Monomicrobial Fournier's Gangrene Caused by Panton-Valentine Leukocidin-negative Methicillin-susceptible Staphylococcus aureus ST8 in Japan

Methicillin-resistant Staphylococcus aureus USA300, belonging to sequence type (ST) 8, is a rare cause of necrotizing fasciitis in the USA. We herein report a case of monomicrobial Fournier's gangrene caused by an ST8, methicillin-susceptible Staphylococcus aureus (designated ksw1). Whole-genome sequencing and analyses for virulence determinants revealed that, unlike USA300, ksw1 lacked virulence genes, such as Panton-Valentine leukocidin and SCCmec, while harboring the toxic shock syndrome toxin-1 gene. These genomic features correlate with ST8 CA-MRSA/J, which is the major genotype of ST8 in Japan.

Microbial Superantigens as Virulence Factors and Ways to Counteract Their Actions

Microbial superantigens represent a group of molecules that is able to cause massive activation of the host immune system. Human diseases originating from superantigen-secreting bacterial agents are characterized by shock, which continues to pose major health problems. Presently, the treatment of superantigen-mediated infections is limited to the administration of antibiotics and handling of the state of shock. However, the development of multiple antibiotic-resistant, superantigen-producing bacterial strains increases the threat of these infections, and prompts researchers to better understand and treat disease states in which exposure to superantigens is at least partly responsible for the outcome. In the past decade, significant understanding has been achieved regarding the molecular mechanisms of superantigen-host interactions. Based on this understanding, a variety of promising strategies directed against superantigens have been developed. In this review, we discuss some of these strategies, as well as the potential for therapeutic applications of superantigens for the benefit of the host.

Therapeutic approaches to superantigen-based diseases: a review

Superantigens secreted by the bacterial pathogen Staphyloccocus aureus are extremely potent toxins that overstimulate the host immune system by binding to the MHC class II and T cell receptors and activating a large population of T cells. Superantigen infection has been shown to be the causative agents in acute diseases, food poisoning and toxic shock syndrome, and in more chronic conditions such as inflammatory skin diseases. In addition to the toll on public health, S. aureus superantigens also represent a potential biothreat to our national security. To address these risks, a number of different therapeutic strategies have been developed that target different aspects of the pathogenic mechanism of S. aureus and superantigen infection. These therapies, which encompass strategies as diverse as production of neutralizing antibodies, inhibitory peptide/receptor design and blockage of superantigen gene transcription, are being tested for treatment of established S. aureus infections in pre- and post-exposure scenarios. In this review, we will describe these different strategies and their efficacies in inhibition of superantigen-induced effects in the host, and present the future outlook for successfully producing therapies for superantigen-based disease.

Phase I study of single, escalating doses of a superantigen-antibody fusion protein (PNU-214565) in patients with advanced colorectal or pancreatic carcinoma

To develop a T-cell-based therapy for carcinomas, the superantigen staphylococcal enterotoxin A (SEA) was supplied with tumor specificity by means of a recombinant fusion of the Fab fragment of the monoclonal antibody C242 recognizing human colorectal (CRC) and pancreatic carcinomas (PC). Using this Fab-SEA fusion protein (PNU-214565), potent cytotoxicity by activation of T cells can be obtained in the targeted area. Twenty-one patients with CRC and 3 with PC were treated with single, escalating doses of PNU-214565 to establish the maximum tolerated dose (MTD) and to define toxicities. The doses ranged from 0.01 ng/kg to 4.0 ng/kg with three patients at each dose level, except for the dose of 1.5 ng/kg with which six patients were treated because of dose-limiting toxicity. Adverse events (AE) were transient: 13 patients experienced mild to moderate fever. In one patient, a grade 3 fever was followed by a grade 2 hypotension. Other mild or moderate AEs were fatigue, nausea, vomiting, diarrhea, and abdominal pain. No significant hematological toxicity occurred. Immune activation was highly variable with strong activity in peripheral blood seen only in two patients at the dosage level 1.5 ng/kg. They showed pronounced elevations of interleukin-2 (IL-2), IL-6, tumor necrosis factor-alpha, and interferon-gamma, 3-5 hours after the start of infusion. In one patient, IL-2 and IL-6 increased substantially (2,925 U/mL and 32,000 U/mL) concomitantly with grade 3 fever and transient grade 2 neutropenia, grade 2 lymphopenia, and grade 2 monocytopenia. In conclusion, a single 3-hour infusion of PNU-214565 could be safely administered up to 4 ng/kg. MTD was not determined. Instead, a repeat-dose trial was initiated starting at 0.5 ng/kg, considered safe in this trial, with the objective of defining the MTD.

[A case of interstitial nephritis induced by a super antigen produced by methicillin-resistant Staphylococcus aureus (MRSA) presenting as acute renal failure]

We report the case of a 21-year-old man who had been developing acute renal failure with Methicillin-resistant Staphylococcus aureus (MRSA) colitis and sepsis. He was admitted for consciousness disturbance, nausea, vomiting, and diarrhea. Oliguria was also observed and his serum creatinine level was elevated to 10 mg/dl. Urinary protein was positive and an abundance of hyaline cast were seen in urinary sedimentation. Diarrhea and pyrexia were prolonged and serum C-reactive proteins were elevated, but lymphocyte and leukocyte counts temporarily decreased from the 3rd to the 6th hospital day and remained low until normalizing after the 14th day. His clinical symptoms improved with hemodialysis (HD) and effective antibiotic therapies. An MRSA strain producing toxic shock syndrome toxin-1 (TSST-1), a super antigen which specifically stimulates human V beta 2-positive T cells, was separated from his feces and blood. To ascertain the cause of his renal dysfunction, a renal biopsy was performed on the 8th day. His renal histology revealed acute interstitial nephritis with severe inflammatory cell infiltration around the medullary areas without glomerular changes. Most of the infiltrated cells were small monocytes, and lymphoid cells were rich in the interstitium. With immunohistochemical staining, over 70% of T-cells were V beta 2-positive. TSST-1-producing MRSA was detected in his blood specimen. Furthermore, V beta 2-positive T cells were accumulated in the renal intersititium, and transient lymphocytopenia was observed. These data suggested the following possible pathogenesis for interstitial nephritis: TSST-1 acts as a super antigen in the renal interstitium where major histocompatibility complex (MHC) is class-2-positive, thereby resulting in interstitial nephritis with T cell migration.

Staphylococcal enterotoxin B induces arthritis in female DBA/1 mice but fails to induce activation of type II collagen-reactive lymphocytes

It has been proposed that superantigens are involved in the pathogenesis of autoimmune diseases. To test the possibility of superantigens inducing arthritis in naive mice, V beta 8-reactive superantigen staphylococcal enterotoxin B (SEB) was injected into naive mice. We used female DBA/1 mice, because they were susceptible to collagen-induced arthritis (CIA), in which the pathogenic T cells were supposed to preferentially use limited V betas of T cell receptors including V beta 8. Mild monoarthritis developed in uninjected hindlimbs of mice administered with SEB in higher frequency (an average incidence of 24%) than the control phosphate-buffered saline-injected mice (4.2%). Autoimmune responses in mice administered with SEB were compared with those in mice developing CIA. However, activation of type II collagen (IIC)-reactive T cells was not detected in SEB-injected mice. Production of autoantibodies, anti-IIC antibody and rheumatoid factor was also undetected. Although exact mechanisms of pathogenesis of this arthritis remain to be known, V beta 8+ T cells were activated for a long period and the unresponsiveness of V beta 8+ T cells was not detected in this strain. From these results, we discuss the pathogenesis of arthritis induced by SEB and the possibility that superantigen may play a role in the induction of autoimmune diseases.

Can superantigens trigger sudden infant death?

A majority of sudden infant death syndrome (SIDS) victims have respiratory or gastrointestinal infections prior to death. This has led to an investigation of the role of pathogenic bacteria and the potentially lethal toxins they produce as triggers for sudden infant death. A small group of bacteria have been consistently identified in SIDS victims as compared to controls, and remarkably, three of these produce superantigenic toxins. Superantigens exert a powerful effect on the immune system, stimulating T-cells, which subsequently induces the formation of large amounts of cytokines. Generation of an overwhelming inflammatory response may lead to death by shock, or other, as yet unrecognized effects of the toxin on the respiratory or cardiac systems. A SIDS/superantigen model is proposed which may explain many of the pathological characteristics of SIDS and establish quantifiable markers for SIDS.

T cell influence on superantigen-induced arthritis in MRL-lpr/lpr mice

OBJECTIVE

To define the influence of the T cell receptor (TCR) and the lpr autoimmune gene on the induction and progression of superantigen-induced arthritis in V beta 8 transgenic MRL-lpr/lpr mice.

METHODS

The time to onset and the extent of synovial hyperplasia after the induction of arthritis by intraarticular injection of staphylococcal enterotoxin B (SEB) were compared in mice having T cells that bear the V beta 8 transgene alone (V beta 8 TCR transgenic MRL-+/+), the lpr gene without the V beta 8 gene (nontransgenic MRL-lpr/lpr), both the V beta 8 gene and the lpr gene (V beta 8 transgenic MRL-lpr/lpr), or neither gene (nontransgenic MRL-+/+). Synovial hyperplasia was compared in SEB-injected V beta 8 transgenic MRL-lpr/lpr mice after treatment with cyclosporin A (CSA), anti-V beta 8 and anti-CD4 monoclonal antibodies, and in V beta 8 transgenic MRL-lpr/lpr mice after injection of a non-V beta 8-reactive superantigen, staphylococcal enterotoxin A (SEA).

RESULTS

At day 30, increased synovial cells were observed in all SEB-treated mice, but the increase was greatest in the V beta 8 transgenic MRL-lpr/lpr mice. T cell involvement was indicated by the inability of either heat-denatured SEB or SEA to induce severe arthritis, the reduction in the severity of the arthritis on systemic treatment with CSA or anti-V beta 8, and the correlation of synovial hyperplasia with in vitro SEB reactivity of T cells.

CONCLUSION

These observations suggest that superantigens can induce chronic arthritis and that the induction and progression of the arthritis requires an underlying T cell defect in anergy induction in addition to exposure to the superantigen.