Cytokine Maturation Research Articles

Chlamydia pneumoniae is present in the dental plaque of periodontitis patients and stimulates an inflammatory response in gingival epithelial cells

Chlamydia pneumoniae is an airborne, Gram-negative, obligate intracellular bacterium which causes human respiratory infections and has been associated with atherosclerosis. Because individuals with periodontitis are at greater risk for atherosclerosis as well as respiratory infections, we in-vestigated the role of C. pneumoniae in inflammation and periodontal dis-ease. We found that C. pneumoniae was more frequently found in subgingival dental plaque obtained from periodontally diseased sites of the mouth versus healthy sites. The known periodontal pathogens, Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, were also found in the plaque. In addition, C. pneumoniae could efficiently invade human gingival epithelial cells (GECs) in vitro, causing translocation of NF-κB to the nucleus along with increased secretion of mature IL-1β cytokine. Supernatants collected from C. pneumoniae-infected GECs showed increased activation of caspase-1 protein, which was significantly reduced when nlrp3 gene expression was silenced using shRNA lentiviral vectors. Our results demonstrate that C. pneumoniae was found in higher levels in periodontitis patients compared to control pa-tients. Additionally, C. pneumoniae could infect GECs, leading to inflammation caused by activation of NF-κB and the NLRP3 inflammasome. We propose that the presence of C. pneumoniae in subgingival dental plaque may contribute to periodontal disease and could be used as a potential risk indicator of perio-dontal disease.

Structural Basis for NLRP6 Inflammasome Assembly and Activation

Inflammasomes are multi‐protein complexes that detect infectious microbes and cellular stressors, and that activate inflammatory caspases for cytokine maturation and pyroptosis. NLRP6, a sensor protein in the nucleotide‐binding domain (NBD) and leucine‐rich repeat (LRR)containing (NLR) family, is shown to play multiple roles in regulation of inflammation and other innate immune signaling pathways. However, little is known about the molecular mechanism of NLRP6 inflammasome assembly and activation. Using cryo‐Electron Microscopy (Cryo‐EM) and X‐ray crystallography, we found that NLRP6 PYD domain is able to self‐assemble into filamentous structures accompanied by large conformational changes, and can recruit the adaptor protein ASC through homotypic PYD/PYD interactions. We further observed that full‐length NLRP6 assembles into wider filaments in a concentration dependent manner with a PYD core surrounded by the NBD and LRR domain. In conclusion, our results indicate a unified filamentous assembly mode of NLRP family proteins for downstream signal transduction. These findings will be of value for researchers to conceive the structural study of full‐length NLRP inflammasomes.Support or Funding InformationThis work was supported by US National Institutes of Health grants Al124491 and HD087988 (to H.W.) and the Harvard Digestive and Disease Center Grant HDDC P30 DK034854 (to T.M.F.).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Do porcine Sertoli cells represent an opportunity for Duchenne muscular dystrophy?

Sertoli cells (SeC) are responsible for the immunoprivileged status of the testis thanks to which allogeneic or xenogeneic engraftments can survive without pharmacological immune suppression if co‐injected with SeC. This peculiar ability of SeC is dependent on secretion of a plethora of factors including maturation factors, hormones, growth factors, cytokines and immunomodulatory factors. The anti‐inflammatory and trophic properties of SeC have been largely exploited in several experimental models of diseases, diabetes being the most studied. Duchenne muscular dystrophy (DMD) is a lethal X‐linked recessive pathology in which lack of functional dystrophin leads to progressive muscle degeneration culminating in loss of locomotion and premature death. Despite a huge effort to find a cure, DMD patients are currently treated with anti‐inflammatory steroids. Recently, encapsulated porcine SeC (MC‐SeC) have been injected ip in the absence of immunosuppression in an animal model of DMD resulting in reduction of muscle inflammation and amelioration of muscle morphology and functionality, thus opening an additional avenue in the treatment of DMD. The novel protocol is endowed with the advantage of being potentially applicable to all the cohort of DMD patients regardless of the mutation. This mini‐review addresses several issues linked to the possible use of MC‐SeC injected ip in dystrophic people.

LKB1 orchestrates dendritic cell metabolic quiescence and anti-tumor immunity

Dendritic cells (DCs) play a pivotal role in priming adaptive immunity. However, the involvement of DCs in controlling excessive and deleterious T cell responses remains poorly defined. Moreover, the metabolic dependence and regulation of DC function are unclear. Here we show that LKB1 signaling in DCs functions as a brake to restrain excessive tumor-promoting regulatory T cell (Treg) and Th17 cell responses, thereby promoting protective anti-tumor immunity and maintaining proper immune homeostasis. LKB1 deficiency results in dysregulated metabolism and mTOR activation of DCs. Loss of LKB1 also leads to aberrant DC maturation and production of cytokines and immunoregulatory molecules. Blocking mTOR signaling in LKB1-deficient DCspartially rectifies the abnormal phenotypes of DC activation and Treg expansion, whereas uncontrolled Th17 responses depend upon IL-6-STAT3 signaling. By coordinating metabolic and immune quiescence of DCs, LKB1 acts as a crucial signaling hub in DCs to enforce protective anti-tumor immunity and normal immune homeostasis.

Identification of the IL-33 protein segment that controls subcellular localization, extracellular secretion, and functional maturation

Proteolytic activation of the IL-33 precursor, full-length interleukin-33 (FLIL33), at multiple sites within the sensor domain (aa 95–109) yields several functionally mature (MIL33) forms. Unlike nuclear FLIL33, intracellular MIL33 occurs in the cytoplasm, is secreted from source cells, and exerts biological effects by activating the ST2 receptor on target cells. Previous studies and our findings in this report indicated that IL-33 forms that are substantially longer than those produced by cleavage within the sensor domain are biologically indistinguishable from classical MIL33. We utilized a series of human and mouse N-terminal FLIL33 mutants to narrow down the boundaries of the nuclear localization sequence to aa 46–67, a segment known to include a portion of the chromatin-binding motif as well as another site controlling intracellular stability of FLIL33 in an importin-5-dependent fashion. The N-terminal FLIL33 deletion mutants starting prior to this region were intranuclear, non-secreted in cell culture, and manifested modest functional activity in vivo, similar to FLIL33. By contrast, the mutants starting after this region were cytoplasmic, secreted from cells in culture, and overtly biologically active in vivo, similar to MIL33. The deletion mutants starting within this region manifested an intermediate phenotype between FLIL33 and MIL33. Thus, this segment of IL-33 molecule controls multiple aspects of its biology, including subcellular localization, extracellular secretion, and functional maturation into the longest possible form of mature IL-33 cytokine. Future anti-IL-33 therapies may be based on interfering with this segment, thus restraining extracellular release and maturation of IL-33 into the active cytokine.

Tetramethylpyrazine ameliorates depression by inhibiting TLR4-NLRP3 inflammasome signal pathway in mice.

Depression is a common but serious mental illness; meanwhile, it is also an inflammatory disorder. Toll-like receptor 4 (TLR4), as the pattern recognition receptor, has been shown to play a vital role in neuroinflammation. The nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome acts as an important signaling molecule downstream of TLR4 and can promote the maturation of inflammatory cytokines, such as interleukin-1β (IL-1β). Tetramethylpyrazine (TMP) is a natural compound with neuroprotective effects but with unknown mechanisms on its antidepressant-like effect. In this study, we hypothesized that TMP ameliorates depression may be through the inhibition of the TLR4-NF-κB-NLRP3 signal pathway. Our results have shown that chronic unpredictable mild stress (CUMS) that induced the decreased sucrose preference and increased immobile time was prominently reversed by TMP and fluoxetine. Additionally, we also found that CUMS induced the upregulation of proinflammatory cytokines; TLR4 and NLRP3-associated proteins were significantly suppressed by TMP in the prefrontal cortex and hippocampus. TMP also exhibited potent antioxidant effects and increased the monoamine levels in the serum and brain, such as increasing the activity of SOD and GSH-Px, and reducing the activity of MDA in the serum, and elevating the 5-HT and NE concentration in the serum and brain. Moreover, treatment with Cli-095 (TLR4 inhibitor) also markedly inhibited CUMS-induced depression-like behaviors. Taken together, our findings suggested that TMP exerted a potential antidepressant-like effect in CUMS mice, and the molecular mechanisms may relate to inhibit the TLR4-NF-κB-NLRP3 signaling pathway in the brain.

Beta2-Integrins and Interacting Proteins in Leukocyte Trafficking, Immune Suppression, and Immunodeficiency Disease.

Beta2-integrins are complex leukocyte-specific adhesion molecules that are essential for leukocyte (e.g., neutrophil, lymphocyte) trafficking, as well as for other immunological processes such as neutrophil phagocytosis and ROS production, and T cell activation. Intriguingly, however, they have also been found to negatively regulate cytokine responses, maturation, and migratory responses in myeloid cells such as macrophages and dendritic cells, revealing new, and unexpected roles of these molecules in immunity. Because of their essential role in leukocyte function, a lack of expression or function of beta2-integrins causes rare immunodeficiency syndromes, Leukocyte adhesion deficiency type I, and type III (LAD-I and LAD-III). LAD-I is caused by reduced or lost expression of beta2-integrins, whilst in LAD-III, beta2-integrins are expressed but dysfunctional because a major integrin cytoplasmic regulator, kindlin-3, is mutated. Interestingly, some LAD-related phenotypes such as periodontitis have recently been shown to be due to an uncontrolled inflammatory response rather than to an uncontrolled infection, as was previously thought. This review will focus on the recent advances concerning the regulation and functions of beta2-integrins in leukocyte trafficking, immune suppression, and immune deficiency disease.

FimH as a mucosal adjuvant enhances persistent antibody response and protective efficacy of the anti-caries vaccine

ObjectiveTo investigate whether the recombinant FimH-S.T protein could modulate immune response to anti-caries vaccine in vitro and in vivo. DesignRecombinant FimH protein derived from Salmonella was constructed and purified. The expression of dendritic cell maturation markers and cytokines release were performed by flow cytometry, Real-time PCR and ELISA. In addition, BALB/c mice were administered with anti-caries PAc vaccine plus FimH-S.T, antibody responses were evaluated by ELISA. Splenocytes of immunized mice were detected for their proliferative ability in response to in vitro retreatment with PAc antigen by flow cytometry. Caries protection against dental caries formation was also investigated. ResultsThe purified FimH-S.T induced phenotypic maturation of DC2.4 by up-regulating the expression of costimulatory molecules and MHC II, provoked the production and secretion of cytokines via TLR4-dependent signaling pathway in vitro. Furthermore, the mice immunized with the mixture of FimH-S.T and PAc significantly enhanced the PAc-specific antibodies in the serum along with saliva and promoted splenocyte proliferation. Our results also confirmed that PAc+FimH-S.T decreased the caries lesions formation which provided high protective efficacy against dental caries. ConclusionOur study demonstrates that recombinant FimH-S.T could enhance specific IgA responses and protection of anti-caries vaccine, possessing mucosal adjuvant ability by activating DC2.4 via TLR4 signaling pathway.

Tumors and Their Microenvironment Dual-Targeting Chemotherapy with Local Immune Adjuvant Therapy for Effective Antitumor Immunity against Breast Cancer.

Chemotherapy turns tumor cells into “tumor vaccines” by immunogenic cell death (ICD). However, it remains a challenge to exploit chemotherapy‐induced “tumor vaccines” for solid cancer immunotherapy due to the inefficient effector T cells activation and tumor microenvironment immunosuppression. Here, a matrix metalloprotease 2 responsive liposome (PEG‐FA‐Lip) composed of cleavable PEG chains covering the folate (FA)‐modified liposome is developed to deliver ICD inducer doxorubicin. In breast cancer‐bearing mice, PEG‐FA‐Lip targets both 4T1 breast cancer cells and M2‐tumor associated macrophages (M2‐TAMs) via FA‐receptor mediated endocytosis, resulting in abundant “tumor vaccines” and efficient elimination of M2‐TAMs. The combination of local cytosine‐phosphate‐guanine (CpG) therapy facilitates PEG‐FA‐Lip induced “tumor vaccines” to effectively arouse systematic effector T cells immune response through promoting dendritic cell maturation and immunostimulatory cytokines secretion. The simultaneous elimination of M2‐TAMs ensures the activated effector T cells exert antitumor immunity within tumor via decreasing immunosuppressive cytokines secretion and tumor infiltration of Treg cells. After receiving the combined treatment, 30.1% of breast cancer‐bearing mice (initial tumor volume > 100 mm3) achieves the goal of tumor eradication. Remarkably, this combination therapy greatly inhibits lung metastasis and controls the growth of already metastasized breast cancers (initial tumor volume > 100 mm3).

Bioimmunological activities of Candida glabrata cellular mannan.

Candida glabrata is a second most common human opportunistic pathogen which causes superficial but also life-threatening systemic candidosis. According to the localisation of mannans and mannoproteins in the outermost layer of the cell wall, mannan detection could be one of the first steps in the cell recognition of Candida cells by the host innate immune system. Mannans from the cell wall provide important immunomodulatory activities, comprising stimulation of cytokine production, induction of dendritic cells (DCs) maturation and T-cell immunity. The model of DCs represents a promising tool to study immunomodulatory interventions throughout the vaccine development. Activated DCs induce, activate and polarise T-cell responses by expression of distinct maturation markers and cytokines regulating the adaptive immune responses. In addition, they are uniquely adept at decoding the fungus-associated information and translate it in qualitatively different T helper responses. We find out, that C. glabrata mannan is able to induce proliferation of splenocytes and to increase the production of TNF-α and IL-4. Next, increased the expression of co-stimulatory molecules CD80 and CD86 and the proportion of CD4+CD25+ and CD4+CD28+ T cells during in vitro stimulation of splenocytes. Reported results provide C. glabrata mannan capability to modulate cytokine production, DCs activation and antigen presentation activity, influencing T-cell phenotype in response to stimulation.

Molecular mechanism for NLRP6 inflammasome assembly and activation

Inflammasomes are large protein complexes that trigger host defense in cells by activating inflammatory caspases for cytokine maturation and pyroptosis. NLRP6 is a sensor protein in the nucleotide-binding domain (NBD) and leucine-rich repeat (LRR)-containing (NLR) inflammasome family that has been shown to play multiple roles in regulating inflammation and host defenses. Despite the significance of the NLRP6 inflammasome, little is known about the molecular mechanism behind its assembly and activation. Here we present cryo-EM and crystal structures of NLRP6 pyrin domain (PYD). We show that NLRP6 PYD alone is able to self-assemble into filamentous structures accompanied by large conformational changes and can recruit the ASC adaptor using PYD-PYD interactions. Using molecular dynamics simulations, we identify the surface that the NLRP6 PYD filament uses to recruit ASC PYD. We further find that full-length NLRP6 assembles in a concentration-dependent manner into wider filaments with a PYD core surrounded by the NBD and the LRR domain. These findings provide a structural understanding of inflammasome assembly by NLRP6 and other members of the NLR family.

Application of immobilized ATP to the study of NLRP inflammasomes

The NLRP proteins are a subfamily of the NOD-like receptor (NLR) innate immune sensors that possess an ATP-binding NACHT domain. As the most well studied member, NLRP3 can initiate the assembly process of a multiprotein complex, termed the inflammasome, upon detection of a wide range of microbial products and endogenous danger signals and results in the activation of pro-caspase-1, a cysteine protease that regulates multiple host defense pathways including cytokine maturation. Dysregulated NLRP3 activation contributes to inflammation and the pathogenesis of several chronic diseases, and the ATP-binding properties of NLRPs are thought to be critical for inflammasome activation. In light of this, we examined the utility of immobilized ATP matrices in the study of NLRP inflammasomes. Using NLRP3 as the prototypical member of the family, P-linked ATP Sepharose was determined to be a highly-effective capture agent. In subsequent examinations, P-linked ATP Sepharose was used as an enrichment tool to enable the effective profiling of NLRP3-biomarker signatures with selected reaction monitoring-mass spectrometry (SRM-MS). Finally, ATP Sepharose was used in combination with a fluorescence-linked enzyme chemoproteomic strategy (FLECS) screen to identify potential competitive inhibitors of NLRP3. The identification of a novel benzo[d]imidazol-2-one inhibitor that specifically targets the ATP-binding and hydrolysis properties of the NLRP3 protein implies that ATP Sepharose and FLECS could be applied other NLRPs as well.

AIM2 Inflammasome Assembly and Signaling.

AIM2 (absent in melanoma 2) is a cytoplasmic sensor of double-stranded DNA from pathogens or damaged cellular organelles. It recruits ASC (apoptosis-associated specklike protein containing a CARD) and caspase-1 to form the AIM2 inflammasome, activate caspase-1, and elicit inflammatory responses via cytokine maturation and pyroptotic cell death. Structural studies from X-ray crystallography, NMR, and cryo-EM have revealed many details in AIM2 inflammasome activation, assembly, and regulation. Many principles learned from AIM2 inflammasome also apply to other inflammasomes. In this chapter, we discuss the interactions between dsDNA and AIM2-like receptors, between AIM2 and adaptor protein ASC, and between ASC and caspase-1 with the focus on helical filament assembly formed by PYD and CARD domains.

RORγ regulates the NLRP3 inflammasome

RAR-related orphan receptor γ (RORγ) is a nuclear receptor that plays an essential role in the development of T helper 17 (Th17) cells of the adaptive immune system. The NLRP3 inflammasome is a component of the innate immune system that processes interleukin (IL)-1β into a mature cytokine. Elevated activity of the NLRP3 inflammasome contributes to the progression of an array of inflammatory diseases. Bone marrow-derived macrophages (BMDMs) isolated from RORγ-null mice displayed reduced capacity to secrete IL-1β, and they also displayed a reduction in Nlrp3 and Il1b gene expression. Examination of the promoters of the Il1b and Nlrp3 genes revealed multiple putative ROR response elements (ROREs) that were occupied by RORγ. RORγ inverse agonists were effective inhibitors of the inflammasome. RORγ inverse agonists suppressed lipopolysaccharide (LPS)/ATP-stimulated IL-1β secretion and expression of Il1b and Nlrp3 in BMDMs. Additionally, the ability of the RORγ inverse agonists to suppress IL-1β secretion was lost in Nlrp3-null macrophages. The potential for targeting the NLRP3 inflammasome in vivo using RORγ inverse agonists was examined in two models: LPS-induced sepsis and fulminant hepatitis. Pharmacological inhibition of RORγ activity reduced plasma IL-1β as well as IL-1β production by peritoneal macrophages in a model of LPS-induced sepsis. Additionally, RORγ inverse agonists reduced mortality in an LPS/d-galactosamine-induced fulminant hepatitis mouse model. These results illustrate a major role for RORγ in regulation of innate immunity via modulation of NLRP3 inflammasome activity. Furthermore, these data suggest that inhibiting the NLRP3 inflammasome with RORγ inverse agonists may be an effective method to treat NLRP3-associated diseases.

Role of Inflammasome in Chronic Kidney Disease.

The inflammasome is a multiprotein complex assembled by intracytoplasmic pattern recognition receptors and is a key component of the innate immune system for host defense. Inflammasome recruits and activates the proinflammatory protease caspase-1 by recognizing pathogen-associated molecular patterns (PAMPs) or host-derived damage-associated molecular patterns (DAMPs). Activated caspase-1 cleaves the precursors of IL-1β and IL-18 to produce the corresponding mature cytokines. Several types of inflammasomes have been identified, such as NLRP3, NLRP1, IPAF (NLRC4) and AIM2. NLRP3 has recently been reported as a central pathogenic mechanism of chronic kidney disease (CKD). In this chapter, we briefly summarize the current knowledge about the roles of inflammasomes in the pathogenesis of CKD. A better understanding of the function of inflammasomes will provide unexpected opportunities to develop new therapies for kidney diseases by modulation of the innate immune system.

Mechanisms of Inflammasome Signaling, microRNA Induction and Resolution of Inflammation by Helicobacter pylori.

Inflammasome-controlled transcription and subsequent cleavage-mediated activation of mature IL-1β and IL-18 cytokines exemplify a crucial innate immune mechanism to combat intruding pathogens. Helicobacter pylori represents a predominant persistent infection in humans, affecting approximately half of the population worldwide, and is associated with the development of chronic gastritis, peptic ulcer disease, and gastric cancer. Studies in knockout mice have demonstrated that the pro-inflammatory cytokine IL-1β plays a central role in gastric tumorigenesis. Infection by H. pylori was recently reported to stimulate the inflammasome both in cells of the mouse and human immune systems. Using mouse models and in vitro cultured cell systems, the bacterial pathogenicity factors and molecular mechanisms of inflammasome activation have been analyzed. On the one hand, it appears that H. pylori-stimulated IL-1β production is triggered by engagement of the immune receptors TLR2 and NLRP3, and caspase-1. On the other hand, microRNA hsa-miR-223-3p is induced by the bacteria, which controls the expression of NLRP3. This regulating effect by H. pylori on microRNA expression was also described for more than 60 additionally identified microRNAs, indicating a prominent role for inflammatory and other responses. Besides TLR2, TLR9 becomes activated by H. pylori DNA and further TLR10 stimulated by the bacteria induce the secretion of IL-8 and TNF, respectively. Interestingly, TLR-dependent pathways can accelerate both pro- and anti-inflammatory responses during H. pylori infection. Balancing from a pro-inflammation to anti-inflammation phenotype results in a reduction in immune attack, allowing H. pylori to persistently colonize and to survive in the gastric niche. In this chapter, we will pinpoint the role of H. pylori in TLR- and NLRP3 inflammasome-dependent signaling together with the differential functions of pro- and anti-inflammatory cytokines. Moreover, the impact of microRNAs on H. pylori-host interaction will be discussed, and its role in resolution of infection versus chronic infection, as well as in gastric disease development.

Maturation of dendritic cells by maitake α-glucan enhances anti-cancer effect of dendritic cell vaccination

Dendritic cells (DCs) play a primary role in antigen presentation to CD4+ and CD8+ T cells and induce acquired immune response against cancer cells. Therefore, determining positive modulators of DC activation to improve therapeutic approaches for cancer immunotherapy is greatly needed. In this study, we investigated the effect of maitake α-glucan YM-2A, isolated from Grifola frondosa, on the maturation and function of DCs and its adjuvant effect on a tumor-associated antigen (TAA)-loaded DC vaccine against murine tumor. We showed that YM-2A induced morphological changes and increased cell-surface maturation markers and cytokine production in DCs. In a mixed lymphocyte reactions assay, YM-2A-treated DCs increased proliferation and production of IFN-γ by allogeneic CD4+ and CD8+ T cells. These results indicate that YM-2A phenotypically and functionally activates DCs. Furthermore, YM-2A-treated TAA-loaded DC vaccine significantly reduced tumor growth and improved survival in two murine tumor models, CT-26 tumor-bearing BALB/c mice and B16 melanoma-bearing C57BL/6 mice. YM-2A-treated TAA-loaded DC vaccine increased splenic IFN-γ producing CD4+ and CD8+ T cells in CT-26 tumor-bearing BALB/c mice. Antibody neutralization studies indicated that YM-2A-induced DC maturation is mediated, in part, by the Dectin-1-dependent pathway. Overall, YM-2A-treatment with a TAA-loaded DC vaccine could be an excellent candidate for immunotherapy against cancer.

CASP4 gene silencing in epithelial cancer cells leads to impairment of cell migration, cell-matrix adhesion and tissue invasion

Inflammatory caspases, including human caspase-4 (CASP4), play key roles in innate immune responses to promote fusion of phagosomes harboring pathogenic bacteria with lysosomes, halt intracellular replication of pathogens, maturation and secretion of pro-inflammatory cytokines. The role of inflammatory caspases in cancer cells remains poorly investigated. Here, we explored the consequences of modulating CASP4 expression levels on the migratory behavior of epithelial cancer cell lines. By a gene silencing approach and in vitro and in vivo studies we show that down-regulation of CASP4 leads to impaired cell migration and cell-matrix adhesion. This phenotype is accompanied by an increased actin cytoskeleton polymerization, changes in the overall organization of adherens junctions (AJs) and number and size of focal adhesions. Interestingly, the cell migration deficit could be reversed by epithelial growth factor treatment, and depletion of calcium ions unveiled a role of CASP4 in the novo assembly of AJs, suggesting that the role of CASP4 is not cell-autonomous. Finally, CASP4-silenced A431 cells exhibited a severe reduction in their ability to invade lung tissue, when injected into nude mice. Overall, our data support the emerging evidence that inflammatory caspases can regulate cell migration through actin remodeling and uncover a novel role of CASP4 in cancer cell behavior.

Caspase-8 is a player in pyroptosis

Immunology The activation of certain pattern-recognition receptors by pathogen-associated molecular patterns results in the formation of inflammasome complexes. Inflammasome complexes can initiate both the maturation of inflammatory cytokines and pyroptotic cell death via the caspase-mediated cleavage of gasdermin D (GSDMD). As of now, the only known regulators of GSDMD in macrophages are caspase-1 and caspase-11. Orning et al. report an additional pathway controlling GSDMD processing. YopJ, an effector molecule produced by Yersinia (the causative agent of plague), inhibits TAK1–IκB kinase signaling. This, in turn, results in caspase-8–directed cleavage of GSDMD, pyroptosis, and the release of interleukin 1β (IL-1β) and IL-18. Thus, in the arms race between host and pathogen, the host recognizes signaling disturbances as pathogenic and counters with inflammation and cell death. Science , this issue p. [1064][1] [1]: /lookup/doi/10.1126/science.aau2818

Staphylococcus aureus PSM Peptides Modulate Human Monocyte-Derived Dendritic Cells to Prime Regulatory T Cells.

Staphylococcus aureus (Sa), as one of the major human pathogens, has very effective strategies to subvert the human immune system. Virulence of the emerging community-associated methicillin-resistant Sa (CA-MRSA) depends on the secretion of phenol-soluble modulin (PSM) peptide toxins e.g., by binding to and modulation of innate immune cells. Previously, by using mouse bone marrow-derived dendritic cells we demonstrated that PSMs in combination with various Toll-like receptor (TLR) ligands induce a tolerogenic DC phenotype (tDC) characterized by the production of IL-10 and impaired secretion of pro-inflammatory cytokines. Consequently, PSM-induced tDCs favored priming of CD4+CD25+FoxP3+ Tregs with suppressor function while impairing the Th1 response. However, the relevance of these findings for the human system remained elusive. Here, we analyzed the impact of PSMα3 on the maturation, cytokine production, antigen uptake, and T cell stimulatory capacity of human monocyte-derived DCs (moDCs) treated simultaneously with either LPS (TLR4 ligand) or Sa cell lysate (TLR2 ligand). Herein, we demonstrate that PSMs indeed modulate human moDCs upon treatment with TLR2/4 ligands via multiple mechanisms, such as transient pore formation, impaired DC maturation, inhibited pro- and anti-inflammatory cytokine secretion, as well as reduced antigen uptake. As a result, the adaptive immune response was altered shown by an increased differentiation of naïve and even CD4+ T cells from patients with Th1/Th17-induced diseases (spondyloarthritis and rheumatoid arthritis) into CD4+CD127−CD25hiCD45RA−FoxP3hi regulatory T cells (Tregs) with suppressor function. This Treg induction was mediated most predominantly by direct DC-T-cell interaction. Thus, PSMs from highly virulent Sa strains affect DC functions not only in the mouse, but also in the human system, thereby modulating the adaptive immune response and probably increasing the tolerance toward the bacteria. Moreover, PSMα3 might be a novel peptide for tolerogenic DC induction that may be used for DC vaccination strategies.