Superantigenicity of helper T-cell mitogen (SPM-2) isolated from culture supernatants of Streptococcus pyogenes

Conserved mycobacterial lipoglycoproteins activate TLR2 but also require glycosylation for MHC class II-restricted T cell activation

CD4(+) T cell clones derived from a leprosy lesion and patient blood were used to monitor the isolation and identification of an Ag associated with the self-limited form of the disease. Biochemical purification and genetic analysis identified the T cell Ag as a conserved mycobacterial lipoglycoprotein LprG. LprG-mediated activation of CD4(+) T cells required specific MHC class II restriction molecules and intracellular processing. Although LprG activated TLR2, this alone was not sufficient to stimulate or inhibit T cell activation. A striking finding was that the carbohydrate moieties of LprG were required for optimal T cell activation, because recombinant LprG produced in Escherichia coli, or recombinant LprG produced in Mycobacterium smegmatis and digested by alpha-mannosidase, did not activate T cells. This study demonstrates that the universe of bacterial T cell Ags includes lipoglycoproteins, which act as TLR2 ligands but also require glycosylation for MHC class II-restricted T cell activation in vivo.

Making sense of equine uterine infections: the many faces of physical clearance

Equine uterine infections inflict major losses on the equine industry. Persistent inflammation of the oviduct and uterus leads to loss of the conceptus and mares susceptible to infection have weakened uterine defences partly due to retention of inflammatory exudate. Bacteria may trigger inflammation, resist phagocytosis, or adhere to the endometrium and types of infection range from genital commensals in susceptible mares to reproductive pathogens in normal mares. Uterine infections are diagnosed by history, detection of uterine inflammation, and isolation of typical organisms and susceptible mares may be identified by detection of intrauterine fluid during oestrus, or at 6-48 h post-breeding. Therapy includes oxytocin, uterine lavage, antibiotics, and prostaglandin analogues and clinical studies indicate additive benefits of oxytocin and antibiotics. Improved conception rates have been associated with autologous, intrauterine plasma, despite controversy about its bactericidal efficacy. Because of the potential for endometrial damage, intrauterine antiseptics require caution.

The bacterial superantigen streptococcal mitogenic exotoxin Z is the major immunoactive agent of Streptococcus pyogenes

The gene encoding streptococcal mitogenic exotoxin Z (SMEZ) was disrupted in Streptococcus pyogenes. Despite the presence of other superantigen genes, mitogenic responses in human and murine HLA-DQ transgenic cells were abrogated when cells were stimulated with supernatant from the smez(-) mutant compared with the parent strain. Remarkably, disruption of smez led to a complete inability to elicit cytokine production (TNF-alpha, lymphotoxin-alpha, IFN-gamma, IL-1 and -8) from human cells, when cocultured with streptococcal supernatants. The potent effects of SMEZ were apparent even though transcription and expression of SMEZ were barely detectable. Human Vbeta8(+) T cell proliferation in response to S. pyogenes was SMEZ-dependent. Cells from HLA-DQ8 transgenic mice were 3 logs more sensitive to SMEZ-13 than cells from HLA-DR1 transgenic or wild-type mice. In the mouse, SMEZ targeted the human Vbeta8(+) TCR homologue, murine Vbeta11, at the expense of other TCR T cell subsets. Expression of SMEZ did not affect bacterial clearance or survival from peritoneal streptococcal infection in HLA-DQ8 mice, though effects of SMEZ on pharyngeal infection are unknown. Infection did lead to a rise in Vbeta11(+) T cells in the spleen which was partly reversed by disruption of the smez gene. Most strikingly, a clear rise in murine Vbeta4(+) cells was seen in mice infected with the smez(-) mutant S. pyogenes strain, indicating a potential role for SMEZ as a repressor of cognate anti-streptococcal responses.

Superantigen bacterial toxins: state of the art

Superantigens (SAgs) are viral and bacterial proteins exhibiting a highly potent polyclonal lymphocyte-proliferating activity for CD4(+), CD8(+) and sometimes gammadelta(+) T cells of human and (or) various animal species. Unlike conventional antigens, SAgs bind as unprocessed proteins to invariant regions of major histocompatibility complex (MHC) class II molecules on the surface of antigen-presenting cells (APCs) and to particular motifs of the variable region of the beta chain (Vbeta) of T-cell receptor (TcR) outside the antigen-binding groove. As a consequence, SAgs stimulate at nano-to picogram concentrations up to 10 to 30% of host T-cell repertoire while only one in 10(5)-10(6) T cells (0.01-0.0001%) are activated upon conventional antigenic peptide binding to TcR. SAg activation of an unusually high percentage of T lymphocytes initiates massive release of pro-inflammatory and other cytokines which play a pivotal role in the pathogenesis of the diseases provoked by SAg-producing microorganisms. We briefly describe in this review the molecular and biological properties of the bacterial superantigen toxins and mitogens identified in the past decade.

Effects of superantigen and lipopolysaccharide on induction of CD80 through apoptosis of human monocytes

To investigate the mechanisms underlying superantigen (SAg) stimulation, we analyzed the effect of SAg on monocyte responses with or without lipopolysaccharide (LPS). Addition of gamma interferon (IFN-gamma) to unstimulated cultures induced a marked increase in the number of CD80(+) monocytes, which was inhibited by LPS through the action of interleukin-10. However, CD80(+) monocytes began to increase before IFN-gamma production, observed after 9 h of stimulation with staphylococcal enterotoxin B (SEB). SEB selectively increased the number of apoptotic CD80(-) monocytes, whereas LPS-treated monocytes were resistant to the apoptotic action of SEB. This SEB-induced killing was abrogated by anti-CD95 monoclonal antibody (MAb) ZB4 and anti-CD95 ligand (CD95L) MAb NOK2, suggesting a CD95-based pathway of apoptosis. Furthermore, the numbers of SEB-induced CD80(+) monocytes were partially decreased by anti-CD119 (IFN-gamma receptor) MAb and by anti-CD95L (NOK2) MAb. The CD30 expression of CD27(high) T cells induced by SEB was increased by agonistic anti-CD95 (CH11) MAb. Together, our findings showed that SEB-induced monocyte apoptosis is closely associated with the enrichment of CD80(+) monocytes generated before IFN-gamma production, followed by up-regulation of CD80 by IFN-gamma, and that LPS has negative effects in both cases. These results also suggested that induction of monocyte apoptosis is an important mechanism by which SAg exerts its anti-inflammatory effects.

Normal proliferative responses of peripheral blood mononuclear cells to streptococcal preparation OK-432 in patients with pustulosis palmaris et plantaris constitute a distinct feature from the reduced responses observed in those with psoriasis vulgaris, pustular psoriasis, and acrodermatitis continua of Hallopeau

It was previously reported that peripheral blood mononuclear cells (PBMC) from the patients with psoriasis vulgaris (PV) showed a reduced proliferative response in vitro to the stimulation of a lyophilized preparation of penicillin-treated low virulence Su-strain of Streptococcus pyogenes group 3, OK-432. In this study, at first it was examined whether OK-432 acts as a superantigen. By analyzing the usage of Vbeta T-cell receptor (TCR) of proliferating T cells stimulated with OK-432, it was found that OK-432 stimulated preferentially Vbeta2 TCR-bearing T cells. Next, to find differences in in vitro responses of PBMC among various types of sterile pustular dermatoses such as pustulosis palmaris et plantaris (PPP), acrodermatitis continua of Hallopeau (AC), and generalized pustular psoriasis (GPP), the proliferative responses of PBMC obtained from these patients under the stimulation of OK-432 were compared. When the PBMC was stimulated with interleukin (IL)-2, no significant difference was found in their proliferative responses among those obtained from the patients with these sterile pustular dermatoses, PV or healthy controls. However, like those from PV patients, PBMC from AC and GPP patients showed significantly smaller responses to OK-432 than those from the healthy controls. In contrast, the proliferative responses of PBMC from the patients with PPP to OK-432 was comparable to those from healthy controls. These results, in addition to its unique clinical and histopathological characteristics, suggest that PPP has a different pathogenetic background from that underlying PV, AC, or GPP.

Lipopolysaccharide-dependent down-regulation of CD27 expression on T cells activated with superantigen

To investigate the mechanisms underlying T-cell responses during superantigen (SAg) stimulation, we analysed the effects of SAg on CD27 expression with or without lipopolysaccharide (LPS) as a novel regulator of T-cell function. CD27 is expressed on the majority of resting peripheral blood T cells (CD27low). Activation of T cells by SAg induces high levels of CD27 surface expression (CD27high) accompanied with simultaneous CD30 receptor expression. After prolonged activation in vitro, the level of CD27 expression became intermediate. The effects of LPS on down-regulation of CD27high expression on CD30+ T cells were dose-dependent. Separating LPS-stimulated monocytes from T cells by mechanical dispersion abolished its inhibitory effect, indicating the requirement for direct interactions between monocytes and T cells. We also found that SAg up-regulated CD80 expression on CD14+ monocytes and LPS inhibited SAg-induced CD80 expression after 24 hr of stimulation. Up-regulation of CD152 (CTLA-4) was selective, since it was found to be preferentially expressed on the CD30+ population. Competitive experiments using soluble blocking peptides showed that addition of CD28 or CD80 peptide recovered LPS-induced down-regulation of CD27high expression on CD30+ T cells. These observations suggested that the presence of low levels of CD80 on monocytes may partially inhibit CD27 expression due to inefficient delivery of positive signals via CD28/CD80 interaction, and that the increased levels of CD80 enhance the inhibition through interactions with CD152 which is expressed at the highest levels after 48 hr of activation.