Signaling via the IL-20 receptor inhibits cutaneous production of IL-1ß and IL-17A to promote infection with methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus causes most infections of human skin and soft tissue and is a major infectious cause of mortality. Host defense mechanisms against S. aureus are incompletely understood. Interleukin 19 (IL-19), IL-20 and IL-24 signal through type I and type II IL-20 receptors and are associated with inflammatory skin diseases such as psoriasis and atopic dermatitis. We found here that those cytokines promoted cutaneous infection with S. aureus in mice by downregulating IL-1ß- and IL-17A-dependent pathways. We noted similar effects of those cytokines in human keratinocytes after exposure to S. aureus, and antibody blockade of the IL-20 receptor improved outcomes in infected mice. Our findings identify an immunosuppressive role for IL-19, IL-20 and IL-24 during infection that could be therapeutically targeted to alter susceptibility to infection.

Loss of GdpP Function in Staphylococcus aureus Leads to ß-Lactam Tolerance and Enhanced Evolution of ß-Lactam Resistance.

Infections caused by Staphylococcus aureus are a leading cause of mortality. Treating infections caused by S. aureus is difficult due to resistance against most traditional antibiotics, including ß-lactams. We previously reported the presence of mutations in gdpP among S. aureus strains that were obtained by serial passaging in ß-lactam drugs. Similar mutations have recently been reported in natural S. aureus isolates that are either nonsusceptible or resistant to ß-lactam antibiotics. gdpP codes for a phosphodiesterase that cleaves cyclic-di-AMP (CDA), a newly discovered second messenger. In this study, we sought to identify the role of gdpP in ß-lactam resistance in S. aureus. Our results showed that gdpP-associated mutations caused loss of phosphodiesterase function, leading to increased CDA accumulation in the bacterial cytosol. Deletion of gdpP led to an enhanced ability of the bacteria to withstand a ß-lactam challenge (2 to 3 log increase in bacterial CFU) by promoting tolerance without enhancing MICs of ß-lactam antibiotics. Our results demonstrated that increased drug tolerance due to loss of GdpP function can provide a selective advantage in acquisition of high-level ß-lactam resistance. Loss of GdpP function thus increases tolerance to ß-lactams that can lead to its therapy failure and can permit ß-lactam resistance to occur more readily.

Prostaglandin E2 suppresses antifungal immunity by inhibiting interferon regulatory factor 4 function and interleukin-17 expression in T cells.

T helper 17 (Th17) cells play an important role in mucosal host defense through production of the signature cytokines IL-17 and IL-22. Prostaglandin E2 (PGE2) has been shown to enhance IL-17 production by mature Th17 cells. However, when present during Th17 cell differentiation, we found that PGE2 inhibited the transcription factor IRF4 and suppressed production of IL-17 but not IL-22. We show that IRF4 was required for IL-17 expression but inhibited IL-22 expression, highlighting the potential for discordant regulation of these two cytokines in Th17 cells. The pathogenic fungus Cryptococcus neoformans produces PGE2, and we found that it uses PGE2- and IRF4-dependent mechanisms to specifically inhibit induction of IL-17 during Th17 cell differentiation. Blockade of host PGE2 during infection led to increased IL-17 production from CD4(+) T cells and increased survival of mice. These findings suggest that host- or pathogen-derived PGE2 can act directly on Th17 cells during differentiation to inhibit IL-17-dependent antimicrobial responses.

IL-20 Signaling in Activated Human Neutrophils Inhibits Neutrophil Migration and Function.

Neutrophils possess multiple antimicrobial mechanisms that are critical for protection of the host against infection with extracellular microbes, such as the bacterial pathogen Staphylococcus aureus Recruitment and activation of neutrophils at sites of infection are driven by cytokine and chemokine signals that directly target neutrophils via specific cell surface receptors. The IL-20 subfamily of cytokines has been reported to act at epithelial sites and contribute to psoriasis, wound healing, and anti-inflammatory effects during S. aureus infection. However, the ability of these cytokines to directly affect neutrophil function remains incompletely understood. In this article, we show that human neutrophils altered their expression of IL-20R chains upon migration and activation in vivo and in vitro. Such activation of neutrophils under conditions mimicking infection with S. aureus conferred responsiveness to IL-20 that manifested as modification of actin polymerization and inhibition of a broad range of actin-dependent functions, including phagocytosis, granule exocytosis, and migration. Consistent with the previously described homeostatic and anti-inflammatory properties of IL-20 on epithelial cells, the current study provides evidence that IL-20 directly targets and inhibits key inflammatory functions of neutrophils during infection with S. aureus.

Adaptive Immunity Against Staphylococcus aureus.

A complex interplay between host and bacterial factors allows Staphylococcus aureus to occupy its niche as a human commensal and a major human pathogen. The role of neutrophils as a critical component of the innate immune response against S. aureus, particularly for control of systemic infection, has been established in both animal models and in humans with acquired and congenital neutrophil dysfunction. The role of the adaptive immune system is less clear. Although deficiencies in adaptive immunity do not result in the marked susceptibility to S. aureus infection that neutrophil dysfunction imparts, emerging evidence suggests both T cell- and B cell-mediated adaptive immunity can influence host susceptibility and control of S. aureus. The contribution of adaptive immunity depends on the context and site of infection and can be either beneficial or detrimental to the host. Furthermore, S. aureus has evolved mechanisms to manipulate adaptive immune responses to its advantage. In this chapter, we will review the evidence for the role of adaptive immunity during S. aureus infections. Further elucidation of this role will be important to understand how it influences susceptibility to infection and to appropriately design vaccines that elicit adaptive immune responses to protect against subsequent infections.

Lethal CD4 T Cell Responses Induced by Vaccination Against Staphylococcus aureus Bacteremia.

Multiple candidate vaccines against Staphylococcus aureus infections have failed in clinical trials. Analysis of a recent prematurely halted vaccine trial revealed increased mortality rates among vaccine recipients in whom postsurgical S. aureus infection developed, emphasizing the potential for induction of detrimental immune responses and the need to better understand the requirements for protective immunity against S. aureus. These failures of single-antigen vaccines have prompted ongoing development of multicomponent vaccines to target the multitude of S. aureus virulence factors. In the current study, we used lethally irradiated S. aureus as a model multicomponent vaccine and showed that vaccination of mice decreased survival in a bacteremia challenge model. These deleterious effects were due to a CD4 T-cell-dependent interferon γ response and could be prevented by inhibiting development of this response during vaccination. Our results identify the potential for vaccination to induce pathological immune responses, and they have implications for recent vaccine failures and the design of future staphylococcal vaccines.

PBP4 Mediates ß-Lactam Resistance by Altered Function.

Penicillin binding protein 4 (PBP4) can provide high-level ß-lactam resistance in Staphylococcus aureus A series of missense and promoter mutations associated with pbp4 were detected in strains that displayed high-level resistance. We show here that the missense mutations facilitate the ß-lactam resistance mediated by PBP4 and the promoter mutations lead to overexpression of pbp4 Our results also suggest a cooperative interplay among PBPs for ß-lactam resistance.

CARD9-Dependent Neutrophil Recruitment Protects against Fungal Invasion of the Central Nervous System.

Candida is the most common human fungal pathogen and causes systemic infections that require neutrophils for effective host defense. Humans deficient in the C-type lectin pathway adaptor protein CARD9 develop spontaneous fungal disease that targets the central nervous system (CNS). However, how CARD9 promotes protective antifungal immunity in the CNS remains unclear. Here, we show that a patient with CARD9 deficiency had impaired neutrophil accumulation and induction of neutrophil-recruiting CXC chemokines in the cerebrospinal fluid despite uncontrolled CNS Candida infection. We phenocopied the human susceptibility in Card9-/- mice, which develop uncontrolled brain candidiasis with diminished neutrophil accumulation. The induction of neutrophil-recruiting CXC chemokines is significantly impaired in infected Card9-/- brains, from both myeloid and resident glial cellular sources, whereas cell-intrinsic neutrophil chemotaxis is Card9-independent. Taken together, our data highlight the critical role of CARD9-dependent neutrophil trafficking into the CNS and provide novel insight into the CNS fungal susceptibility of CARD9-deficient humans.

Altered inactivation of commensal LPS due to acyloxyacyl hydrolase deficiency in colonic dendritic cells impairs mucosal Th17 immunity.

Interleukin (IL) 17-secreting CD4(+) helper T cells (Th17 cells) are essential for host defense at mucosal surfaces, and Th17 cell dysregulation can result in autoimmunity. Exposure to microbial products, such as bacterial LPS, can affect the ability of dendritic cells (DCs) to polarize Th17 cells. Acyloxyacyl hydrolase (AOAH) is a mammalian enzyme expressed by antigen (Ag)-presenting cells that deacylates and thereby inactivates LPS in host tissues. We hypothesized that inactivation of intestinal microbiota-derived LPS by AOAH influences the ability of DCs to polarize and generate Th17 effector cells. We found that LPS-containing Gram-negative microbiota augmented the differentiation of Ag-specific Th17 cells, and identified a colonic DC subset (CD103(+)CD11b(+)ALDH(-)) displaying a unique capacity to both express AOAH and polarize Th17 cells. Compared with WT, these Aoah(-/-) colonic DCs produce less IL-6, resulting in diminished Ag-specific Th17 polarization and increased regulatory T-cell induction in vitro. Oral administration of LPS led to reduced IL-6 production from CD103(+)CD11b(+)ALDH(-) colonic DCs in Aoah(-/-) mice compared with Aoah(+/+) mice, resulting in an abrogated Ag-specific Th17 response in the colon after mucosal immunization that could be rescued by systemic delivery of recombinant IL-6. These data identify the ability of AOAH to modulate microbiota signals that drive Th17 polarization and influence mucosal T-cell immunity, and suggest that host pathways to handle microbiota-derived products may be targeted to modulate Th17 responses in the context of inflammatory disorders or infection at mucosal surfaces.

A method for culturing Gram-negative skin microbiota.

BACKGROUND: Commensal Gram-negative (CGN) microbiota have been identified on human skin by DNA sequencing; however, methods to reliably culture viable Gram-negative skin organisms have not been previously described. RESULTS: Through the use of selective antibiotics and minimal media we developed methods to culture CGN from skin swabs. We identified several previously uncharacterized CGN at the species level by optimizing growth conditions and limiting the inhibitory effects of nutrient shock, temperature, and bacterial competition, factors that may have previously limited CGN isolation from skin cultures. CONCLUSIONS: Our protocol will permit future functional studies on the influences of CGN on skin homeostasis and disease.

Oral delivery of IL-27 recombinant bacteria attenuates immune colitis in mice.

BACKGROUND & AIMS: Treatment of inflammatory bowel disease would benefit from specific targeting of therapeutics to the intestine. We developed a strategy for localized delivery of the immunosuppressive cytokine interleukin (IL)-27, which is synthesized actively in situ by the food-grade bacterium Lactococcus lactis (LL-IL-27), and tested its ability to reduce colitis in mice. METHODS: The 2 genes encoding mouse IL-27 were synthesized with optimal codon use for L lactis and joined with a linker; a signal sequence was added to allow for product secretion. The construct was introduced into L lactis. Colitis was induced via transfer of CD4(+)CD45RB(hi) T cells into Rag(-/-) mice to induce colitis; 7.5 weeks later, LL-IL-27 was administered to mice via gavage. Intestinal tissues were collected and analyzed. RESULTS: LL-IL-27 administration protected mice from T-cell transfer-induced enterocolitis and death. LL-IL-27 reduced disease activity scores, pathology features of large and small bowel, and levels of inflammatory cytokines in colonic tissue. LL-IL-27 also reduced the numbers of CD4(+) and IL-17(+) T cells in gut-associated lymphoid tissue. The effects of LL-IL-27 required production of IL-10 by the transferred T cells. LL-IL-27 was more effective than either LL-IL-10 or systemic administration of recombinant IL-27 in reducing colitis in mice. LL-IL-27 also reduced colitis in mice after administration of dextran sodium sulfate. CONCLUSIONS: LL-IL-27 reduces colitis in mice by increasing the production of IL-10. Mucosal delivery of LL-IL-27 could be a more effective and safer therapy for inflammatory bowel disease.

Parental dietary fat intake alters offspring microbiome and immunity.

Mechanisms underlying modern increases in prevalence of human inflammatory diseases remain unclear. The hygiene hypothesis postulates that decreased microbial exposure has, in part, driven this immune dysregulation. However, dietary fatty acids also influence immunity, partially through modulation of responses to microbes. Prior reports have described the direct effects of high-fat diets on the gut microbiome and inflammation, and some have additionally shown metabolic consequences for offspring. Our study sought to expand on these previous observations to identify the effects of parental diet on offspring immunity using mouse models to provide insights into challenging aspects of human health. To test the hypothesis that parental dietary fat consumption during gestation and lactation influences offspring immunity, we compared pups of mice fed either a Western diet (WD) fatty acid profile or a standard low-fat diet. All pups were weaned onto the control diet to specifically test the effects of early developmental fat exposure on immune development. Pups from WD breeders were not obese or diabetic, but still had worse outcomes in models of infection, autoimmunity, and allergic sensitization. They had heightened colonic inflammatory responses, with increased circulating bacterial LPS and muted systemic LPS responsiveness. These deleterious impacts of the WD were associated with alterations of the offspring gut microbiome. These results indicate that parental fat consumption can leave a "lard legacy" impacting offspring immunity and suggest inheritable microbiota may contribute to the modern patterns of human health and disease.

Mucosal adjuvant activity of cholera toxin requires Th17 cells and protects against inhalation anthrax.

Cholera toxin (CT) elicits a mucosal immune response in mice when used as a vaccine adjuvant. The mechanisms by which CT exerts its adjuvant effects are incompletely understood. We show that protection against inhalation anthrax by an irradiated spore vaccine depends on CT-mediated induction of IL-17-producing CD4 Th17 cells. Furthermore, IL-17 is involved in the induction of serum and mucosal antibody responses by CT. Th17 cells induced by CT have a unique cytokine profile compared with those induced by IL-6 and TGF-beta, and their induction by CT requires cAMP-dependent secretion of IL-1beta and beta-calcitonin gene-related peptide by dendritic cells. These findings demonstrate that Th17 cells mediate mucosal adjuvant effects of CT and identify previously unexplored pathways involved in Th17 induction that could be targeted for development of unique mucosal adjuvants.

T cell and APC dynamics in situ control the outcome of vaccination.

The factors controlling the progression of an immune response to generation of protective memory are poorly understood. We compared the in situ and ex vivo characteristics of CD8 T cells responding to different forms of the same immunogen. Immunization with live Listeria monocytogenes, irradiated L. monocytogenes (IRL), or heat-killed L. monocytogenes (HKL) induced rapid activation of CD8 T cells. However, only IRL and live L. monocytogenes inoculation induced sustained proliferation and supported memory development. Gene and protein expression analysis revealed that the three forms of immunization led to three distinct transcriptional and translational programs. Prior to cell division, CD8 T cell-dendritic cell clusters formed in the spleen after live L. monocytogenes and IRL but not after HKL immunization. Furthermore, HKL immunization induced rapid remodeling of splenic architecture, including loss of marginal zone macrophages, which resulted in impaired bacterial clearance. These results identify initial characteristics of a protective T cell response that have implications for the development of more effective vaccination strategies.

Prevention of autoimmune disease by induction of tolerance to Toll-like receptor 7.

Activation of Toll-like receptors (TLR) contributes to the initiation and maintenance of chronic inflammation in autoimmune diseases, yet repeated exposure to a TLR agonist can induce hyporesponsiveness to subsequent TLR stimulation. Here, we used a synthetic TLR7 agonist, 9-benzyl-8-hydroxy-2-(2-methoxyethoxy) adenine (SM360320, 1V136) to study TLR7 induced attenuation of inflammatory responses and its application to autoimmune diseases. Repeated low dose administration of this TLR7 agonist induced hyporesponsiveness or tolerance to TLR2, -7, and -9 activators and limited the course of neural inflammation in an experimental allergic encephalomyelitis model. The hyporesponsiveness did not depend on T or B lymphocytes, but did require bone marrow derived cells. In addition, TLR7 tolerance reduced inflammation in a passive antibody mediated arthritis model. TLR7 tolerance did not cause global immunosuppression, because susceptibility to Listeria monocytogenes infection was not altered. The mechanism of TLR7 tolerance involved the up-regulation of 2 inhibitors of TLR signaling: Interleukin 1 Receptor Associated Kinase (IRAK) M, and Src homology 2 domain-containing inositol polyphosphate phosphatase (SHIP)-1. These findings suggest that induction of TLR7 tolerance might be a new therapeutic approach to subdue inflammation in autoimmune diseases.

Frontline Science: Breast milk confers passive cellular immunity via CD8-dependent mechanisms.

Most modern research into the immune effects of breast milk has focused on the impacts of immunoglobulin or oligosaccharide content. However, immediately prior to parturition, the cell populations of breast milk become selectively enriched for CD8+ T cells of an effector memory subtype. Despite this observation that the cellular content of breast milk contains a distinct leukocyte population when compared to peripheral blood, the physiologic role of these CD8+ effector memory cells is unknown. Research encompassing animal models and humans has demonstrated that leukocytes are capable of transferring antigen-specific immunity even when lysed, dialyzed to enrich for fractions less than 10 kDa, and orally administered. Our previous work built upon these reports to elucidate several aspects of this dialyzable leukocyte extract (DLE) activity: only DLE from T effector memory CD8+ cells was capable of transferring antigen-specific immunity; the DLE activity was TCRß dependent; dendritic cells (DCs) were the cellular target of DLE; and DLE enhanced immune activity in epithelial challenge models via induction of IL-6 from DCs. Herein, we reveal that breast milk dialysate activates similar cytokine and genetic pathways as DLE taken from peripheral blood and murine spleens through TCRß- and CD8-dependent mechanisms. These findings suggest that the CD8+ memory T cells enriched in breast milk, even after potential lysis in the infant gut, may represent a mechanism for passive transfer of cellular immunity from mother to child.

Therapeutic responses to Roseomonas mucosa in atopic dermatitis may involve lipid-mediated TNF-related epithelial repair.

Dysbiosis of the skin microbiota is increasingly implicated as a contributor to the pathogenesis of atopic dermatitis (AD). We previously reported first-in-human safety and clinical activity results from topical application of the commensal skin bacterium Roseomonas mucosa for the treatment of AD in 10 adults and 5 children older than 9 years of age. Here, we examined the potential mechanism of action of R. mucosa treatment and its impact on children with AD less than 7 years of age, the most common age group for children with AD. In 15 children with AD, R. mucosa treatment was associated with amelioration of disease severity, improvement in epithelial barrier function, reduced Staphylococcus aureus burden on the skin, and a reduction in topical steroid requirements without severe adverse events. Our observed response rates to R. mucosa treatment were greater than those seen in historical placebo control groups in prior AD studies. Skin improvements and colonization by R. mucosa persisted for up to 8 months after cessation of treatment. Analyses of cellular scratch assays and the MC903 mouse model of AD suggested that production of sphingolipids by R. mucosa, cholinergic signaling, and flagellin expression may have contributed to therapeutic impact through induction of a TNFR2-mediated epithelial-to-mesenchymal transition. These results suggest that a randomized, placebo-controlled trial of R. mucosa treatment in individuals with AD is warranted and implicate commensals in the maintenance of the skin epithelial barrier.

Differing Virulence of Healthy Skin Commensals in Mouse Models of Infection.

Introduction: As therapies for atopic dermatitis (AD) based on live biotherapeutic products (LBP) are developed, the potential displacement of biotherapeutic strains, and species to mucosal sites where they are not naturally found is of investigative interest. However, formal assessment of the toxicity potential of healthy skin commensal organisms has not been reported in the literature. Our previous research indicates that topical application of live Roseomonas mucosa to treat AD was associated with clinical benefit on the skin, but the effects of exposure via inhalation, eye inoculation, and ingestion were unknown. Methods: Herein we report our findings from mice inoculated with commensal strains of R. mucosa, coagulase negative Staphylococci (CNS), and Pseudomonas aeruginosa. Bacterial isolates were collected under clinical trial NCT03018275, however these results do not represent an interventional clinical trial. Results: Our tested R. mucosa isolates did not display significant infection or inflammation. However, neutropenic mice inoculated with CNS had infection without major inflammation in pulmonary models. In contrast, systemic infection generated hepatic and splenic pathology for P. aeruginosa and CNS, which was worsened by the presence of neutropenia. Discussion: Our results suggest that LBP derived from bacteria without significant infectivity histories, such as R. mucosa, may represent safer options than known pathobionts like P. aeruginosa and Staphylococcus spp. Overall, these results suggest that topically applied LBP from select skin commensals are likely to present safe therapeutic options and reinforce our prior clinical findings.

Vaccine display on artificial bacterial spores enhances protective efficacy against Staphylococcus aureus infection.

Spores of Bacillus subtilis are encased in a protein coat composed of ∼80 different proteins. Recently, we reconstituted the basement layer of the coat, composed of two structural proteins (SpoVM and SpoIVA) around spore-sized silica beads encased in a lipid bilayer, to create synthetic spore-like particles termed 'SSHELs'. We demonstrated that SSHELs could display thousands of copies of proteins and small molecules of interest covalently linked to SpoIVA. In this study, we investigated the efficacy of SSHELs in delivering vaccines. We show that intramuscular vaccination of mice with undecorated one micron-diameter SSHELs elicited an antibody response against SpoIVA. We further demonstrate that SSHELs covalently modified with a catalytically inactivated staphylococcal alpha toxin variant (HlaH35L), without an adjuvant, resulted in improved protection against Staphylococcus aureus infection in a bacteremia model as compared to vaccination with the antigen alone. Although vaccination with either HlaH35L or HlaH35L conjugated to SSHELs similarly elicited the production of neutralizing antibodies to Hla, we found that a subset of memory T cells was differentially activated when the antigen was delivered on SSHELs. We propose that the particulate nature of SSHELs elicits a more robust immune response to the vaccine that results in superior protection against subsequent S. aureus infection.

Prolonging culture of primary human keratinocytes isolated from suction blisters with the Rho kinase inhibitor Y-27632.

Keratinocytes are the most abundant cell type in the epidermis. They prevent desiccation and provide immunological and barrier defense against potential pathogens such as Staphylococcus aureus and Candida albicans. The study of this first line of immune defense may be hindered by invasive isolation methods and/or improper culture conditions to support stem cell maintenance and other potential mechanisms contributing to long-term subcultivation in vitro. Primary keratinocytes have been successfully isolated from blister roofs induced by negative pressure, which separates the epidermis from the dermis in vivo in human subjects. This method allows collection of pure epidermal cells without dermal contamination in a minimally invasive manner. However, the isolated keratinocytes differentiate and senesce when cultured in vitro beyond five passages. Here, we present evidence that the Rho kinase (ROCK) inhibitor Y-27632 can be used to effectively increase the proliferative capabilities of keratinocytes isolated using the suction blister method, similar to what has been previously reported for primary keratinocytes isolated using alternative methods. We show that the increase in passage number is directly correlated to delayed differentiation, and that cells passaged long term with the inhibitor retain their ability to stratify in organotypic raft cultures and respond to cytokine treatment; additionally, the late passage cells have a heterogeneous mix of differentiated and non-differentiated cells which may be predicted by a ratio of select differentiation markers. The described method presents a minimally invasive procedure for keratinocyte isolation and prolonged culture that allows analysis of keratinocyte function in both healthy volunteers and patients with dermatologic diseases.