Interleukin-4 and interleukin-10 are involved in host resistance to Staphylococcus aureus infection through regulation of gamma interferon

Inactivation of the Sts enzymes promotes resistance to lethal Staphylococcus aureus infection

Staphylococcus aureus is a highly infective Gram-positive bacterial pathogen that causes a wide range of diseases in both healthy and immunocompromised individuals. It can evade host immune defenses by expressing numerous virulence factors and toxins. Coupled with the inability of the human host to develop protective immunity against S. aureus, the emergence of antibiotic-resistant strains complicates treatment options. The non-canonical Sts phosphatases negatively regulate signaling pathways in varied immune cell types. To determine the role of the Sts proteins in regulating host responses to a Gram-positive microorganism, we investigated the response of mice lacking Sts expression to S. aureus infection. Herein, we demonstrate that Sts -/- animals are significantly resistant to lethal intravenous doses of S. aureus strain USA300. Resistance is characterized by significantly enhanced survival and accelerated bacterial clearance in multiple peripheral organs. Infected Sts -/- animals do not display increased levels of cytokines TNFα, IFNγ, and IL-6 in the spleen, liver, and kidney during the early stages of the infection, suggesting that a heightened pro-inflammatory response does not underlie the resistance phenotype. In vivo ablation of mononuclear phagocytes compromises the Sts -/- enhanced CFU clearance phenotype. Additionally, Sts -/- bone marrow-derived macrophages demonstrate significantly enhanced restriction of intracellular S. aureus following ex vivo infection. These results reveal the Sts enzymes to be critical regulators of host immunity to a virulent Gram-positive pathogen and identify them as therapeutic targets for optimizing host anti-microbial responses.

IL-10 in combination with IL-12 and TNF-α attenuates CXCL8/CXCR1 axis in peritoneal macrophages of mice infected with Staphylococcus aureus through the TNFR1-IL-1R-NF-κB pathway

Overexpression of Staphylococcus aureus mediated CXCL8/CXCR1 axis is a major cause of sepsis and severe inflammatory diseases. This chemokine acts conjointly with various pro-inflammatory and anti-inflammatory cytokines that govern the severity of inflammation. The effects of different combinations of exogenous cytokines on CXCR1 expression in macrophages remain undetermined. Exogenous cytokine and anti-inflammatory cytokine therapy had been used to modulate CXCL8 and CXCR1 expression in peritoneal macrophages. Male Swiss albino mice were inoculated with live S. aureus (10⁶ cells/ mouse) for the development of infection. Exogenous cytokines (TNF-α, IL-12, IFN-γ and IL-10) were administered intraperitoneally (single or combination) 24 h post S. aureus infection. The mice were sacrificed and peritoneal macrophages were isolated three days post infection. CXCL8, IL-12, IL-10 secretion, ROS generation and the bacterial phagocytic process had been evaluated. Western blot was used to study the expressions of TNFR1, IL-1R, CXCR1 and NF-κB. TNF-α, IL-12 and IFN-γ treatments aggravated CXCL8 and CXCR1 expression in the macrophages of infected mice. TNF-α + IFN-γ treatment was a major inducer of nitric oxide release and mediated maximum bacterial killing. IL-12 + TNF-α treatment was most potent in increasing ROS, CXCL8/CXCR1 expression through increased levels of TNFR1, IL-1R and NF-κB activation. IL-10 reversed the effects of exogenous cytokines but also impaired the bacterial clearance phenomenon in peritoneal lavage. Treatment with IL-12 + TNF-α + IL-10 was most effective in ameliorating oxidative stress, reduced CXCL8 release and expression levels of TNFR1, IL-1R, and NF-κB. Concludingly, IL-12 + TNF-α + IL-10 treatment mitigated CXCL8/CXCR1 expression and inflammatory signalling via downregulation of TNFR1-IL-1R-NF-κB pathway in peritoneal macrophages and inflammatory sequelae during S. aureus infection.

Evaluation of the immune response to a multi-epitope vaccine candidate in comparison with HlaH35L, MntC, and SACOL0723 proteins against MRSA infection

Staphylococcus aureus is an important human opportunistic pathogen that can have a major influence on public health. Here, we aimed to evaluate different aspects of the immune response to a novel multi-epitope fusion protein (HMS) based on Hla_H35L, MntC, and SACOL0723 proteins in comparison to the individual antigens. For this purpose, specific total IgG, IgG1, and IgG2a isotypes and the cytokines related to Th1, Th2, and Th17 were assessed. The Bio-efficiency of the fusion protein was evaluated by opsonic killing activity. The HMS fusion protein elicited a high specific IgG level and also induced a higher level of Th1, Th2, and Th17-related cytokines which were more polarized towards the Th1 and Th17 compared to individual antigens. The HMS-specific antisera also significantly promoted phagocytosis of S. aureus COL strain by mouse macrophages. In conclusion, the fusion protein might be an effective vaccine for potential protective immunity against a lethal infection of S. aureus in mice.

Staphylococcus aureus β-Hemolysin Up-Regulates the Expression of IFN-γ by Human CD56bright NK Cells

IFN-γ is produced upon stimulation with S. aureus and may play a detrimental role during infection. However, whether hemolysins play a role in the mechanism of IFN-γ production has not been fully characterized. In this study, we demonstrated that Hlb, one of the major hemolysins of S. aureus, upregulated IFN-γ production by CD56^bright NK cells from human peripheral blood mononuclear cells (PBMCs). Further investigation showed that Hlb increased calcium influx and induced phosphorylation of ERK1/2. Either blocking calcium or specifically inhibiting phosphorylation of ERK1/2 decreased the production of IFN-γ induced by Hlb. Moreover, we found that this process was dependent on the sphingomyelinase activity of Hlb. Our findings revealed a novel mechanism of IFN-γ production in NK cells induced by Hlb, which may be involved in the pathogenesis of S. aureus.

Difference in Host Immune response to Methicillin-Resistant and Methicillin Sensitive Staphylococcus aureus (MRSA and MSSA) Endophthalmitis

PURPOSE

The study aimed to understand the differential immune response of methicillin susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains in in vitro models of endophthalmitis.

METHODS

Retinal pigment epithelium (RPE) and microglia cells (CHME-3) were exposed to MRSA and MSSA strains and analyzed for expression of inflammatory mediators by real-time quantitative PCR and validated by ELISA or immunofluorescence assay. Heatmap and STRING analysis was used to assess the differential immune expression.

RESULTS

Both microglia and RPE expressed TLR-2, TLR-1, TLR-6, and TLR -9 after challenge with MRSA and MSSA strains though the expression varied. MRSA-infected cells induced higher expression of IL-1β, IL-8, 1 L-10, IL-6, and GM-CSF, while TNF-α and IFN-ϒ were downregulated in comparison to MSSA-infected cells. We also demonstrate that MRSA infection leads to increased activation of MMP-9 and MMP-2 in RPE cells, while microglia expressed only MMP-9 in MRSA-infected cells.

CONCLUSIONS

MRSA strain can induce an exacerbated immune response in retinal cells. Giving clues for potential targets in immunomodulatory therapies.

The immune-enhancing effect of anthocyanin-fucoidan nanocomplex in RAW264.7 macrophages and cyclophosphamide-induced immunosuppressed mice

Aronia, a healthy fruit well known as black chokeberry, has health-promoting effects on hypertension, oxidative stress, and diabetes. Despite many reports of bioactivities of aronia, there is little scientific research on the potential for immune-enhancement. So, anthocyanin-fucoidan nanocomplex (AFNC, a nanocomplex of aronia extract and fucoidan) has been developed to improve immune-enhancement. This study aimed to identify immunomodulatory effects and underlying mechanisms of AFNC using RAW264.7 macrophages and cyclophosphamide-induced immunosuppressed mice. As a result, AFNC-treated RAW264.7 macrophages elevated the production of IL-2, IL-6, tumor necrosis factor (TNF)-α, and nitric oxide (NO). AFNC-enhanced inducible NO synthase expression via nuclear factor-κB signaling pathways. AFNC dose-dependently increased levels of IL-2, IL-6, TNF-α, IL-10, IL-12, interferon-γ, or IL-4 in the serum and spleen of immunosuppressed mice. Taken together, AFNC encourages the immune-enhancing activity through immunostimulatory cytokine production by activation of macrophage. Therefore, these results suggest that AFNC is useful for immunodeficiency-related disorders. PRACTICAL APPLICATIONS: In these days of prevalence of infectious diseases, individual immunity is very important. AFNC has the immune-enhancing effects through immunostimulatory cytokine production by activation of macrophage. Therefore, AFNC could be widely applied to ameliorate a variety of diseases caused by immunosuppression such as infectious diseases.

Comparative study of the immune responses to the HMS-based fusion protein and capsule-based conjugated molecules as vaccine candidates in a mouse model of Staphylococcus aureus systemic infection

Staphylococcus aureus is a powerful pathogen that causes a wide range of infectious diseases and results in a high mortality rate in humans. Treating S. aureus-related infections is extremely difficult because of its ability to resist many antibiotics; therefore, developing an effective vaccine against this infection can be an alternative and promising approach. In this study, we evaluated the protective effects of a Hla-MntC-SACOL0723 multi-epitope protein (HMS) compared with HMS conjugated to polysaccharides 5 and 8 (CP5 and CP8) of S. aureus and CP5 and CP8 in a mouse sepsis model. To evaluate the type of induced immune response, specific IgG, and antibody isotypes (IgG1 and IgG2a) were determined using the ELISA method. The functional activity of these vaccine candidates was assessed by opsonophagocytosis. Mice were infected with S. aureus COL strain and evaluated for bacterial load in the kidney and spleen homogenates. Th1, Th2, and Th17-related cytokines in the spleen cell supernatants were assessed by flow cytometry. The therapeutic effect of specific anti-HMS protein IgG antibodies against S. aureus COL strain infection was evaluated by passive immunization. HMS recombinant protein induced a higher level of Th1, Th2, and Th17-related cytokines compared with conjugated molecules. Also, mice immunized with the HMS protein reduced the bacterial load in the kidney and spleen more than the one that received the conjugated molecules. Our study suggests that the HMS fusion protein and conjugate molecule vaccine candidates could be suitable candidates for the removal of S. aureus in the mouse sepsis model but HMS protein can be a more effective candidate.

IFN-γ Activates the TLR4-CCL5 Signaling Through Reducing Arginine Level, Leading to Enhanced Susceptibility of Bovine Mammary Epithelial Cells to Staphylococcus aureus

Dairy cow mastitis is a common bacterial infectious disease which seriously threatens the development of the dairy cow industry. Previous studies have found that increased IFN-γ expression in dairy cows makes dairy cows more susceptible to mastitis, but the underlying mechanism is still not known. In this study, we utilized the in vitro bovine mammary epithelial cells (BMECs) model to explore the molecular mechanism via transcriptome sequencing technology, immunofluorescence, and Western blotting. It was found that IFN-γ promoted the adhesion and invasion of Staphylococcus aureus to BMECs through increasing the expression of TLR4-mediated CCL5 in BMECs. IFN-γ increased the activity of arginase II and reduced the level of arginine in cells, while the addition of arginine inhibited the expression of TLR4 and CCL5. An invasion experiment in mice further validated that IFN-γ treatment significantly increased the bacterial load in mammary glands and blood. However, the colonization and diffusion of S. aureus were interestingly decreased after Arg supplement. These data reveal that increased IFN-γ reduces arginine levels and activates TLR4-CCL5 signaling, leading to enhanced susceptibility of BMECs to S. aureus. Our findings are helpful to understand the pathogenesis of dairy cow mastitis and provide a theoretical basis for improvement of mastitis resistance in dairy cows.

Group 1 CD1-restricted T cells contribute to control of systemic Staphylococcus aureus infection

Staphylococcus aureus (SA) is the causative agent of both skin/soft tissue infections as well as invasive bloodstream infections. Though vaccines have been developed to target both humoral and T cell-mediated immune responses against SA, they have largely failed due to lack of protective efficacy. Group 1 CD1-restricted T cells recognize lipid rather than peptide antigens. Previously found to recognize lipids derived from cell wall of Mycobacterium tuberculosis (Mtb), these cells were associated with protection against Mtb infection in humans. Using a transgenic mouse model expressing human group 1 CD1 molecules (hCD1Tg), we demonstrate that group 1 CD1-restricted T cells can recognize SA-derived lipids in both immunization and infection settings. Systemic infection of hCD1Tg mice showed that SA-specific group 1 CD1-restricted T cell response peaked at 10 days post-infection, and hCD1Tg mice displayed significantly decreased kidney pathology at this time point compared with WT control mice. Immunodominant SA lipid antigens recognized by group 1 CD1-restricted T cells were comprised mainly of cardiolipin and phosphatidyl glycerol, with little contribution from lysyl-phosphatidyl glycerol which is a unique bacterial lipid not present in mammals. Group 1 CD1-restricted T cell lines specific for SA lipids also conferred protection against SA infection in the kidney after adoptive transfer. They were further able to effectively control SA replication in vitro through direct antigen presentation by group 1 CD1-expressing BMDCs. Together, our data demonstrate a previously unknown role for group 1 CD1-restricted SA lipid-specific T cells in the control of systemic MRSA infection.

Suppression of Staphylococcus aureus Superantigen-Independent Interferon Gamma Response by a Probiotic Polysaccharide

Staphylococcus aureus is a Gram-positive opportunistic pathogen that causes a variety of diseases. Bloodstream infection is the most severe, with mortality rates reaching 20 to 50%. Exopolysaccharide (EPS) from the probiotic Bacillus subtilis reduces bacterial burden and inflammation during S. aureus bloodstream infection in mice. Protection is due, in part, to hybrid macrophages that restrict S. aureus growth through reactive oxygen species and to limiting superantigen-induced T cell activation and interferon gamma (IFN-γ) production during infection. A decrease in IFN-γ production was observed within 24 h after infection, and here, we investigated how EPS abrogates its production. We discovered that S. aureus uses a rapid, superantigen-independent mechanism to induce host IFN-γ and that this is mediated by interleukin-12 (IL-12) activation of NK cells. Furthermore, we found that EPS limits IFN-γ production by modulating host immunity in a Toll-like receptor 4 (TLR4)-dependent manner, a signaling pathway that is required for EPS-mediated protection from S. aureus infection in vivo We conclude that EPS protects hosts from acute bloodstream S. aureus infection not only by inducing macrophages that restrict S. aureus growth and inhibit superantigen-activated T cells but also by limiting NK cell production of IFN-γ after S. aureus infection in a TLR4-dependent manner.

Interleukin-10 (IL-10) Produced by Mutant Toxic Shock Syndrome Toxin 1 Vaccine-Induced Memory T Cells Downregulates IL-17 Production and Abrogates the Protective Effect against Staphylococcus aureus Infection

Development of long-term memory is crucial for vaccine-induced adaptive immunity against infectious diseases such as Staphylococcus aureus infection. Toxic shock syndrome toxin 1 (TSST-1), one of the superantigens produced by S. aureus, is a possible vaccine candidate against infectious diseases caused by this pathogen. We previously reported that vaccination with less toxic mutant TSST-1 (mTSST-1) induced T helper 17 (Th17) cells and elicited interleukin-17A (IL-17A)-mediated protection against S. aureus infection 1 week after vaccination. In the present study, we investigated the host immune response induced by mTSST-1 vaccination in the memory phase, 12 weeks after the final vaccination. The protective effect and IL-17A production after vaccination with mTSST-1 were eliminated because of IL-10 production. In the presence of IL-10-neutralizing monoclonal antibody (mAb), IL-17A production was restored in culture supernatants of CD4⁺ T cells and macrophages sorted from the spleens of vaccinated mice. Vaccinated mice treated with anti-IL-10 mAb were protected against systemic S. aureus infection in the memory phase. From these results, it was suggested that IL-10 produced in the memory phase suppresses the IL-17A-dependent vaccine effect through downregulation of IL-17A production.

Staphylococcus aureus and Host Immunity in Recurrent Furunculosis

Staphylococcus aureus is one of the severest and most persistent bacterial pathogens. The most frequent S. aureus infections include impetigo, folliculitis, furuncles, furunculosis, abscesses, hidradenitis suppurativa, and mastitis. S. aureus produces a great variety of cellular and extracellular factors responsible for its invasiveness and ability to cause pathological lesions. Their expression depends on the growth phase, environmental factors, and location of the infection. Susceptibility to staphylococcal infections is rooted in multiple mechanisms of host immune responses and reactions to bacterial colonization. Immunological and inflammatory processes of chronic furunculosis are based on the pathogenicity of S. aureus as well as innate and acquired immunity. In-depth knowledge about them may help to discover the whole pathomechanism of the disease and to develop effective therapeutic options. In this review, we focus on the S. aureus-host immune interactions in the pathogenesis of recurrent furunculosis according to the most recent experimental and clinical findings.

Probiotic Exopolysaccharide Protects against Systemic Staphylococcus aureus Infection, Inducing Dual-Functioning Macrophages That Restrict Bacterial Growth and Limit Inflammation

Staphylococcus aureus causes severe systemic infection with high mortality rates. We previously identified exopolysaccharide (EPS) from a probiotic, Bacillus subtilis, that induces anti-inflammatory macrophages with an M2 phenotype and protects mice from Citrobacter rodentium-induced colitis. We tested if EPS could protect from systemic infection induced by S. aureus and found that EPS-treated mice had enhanced survival as well as reduced weight loss, systemic inflammation, and bacterial burden. While macrophages from EPS-treated mice display an M2 phenotype, they also restrict growth of internalized S. aureus through reactive oxygen species (ROS), reminiscent of proinflammatory phagocytes. These EPS-induced macrophages also limit T cell activation by S. aureus superantigens, and EPS abrogates systemic induction of gamma interferon after infection. We conclude that B. subtilis EPS is an immunomodulatory agent that induces hybrid macrophages that bolster antibacterial immunity and simultaneously limit inflammation, reducing disease burden and promoting host survival.

Neutralization of MMP-2 and TNFR1 Regulates the Severity of S. aureus-Induced Septic Arthritis by Differential Alteration of Local and Systemic Proinflammatory Cytokines in Mice

Despite advancement in the field of antibiotics septic arthritis remains a serious concern till date. Staphylococcus aureus is the most common bacterium that causes septic arthritis. Severity of this disease is directly correlated with chronic inflammation induced by proinflammatory cytokines like TNF-α, interleukin (IL)-1β, IL-6, and induction of matrix metalloproteinases (MMPs) including MMP-2. The objective of our study was to evaluate the role of MMP-2 and tumor necrosis factor receptor 1 (TNFR1) in the pathogenesis of S. aureus infection-induced septic arthritis. Mice were infected with live S. aureus (5 × 10⁶ cells/ml) followed by administration of MMP-2 inhibitor and TNFR1 antibody. Arthritis index showed highest reduction in severity of arthritis in mice treated with both MMP-2 inhibitor and TNFR1 antibody after infection. Combined neutralization of MMP-2 and TNFR1 led to marked diminution in bacterial count in the combined group. Lowest levels of pro inflammatory cytokines like TNF-α, IL-1β, IL-6, and IFN-γ were observed in both serum and synovial tissues indicating maximum protection in S. aureus arthritis during combination treatment. Increment in the level of IL-10 in the combination group could be positively correlated with the recovery of arthritis. Similarly, expressions of COX-2 and iNOS, markers of acute inflammation were also significantly reduced in the combination group due to resolution of inflammation. Levels of O2^.- and NO also showed a significant fall in case of the group treated with MMP-2 inhibitor and TNFR1 antibody both. Neutralization of both MMP-2 and TNFR1 caused rapid decline in recruitment of neutrophil and macrophages in the synovial tissues as evident from reduced MPO and MCP-1 levels, respectively, compared to other groups. Overall, it can be suggested that administration of MMP-2 inhibitor and TNFR1 antibody in combination is protective against the severity of inflammation and cartilage destruction associated with S. aureus infection-induced septic arthritis by altering the levels of cytokines.

The effect of immunoregulation of Streptococcus lactis L16 strain upon Staphylococcus aureus infection

BACKGROUND

Staphylococcus aureus is an important pathogen that causes various infections in medical facilities. However, resistance to multiple drugs has made this infection difficult to manage. Thus, new therapeutic strategies are urgently needed to solve this worldwide public health problem. The Streptococcus lactis L16 strain was isolated from the fermented hot chili sauce. To explore whether it can be used as a protective agent against S. aureus infection, we designed a mouse model of S. aureus infection to evaluate the therapeutic potency of S. lactis. Mice were grouped into pre-(P) and post-(T) S. aureus infection groups following oral administration of S. lactis L16. The protection and treatment effects were assessed by examining body weight, internal organ weight, serum cytokines and intestinal secretory IgA alternations.

RESULT

Oral administration of the S. lactis L16 strain reduced the loss of body weight in mice post-infection and alleviated infection-induced hepatomegaly. In particular, the PL16 group (protection with L16) showed more effective resistance to S. aureus than the TL16 group (treatment with L16). The level of serum cytokine interferon gamma following oral administration of the L16 strain was remarkably increased during infection, as were interleukin-4 levels during convalescence. The probiotic L16 strain induced more sIgA production than S. aureus.

CONCLUSION

Our data suggest that S. lactis L16 is an effective strain with anti-Staphylococcus activity. By regulating the Th1/Th2 response, S. lactis can effectively reduce lesions from infection, indicating its therapeutic potential in overcoming antibiotic resistance in this mouse infection model that mimics infections observed in humans.

Ratio of T-Helper Type 1 (Th1) to Th17 Cytokines in Whole Blood Is Associated With Human β-Defensin 3 Expression in Skin and Persistent Staphylococcus aureus Nasal Carriage

BACKGROUND

 Nasal colonization has gained attention as an effect modifier in Staphylococcus aureus vaccine trials, suggesting interference of carriage with T-cell immunity. Likewise, T-cell signals may be involved in regulating effectors of epithelial innate defense.

METHODS

 Whole blood from 43 persistent carriers and 49 noncarriers was stimulated with viable S. aureus T-helper type 1 (Th1), Th2, and Th17 cytokine expression was measured, compared between carrier groups, and linked with data on human β-defensin 3 (hBD-3) messenger RNA (mRNA) in skin while adjusting for transcriptionally relevant promoter haplotypes.

RESULTS

 Compared with carriers, stimulated whole blood from noncarriers contained on average 60% more interferon γ mRNA (P = .031) and 19% less interleukin 17A (IL-17A) mRNA (P = .11), resulting in, on average, a 90% higher IFN-γ to IL-17A mRNA ratio (P = .003). In a multivariable model, per duplication of the mRNA template, the risk of being a carrier increased by 93% for IL-17A (odds ratio [OR], 1.93; 95% confidence interval [CI], 1.10-3.41; P = .023) and decreased by 35% for IFN-γ (OR, 0.65; 95% CI, 0.47-0.91; P = .01). Independent of carriage and DEFB promotor haplotype, a 1-unit increase in the IFN-γ to IL-17A mRNA ratio (mean ± SD, 5.93 ± 1.60) led to a 24% increase in hBD-3 transcription in experimentally wounded human skin (P = .003).

CONCLUSIONS

 A low Th1 to Th17 mRNA ratio increases the propensity for persistent S. aureus nasal colonization, with downregulated hBD-3 transcription providing a potential link.

Neutralization of MMP-2 protects Staphylococcus aureus infection induced septic arthritis in mice and regulates the levels of cytokines

Matrix metalloproteinases (MMPs) are crucial players in Staphylococcus aureus mediated synovial tissue destruction in the pathogenesis of septic arthritis. Bacterial insult increases proteolytic matrix fragments by activated chondrocytes and synovial fibroblasts leading to induction of matrix metalloproteinases. Tissue destruction via MMPs induced by bacterial products, necrotic tissues and proinflammatory cytokines have been reported. Cytokines like TNF-α, IL-1β released from host cells in response to S. aureus infection promote cartilage degradation by stimulating the production of MMPs. Antibiotic treatment can eradicate invading bacteria but elevated levels of cytokines and cytokines induced MMPs activation lead to progressive and devastating bone and cartilage destruction even after bacterial clearance. Like other MMPs, MMP-2 also contributes to extracellular matrix degradation in different types of arthritis. Release of certain pro inflammatory cytokines can also be regulated by MMP-2 activation leading to further tissue destruction. The role of MMP-2 in the pathogenesis of S. aureus infection induced septic arthritis and its influence on cytokines regulation needs further investigation. Whether neutralization of MMP-2 provides protection against Staphylococcus aureus infection induced septic arthritis in mice is an obvious question. Here we reported that neutralization of MMP-2 during S. aureus infection induced septic arthritis might be beneficial for preventing infection induced extracellular matrix destruction thereby decreasing bacterial burden in synovial tissues and regulating inflammatory cytokines in arthritic mice.

Collaborative Interferon-γ and Interleukin-17 Signaling Protects the Oral Mucosa from Staphylococcus aureus

Infections with Staphylococcus aureus are a continuing and growing problem in community and hospital settings. Preclinical animal modeling of S. aureus relies on experimental infection, which carries some limitations. We describe here a novel, spontaneous model of oral staphylococcal infection in double knockout mice, deficient in the receptors for IL-17 (IL-17RA) and interferon (IFN)-γ (IFNγRI), beginning at 6 to 8 weeks of age. IFNγRI(-/-)IL17RA(-/-) (GRAKO) mice developed progressive oral abscesses. Cytometric methods revealed extensive neutrophilic infiltration of oral tissues in GRAKO mice; further investigation evidenced that IL-17 predominated neutrophil defects in these mice. To investigate the contribution of IFN-γ signaling to this native host defense to S. aureus, we observed perturbations of monocyte recruitment and macrophage differentiation in the oral tissues of GRAKO mice, and CXCL9/chemokine ligand receptor (CXCR)3-driven recruitment of T-cell oral tissues and draining lymph nodes. To address the former finding, we depleted macrophages and monocytes in vivo from IL17RA(-/-) mice using liposomes loaded with clodronate. This treatment elicited oral abscesses, recapitulating the phenotype of GRAKO mice. From these findings, we propose novel collaborative functions of IL-17 and IFN-γ, acting through neutrophils and macrophages, respectively, in native mucocutaneous host defenses to S. aureus.

Identification of CD4+ T-cell epitopes on iron-regulated surface determinant B of Staphylococcus aureus

Iron-regulated surface determinant B (IsdB) of Staphylococcus aureus (S. aureus) is a highly conserved surface protein that can induce protective CD4(+) T-cell immune response. A pivotal role of CD4(+) T-cells in effective immunity against S. aureus infection has been proved, but CD4(+) T-cell epitopes on the S. aureus IsdB have not been well identified. In this study, MHC binding assay was firstly used to predict CD4(+) T-cell epitopes on S. aureus IsdB protein, and six peptides were synthesized to validate the probable epitopes. Two novel IsdB CD4(+) T-cell epitopes, P1 (residues 159-178) and P4 (residues 287-306), were for the first time identified using CD4(+) T-cells obtained from IsdB-immunized C57BL/6 (H-2(b)) and BALB/c (H-2(d)) mice spleen based on cell proliferation and cytokines response. The results showed that P1 and P4 emulsified in Freund's adjuvant (FA) induced much higher cell proliferation compared with PBS emulsified in FA. CD4(+) T-cells stimulated with peptides P1 and P4 secreted significantly higher levels of IFN-γ and IL-17A. However, the level of the cytokine IL-4 almost remained unchanged, suggesting that P1 and P4 preferentially elicited polarized Th1-type responses. In addition, BALB/c mice just respond to P4 not P1, while C57BL/6 mice respond to P1 not P4, implying that epitope P1 and P4 were determined as H-2(b) and H-2(d) restricted epitope, respectively. Taken together, our data may provide an explanation of the IsdB-induced protection against S. aureus and highlight the possibility of developing the epitope-based vaccine against the S. aureus.

Clinical associations of host genetic variations in the genes of cytokines in critically ill patients

Host genetic variations may influence a changing profile of biochemical markers and outcome in patients with trauma/injury. The objective of this study was to assess clinical associations of single nucleotide polymorphisms (SNPs) in the genes of cytokines in critically ill patients. A total of 430 patients were genotyped for SNPs in the genes of pro- (IL1B, IL6, IL8) and anti-inflammatory (IL4, IL10, IL13) cytokines. The main end-points were sepsis, mortality and adult respiratory distress syndrome (ARDS). We evaluated the dynamic levels of bilirubin, blood urea nitrogen, creatine kinase, creatinine and lactate dehydrogenase in five points of measurements (between 1 and 14 days after admission) and correlated them with SNPs. High-producing alleles of proinflammatory cytokines protected patients against sepsis (IL1B -511A and IL8 -251A) and mortality (IL1B -511A). High-producing alleles of anti-inflammatory cytokines IL4 -589T and IL13 431A (144Gln) were less frequent in ARDS patients. The carriers of IL6 -174C/C genotypes were prone to the increased levels of biochemical markers and acute kidney and liver insufficiency. Genotype-dependent differences in the levels of biochemical indicators gradually increased to a maximal value on the 14th day after admission. These findings suggest that genetic variability in pro- and anti-inflammatory cytokines may contribute to different clinical phenotypes in patients at high risk of critical illness.

[Host responses to bacterial infections]

Pathogenic bacteria and host defense system have been evolved by their offense and defense. In vivo research is crucial for elucidation of interactions between them. I have investigated their offence and defense by various standpoints using mouse models of Listeria monocytogenes and Staphylococcus aureus infections. Herein, the results of my research including the roles of endogenous cytokines in host defense, the attenuation of host defense mechanism in obesity and diabetes, the development of vaccines against S. aureus infection by staphylococcal enterotoxin (SE) family molecules, and the emesis-inducing mechanism of SEA are described.

Staphylococcus aureus Colonization: Modulation of Host Immune Response and Impact on Human Vaccine Design

In apparent contrast to its invasive potential Staphylococcus aureus colonizes the anterior nares of 20–80% of the human population. The relationship between host and microbe appears particularly individualized and colonization status seems somehow predetermined. After decolonization, persistent carriers often become re-colonized with their prior S. aureus strain, whereas non-carriers resist experimental colonization. Efforts to identify factors facilitating colonization have thus far largely focused on the microorganism rather than on the human host. The host responds to S. aureus nasal colonization via local expression of anti-microbial peptides, lipids, and cytokines. Interplay with the co-existing microbiota also influences colonization and immune regulation. Transient or persistent S. aureus colonization induces specific systemic immune responses. Humoral responses are the most studied of these and little is known of cellular responses induced by colonization. Intriguingly, colonized patients who develop bacteremia may have a lower S. aureus-attributable mortality than their non-colonized counterparts. This could imply a staphylococcal-specific immune “priming” or immunomodulation occurring as a consequence of colonization and impacting on the outcome of infection. This has yet to be fully explored. An effective vaccine remains elusive. Anti-S. aureus vaccine strategies may need to drive both humoral and cellular immune responses to confer efficient protection. Understanding the influence of colonization on adaptive response is essential to intelligent vaccine design, and may determine the efficacy of vaccine-mediated immunity. Clinical trials should consider colonization status and the resulting impact of this on individual patient responses. We urgently need an increased appreciation of colonization and its modulation of host immunity.

Biofilm matrix exoproteins induce a protective immune response against Staphylococcus aureus biofilm infection

The Staphylococcus aureus biofilm mode of growth is associated with several chronic infections that are very difficult to treat due to the recalcitrant nature of biofilms to clearance by antimicrobials. Accordingly, there is an increasing interest in preventing the formation of S. aureus biofilms and developing efficient antibiofilm vaccines. Given the fact that during a biofilm-associated infection, the first primary interface between the host and the bacteria is the self-produced extracellular matrix, in this study we analyzed the potential of extracellular proteins found in the biofilm matrix to induce a protective immune response against S. aureus infections. By using proteomic approaches, we characterized the exoproteomes of exopolysaccharide-based and protein-based biofilm matrices produced by two clinical S. aureus strains. Remarkably, results showed that independently of the nature of the biofilm matrix, a common core of secreted proteins is contained in both types of exoproteomes. Intradermal administration of an exoproteome extract of an exopolysaccharide-dependent biofilm induced a humoral immune response and elicited the production of interleukin 10 (IL-10) and IL-17 in mice. Antibodies against such an extract promoted opsonophagocytosis and killing of S. aureus. Immunization with the biofilm matrix exoproteome significantly reduced the number of bacterial cells inside a biofilm and on the surrounding tissue, using an in vivo model of mesh-associated biofilm infection. Furthermore, immunized mice also showed limited organ colonization by bacteria released from the matrix at the dispersive stage of the biofilm cycle. Altogether, these data illustrate the potential of biofilm matrix exoproteins as a promising candidate multivalent vaccine against S. aureus biofilm-associated infections.

Contribution of toll-like receptor 2 to the innate response against Staphylococcus aureus infection in mice

Staphylococcus aureus is a common pathogen that causes a wide range of infectious diseases. The function of TLRs, specifically TLR2, during S. aureus infection is still debated. In this study, we investigated the extent to which TLR2 contributes to the host innate response against the bacterial infection using TLR2-deficient mice. Intravenous inoculation with S. aureus resulted in all TLR2-deficient mice dying within 4 d, along with a high bacterial burden in the livers. However, histological examination showed the same degree of macrophage and neutrophil accumulation in the livers of infected TLR2-deficient mice as that in infected wild-type (WT) mice. TLR2-deficient mouse macrophages also showed normal phagocytic activity, although they failed to express CD36 that appeared on the surface of WT mouse cells upon challenge with heat-killed S. aureus. These data indicate that TLR2, as well as CD36, does not directly affect S. aureus clearance and that CD36 expression on macrophages depends on the presence of TLR2. In vivo infection with S. aureus caused significantly elevated production of TNF-α and IL-6 in the livers and blood of TLR2-deficient mice compared with those in WT mice, while the hepatic and serum levels of IL-10 decreased in these mice. In contrast, lower expression of IL-6 and IL-10, but not of TNF-α, at both the gene and protein levels was found in TLR2-deficient mouse macrophages compared to that in WT mouse cells, in response to challenge with heat-killed S. aureus. These findings suggest that the S. aureus-induced pro-inflammatory cytokine response is not dependent on macrophages and that TLR2 deficiency results in decreased IL-10 release by macrophages, which contributes to dysregulated cytokine balance, impaired bacterial clearance, and mouse death. Therefore, TLR2 possesses a protective function during S. aureus infection by regulating pro- and anti-inflammatory cytokine responses.

The SaeR/S two-component system induces interferon-gamma production in neutrophils during invasive Staphylococcus aureus infection

Invasive Staphylococcus aureus (S. aureus) disease is associated with neutrophil activity and pro-inflammatory cytokine expression, including interferon-gamma (IFNγ). Using a mouse model of S. aureus peritonitis, we identify neutrophils as the predominant source of IFNγ and link this induction with the SaeR/S two-component gene regulatory system. Relative to wild-type (BALB/c) mice, IFNγ-deficient mice demonstrated increased bacterial clearance and reduced cellular cytotoxicity following intraperitoneal challenge with S. aureus. Interestingly, bacterial burden and cytotoxicity were similar in BALB/c and IFNγ-deficient mice when infected with an isogenic saeR/S mutant strain. These findings suggest saeR/S-mediated neutrophil-derived IFNγ diminishes innate antibacterial mechanisms against S. aureus.

Virulence strategies of the dominant USA300 lineage of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious threat to worldwide health. Historically, MRSA clones have strictly been associated with hospital settings, and most hospital-associated MRSA (HA-MRSA) disease resulted from a limited number of virulent clones. Recently, MRSA has spread into the community causing disease in otherwise healthy people with no discernible contact with healthcare environments. These community-associated MRSA clones (CA-MRSA) are phylogenetically distinct from traditional HA-MRSA clones, and CA-MRSA strains seem to exhibit hypervirulence and more efficient host : host transmission. Consequently, CA-MRSA clones belonging to the USA300 lineage have become dominant sources of MRSA infections in North America. The rise of this successful USA300 lineage represents an important step in the evolution of emerging pathogens and a great deal of effort has been exerted to understand how these clones evolved. Here, we review much of the recent literature aimed at illuminating the source of USA300 success and broadly categorize these findings into three main categories: newly acquired virulence genes, altered expression of common virulence determinants and alterations in protein sequence that increase fitness. We argue that none of these evolutionary events alone account for the success of USA300, but rather their combination may be responsible for the rise and spread of CA-MRSA.

Immunization with Staphylococcus aureus iron regulated surface determinant B (IsdB) confers protection via Th17/IL17 pathway in a murine sepsis model

We have previously shown that IsdB, a conserved protein expressed by Staphylococcus aureus, induces a robust antibody response which correlates with protection in a murine challenge model. Here we investigate the role of cellular immunity in IsdB mediated protection using lymphocyte deficient SCID mice. As opposed to WT CB-17 mice the CB-17 SCID mice were not protected against a lethal challenge of S. aureus after active and passive immunizations with IsdB. Adoptive transfer of in vitro isolated lymphocyte subsets revealed that reconstituting mice with IsdB specific CD3+ or CD4+ T-cells conferred antigen specific protection while CD8⁺ T-cells, CD19⁺ B-cells and plasma cells (CD138^highB220^intCD19^lo) alone were not protective. A combination of CD3⁺ T-cells plus CD19⁺ B-cells conferred protection in CB-17 SCID mice, whereas bovine serum albumin (BSA) immune lymphocytes did not confer protection. Active immunization experiments indicated that IsdB immunized Jh mice (B-cell deficient) were protected against lethal challenge, while nude (T-cell deficient) mice were not. In vitro assays indicated that isolated IsdB specific splenocytes from immunized mice produced abundant IL-17A, much less IFN-γ and no detectable IL-4. IL-23 deficient mice were not protected from a lethal challenge by IsdB vaccination, pointing to a critical role for CD4⁺ Th17 in IsdB-mediated vaccination. Neutralizing IL-17A, but not IL-22 in vivo significantly increased mortality in IsdB immunized mice; whereas, neutralizing IFN-γ did not alter IsdB-mediated protection. These findings suggest that IL-17A producing Th17 cells play an essential role in IsdB vaccine-mediated defense against invasive S. aureus infection in mice.

Effect of IL-10 antisense gene therapy in severely burned mice intradermally infected with MRSA

The effect of IL-10 antisense oligodeoxynucleotides (ODN) on the susceptibility of burned mice to intradermal (i.d.) infection of methicillin-resistant Staphylococcus aureus (MRSA) was studied. Abscesses formed and sepsis did not develop in normal mice infected i.d. with 10(8)CFU/mouse of MRSA. Similarly, sepsis caused by MRSA i.d. infection did not develop and abscesses formed in burned mice treated with IL-10 antisense ODN. However, all of the burned mice treated with scrambled ODN (control group) died by infectious complications stemming from MRSA i.d. infection, and an MRSA-abscess did not form in these mice. Macrophages (Mϕ) isolated from the infection site tissue of burned mice that were treated with IL-10 antisense ODN were identified as M1Mϕ, while Mϕ isolated from burned mice that were treated with scrambled ODN were shown to be M2Mϕ. MRSA-abscesses formed in burned mice inoculated with M1Mϕ, and these mice resisted a lethal dose of MRSA i.d. infection. However, an abscess did not form, and sepsis caused by MRSA i.d. infection developed in burned mice that were inoculated with M2Mϕ. These results indicate that severely burned mice treated with IL-10 antisense ODN are resistant against i.d. infection with MRSA. M1Mϕ appeared in the infection site tissues of severely burned mice that were treated with IL-10 antisense ODN may play a role on the abscess formation and inhibiting sepsis caused by MRSA i.d. infection.

Gene expression profiling of dendritic cells reveals important mechanisms associated with predisposition to Staphylococcus infections

BACKGROUND

Staphylococcus aureus is a major pathogen of humans and animals and emerging antibiotic-resistant strains have further increased the concern of this health issue. Host genetics influence susceptibility to S. aureus infections, and the genes determining the outcome of infections should be identified to find alternative therapies to treatment with antibiotics. Here, we used outbred animals from a divergent selection based on susceptibility towards Staphylococcus infection to explore host immunogenetics.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated how dendritic cells respond to heat-inactivated S. aureus and whether dendritic cells from animals showing different degrees of susceptibility had distinct gene expression profiles. We measured gene expression levels of in vitro S. aureus-stimulated bone marrow-derived dendritic cells at three different time points (0, 3 and 8 hrs) by using 15 k ovine Agilent microarrays. Furthermore, differential expression of a selected number of genes was confirmed by RT-qPCR. Gene signatures of stimulated DCs were obtained and showed that genes involved in the inflammatory process and T helper cell polarization were highly up-regulated upon stimulation. Moreover, a set of 204 genes were statistically differentially expressed between susceptible and resistant animals, and grouped them according to their predisposition to staphylococcal infection. Interestingly, over-expression of the C1q and Ido1 genes was observed in the resistant line and suggested a role of classical pathway of complement and early regulation of inflammation pathways, respectively. On the contrary, over expression of genes involved in the IL1R pathway was observed in susceptible animals. Furthermore, the leucocyte extravasation pathway was also found to be dominant in the susceptible line.

CONCLUSION/SIGNIFICANCE

We successfully obtained Staphylococcus aureus associated gene expression of ovine BM-DC in an 8-hour kinetics experiment. The distinct transcriptional profiles of dendritic cells obtained from resistant and susceptible animals may explain susceptibility towards S. aureus infections in a broader context.

The SaeR/S gene regulatory system induces a pro-inflammatory cytokine response during Staphylococcus aureus infection

Community-associated methicillin-resistant Staphylococcus aureus accounts for a large portion of the increased staphylococcal disease incidence and can cause illness ranging from mild skin infections to rapidly fatal sepsis syndromes. Currently, we have limited understanding of S. aureus-derived mechanisms contributing to bacterial pathogenesis and host inflammation during staphylococcal disease. Herein, we characterize an influential role for the saeR/S two-component gene regulatory system in mediating cytokine induction using mouse models of S. aureus pathogenesis. Invasive S. aureus infection induced the production of localized and systemic pro-inflammatory cytokines, including tumor necrosis factor alpha (TNF-α), interferon gamma (IFN-γ), interleukin (IL)-6 and IL-2. In contrast, mice infected with an isogenic saeR/S deletion mutant demonstrated significantly reduced pro-inflammatory cytokine levels. Additionally, secreted factors influenced by saeR/S elicited pro-inflammatory cytokines in human blood ex vivo. Our study further demonstrated robust saeR/S-mediated IFN-γ production during both invasive and subcutaneous skin infections. Results also indicated a critical role for saeR/S in promoting bacterial survival and enhancing host mortality during S. aureus peritonitis. Taken together, this study provides insight into specific mechanisms used by S. aureus during staphylococcal disease and characterizes a relationship between a bacterial global regulator of virulence and the production of pro-inflammatory mediators.

Host chemokines bind to Staphylococcus aureus and stimulate protein A release

There are few examples of host signals that are beneficial to bacteria during infection. Here we found that 31 out of 42 host immunoregulatory chemokines were able to induce release of the virulence factor protein A (SPA) from a strain of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA). Detailed study of chemokine CXCL9 revealed that SPA release occurred through a post-translational mechanism and was inversely proportional to bacterial density. CXCL9 bound specifically to the cell membrane of CA-MRSA, and the related SPA-releasing chemokine CXCL10 bound to both cell wall and cell membrane. Clinical samples from patients infected with S. aureus and samples from a mouse model of CA-MRSA skin abscess all contained extracellular SPA. Further, SPA-releasing chemokines were present in mouse skin lesions infected with CA-MRSA. Our data identify a potential new mode of immune evasion, in which the pathogen exploits a host defense factor to release a virulence factor; moreover, chemokine binding may serve a scavenging function in immune evasion by S. aureus.

Understanding the significance of Staphylococcus epidermidis bacteremia in babies and children

PURPOSE OF REVIEW

This article provides an overview of Staphylococcus epidermidis bacteremia/sepsis and coagulase-negative staphylococci (CoNS) infections in neonates and children.

RECENT FINDINGS

The incidence of S. epidermidis and CoNS sepsis in neonates is still very high and preventing and treating disease remains difficult. There has been recent progress in understanding the pathogenesis of S. epidermidis infection, interaction of S. epidermidis with host defenses, and risk factors for the development of S. epidermidis disease. For example, we have gained more insight into the development of biofilm-associated catheter infections, which are responsible for recurrent CoNS infections in hospitalized premature neonates and are especially difficult to treat owing to intrinsic resistance of biofilms to antibiotics.

SUMMARY

Biofilm-associated catheter infections by S. epidermidis occur frequently in neonates and adults. S. epidermidis bloodstream infections are particularly problematic in neonates. Prophylaxis in the form of eradicating colonizing S. epidermidis may be a double-edged sword, as S. epidermidis colonization may be beneficial to the host. New drugs may arise from a better understanding of S. epidermidis virulence and analysis of risk factors may help identify neonates susceptible to bacterial sepsis. However, reducing morbidity should always begin by increasing hygiene in hospital settings to reduce the introduction of potentially harmful opportunistic pathogens such as S. epidermidis on indwelling medical devices or during surgery.

IFN-gamma plays a detrimental role in murine defense against nasal colonization of Staphylococcus aureus

The anterior nares are the major reservoir in humans of Staphylococcus aureus with the risk of developing endogenous infections or transmitting infections to susceptible persons. The mechanisms that mediate attachment of staphylococci to the nasal mucosa are little known. The purpose of the present work was to study some factors that could influence the nasal colonization in an animal model of mice. We investigated the possible role of IFN-gamma. We used S. aureus ATCC 35556 (SA113) slime-producing and ATCC 25923 non-slime-producing strains. Male 6-week-old BALB/c, C57BL/6 (wild-type, WT), and gene-deficient IL-12p40 (IL-12p40-/-) or IL-4 (IL-4-/-) mice on C57BL/6 background were infected with a dose of S. aureus of 10(6) CFU in 10mul of saline. The total number of S. aureus CFU per nose and lung, specific IgA response and IFN-gamma levels were evaluated. Significant higher CFU were recovery from the narines of C57BL/6 compared with BALB/c mice either after ATCC 35556 (p<0.0001) and ATCC 25923 (p<0.02) strain infection. Low IgA response correlated with high bacterial counting in the C57BL/6 nasal region. Moreover, C57BL/6 mice showed major colonization of slime-producing S. aureus ATCC 35556 than non-slime-producing ATCC 25923 S. aureus strain (p<0.02). IL-12p40-/-mice clarified the bacteria from their nose more efficiently that WT mice after slime-producing S. aureus (p<0.0001). Accordingly, significant lower level of IFN-gamma were detected in IL-12p40-/- compared with WT mice after infection with this strain (p<0.03). The results suggested the influence of the slime production in nasal colonization of S. aureus, and indicate at first time that IFN-gamma may play a detrimental role in this mucosal infection. These results could contribute to elucidate mucosal immune mechanisms involved in S. aureus colonization and then control infections in susceptible persons.

Host polymorphisms in interleukin 4, complement factor H, and C-reactive protein associated with nasal carriage of Staphylococcus aureus and occurrence of boils

BACKGROUND

Staphylococcus aureus is capable of persistently colonizing the vestibulum nasi. We hypothesized that polymorphisms in host inflammatory response genes and genetic variation in S. aureus contribute to susceptibility to S. aureus carriage and infection.

METHODS

The prevalence of persistent nasal carriage of S. aureus in 3851 participants aged 61-101 years was 18% (678 of 3851 participants), whereas 73% of volunteers (2804 of 3851) were not colonized. A total of 1270 individuals had boils. Polymorphisms in TNFA (C -863T), IL4 (C -542T), CFH (Tyr402His), and CRP (C1184T, C2042T, and C2911G) were determined. Genetic similarity among 428 S. aureus isolates was determined by use of amplified fragment length polymorphism analysis (AFLP)-mediated genotyping.

RESULTS

The IL4 -524 C/C host genotype was associated with an increased risk of persistent S. aureus carriage, irrespective of S. aureus AFLP genotype. The CRP haplotype 1184C; 2042C; 2911C was overrepresented in individuals who were not colonized . In individuals with boils, carriers of the CFH Tyr402 variant, and the CRP 2911 C/C genotype were overrepresented.

CONCLUSION

Persistent carriage of S. aureus is influenced by genetic variation in host inflammatory response genes. As would be expected in multifactorial host-microbe interactions, these effects are limited. Interestingly, host genotype was associated with the carriage of certain S. aureus genotypes. Apparently, a close interaction between host and bacterial determinants are prerequisites for long-term colonization.

The antifungal vaccine derived from the recombinant N terminus of Als3p protects mice against the bacterium Staphylococcus aureus

Vaccination with the recombinant N terminus of the candidal adhesin Als3p (rAls3p-N) protects mice from lethal candidemia. Candidal Als3p also is structurally similar to the microbial surface components recognizing adhesive matrix molecule adhesin, clumping factor, from Staphylococcus aureus. To determine the potential for cross-kingdom vaccination, we immunized mice with rAls3p-N or negative control proteins and challenged them via the tail vein with S. aureus or other gram-positive or gram-negative pathogens. The rAls3p-N vaccine, but neither tetanus toxoid nor a related Als protein (Als5p), improved the survival of vaccinated mice subsequently infected with multiple clinical isolates of S. aureus, including methicillin-resistant strains. The rAls3p-N vaccine was effective against S. aureus when combined with aluminum hydroxide adjuvant. However, the vaccine did not improve the survival of mice infected with other bacterial pathogens. Vaccinated, infected mice mounted moderated type 1 immune responses. T lymphocyte-deficient mice were more susceptible to S. aureus infection, but B lymphocyte-deficient mice were not. Furthermore, T but not B lymphocytes from vaccinated mice mediated protection in adoptive transfer studies. The passive transfer of immune serum was not protective. These data provide the foundation for cross-kingdom vaccine development against S. aureus and Candida, which collectively cause 200,000 bloodstream infections resulting in >/=40,000 to 50,000 deaths annually in the United States alone.

Increased weight loss with reduced viral replication in interleukin-10 knock-out mice infected with murine cytomegalovirus

The anti-inflammatory cytokine interleukin (IL)-10 plays an important role in the regulation of host-immune responses. Here we studied the role IL-10 plays in host responses to cytomegalovirus (CMV) infection. We demonstrate that manifestations of murine CMV (MCMV) disease are more severe in IL-10 knock-out mice, despite significantly reduced levels of viral replication. Cytokine analysis of serum revealed increased levels of interferon (IFN)-gamma, monocyte chemotactic protein 1 (MCP-1) and IL-6, all of which are potent stimulators of inflammatory responses. Depletion of IFN-gamma by monoclonal antibodies in IL-10 knock-out mice failed to improve the physical condition of the mice, while increasing viral replication. In contrast, serum levels of IL-6 in the knock-out animals were unaffected by IFN-gamma depletion and remained significantly elevated early in the course of infection. These data suggest that increased weight loss observed in IL-10 knock-out mice may be attributed to the uncontrolled production of proinflammatory cytokines, including IL-6.

Gamma interferon confers resistance to infection with Staphylococcus aureus in human vascular endothelial cells by cooperative proinflammatory and enhanced intrinsic antibacterial activities

Vascular endothelium is an exposed target in systemic endovascular Staphylococcus aureus infections. We reported earlier that the proinflammatory and procoagulant activities of primary human umbilical vein endothelial cells (ECs) after binding and ingestion of S. aureus organisms provide the cells effective means for leukocyte-mediated bacterial elimination. Expanding on this, we now show that these ECs exhibit a modest intrinsic capacity for eliminating intracellular S. aureus that was influenced by cytokines relevant to S. aureus infections. Using various EC infection assays, we showed that gamma interferon (IFN-gamma), applied to cultures of ECs prior to or after infection with S. aureus, markedly reduced the level of infection, illustrated by lower percentages of S. aureus-infected ECs and less intracellular bacteria per infected cell. IFN-gamma-activated ECs had unaltered abilities to bind S. aureus and processed ingested bacteria by a seemingly conventional phagocytic pathway. IFN-gamma treatment rescued EC monolayers from severe injury by virulent clinical S. aureus strains or excessive bacterial numbers. Mechanistically, IFN-gamma controls S. aureus infection via IFN-gamma receptor, most likely through stimulation of intrinsic endothelial antibacterial mechanisms but independent of processes that deprive bacteria of intracellular L-tryptophan or iron. The antibacterial activity of IFN-gamma-stimulated ECs coincided with sustained or slightly elevated endothelial proinflammatory responses that supported monocyte recruitment. In conclusion, we identify IFN-gamma as a potent regulatory Th1 cytokine possessing exclusive abilities to augment intrinsic antistaphylococcal effector mechanisms in human ECs without ablating the S. aureus-induced proinflammatory EC responses and, as such, coordinating a protective efficacy of ECs against blood-borne S. aureus infection.

Effect of laparotomy on clearance and cytokine induction in Staphylococcus aureus infected lungs

RATIONALE

Staphylococcus aureus is a major pathogen complicating postsurgical care.

OBJECTIVES

To test the effect of sterile laparotomy (LAP) on pulmonary clearance of S. aureus in a murine model.

METHODS

Control and LAP mice were infected intranasally with 10(8) cfu of S. aureus. Microbial clearance, pulmonary leukocyte recruitment, and cytokine profiles were compared between the groups. Antibody neutralization or cytokine gene knockout mice were used to evaluate the role of cytokines.

MEASUREMENTS AND MAIN RESULTS

Laparotomy resulted in a 10-fold increase in S. aureus lung colony-forming units on Days 2 and 3 postinfection. Both groups cleared the infection by Day 4. No defect in leukocyte recruitment into the lungs was observed in infected LAP animals; however, an increase in the number of Mac-3-positive cells and a significant decrease of cells with high surface expression of Fc-gammaR suggest suboptimal activation of leukocytes in the lungs of infected LAP animals. Infected LAP mice had decreased expression of interferon (IFN)-gamma and increased expression of mRNA for IL-13 in the lungs on Day 1 postinfection and decreased levels of IL-6, keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-2 (MIP-2) in bronchoalveolar lavage at Day 2 postinfection. Neutralization of IFN-gamma mimicked the effect of LAP with impaired clearance on Day 2.

CONCLUSIONS

Sterile LAP induced temporary deactivation of innate immune responses to pulmonary S. aureus challenge. Impaired microbial clearance was accompanied by altered cytokine expression and suboptimal activation of pulmonary leukocytes. Lack of early IFN-gamma induction in the infected lungs of LAP animals is a likely mechanism contributing to the observed phenotype.

The corneal response to infection withStaphylococcus aureusin the absence of interleukin‐4

Interleukin-4 (IL-4) has previously been implicated in a protective response to Staphylococcus aureus corneal infection. Consequently, the specific role of IL-4 during S. aureus corneal infection was investigated using IL-4 gene knockout mice. The eyes of IL-4-/- mice and wild-type mice were challenged topically with S. aureus and examined at 24 h post-infection. Keratitis was examined clinically and histologically. Bacterial and polymorphonuclear leucocytes (PMN) numbers were enumerated and cytokine and chemokine levels determined by enzyme-linked immunosorbent assay. Exogenous IL-4 was administered to both IL-4-/- and wild-type mice and clinical parameters were determined. A lack of IL-4 resulted in a significant increase in clinical scores, pathology, bacterial load and neutrophil numbers. The absence of IL-4 also resulted in an upregulation of interferon (IFN)-gamma and a downregulation of IL-6, IL-10 and the chemokines KC and macrophage inflammatory protein-2. Administration of exogenous IL-4 to IL-4-/- mice was protective but time-dependent. This study highlights the protective role of IL-4 during S. aureus infection and emphasizes the balance between IL-4 and IFN-gamma in achieving bacterial control and maintaining the integrity of the cornea. This information may lead to the development of novel therapeutic strategies potentially improving the prognosis for infection of this unique avascular site.

Phytol-based novel adjuvants in vaccine formulation: 2. Assessment of efficacy in the induction of protective immune responses to lethal bacterial infections in mice

BACKGROUND

Adjuvants are known to significantly enhance vaccine efficacy. However, commercial adjuvants often have limited use because of toxicity in humans. The objective of this study was to determine the comparative effectiveness of a diterpene alcohol, phytol and its hydrogenated derivative PHIS-01, relative to incomplete Freund's adjuvant (IFA), a commonly used adjuvant in augmenting protective immunity in mice against E. coli and S. aureus, and in terms of inflammatory cytokines.

METHODS

Vaccines, consisting of heat-attenuated E. coli or S. aureus and either of the two phytol-based adjuvants or IFA, were tested in female BALB/c mice. The vaccines were administered intraperitoneally at 10-day intervals. The efficacy of the phytol and PHIS-01, as compared to IFA, was assessed by ELISA in terms of anti-bacterial antibody and inflammatory cytokines. We also examined the ability of the vaccines to induce specific protective immunity by challenging mice with different doses of live bacteria.

RESULTS AND DISCUSSION

IFA, phytol, and PHIS-01 were equally efficient in evoking anti-E. coli antibody response and in providing protective immunity against live E. coli challenges. In contrast, the antibody response to S. aureus was significant when PHIS-01 was used as the adjuvant. However, in terms of the ability to induce protective immunity, phytol was most effective against S. aureus. Moreover, during challenges with live E. coli and S. aureus immune mice produced much less IL-6, the mediators of fatal septic shock syndromes.

CONCLUSION

Our results show that vaccine formulations containing phytol and PHIS-01 as adjuvants confer a robust and protective immunity against both Gram-negative and Gram-positive bacteria without inducing adverse inflammatory cytokine due to IL-6.

Intranasal vaccination with a double mutant of staphylococcal enterotoxin C provides protection against Staphylococcus aureus infection

Staphylococcus aureus expresses a repertoire of factors including staphylococcal exotoxins (SEs), exoenzymes, and numerous cell-associated components that contribute to the pathogenesis of disease. We constructed and expressed a nontoxic double mutant SEC (dmSEC), devoid of superantigenic activity, and investigated the ability of intranasal vaccination with dmSEC plus cholera toxin (CT) adjuvant to protect mice against S. aureus infection. Mice were vaccinated with dmSEC and inoculated with a viable S. aureus clinical isolate strain. The survival rate in the immunized mice was higher, and bacterial counts in the organs were significantly lower than those in the control group. Intranasal vaccination with dmSEC induced the production of SEC-specific antibodies such as IgG1, IgG2b and IgA. dmSEC-vaccinated mice elicited significantly higher titers of interleukin-4 (IL-4) and IL-10, and lower levels of interferon-gamma (IFN-gamma) after challenge with S. aureus compared with the control group. Furthermore, the sera from dmSEC-immunized mice significantly inhibited IFN-gamma and tumor necrosis factor-alpha production in vitro. These results indicate that intranasal vaccination with dmSEC devoid of superantigenic properties induces systemic immune responses and provides protection against S. aureus infection.

Local delivery of soluble interleukin-6 receptors to improve the outcome of alpha-toxin producing Staphylococcus aureus infection in mice

Staphylococcal alpha-toxin enhances interleukin (IL)-6 secretion in mice infected with Staphylococcus aureus. The role of alpha-toxin-induced IL-6 secretion in host defense has not been sufficiently clarified. In the present study, IL-6 signaling was transiently regulated using soluble IL-6 receptors (sIL-6R) to investigate the role of IL-6 in the early stage of abdominal S. aureus infection. In mice challenged with bacteria producing high alpha-toxin levels, the local delivery of sIL-6R was effective in improving the survival rate, the resolution of neutrophilia and the bacteria clearance. Mice that had received sIL-6R and survived showed high levels of IL-6, monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha. In contrast, mice that died in spite of the delivery of sIL-6R showed high levels of interferon (IFN)-gamma and IL-1alpha and low TNF-alpha level. When the effect of soluble gp130, a sIL-6R antagonist, was examined, the number of neutrophils increased significantly and the MCP-1 level decreased significantly, compared to the group that received sIL-6R alone; the number of viable bacteria also tended to increase as a result of the inhibition of IL-6 signaling. The cellular phosphotyrosine level in alpha-toxin-treated macrophages was reduced in cultures supplemented with recombinant IL-6 in vitro. These results suggest that IL-6 enhances bactericidal activity and reduces the number of immune cells that are activated abnormally through the regulation of inflammatory cytokines during the early stage of infection in alpha-toxin producers.

The role of gamma interferon in acquired host resistance against Staphylococcus aureus infection in mice

We investigated the expression of an acquired host resistance against Staphylococcus aureus infection in mice. When C57BL/6 mice were immunized with viable S. aureus and challenged with S. aureus eight weeks later, the elimination of S. aureus from the spleen and liver was enhanced in the immunized mice compared with the nonimmunized mice. When gamma interferon (IFN-gamma(-/-)) mice were immunized and challenged, the bacterial numbers in the organs of immunized mice were comparable to those in the nonimmunized mice, suggesting that IFN-gamma plays a critical role in an acquired host resistance against S. aureus infection. IFN-gamma(-/-) mice produced the lower level of anti-S. aureus immunoglobulin M (IgM) and IgG2a antibodies compared with C57BL/6 mice. To elucidate the role of IFN-gamma produced during a challenge with S. aureus, a single injection of anti-IFN-gamma monoclonal antibody to mice was carried out 1 h before challenge. An acquired resistance against S. aureus infection was inhibited by injecting with anti-IFN-gamma monoclonal antibody. However, anti-IFN-gamma monoclonal antibody treatment failed to modulate anti-S. aureus IgM, IgG1 or IgG2a responses in these animals. These results demonstrated that IFN-gamma is required for an acquired resistance against S. aureus infection in mice. However, IFN-gamma induced during the challenge failed to affect the secondary antibody responses.

Identification of Staphylococcus aureus proteins recognized by the antibody-mediated immune response to a biofilm infection

Staphylococcus aureus causes persistent, recurrent infections (e.g., osteomyelitis) by forming biofilms. To survey the antibody-mediated immune response and identify those proteins that are immunogenic in an S. aureus biofilm infection, the tibias of rabbits were infected with methicillin-resistant S. aureus to produce chronic osteomyelitis. Sera were collected prior to infection and at 14, 28, and 42 days postinfection. The sera were used to perform Western blot assays on total protein from biofilm grown in vitro and separated by two-dimensional gel electrophoresis. Those proteins recognized by host antibodies in the harvested sera were identified via matrix-assisted laser desorption ionization-time of flight analysis. Using protein from mechanically disrupted total and fractionated biofilm protein samples, we identified 26 and 22 immunogens, respectively. These included a cell surface-associated beta-lactamase, lipoprotein, lipase, autolysin, and an ABC transporter lipoprotein. Studies were also performed using microarray analyses and confirmed the biofilm-specific up-regulation of most of these genes. Therefore, although the biofilm antigens are recognized by the immune system, the biofilm infection can persist. However, these proteins, when delivered as vaccines, may be important in directing the immune system toward an early and effective antibody-mediated response to prevent chronic S. aureus infections. Previous works have identified S. aureus proteins that are immunogenic during acute infections, such as sepsis. However, this is the first work to identify these immunogens during chronic S. aureus biofilm infections and to simultaneously show the global relationship between the antigens expressed during an in vivo infection and the corresponding in vitro transcriptomic and proteomic gene expression levels.

Animal models of sepsis: setting the stage

Sepsis is a state of disrupted inflammatory homeostasis that is often initiated by infection. The development and progression of sepsis is multi-factorial, and affects the cardiovascular, immunological and endocrine systems of the body. The complexity of sepsis makes the clinical study of sepsis and sepsis therapeutics difficult. Animal models have been developed in an effort to create reproducible systems for studying sepsis pathogenesis and preliminary testing of potential therapeutic agents. However, demonstrated benefit from a therapeutic agent in animal models has rarely been translated into success in human clinical trials. This review summarizes the common animal sepsis models and highlights how results of recent human clinical trials might affect their use.