Histopathologic changes in kidney and liver correlate with streptococcal pyrogenic exotoxin B production in the mouse model of group A streptococcal infection

Dextromethorphan Attenuates NADPH Oxidase-Regulated Glycogen Synthase Kinase 3β and NF-κB Activation and Reduces Nitric Oxide Production in Group A Streptococcal Infection

Group A Streptococcus (GAS) is an important human pathogen that causes a wide spectrum of diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Dextromethorphan (DM), an antitussive drug, has been demonstrated to efficiently reduce inflammatory responses, thereby contributing to an increased survival rate of GAS-infected mice. However, the anti-inflammatory mechanisms underlying DM treatment in GAS infection remain unclear. DM is known to exert neuroprotective effects through an NADPH oxidase-dependent regulated process. In the present study, membrane translocation of NADPH oxidase subunit p47^phox and subsequent reactive oxygen species (ROS) generation induced by GAS infection were significantly inhibited via DM treatment in RAW264.7 murine macrophage cells. Further determination of proinflammatory mediators revealed that DM effectively suppressed inducible nitric oxide synthase (iNOS) expression and NO, tumor necrosis factor alpha, and interleukin-6 generation in GAS-infected RAW264.7 cells as well as in air-pouch-infiltrating cells from GAS/DM-treated mice. GAS infection caused AKT dephosphorylation, glycogen synthase kinase-3β (GSK-3β) activation, and subsequent NF-κB nuclear translocation, which were also markedly inhibited by treatment with DM and an NADPH oxidase inhibitor, diphenylene iodonium. These results suggest that DM attenuates GAS infection-induced overactive inflammation by inhibiting NADPH oxidase-mediated ROS production that leads to downregulation of the GSK-3β/NF-κB/NO signaling pathway.

Galectin-3 Inhibits Galectin-8/Parkin-Mediated Ubiquitination of Group A Streptococcus

Group A streptococcus (GAS) is an important human pathogen that causes a wide variety of cutaneous and systemic infections. Although originally thought to be an extracellular bacterium, numerous studies have demonstrated that GAS can trigger internalization into nonimmune cells to escape from immune surveillance or antibiotic-mediated killing. Epithelial cells possess a defense mechanism involving autophagy-mediated targeting and killing of GAS within lysosome-fused autophagosomes. In endothelial cells, in contrast, we previously showed that autophagy is not sufficient for GAS killing. In the present study, we showed higher galectin-3 (Gal-3) expression and lower Gal-8 expression in endothelial cells than in epithelial cells. The recruitment of Gal-3 to GAS is higher and the recruitment of Gal-8 to GAS is lower in endothelial cells than in epithelial cells. We further showed that Gal-3 promotes GAS replication and diminishes the recruitment of Gal-8 and ubiquitin, the latter of which is a critical protein for autophagy sequestration. After knockdown of Gal-3 in endothelial cells, the colocalization of Gal-8, parkin, and ubiquitin-decorated GAS is significantly increased, as is the interaction of Gal-8 and parkin, an E3 ligase. Furthermore, inhibition of Gal-8 in epithelial cells attenuates recruitment of parkin; both Gal-8 and parkin contribute to ubiquitin recruitment and GAS elimination. Animal studies confirmed that Gal-3-knockout mice develop less-severe skin damage and that GAS replication can be detected only in the air pouch and not in organs and endothelial cells. These results demonstrate that Gal-3 inhibits ubiquitin recruitment by blocking Gal-8 and parkin recruitment, resulting in GAS replication in endothelial cells.

In epithelial cells, GAS can be efficiently killed within the lysosome-fused autophaosome compartment. However, we previously showed that, in spite of LC-3 recruitment, the autophagic machinery is not sufficient for GAS killing in endothelial cells. In this report, we provide the first evidence that Gal-3, highly expressed in endothelial cells, blocks the tagging of ubiquitin to GAS by inhibiting recruitment of Gal-8 and parkin, leading to an enhancement of GAS replication. We also provide the first demonstration that Gal-8 can interact with parkin, the critical E3 ligase, for resistance to intracellular bacteria by facilitating the decoration of bacteria with ubiquitin chains. Our findings reveal that differential levels of Gal-3 and Gal-8 expression and recruitment to GAS between epithelial cells and endothelial cells may contribute to the different outcomes of GAS elimination or survival and growth of GAS in these two types of cells.

Immunization with a streptococcal multiple-epitope recombinant protein protects mice against invasive group A streptococcal infection

Streptococcus pyogenes (group A Streptococcus; GAS) causes clinical diseases, including pharyngitis, scarlet fever, impetigo, necrotizing fasciitis and streptococcal toxic shock syndrome. A number of group A streptococcus vaccine candidates have been developed, but only one 26-valent recombinant M protein vaccine has entered clinical trials. Differing from the design of a 26-valent recombinant M protein vaccine, we provide here a vaccination using the polyvalence epitope recombinant FSBM protein (rFSBM), which contains four different epitopes, including the fibronectin-binding repeats domain of streptococcal fibronectin binding protein Sfb1, the C-terminal immunogenic segment of streptolysin S, the C3-binding motif of streptococcal pyrogenic exotoxin B, and the C-terminal conserved segment of M protein. Vaccination with the rFSBM protein successfully prevented mortality and skin lesions caused by several emm strains of GAS infection. Anti-FSBM antibodies collected from the rFSBM-immunized mice were able to opsonize at least six emm strains and can neutralize the hemolytic activity of streptolysin S. Furthermore, the internalization of GAS into nonphagocytic cells is also reduced by anti-FSBM serum. These findings suggest that rFSBM can be applied as a vaccine candidate to prevent different emm strains of GAS infection.

Streptococcal pyrogenic exotoxin B inhibits apoptotic cell clearance by macrophages through protein S cleavage

Clearance of apoptotic cells by macrophages plays an important role in maintaining tissue homeostasis. Previous study indicated that streptococcal pyrogenic exotoxin B (SPE B) reduces phagocytic activity in group A streptococcus (GAS) infection. Here, we demonstrate that SPE B causes an inhibitory effect on protein S-mediated phagocytosis. In the presence of SPE B, serum- and purified protein S-mediated phagocytosis of apoptotic cells were significantly inhibited. The binding abilities of protein S to apoptotic cells were decreased by treatment with SPE B. Bacterial culture supernatants from GAS NZ131 strain also caused a reduction of protein S binding to apoptotic cells, but speB mutant strain did not. SPE B directly cleaved protein S in vitro and in vivo, whereas a lower level of cleavage occurred in mice infected with a speB isogenic mutant strain. SPE B-mediated initial cleavage of protein S caused a disruption of phagocytosis, and also resulted in a loss of binding ability of protein S-associated C4b-binding protein to apoptotic cells. Taken together, these results suggest a novel pathogenic role of SPE B that initiates protein S degradation followed by the inhibition of apoptotic cell clearance by macrophages.

Application of the C3-binding motif of streptococcal pyrogenic exotoxin B to protect mice from invasive group a streptococcal infection

Group A streptococcus (GAS) is an important human pathogen that produces several extracellular exotoxins to facilitate invasion and infection. Streptococcal pyrogenic exotoxin B (SPE B) has been demonstrated to be an important virulence factor of GAS. Our previous studies indicate that SPE B cleaves complement 3 (C3) and inhibits the activation of complement pathways. In this study, we constructed and expressed recombinant fragments of SPE B to examine the C3-binding site of SPE B. Using enzyme-linked immunosorbent assays and pull-down assays, we found that the C-terminal domain, containing amino-acid residues 345–398, of SPE B was the major binding site of human serum C3. We further identified a major, Ala³⁷⁶-Pro³⁹⁸, and a minor C3-binding motif, Gly³⁴⁶-Gly³⁶⁰, that both mediated the binding of C3 complement. Immunization with the C3-binding motifs protected mice against challenge with a lethal dose of non-invasive M49 strain GAS but not invasive M1 strains. To achieve higher efficiency against invasive M1 GAS infection, a combination of synthetic peptides derived from C-terminal epitope of streptolysin S (SLSpp) and from the major C3-binding motif of SPE B (PP6, Ala³⁷⁶-Pro³⁹⁸) was used to elicit specific immune response to those two important streptococcal exotoxins. Death rates and the severity of skin lesions decreased significantly in PP6/SLSpp-immunized mice that were infected with invasive M1 strains of GAS. These results indicate a combination of the C3-binding motif of SPE B and the protective epitope of SLS could be used as a subunit vaccine against invasive M1 strains group A streptococcal infection.

Adhesin competence repressor (AdcR) from Streptococcus pyogenes controls adaptive responses to zinc limitation and contributes to virulence

Altering zinc bioavailability to bacterial pathogens is a key component of host innate immunity. Thus, the ability to sense and adapt to the alterations in zinc concentrations is critical for bacterial survival and pathogenesis. To understand the adaptive responses of group A Streptococcus (GAS) to zinc limitation and its regulation by AdcR, we characterized gene regulation by AdcR. AdcR regulates the expression of 70 genes involved in zinc acquisition and virulence. Zinc-bound AdcR interacts with operator sequences in the negatively regulated promoters and mediates differential regulation of target genes in response to zinc deficiency. Genes involved in zinc mobilization and conservation are derepressed during mild zinc deficiency, whereas the energy-dependent zinc importers are upregulated during severe zinc deficiency. Further, we demonstrated that transcription activation by AdcR occurs by direct binding to the promoter. However, the repression and activation by AdcR is mediated by its interactions with two distinct operator sequences. Finally, mutational analysis of the metal ligands of AdcR caused impaired DNA binding and attenuated virulence, indicating that zinc sensing by AdcR is critical for GAS pathogenesis. Together, we demonstrate that AdcR regulates GAS adaptive responses to zinc limitation and identify molecular components required for GAS survival during zinc deficiency.

Kallistatin modulates immune cells and confers anti-inflammatory response to protect mice from group A streptococcal infection

Group A streptococcus (GAS) infection may cause severe life-threatening diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Despite the availability of effective antimicrobial agents, there has been a worldwide increase in the incidence of invasive GAS infection. Kallistatin (KS), originally found to be a tissue kallikrein-binding protein, has recently been shown to possess anti-inflammatory properties. However, its efficacy in microbial infection has not been explored. In this study, we transiently expressed the human KS gene by hydrodynamic injection and investigated its anti-inflammatory and protective effects in mice via air pouch inoculation of GAS. The results showed that KS significantly increased the survival rate of GAS-infected mice. KS treatment reduced local skin damage and bacterial counts compared with those in mice infected with GAS and treated with a control plasmid or saline. While there was a decrease in immune cell infiltration of the local infection site, cell viability and antimicrobial factors such as reactive oxygen species actually increased after KS treatment. The efficiency of intracellular bacterial killing in neutrophils was directly enhanced by KS administration. Several inflammatory cytokines, including tumor necrosis factor alpha, interleukin 1β, and interleukin 6, in local infection sites were reduced by KS. In addition, KS treatment reduced vessel leakage, bacteremia, and liver damage after local infection. Therefore, our study demonstrates that KS provides protection in GAS-infected mice by enhancing bacterial clearance, as well as reducing inflammatory responses and organ damage.

Regulatory role of GSK-3 β on NF- κ B, nitric oxide, and TNF- α in group A streptococcal infection

Group A streptococcus (GAS) imposes a great burden on humans. Efforts to minimize the associated morbidity and mortality represent a critical issue. Glycogen synthase kinase-3β (GSK-3β) is known to regulate inflammatory response in infectious diseases. However, the regulation of GSK-3β in GAS infection is still unknown. The present study investigates the interaction between GSK-3β, NF-κB, and possible related inflammatory mediators in vitro and in a mouse model. The results revealed that GAS could activate NF-κB, followed by an increased expression of inducible nitric oxide synthase (iNOS) and NO production in a murine macrophage cell line. Activation of GSK-3β occurred after GAS infection, and inhibition of GSK-3β reduced iNOS expression and NO production. Furthermore, GSK-3β inhibitors reduced NF-κB activation and subsequent TNF-α production, which indicates that GSK-3β acts upstream of NF-κB in GAS-infected macrophages. Similar to the in vitro findings, administration of GSK-3β inhibitor in an air pouch GAS infection mouse model significantly reduced the level of serum TNF-α and improved the survival rate. The inhibition of GSK-3β to moderate the inflammatory effect might be an alternative therapeutic strategy against GAS infection.

Determining antibody-binding site of streptococcal pyrogenic exotoxin B to protect mice from group a streptococcus infection

Streptococcal pyrogenic exotoxin B (SPE B), a cysteine protease, is an important virulence factor in group A streptococcal (GAS) infection. SPE B binds and cleaves antibody isotypes and further impairs the immune system by inhibiting complement activation. In this study, we examined the antibody-binding site of SPE B and used it to block SPE B actions during GAS infection. We constructed different segments of the spe B gene and induced them to express different recombinant fragments of SPE B. Using an enzyme-linked immunosorbent assay (ELISA), we found that residues 345–398 of the C-terminal domain of SPE B (rSPE B_345–398), but not the N-terminal domain, was the major binding site for antibody isotypes. Using a competitive ELISA, we also found that rSPE B_345–398 bound to the Fc portion of IgG. The in vitro functional assays indicate that rSPE B_345–398 not only interfered with cleavage of antibody isotypes but also interfered with SPE B-induced inhibition of complement activation. Immunization of BALB/c mice using rSPE B_345–398 was able to induce production of a high titer of anti-rSPE B_345–398 antibodies and efficiently protected mice from GAS-induced death. These findings suggest that SPE B uses its C-terminal domain to bind the Fc portion of IgG and that immunization of mice with this binding domain (rSPE B_345–398) could protect mice from GAS infection.

Synergistic effects of streptolysin S and streptococcal pyrogenic exotoxin B on the mouse model of group A streptococcal infection

Streptococcus pyogenes is a group A streptococcus (GAS) and an important human pathogen that causes a variety of diseases. Streptococcal pyrogenic exotoxin B (SPE B) and streptolysin S (SLS) are important virulence factors involved in GAS infection, but it is not clear which one is more virulent. Using an air pouch infection model, the wild-type strain NZ131, its isogenic mutants, and complementary mutants were used to examine the effects of SPE B and SLS on GAS infection. The results of the skin lesion and mouse mortality assays showed that although SPE B and SLS had a synergistic effect on GAS infection, SPE B played a more important role in local tissue damage while SLS had a more prominent effect on mouse mortality. Surveys of the exudates from the air pouch revealed that the expression of inflammatory cytokines was significantly inhibited in the sagB/speB-double-mutant JM4-infected mice. Furthermore, in vivo and in vitro studies showed that the isogenic mutant strains were more susceptible to the immune cell killing than the wild-type strain and that the sagB/speB-double-mutant JM4 was the most sensitive among these strains. Moreover, infection with the sagB/speB-double-mutant JM4 strain caused the least amount of macrophage apoptosis compared to infection with the wild-type NZ131 and the other complementary strains, which express only SPE B or SLS or both. Taken together, these results indicate that both SPE B and SLS contributed to GAS evasion from immune cell killing, local tissue damage, and mouse mortality.

Dextromethorphan efficiently increases bactericidal activity, attenuates inflammatory responses, and prevents group a streptococcal sepsis

Group A streptococcus (GAS) is an important human pathogen that causes a wide spectrum of diseases, ranging from mild throat and skin infections to severe invasive diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. Dextromethorphan (DM), a dextrorotatory morphinan and a widely used antitussive drug, has recently been reported to possess anti-inflammatory properties. In this study, we investigated the potential protective effect of DM in GAS infection using an air pouch infection mouse model. Our results showed that DM treatment increased the survival rate of GAS-infected mice. Bacterial numbers in the air pouch were lower in mice treated with DM than in those infected with GAS alone. The bacterial elimination efficacy was associated with increased cell viability and bactericidal activity of air-pouch-infiltrating cells. Moreover, DM treatment prevented bacterial dissemination in the blood and reduced serum levels of the proinflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), and IL-1β and the chemokines monocyte chemotactic protein 1 (MCP-1), macrophage inflammatory protein 2 (MIP-2), and RANTES. In addition, GAS-induced mouse liver injury was reduced by DM treatment. Taken together, DM can increase bacterial killing and reduce inflammatory responses to prevent sepsis in GAS infection. The consideration of DM as an adjunct treatment in combination with antibiotics against bacterial infection warrants further study.

Molecular mimicry between streptococcal pyrogenic exotoxin B and endothelial cells

Molecular mimicry between group A streptococcus and host antigens has important roles in the development of post-streptococcal sequelae, including glomerulonephritis and rheumatic heart disease (RHD). The etiology of RHD involves host cross-reactivity with M proteins and carbohydrate antigens. In this study, we show that anti-streptococcal pyrogenic exotoxin B (SPE B) antibodies exhibited characteristics of autoantibodies, which cross-react with endothelial cells. Immunoglobulin G (IgG) deposition and complement activation were observed in the heart valve of SPE B-immunized mice. In addition, apoptosis in the heart valve was detected in SPE B-immunized mice. An anti-SPE B monoclonal antibody (mAb) 10G showed cross-reactivity with human microvascular endothelial (HMEC-1) cells and mouse valve endothelial cells. Passive immunization with mAb 10G also caused IgG deposition, complement activation, and apoptotic cell death in the mouse heart valve. We conducted peptide array and ELISA using synthetic peptides to identify the SPE B antigenic epitope recognized by mAb 10G. Results showed that the major epitope of mAb 10G is localized to amino-acid residues 296-310 of SPE B (P7-8). The cross-reactivity of mAb 10G with endothelial cells was inhibited using P7-8 peptides for competition. These results suggest that anti-SPE B antibodies cross-react with endothelial cells, and that a dominant epitope is located within the amino-acid residues 296-310 of SPE B. Moreover, we found that mAb 10G can also bind to N-acetyl-β-D-glucosamine (GlcNAc) conjugated with bovine serum albumin (BSA), but not to BSA or M1 protein. Competition assay showed that the binding activity of mAb 10G with GlcNAc-BSA and P7-8 of SPE B was inhibited by pretreatment with GlcNAc-BSA or P7-8 peptides. Therefore, our results suggest that conformational molecular mimicry may exist between SPE B and GlcNAc.

emm1/sequence type 28 strains of group A streptococci that express covR at early stationary phase are associated with increased growth and earlier SpeB secretion

Streptococcus pyogenes (group A streptococcus [GAS]) is a versatile human pathogen, and emm1/sequence type 28 (ST28) is the most frequently isolated type from GAS infections. The emm1/ST28 strain is associated with necrotizing fasciitis and streptococcal toxic shock syndrome. Growth-phase regulation is one of the important regulatory mechanisms in GAS, which controls gene expression at restricted phases of growth. CovRS, a two-component regulatory system, is considered the regulator of streptococcal pyrogenic exotoxin B (SpeB) and is thought to be activated in the exponential phase of growth. In the present study, Northern hybridization analysis showed that 52% of the analyzed GAS strains expressed covR at the exponential phase, but 48% of the strains expressed covR at the early stationary phase of growth. Strains transcribing covR at the early stationary phase showed better growth and earlier SpeB expression than the other group of strains. Multilocus sequence typing and pulsed-field gel electrophoresis analysis showed only emm1/ST28 strains (which comprise a clonal cluster) were expressing covR at the early stationary phase of growth, indicating that emm1/ST28 strains have special characteristics which may be related to their worldwide distribution.

Inhibition of group A streptococcal infection by Melaleuca alternifolia (tea tree) oil concentrate in the murine model

AIMS

To investigate the effect of a water-soluble Melaleuca alternifolia concentrate (MAC) on group A streptococcus (GAS; Streptococcus pyogenes)-induced necrotizing fasciitis.

METHODS AND RESULTS

MAC pretreatment (1% and 2% v/v) was able to protect mice from GAS infection in an air pouch model. GAS-induced mouse death and skin injury were inhibited dose dependently by MAC. Administration of MAC at 6 h post-GAS infection partially delayed mouse death. Surveys of the exudates of the air pouch of MAC-treated mice revealed that the survival of infiltrating cells was prolonged, the bacteria were eliminated, and the production of inflammatory cytokines was inhibited. MAC could directly inhibit the growth of GAS in vitro, and the minimal inhibitory concentration (MIC) of MAC for GAS was determined as 0.05% v/v using the time-kill assay. Furthermore, a sub-MIC dose of MAC not only enhanced the bactericidal activity of RAW264.7 macrophage cells against GAS but also increased susceptibility of GAS for blood clearance.

CONCLUSIONS

These results suggest that MAC may inhibit GAS-induced skin damage and mouse death by directly inhibiting GAS growth and enhancing the bactericidal activity of macrophages.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results provide scientific data on the use of MAC for the treatment of GAS-induced necrotizing fasciitis in the murine model.

Genome sequence of a nephritogenic and highly transformable M49 strain of Streptococcus pyogenes

The 1,815,783-bp genome of a serotype M49 strain of Streptococcus pyogenes (group A streptococcus [GAS]), strain NZ131, has been determined. This GAS strain (FCT type 3; emm pattern E), originally isolated from a case of acute post-streptococcal glomerulonephritis, is unusually competent for electrotransformation and has been used extensively as a model organism for both basic genetic and pathogenesis investigations. As with the previously sequenced S. pyogenes genomes, three unique prophages are a major source of genetic diversity. Two clustered regularly interspaced short palindromic repeat (CRISPR) regions were present in the genome, providing genetic information on previous prophage encounters. A unique cluster of genes was found in the pathogenicity island-like emm region that included a novel Nudix hydrolase, and, further, this cluster appears to be specific for serotype M49 and M82 strains. Nudix hydrolases eliminate potentially hazardous materials or prevent the unbalanced accumulation of normal metabolites; in bacteria, these enzymes may play a role in host cell invasion. Since M49 S. pyogenes strains have been known to be associated with skin infections, the Nudix hydrolase and its associated genes may have a role in facilitating survival in an environment that is more variable and unpredictable than the uniform warmth and moisture of the throat. The genome of NZ131 continues to shed light upon the evolutionary history of this human pathogen. Apparent horizontal transfer of genetic material has led to the existence of highly variable virulence-associated regions that are marked by multiple rearrangements and genetic diversification while other regions, even those associated with virulence, vary little between genomes. The genome regions that encode surface gene products that will interact with host targets or aid in immune avoidance are the ones that display the most sequence diversity. Thus, while natural selection favors stability in much of the genome, it favors diversity in these regions.

Degradation of complement 3 by streptococcal pyrogenic exotoxin B inhibits complement activation and neutrophil opsonophagocytosis

Streptococcal pyrogenic exotoxin B (SPE B), a cysteine protease, is an important virulence factor in group A streptococcus (GAS) infection. The inhibition of phagocytic activity by SPE B may help prevent bacteria from being ingested. In this study, we examined the mechanism SPE B uses to enable bacteria to resist opsonophagocytosis. Using an enzyme-linked immunosorbent assay, we found that SPE B-treated serum impaired the activation of the classical, the lectin, and the alternative complement pathways. In contrast, C192S, a SPE B mutant lacking protease activity, had no effect on complement activation. Further study showed that cleavage of serum C3 by SPE B, but not C192S, blocked zymosan-induced production of reactive oxygen species in neutrophils as a result of decreased deposition of C3 fragments on the zymosan surface. Reconstitution of C3 into SPE B-treated serum unblocked zymosan-mediated neutrophil activation dose dependently. SPE B-treated, but not C192S-treated, serum also impaired opsonization of C3 fragments on the surface of GAS strain A20. Moreover, the amount of C3 fragments on the A20 cell surface, a SPE B-producing strain, was less than that on its isogenic mutant strain, SW507, after opsonization with normal serum. A20 opsonized with SPE B-treated serum was more resistant to neutrophil killing than A20 opsonized with normal serum, and SPE B-mediated resistance was C3 dependent. These results suggest a novel SPE B mechanism, one which degrades serum C3 and enables GAS to resist complement damage and opsonophagocytosis.

Streptococcal pyrogenic exotoxin B antibodies in a mouse model of glomerulonephritis

Streptococcal pyrogenic exotoxin B is an extracellular cysteine protease. Only nephritis-associated strains of group A streptococci secrete this protease and this may be involved in the pathogenesis of post-streptococcal glomerulonephritis. Mice were actively immunized with a recombinant protease inactive exotoxin B mutant or passively immunized with exotoxin B antibody. Characteristics of glomerulonephritis were measured using histology, immunoglobulin deposition, complement activation, cell infiltration, and proteinuria. None of the mice given bovine serum albumin or exotoxin A as controls showed any marked changes. Immunoglobulin deposition, complement activation, and leukocyte infiltration occurred only in the glomeruli of exotoxin B-hyperimmunized mice. One particular anti-exotoxin B monoclonal antibody, 10G, was cross-reactive with kidney endothelial cells and it caused kidney injury and proteinuria when infused into mice. This cross-reactivity may be involved in the pathogenesis of glomerulonephritis following group A streptococcal infection.

Abrogation of streptococcal pyrogenic exotoxin B-mediated suppression of phagocytosis in U937 cells by Cordyceps sinensis mycelium via production of cytokines

Streptococcal pyrogenic exotoxin B (SPE B) is a virulent factor in group A streptococcal infection. We previously showed that SPE B reduced phagocytosis in human monocytic U937 cells. Here we show that the mycelium extract of Cordyceps sinensis (CS), a Chinese immunomodulatory herbal medicine, increased phagocytosis in U937 cells. Neither heat nor trypsin pretreatment prevented CS extract from causing this increase. Further studies indicated that SPE B-mediated suppression of U937 cell phagocytic activity was abrogated by CS extract. Factors in the conditioned medium from CS-extract-treated U937 cells were responsible for blocking the SPE B-mediated suppression of phagocytosis. Heating the conditioned medium eliminated the increase, which suggested that the U937-cell protein products augmented phagocytosis. Analyzing cytokine mRNA expression of U937 cells revealed increases in interferon-gamma (IFN-gamma), interleukin (IL)-12 p35 and p40, and tumor necrosis factor-alpha (TNF-alpha), but not in IL-1beta, IL-6, or IL-8. Treating U937 cells with anti-IFN-gamma, IL-12, and TNF-alpha antibodies also eliminated the conditioned medium-induced increase in phagocytosis. Taken together, SPE B inhibited phagocytosis, but CS mycelium extract abrogated this inhibition by causing cytokine production.

Streptococcal pyrogenic exotoxin B cleaves properdin and inhibits complement-mediated opsonophagocytosis

Streptococcal pyrogenic exotoxin B (SPE B), a cysteine protease, is an important virulence factor in group A streptococcal (GAS) infection. The reduction of phagocytic activity by SPE B may help prevent bacteria from being ingested. In this study, we investigated the mechanism SPE B uses to enable bacteria to resist opsonophagocytosis. Using Western blotting and an affinity column immobilized with SPE B, we found that both SPE B and C192S, an SPE B mutant lacking protease activity, bound to serum properdin, and that SPE B, but not C192S, degraded serum properdin. Further study showed that SPE B-treated, but not C192S-treated, serum blocked the alternative complement pathway. Reconstitution of properdin into SPE B-treated serum unblocked the alternative pathway. GAS opsonized with SPE B-treated serum was more resistant to neutrophil killing than GAS opsonized with C192S-treated or normal serum. These results suggest that a novel SPE B mechanism, one which degrades serum properdin, enables GAS to resist opsonophagocytosis.

Cordyceps sinensis mycelium protects mice from group A streptococcal infection

Group A streptococcus (GAS) infection can cause severe invasive diseases, including necrotizing fasciitis and streptococcal toxic shock syndrome. Cordyceps sinensis, a Chinese herbal medicine, is an immunomodulator. In this study the air-pouch bacterial inoculation model was used to investigate the protective efficacy of C. sinensis mycelium extract against GAS infection. Force-feeding mice with C. sinensis mycelium extract for 3 consecutive days before GAS infection increased the survival rate and reduced local skin-tissue injury compared with mice fed PBS. Bacterial numbers in the air pouch exudates from C. sinensis-treated mice were lower than those from PBS-treated mice. Blood and organs in PBS-treated mice showed bacterial dissemination, but those in C. sinensis-treated mice did not. Three days of pretreatment with C. sinensis extract followed by C. sinensis treatment every other day after GAS infection resulted in 100% survival. The post-GAS-infection levels of aspartate aminotransferase, alanine aminotransferase and blood urea nitrogen in the sera of C. sinensis-treated mice were lower than those of PBS-treated mice. Taken together, these results show that C. sinensis mycelium extract protects by decreasing bacterial growth and dissemination, thereby increasing mouse survival rate. IL-12 and IFN-gamma expression and macrophage phagocytic activity also increased after C. sinensis treatment.