although superantigens share many features, they can have very different biological effects that are potentiated by host genetic and environmental factors. This review focuses on a group of secreted pyrogenic toxins that belong to the superantigen family and highlights some of their structural-functional features and their roles in diseases such as toxic shock and autoimmunity. Deciphering the biological activities of the various superantigens and understanding their role in the pathogenesis of microbial infections and their sequelae will enable us to devise means by which we can intervene with their activity and/or manipulate them to our advantage.

Superantigenic properties of the group A streptococcal exotoxin SpeF (MF)

Streptococcal pyrogenic exotoxin F (SpeF), previously referred to as mitogenic factor, is a newly described potent mitogen produced by group A streptococci. To investigate whether this protein belongs to the family of microbial superantigens, we analyzed the cellular and molecular requirements for its presentation to T cells and compared it with the known streptococcal superantigen pyrogenic exotoxin A (SpeA) and the nonspecific polyclonal T-cell mitogen phytohemagglutinin (PHA). SpeF and SpeA were efficiently presented by autologous antigen-presenting cells (APCs) and an allogeneic B lymphoma cell line, Raji. In contrast, the monocytic cell line U937, which does not express major histocompatibility complex (MHC) class II molecules, failed to present SpeF as well as SpeA but supported the response to PHA. Thus, the presentation of SpeF by APCs was class II dependent but not MHC restricted. The requirement for HLA class II was further supported by the ability of anti-HLA-DQ monoclonal antibody to block the SpeF-induced proliferative response by 75 to 100%. Paraformaldehyde (PFA) fixation of autologous APCs resulted in an impaired ability of SpeF and SpeA to induce optimal T-cell proliferation. In contrast, fixation of Raji cells did not affect the induced proliferation. The stimulatory effect of PHA remained unaffected by both the use of PFA-fixed APCs and the addition of the HLA class II-specific monoclonal antibodies. The addition of a supernatant enriched in interleukin 1 and interleukin 6 to fixed autologous APCs resulted in an increased SpeF-induced response; thus, the impairment was not due to a requirement for processing, but, rather, costimulatory factors produced by metabolically active APCs were needed. SpeF was found to preferentially activate T cells bearing V beta 2, 4, 8, 15, and 19, as determined by quantitative PCR. The data presented clearly show that SpeF is a superantigen. We also studied the prevalence of the speF gene in clinical isolates by Southern blot analyses, and the gene could be detected in 42 group A streptococcal strains, which represented 14 serotypes.

Comparative study of cytokine release by human peripheral blood mononuclear cells stimulated with Streptococcus pyogenes superantigenic erythrogenic toxins, heat-killed streptococci, and lipopolysaccharide

The differences between toxic or septic shocks in humans during infections by streptococci and gram-negative bacteria remain to be fully characterized. For this purpose, a quantitative study of the cytokine-inducing capacity of Streptococcus pyogenes erythrogenic (pyrogenic) exotoxins (ETs) A and C, heat-killed S. pyogenes bacteria, and Neisseria meningitidis endotoxin (lipopolysaccharide [LPS]) on human peripheral blood mononuclear cells (PBMC) and monocytes has been undertaken. The levels of interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-6, IL-8, tumor necrosis factor alpha (TNF-alpha), and TNF-beta induced by these bacterial products and bacteria were determined by using cell supernatants. The capacity of ETs to elicit the monocyte-derived cytokines IL-1 alpha, IL-1 beta, IL-6, and TNF-alpha was found to depend on the presence of T lymphocytes, because of the failure of purified monocytes to produce significant amounts of these cytokines in response to ETs. PMBC elicited large amounts of these cytokines, as well as IL-8 and TNF-beta, with an optimal release after 48 to 96 h. The most abundant cytokine produced in response to ETA was IL-8. In contrast to the superantigens ETA and ETC, LPS and heat-killed streptococci stimulated the production of significant amounts of IL-1 alpha, IL-1 beta, IL-6, and TNF-alpha, with optimal production after 24 to 48 h in monocytes, indicating no significant involvement of T cells in the process. ETs, but neither LPS nor streptococci, were potent inducers of TNF-beta in PBMC. This study outlines the differences in the pathophysiological features of shock evoked by endotoxins and superantigens during infection by gram-negative bacteria and group A streptococci, respectively. The production of TNF-alpha was a common pathway for LPS, streptococcal cells, and ETs, although cell requirements and kinetics of cytokine release were different.

Production of tumour necrosis factors by human T cells stimulated by a superantigen, toxic shock syndrome toxin-1

The capacity of human T cell subsets, CD4+ or CD8+ T cells, to produce tumour necrosis factors (TNF-alpha and TNF-beta) upon stimulation with toxic shock syndrome toxin-1 (TSST-1) and the requirement for MHC class II molecules on accessory cells (AC) in the response were investigated. The capacity of CD4+ T cells was much higher than that of CD8+ T cells in TSST-1-induced production of TNF-alpha and TNF-beta. The expression of MHC class II molecules on AC was required in the response.

Role of human major histocompatibility complex DQ molecules in superantigenicity of streptococcus-derived protein

Antigenicity of peptic extract from type 12 group A streptococci (PEAST12) for T cells was examined in major histocompatibility complex (MHC) class II transgenic mice. PEAST12 was mitogenic for murine T cells when antigen-presenting cells were obtained from human MHC (HLA)-DQ4 alpha beta transgenic mice or from DQ6 alpha beta transgenic mice but was not mitogenic in DR alpha transgenic, DR51 alpha beta transgenic, E alpha transgenic, or nontransgenic mice. In addition, PEAST12 showed mitogenicity for murine T cells in DQ4 alpha singly transgenic mice but not in DQ4 beta singly transgenic mice. T-cell stimulation by PEAST12 was unrestricted by but dependent on the expression of HLA-DQ molecules on antigen-presenting cells, and PEAST12 selectively activated T-cell receptor V beta 11-, V beta 15-, and V beta 18-positive T cells in mice. We propose that PEAST12 contains a superantigen which binds preferentially to the alpha-chain of HLA-DQ molecules. The well-known phenomenon that peptic extracts from group A streptococci are mitogenic in humans but not in mice is likely due to structural differences in MHC class II molecules between these two species of mammals.

Selective anergy of V beta 8+ T cells in human immunodeficiency virus-infected individuals

We have analyzed the V beta usage by CD4+ and CD8+ T cells from human immunodeficiency virus (HIV)-infected individuals in response to an in vitro stimulation with the superantigenic erythrogenic toxin A (ETA) of Streptococcus pyogenes. ETA amplifies specifically CD4+ and CD8+ T cells from control donors expressing the V beta 8 and the V beta 12 elements. When peripheral T cells from asymptomatic HIV-infected individuals were stimulated with ETA, there was a complete lack of activation of the V beta 8+ T cell subset, whereas the V beta 12+ T cell subset responded normally to the superantigen. This V beta-specific anergy, which was also observed in response to staphylococcal enterotoxin E (SEE), affected both CD4+ and CD8+ T cells and represented an intrinsic functional defect rather than a specific lack of response to bacterial superantigens since it was also observed after a stimulation with V beta 8 monoclonal antibodies. The V beta 8 anergic T cells did not express interleukin 2 receptors (IL-2Rs) and failed to proliferate in response to exogenous IL-2 or IL-4, suggesting that this anergy was not a reversible process, at least by the use of these cytokines. The unresponsiveness of the V beta 8 T cell subset is frequent since it was found in 56% of the patients studied, and comparison of the clinical status of responder vs. anergic patients indicated that the only known common factor between them was HIV infection. In addition, it is noteworthy that the anergy of the V beta 8 subset may be a very early phenomenon since it was found in a patient at Centers for Disease Control stage I of the disease. These data provide evidence that a dominant superantigen may be involved in the course of HIV infection and that the contribution of HIV has to be considered.

Cytokine induction by extracellular products of oral viridans group streptococci

During an etiological study of Kawasaki disease (mucocutaneous lymph node syndrome [MCLS]), we found that dominant viridans streptococcal strains on tooth surfaces and in the throat of both MCLS patients and non-MCLS control children formed erythrogenic and biologically active, extracellular products. In this study, we demonstrated that erythrogenic culture supernatant concentrates of representative strains (two Streptococcus mitis and two Streptococcus oralis), when injected intravenously, induced serum tumor necrosis factor alpha, interleukin-6 (IL-6), and gamma interferon in muramyldipeptide- or Propionibacterium acnes-primed C3H/HeN mice. The concentrates also induced tumor necrosis factor alpha, IL-6, and thymocyte-activating factor (essentially IL-1) in murine peritoneal macrophage, human monocyte, and human whole-blood cultures. An erythrogenic, heat-labile extracellular protein fraction (F-1) that was concentrated from the culture supernatants of a representative S. mitis strain exhibited the above-mentioned cytokine-inducing activity. This partially purified F-1 fraction also induced thymocyte-activating factor and IL-6 in human umbilical vascular endothelial cell and gingival fibroblast cultures.