Yin and Yang of Biofilm Formation and Cyclic di-GMP Signaling of the Gastrointestinal Pathogen Salmonella enterica Serovar Typhimurium

Within the last 60 years, microbiological research has challenged many dogmas such as bacteria being unicellular microorganisms directed by nutrient sources; these investigations produced new dogmas such as cyclic diguanylate monophosphate (cyclic di-GMP) second messenger signaling as a ubiquitous regulator of the fundamental sessility/motility lifestyle switch on the single-cell level. Successive investigations have not yet challenged this view; however, the complexity of cyclic di-GMP as an intracellular bacterial signal, and, less explored, as an extracellular signaling molecule in combination with the conformational flexibility of the molecule, provides endless opportunities for cross-kingdom interactions. Cyclic di-GMP-directed microbial biofilms commonly stimulate the immune system on a lower level, whereas host-sensed cyclic di-GMP broadly stimulates the innate and adaptive immune responses. Furthermore, while the intracellular second messenger cyclic di-GMP signaling promotes bacterial biofilm formation and chronic infections, oppositely, Salmonella Typhimurium cellulose biofilm inside immune cells is not endorsed. These observations only touch on the complexity of the interaction of biofilm microbial cells with its host. In this review, we describe the Yin and Yang interactive concepts of biofilm formation and cyclic di-GMP signaling using S. Typhimurium as an example.     

Primary Role for Toll-Like Receptor-Driven Tumor Necrosis Factor Rather than Cytosolic Immune Detection in Restricting Coxiella burnetii Phase II Replication within Mouse Macrophages

Coxiella burnetii replicates within permissive host cells by employing a Dot/Icm type IV secretion system (T4SS) to translocate effector proteins that direct the formation of a parasitophorous vacuole. C57BL/6 mouse macrophages restrict the intracellular replication of the C. burnetii Nine Mile phase II (NMII) strain. However, eliminating Toll-like receptor 2 (TLR2) permits bacterial replication, indicating that the restriction of bacterial replication is immune mediated. Here, we examined whether additional innate immune pathways are employed by C57BL/6 macrophages to sense and restrict NMII replication. In addition to the known role of TLR2 in detecting and restricting NMII infection, we found that TLR4 also contributes to cytokine responses but is not required to restrict bacterial replication. Furthermore, the TLR signaling adaptors MyD88 and Trif are required for cytokine responses and restricting bacterial replication. The C. burnetii NMII T4SS translocates bacterial products into C57BL/6 macrophages. However, there was little evidence of cytosolic immune sensing of NMII, as there was a lack of inflammasome activation, T4SS-dependent cytokine responses, and robust type I interferon (IFN) production, and these pathways were not required to restrict bacterial replication. Instead, endogenous tumor necrosis factor (TNF) produced upon TLR sensing of C. burnetii NMII was required to control bacterial replication. Therefore, our findings indicate a primary role for TNF produced upon immune detection of C. burnetii NMII by TLRs, rather than cytosolic PRRs, in enabling C57BL/6 macrophages to restrict bacterial replication.     

泛素系统在结核分枝杆菌与宿主相互作用中的调控机制研究进展

结核分枝杆菌(Mycobacterium tuberculosis,Mtb)是一种极其成功的胞内病原菌,可通过多种策略实现免疫逃逸,从而在宿主巨噬细胞中长期存活。在对抗病原菌的防御过程中,泛素系统(Ubiquitin system)在激活宿主炎症免疫反应、细胞自噬、吞噬体成熟和细胞死亡等天然免疫功能及相关信号通路中发挥了重要的调控作用。而另一方面,近年的研究表明Mtb 等胞内病原菌可通过分泌效应蛋白(Effector proteins)挟持并利用宿主泛素系统进而抑制宿主的免疫功能,这些病原-宿主互作的界面有望成为抗结核药物研发的新靶点。     

Immunity to bacterial infection in the chicken

Bacterial infections remain important to the poultry industry both in terms of animal and public health, the latter due to the importance of poultry as a source of foodborne bacterial zoonoses such as Salmonella and Campylobacter. As such, much focus of research to the immune response to bacterial infection has been to Salmonella. In this review we will focus on how research on avian salmonellosis has developed our understanding of immunity to bacteria in the chicken from understanding the role of TLRs in recognition of bacterial pathogens, through the role of heterophils, macrophages and γδ lymphocytes in innate immunity and activation of adaptive responses to the role of cellular and humoral immunity in immune clearance and protection. What is known of the immune response to other bacterial infections and in particular infections that have emerged recently as major problems in poultry production including Campylobacter jejuni, Avian Pathogenic Escherichia coli, Ornithobacterium rhinotracheale and Clostridium perfringens are discussed.     

Flagellin from Recombinant Attenuated Salmonella enterica Serovar Typhimurium Reveals a Fundamental Role in Chicken Innate Immunity

Recombinant attenuated Salmonella vaccines have been extensively studied, with a focus on eliciting specific immune responses against foreign antigens. However, very little is known about the innate immune responses, particularly the role of flagellin, in the induction of innate immunity triggered by recombinant attenuated Salmonella in chickens. In the present report, we describe two Salmonella enterica serovar Typhimurium vaccine strains, wild-type (WT) or flagellin-deficient (flhD) Salmonella, both expressing the fusion protein (F) gene of Newcastle disease virus. We examined the bacterial load and spatiotemporal kinetics of expression of inflammatory cytokine, chemokine, and Toll-like receptor 5 (TLR5) genes in the cecum, spleen, liver, and heterophils following oral immunization of chickens with the two Salmonella strains. The flhD mutant exhibited an enhanced ability to establish systemic infection compared to the WT. In contrast, the WT strain induced higher levels of interleukin-1β (IL-1β), CXCLi2, and TLR5 mRNAs in cecum, the spleen, and the heterophils than the flhD mutant at different times postinfection. Collectively, the present data reveal a fundamental role of flagellin in the innate immune responses induced by recombinant attenuated Salmonella vaccines in chickens that should be considered for the rational design of novel vaccines for poultry.     

TLR signaling in B-cell development and activation

Expression of Toll-like receptors (TLRs) in B cells provides a cell-intrinsic mechanism for innate signals regulating adaptive immune responses. In combination with other signaling pathways in B cells, including through the B-cell receptor (BCR), TLR signaling plays multiple roles in B-cell differentiation and activation. The outcome of TLR signaling in B cells is largely context-dependent, which partly explains discrepancies among in vitro and in vivo studies, or studies using different immunogens. We focus on recent findings on how B-cell-intrinsic TLR signaling regulates antibody responses, including germinal center formation and autoantibody production in autoimmune disease models. In addition, TLR signaling also acts on the precursors of B cells, which could influence the immune response of animals by shaping the composition of the immune system. With TLR signaling modulating immune responses at these different levels, much more needs to be understood before we can depict the complete functions of innate signaling in host defense.     

Bacterial TIR-containing proteins and host innate immune system evasion

The innate immune system provides the first line of host defence against invading pathogens. Key to upregulation of the innate immune response are Toll-like receptors (TLRs), which recognize pathogen-associated molecular patterns (PAMPs) and trigger a signaling pathway culminating in the production of inflammatory mediators. Central to this TLR signaling pathway are heterotypic protein–protein interactions mediated through Toll/interleukin-1 receptor (TIR) domains found in both the cytoplasmic regions of TLRs and adaptor proteins. Pathogenic bacteria have developed a range of ingenuous strategies to evade the host immune mechanisms. Recent work has identified a potentially novel evasion mechanism involving bacterial TIR domain proteins. Such domains have been identified in a wide range of pathogenic bacteria, and there is evidence to suggest that they interfere directly with the TLR signaling pathway and thus inhibit the activation of NF-κB. The individual TIR domains from the pathogenic bacteria Salmonella enterica serovar Enteritidis, Brucella sp, uropathogenic E. coli and Yersinia pestis have been analyzed in detail. The individual bacterial TIR domains from these pathogenic bacteria seem to differ in their modes of action and their roles in virulence. Here, we review the current state of knowledge on the possible roles and mechanisms of action of the bacterial TIR domains.     

Coinfection with an Intestinal Helminth Impairs Host Innate Immunity against Salmonella enterica Serovar Typhimurium and Exacerbates Intestinal Inflammation in Mice

Salmonella enterica serovar Typhimurium is a Gram-negative food-borne pathogen that is a major cause of acute gastroenteritis in humans. The ability of the host to control such bacterial pathogens may be influenced by host immune status and by concurrent infections. Helminth parasites are of particular interest in this context because of their ability to modulate host immune responses and because their geographic distribution coincides with those parts of the world where infectious gastroenteritis is most problematic. To test the hypothesis that helminth infection may negatively regulate host mucosal innate immunity against bacterial enteropathogens, a murine coinfection model was established by using the intestinal nematode Heligmosomoides polygyrus and S. Typhimurium. We found that mice coinfected with S. Typhimurium and H. polygyrus developed more severe intestinal inflammation than animals infected with S. Typhimurium alone. The enhanced susceptibility to Salmonella-induced intestinal injury in coinfected mice was found to be associated with diminished neutrophil recruitment to the site of bacterial infection that correlated with decreased expression of the chemoattractants CXCL2/macrophage inflammatory protein 2 (MIP-2) and CXCL1/keratinocyte-derived chemokine (KC), poor control of bacterial replication, and exacerbated intestinal inflammation. The mechanism of helminth-induced inhibition of MIP-2 and KC expression involved interleukin-10 (IL-10) and, to a lesser extent, IL-4 and IL-13. Ly6G antibody-mediated depletion of neutrophils reproduced the adverse effects of H. polygyrus on Salmonella infection. Our results suggest that impaired neutrophil recruitment is an important contributor to the enhanced severity of Salmonella enterocolitis associated with helminth coinfection.     

The Potassium Transporter Trk and External Potassium Modulate Salmonella enterica Protein Secretion and Virulence

Potassium (K⁺) is the most abundant intracellular cation and is essential for many physiological functions of all living organisms; however, its role in the pathogenesis of human pathogens is not well understood. In this study, we characterized the functions of the bacterial Trk K⁺ transport system and external K⁺ in the pathogenesis of Salmonella enterica, a major food-borne bacterial pathogen. Here we report that Trk is important for Salmonella to invade and grow inside epithelial cells. It is also necessary for the full virulence of Salmonella in an animal infection model. Analysis of proteins of Salmonella indicated that Trk is involved in the expression and secretion of effector proteins of the type III secretion system (TTSS) encoded by Salmonella pathogenicity island 1 (SPI1) that were previously shown to be necessary for Salmonella invasion. In addition to the role of the Trk transporter in the pathogenesis of Salmonella, we discovered that external K⁺ modulates the pathogenic properties of Salmonella by increasing the expression and secretion of effector proteins of the SPI1-encoded TTSS and by enhancing epithelial cell invasion. Our studies demonstrated that K⁺ is actively involved in the pathogenesis of Salmonella and indicated that Salmonella may take advantage of the high K⁺ content inside host cells and in the intestinal fluid during diarrhea to become more virulent.     

Immunity to intestinal pathogens: lessons learned from Salmonella

Salmonella are a common source of food- or water-borne infection and cause a wide range of clinical disease in human and animal hosts. Salmonella are relatively easy to culture and manipulate in a laboratory setting, and the infection of laboratory animals induces robust innate and adaptive immune responses. Thus, immunologists have frequently turned to Salmonella infection models to expand understanding of host immunity to intestinal pathogens. In this review, I summarize current knowledge of innate and adaptive immunity to Salmonella and highlight features of this response that have emerged from recent studies. These include the heterogeneity of the antigen-specific T-cell response to intestinal infection, the prominence of microbial mechanisms to impede T- and B-cell responses, and the contribution of non-cognate pathways for elicitation of T-cell effector functions. Together, these different issues challenge an overly simplistic view of host–pathogen interaction during mucosal infection, but also allow deeper insight into the real-world dynamic of protective immunity to intestinal pathogens.     

Conserved type III secretion system exerts important roles in Chlamydia trachomatis

Upon infection, Chlamydiae alter host cellular functions in a variety of ways. Chlamydial infection prevents host cell apoptosis, induces re-organization of the actin cytoskeleton and alters host cellular signaling mechanisms. Chlamydia is among the many pathogenic Gram-negative bacteria that employ the type III secretion system (T3SS) to overcome host defenses and exploit available resources. T3SS are used by many Gram-negative bacterial pathogens to manipulate eukaryotic host cells through the delivery of effector proteins into their cytosol and membranes. T3SS is an evolutionarily refined, virulence determinant of Gram-negative bacteria where more than 20 proteins form an apparatus, generally termed injectisome, to achieve the vectorial secretion and translocation of anti-host effector proteins. This review describes challenges and recent advances that have revealed how Chlamydia trachomatis utilizes diversification to produce a conserved T3SS that exerts an important role in Chlamydia trachomatis.     

A glance at Listeria and Salmonella cell invasion: different strategies to promote host actin polymerization

The facultative intracellular bacterial pathogens Listeria monocytogenes and Salmonella enterica have evolved multiple strategies to invade a large panel of mammalian cells. These pathogens use the host cell actin system for invasion and became a paradigm for the study of host-pathogen interactions and bacterial adaptation to mammalian hosts. The key signaling component that these pathogens use to orchestrate actin remodeling is the Arp2/3 complex, which is related to polymerization of actin filaments. These bacterial pathogens are able to trigger distinct invasion mechanisms. On the one hand, L. monocytogenes invade a host cell in a way dependent on the specific interactions between bacterial and host cell proteins, which in turn activate the host cell actin polymerizing machinery that culminates with bacterial internalization. Also, Listeria escapes from the newly formed parasitophorous vacuole and moves among adjacent cells by triggering actin polymerization. On the other hand, Salmonella invades a host cell by delivering into the cytoplasm virulence factors which directly interact with host regulators of actin polymerization which leads to bacterial uptake. Moreover, Salmonella avoids vacuole lyses and modulates the early and late endosomal markers presented in the vacuole membrane. This mini-review focuses on the different pathways that L. monocytogenes and S. enterica activate to modulate the actin cytoskeleton in order to invade, to form the parasitophorous vacuole, and to migrate inside host cells.     

Decreased potency of the Vibrio cholerae sheathed flagellum to trigger host innate immunity

Vibrio cholerae is a monoflagellated gram-negative bacterium that causes the severe diarrheal disease cholera. In contrast to Salmonella enterica serovar Typhimurium infection, which is accompanied by both acute diarrhea and high-level inflammation, V. cholerae infection is largely noninflammatory in human hosts. Bacterial flagella are composed of flagellin, a highly conserved protein that is also a target of the innate immune response. Because the V. cholerae flagellum is covered by a sheath, we hypothesized that it might be less prone to activation of the innate immune response than nonsheathed flagella, such as those produced by Salmonella serovar Typhimurium. Indeed, compared with Salmonella serovar Typhimurium flagella, V. cholerae flagella demonstrated significantly reduced NF-κB activation in A549 human pulmonary epithelial cells. However, V. cholerae flagellin monomers, FlaD and FlaC, were almost equally potent with purified FliC, a monomer derived from Salmonella serovar Typhimurium flagella, in NF-κB activation. Heat- and acid-induced dissociation assays showed that Salmonella serovar Typhimurium flagella disassembled far more readily into monomeric flagellins than V. cholerae flagella, suggesting that the differential levels of NF-κB activation by V. cholerae and Salmonella serovar Typhimurium flagella are likely attributable to the difference in their flagellin shedding. Our results suggest that monomer dissociation of V. cholerae flagella is suppressed likely due to the presence of the sheath and that this unique structural feature of V. cholerae flagella may have evolved as a strategy to evade flagellin-triggered host innate immune responses in various host species.     

Inhibition of Salmonella typhimurium Invasion by Host Cell Expression of Secreted Bacterial Invasion Proteins

Pathogenic Salmonella species initiate infection of a host by inducing their own uptake into intestinal epithelial cells. An invasive phenotype is conferred to this pathogen by a number of proteins that are components of a type III secretion system. During the invasion process, the bacteria utilize this secretion system to release proteins that enter the host cell and apparently interact with unknown host cell components that induce alterations in the actin cytoskeleton. To investigate the role of secreted proteins as direct modulators of invasion, we have evaluated the ability of Salmonella typhimurium to enter mammalian cells that express portions of the Salmonella invasion proteins SipB and SipC. Plasma membrane localization of SipB and SipC was achieved by fusing carboxyl- and amino-terminal portions of each invasion protein to the intracellular carboxyl-terminal tail of a membrane-bound eukaryotic receptor. Expression of receptor chimeras possessing the carboxyl terminus of SipB or the amino terminus of SipC blocked Salmonella invasion, whereas expression of their chimeric counterparts had no effect on invasion. The effect on invasion was specific for Salmonella since the perturbation of uptake was not extended to other invasive bacterial species. These results suggest that Salmonella invasion can be competitively inhibited by preventing the intracellular effects of SipB or SipC. In addition, these experiments provide a model for examining interactions between bacterial invasion proteins and their host cell targets.     

Role of Salmonella Pathogenicity Island 1 Protein IacP in Salmonella enterica Serovar Typhimurium Pathogenesis

Gram-negative bacteria, including Salmonella enterica serovar Typhimurium, exploit type III secretion systems (T3SSs) through which virulence proteins are delivered into the host cytosol to reinforce invasive and replicative niches in their host. Although many secreted effector proteins and membrane-bound structural proteins in the T3SS have been characterized, the functions of many cytoplasmic proteins still remain unknown. In this study, we found that IacP, encoded by Salmonella pathogenicity island 1, was important for nonphagocytic cell invasion and bacterial virulence. When the iacP gene was deleted from several Salmonella serovar Typhimurium strains, the invasion into INT-407 epithelial cells was significantly decreased compared to that of their parental strains, and retarded rearrangements of actin fibers were observed for the iacP mutant-infected cells. Although IacP had no effect on the secretion of type III translocon proteins, the levels of secretion of the effector proteins SopB, SopA, and SopD into the culture medium were decreased in the iacP mutant. In a mouse infection model, mice infected with the iacP mutant exhibited alleviated pathological signs in the intestine and survived longer than did wild-type-infected mice. Taken together, IacP plays a key role in Salmonella virulence by regulating the translocation of T3SS effector proteins.The injection of bacterial proteins by the type III secretion system (T3SS) into the host cytoplasm has been broadly applied to study pathogen-host interactions ranging from the invasion of plant and animal pathogens to a symbiont interaction of Rhizobium (22, 42). The T3SS is composed of more than 20 different structural proteins that form needle-like appendages through which effector proteins are delivered directly into host cells to manipulate various host cell signaling events. Moreover, cytoplasmic chaperones are involved in the stability and efficient translocation of effector proteins (14). Salmonella enterica serovar Typhimurium, a facultative intracellular pathogen, has evolved two distinct T3SSs encoded by Salmonella pathogenicity island 1 (SPI-1), responsible for the invasion of nonphagocytic cells, and by SPI-2, required for intracellular survival and replication inside the Salmonella-containing vacuole (SCV). The expressions of the two T3SSs are inversely regulated during the pathogenic process. Although the expression of the SPI-1 T3SS at systemic sites has remained controversial, some effector proteins of SPI-1 (e.g., SipA and SopB) are persistently expressed and secreted under favorable conditions for SPI-2 expression during the biogenesis and maturation of the SCV (17).After the SPI-1 T3SS is activated upon host cell contact, the translocators SipB and SipC appear to be inserted into the host cell membrane, where they form a translocation pore, which is connected to the needle complex. A variety of effector proteins encoded within and outside SPI-1 can be translocated into a host cytoplasm and cooperatively induce membrane ruffling (11) and macropinocytosis (16). Among SPI-1 effector proteins, SopE, SopE2, and SopB trigger the actin rearrangement in host cells by activating small GTPases, including Rac1, Cdc42, and RhoG, directly or indirectly (39). A Salmonella serovar Typhimurium mutant carrying null mutations in these effector proteins failed to invade epithelial cells. After bacterial invasion, an activated membrane was subsequently recovered by SptP, another effector protein possessing GTPase-activating protein activity (13).The iacP gene, which is located downstream of sicA- sipBCDA in the SPI-1 locus, was initially identified as a putative acyl carrier protein (ACP) by sequence similarity (26). ACP is an abundant small acidic and highly conserved protein that is essential for various biosynthetic pathways (5). In the process of fatty acid (FA) biosynthesis in Escherichia coli, ACP sequentially delivers the acyl intermediates for FA elongation as a cofactor of FA synthase (20). For the enzymatic activity of ACP, a prosthetic group 4′-phosphopantetheine (4′-PP) that was covalently incorporated into apo-ACP serves as the binding site of acyl groups. It was reported previously that the substitution of serine 36 in Escherichia coli ACP eliminated the attachment site of the 4′-PP and inhibited FA incorporation (27).In addition to lipid biosynthesis, acyl-ACP is required for various bacterial virulence processes: the synthesis of the lipid A moiety of lipopolysaccharide (LPS) (43) and the N-acylhomoserine lactones as signal molecules in quorum sensing (52) and the posttranslational modification of bacterial toxins such as E. coli hemolysin (HlyA) (24). The activation of HlyA requires posttranslational acylation at two internal lysine residues by ACP and the acyl transferase HlyC. The conformation of acylated HlyA is matured into a molten globular form comprised of disordered regions, which is necessary for the hemolytic effects of a toxin to occur (21).As a Salmonella serovar Typhimurium mutant that lacks an entire SPI-1 locus was found to grow as well as the wild type, it is predicted that IacP would be responsible for the modification of other proteins in the T3SS (26). However, it is not known which proteins are targeted by IacP or how the invasion process during SPI-1 activation is affected in the iacP mutant. In this study, we report that IacP promotes SopB, SopA, and SopD secretion during cell entry, thus contributing to the virulence of Salmonella serovar Typhimurium.     

Early Innate Immunity to Bacterial Infection in the Lung Is Regulated Systemically by the Commensal Microbiota via Nod-Like Receptor Ligands

The commensal microbiota is a major regulator of the immune system. The majority of commensal bacteria inhabit the gastrointestinal tract and are known to regulate local mucosal defenses against intestinal pathogens. There is growing appreciation that the commensal microbiota also regulates immune responses at extraintestinal sites. Currently, however, it is unclear how this influences host defenses against bacterial infection outside the intestine. Microbiota depletion caused significant defects in the early innate response to lung infection by the major human pathogen Klebsiella pneumoniae. After microbiota depletion, early clearance of K. pneumoniae was impaired, and this could be rescued by administration of bacterial Nod-like receptor (NLR) ligands (the NOD1 ligand MurNAcTri_DAP and NOD2 ligand muramyl dipeptide [MDP]) but not bacterial Toll-like receptor (TLR) ligands. Importantly, NLR ligands from the gastrointestinal, but not upper respiratory, tract rescued host defenses in the lung. Defects in early innate immunity were found to be due to reduced reactive oxygen species-mediated killing of bacteria by alveolar macrophages. These data show that bacterial signals from the intestine have a profound influence on establishing the levels of antibacterial defenses in distal tissues.     

Targeting of the actin cytoskeleton during infection by Salmonella strains

Many bacterial pathogens produce virulence factors that alter the host cell cytoskeleton to promote infection. Salmonella strains target cellular actin in a carefully orchestrated series of interactions that promote bacterial uptake into host cells and the subsequent proliferation and intercellular spread of the organisms. The Salmonella Pathogenicity Island 1 (SPI1) locus encodes a type III protein secretion system (TTSS) that translocates effector proteins into epithelial cells to promote bacterial invasion through actin cytoskeletal rearrangements. SPI1 effectors interact directly with actin and also alter the cytoskeleton through activation of the regulatory proteins, Cdc42 and Rac, to produce membrane ruffles that engulf the bacteria. SPI1 also restores normal cellular actin dynamics through the action of another effector, SptP. A second TTSS, Salmonella Pathogenecity Island 2 (SPI2), translocates effectors that promote intracellular survival and growth, accompanied by focal actin polymerization around the Salmonella-containing vacuole (SCV). A number of Salmonella strains also carry the spv virulence locus, encoding an ADP-ribosyl transferase, the SpvB protein, which acts later during intracellular infection to depolymerize the actin cytoskeleton. SpvB produces a cytotoxic effect on infected host cells leading to apoptosis. The SpvB effect appears to promote intracellular infection and may facilitate cell-to-cell spread of the organism, thereby enhancing virulence.     

Innate activation of human neutrophils and neutrophil-like cells by the pro-inflammatory bacterial metabolite ADP-heptose and Helicobacter pylori

Lipopolysaccharide inner core heptose metabolites, including ADP-heptose, play a substantial role in the activation of cell-autonomous innate immune responses in eukaryotic cells, via the ALPK1-TIFA signaling pathway, as demonstrated for various pathogenic bacteria. The important role of LPS heptose metabolites during Helicobacter pylori infection of the human gastric niche has been demonstrated for gastric epithelial cells and macrophages, while the role of heptose metabolites on human neutrophils has not been investigated. In this study, we aimed to gain a better understanding of the activation potential of bacterial heptose metabolites for human neutrophil cells. To do so, we used pure ADP-heptose and, as a bacterial model, H. pylori, which can transport heptose metabolites into the human host cell via the Cag Type 4 Secretion System (CagT4SS). Main questions were how bacterial heptose metabolites impact on the pro-inflammatory activation, alone and in the bacterial context, and how they influence maturation of human neutrophils. Results of the present study demonstrated that neutrophils respond with high sensitivity to pure heptose metabolites, and that global regulation networks and neutrophil maturation are influenced by heptose exposure. Furthermore, activation of human neutrophils by live H. pylori is strongly impacted by the presence of LPS heptose metabolites and the functionality of its CagT4SS. Similar activities were determined in cell culture neutrophils of different maturation states and in human primary neutrophils. In conclusion, we demonstrated that specific heptose metabolites or bacteria producing heptoses exhibit a strong activity on cell-autonomous innate responses of human neutrophils.