Augmentation of Helicobacter pylori urease activity by its specific IgG antibody: implications for bacterial colonization enhancement

Paper-based analytical device with colorimetric detection for urease activity determination in soils and evaluation of potential inhibitors

Urease is an enzyme associated with the degradation of urea, an important nitrogen fertilizer in agriculture. Thus, this current report describes the use of a paper-based analytical device (UrePAD) designed to contain a microzone array for colorimetric determination of urease activity in soils in the absence/presence of potential enzyme inhibitors. The UrePAD can be used at the point-of-need (point-of-care), and it offers advantages such as low cost, simplicity in handling, low sample/reagent volumes, and no use of toxic reagents. The acid-base indicator phenol red was used to monitor the urea hydrolysis reaction catalyzed by urease in the evaluated systems. The images were digitalized in a bench scanner, and the analysis was performed using Corel Draw X8 software. The device offered a LOD of 0.10 U mL^-1 with linearity between 0.25 and 4.0 U mL^-1 and a relative standard deviation ≤ 1.38%. UrePAD was tested in four soil samples of different characteristics and with eight urease inhibitors of varied classes. The results obtained through the proposed device did not differ statistically (95% confidence interval) from those employing the classic method based on the Berthelot reaction, thus indicating that UrePAD was effective for determining urease activity and screening inhibitors, besides showing the capacity to simplify fieldwork involving the application of urea in the soil.

Helicobacter urease suppresses cytotoxic CD8 + T cell responses through activating Myh9-dependent induction of PD-L1

As a key virulence factor for persistent colonization, Urease B subunit (UreB) is considered to be an ideal vaccine antigen against Helicobacter pylori (H. pylori) infection. However, the role and molecular mechanisms of UreB involved in immune microenvironment dysregulation still remains largely unknown. In the present study, we evaluated the effects of UreB on macrophage activation and found that UreB induced PD-L1 accumulation on Bone marrow-derived macrophages (BMDMs). Co-culture assays further revealed that UreB-induced PD-L1 expression on BMDMs significantly decreased the proliferation and secretion of cytolytic molecules (granzyme B and perforin) of splenic CD8 + T cells isolated from inactivated H. pylori-immunized mice. More importantly, myosin heavy chain 9 (Myh9) was confirmed to be a direct membrane receptor of UreB via using LC-MS/MS and Co-immunoprecipitation and required for PD-L1 upregulation on BMDMs. Molecular studies further demonstrated that the interaction between UreB and Myh9 decreased GCN2 autophosphorylation and enhanced intracellular pool of amino acids, leading to the upregulation of S6K phosphorylation, a commonly used marker for monitoring activation of mTORC1 signaling activity. Furthermore, blocking mTORC1 activation with its inhibitor Temsirolimus reversed UreB-induced PD-L1 upregulation and the subsequently inhibitory effects of BMDMs on activation of cytotoxic CD8 + T cell responses. Overall, our data unveil a novel immunosuppressive mechanism of UreB during H. pylori infection, which may provide valuable clue for the optimization of H. pylori vaccine.

Neutralizing antibodies for Helicobacter pylori urease inhibit bacterial colonization in the murine stomach in vivo

Helicobacter pylori (H. pylori) urease is a key protein for persistent infection of the bacteria in the stomach. Although H. pylori generally induce anti-H. pylori-specific antibodies (Abs), these Abs do not usually work for eradication or prevention of the H. pylori infection. In our previous study, we identified a linear epitope composed of 19-mer peptides termed UB-33, CHHLDKSIKEDVQFADSRI, within the large subunit of H. pylori urease. Anti-UB-33-specific Abs neutralized the enzymatic activity of H. pylori urease in vitro. In the present study, we evaluated the effect of immunization of BALB/c mice with H. pylori UB-33 peptide. After confirming the production of anti-UB-33-specific Abs, mice were challenged orally with H. pylori Sydney Strain-1 (SS-1). Mice producing anti-UB-33-specific Abs were not infected with SS-1, and the amount of SS-1 isolate in their stomach was significantly reduced. Also, the urease-negative mutant of H. pylori, HPP1801, did not colonize in the stomach, indicating that H. pylori urease was a critical element for infection of H. pylori in the gastric mucosa. Moreover, mice producing UB-33-specific Abs apparently suppressed H. pylori infection in the stomach where anti-UB-33 Abs were secreted in the gastric juice, indicating that H. pylori colonization was inhibited in the presence of anti-UB-33 Abs. In addition, the neutralization activity of sera from mice immunized with purified urease was less potent than that in the sera from mice immunized with UB-33. Furthermore, the recognition of epitope UB-33 was mediated through Toll-like receptor 2 (TLR2) on the B-1 cells using TLR2-knockout BALB/c mice in vivo. These results indicate that liner peptide UB-33 should be used for immunization to induce neutralizing Abs instead of purified H. pylori urease to prevent H. pylori infection and their colonization in the stomach.

Production of autoantibodies by murine B-1a cells stimulated with Helicobacter pylori urease through toll-like receptor 2 signaling

Helicobacter pylori infection is associated with several autoimmune diseases, in which autoantibody-producing B cells must be activated. Among these B cells, CD5-positive B-1a cells from BALB/c mice were confirmed to secrete autoantibodies when cocultured with purified H. pylori urease in the absence of T cells. To determine the mechanisms for autoantibody production, CD5-positive B-1a cells were sorted from murine spleen cells and stimulated with either purified H. pylori urease or H. pylori coated onto plates (referred to hereafter as plate-coated H. pylori), and autoantibody production was measured by enzyme-linked immunosorbent assay (ELISA). Complete urease was not secreted from H. pylori but was visually expressed over the bacterium-like endotoxin. Urease-positive plated-coated H. pylori stimulated B-1a cells to produce autoantibodies, although urease-deficient isotype-matched H. pylori did not. Autoantibody secretion by B-1a cells was inhibited when bacteria were pretreated with anti-H. pylori urease-specific antibody having neutralizing ability against urease enzymatic activity but not with anti-H. pylori urease-specific antibody without neutralizing capacity. The B-1a cells externally express various Toll-like receptors (TLRs): TLR1, TLR2, TLR4, and TLR6. Among the TLRs, blocking of TLR2 on B-1a cells with a specific monoclonal antibody (MAb), T2.5, inhibited autoantibody secretion when B-1a cells were stimulated with plate-coated H. pylori or H. pylori urease. Moreover, B-1a cells from TLR2-knockout mice did not produce those autoantibodies. The present study provides evidence that functional urease expressed on the surface of H. pylori will directly stimulate B-1a cells via innate TLR2 to produce various autoantibodies and may induce autoimmune disorders.

Cross-reaction of antibody against Helicobacter pylori urease B with platelet glycoprotein IIIa and its significance in the pathogenesis of immune thrombocytopenic purpura

Many clinical investigations have suggested that Helicobacter pylori (H. pylori) infection might be associated with immune thrombocytopenic purpura (ITP), but its role in the pathogenesis of ITP is unsettled. In this study, we cultured H. pylori, produced recombinant H. pylori urease (ure) B, and then prepared monoclonal antibody (MoAb) against ureB, 1F11, both 1F11 and MoAb against human platelet glycoprotein (GP) IIIa, SZ21, could bind to the band of GP IIIa of normal platelet lysate, but not to that from a patient with Glanzmann thrombasthenia (GT) whose GP IIb-IIIa complex was absent. Flow cytometry showed that normal platelets were reacted with 1F11 and SZ21, while GT platelets were not. In immuno-radiometric assay, the binding of (125)I-labeled 1F11 to GP IIIa was higher than that to GP Ib, GP IIb, GP VI, and P-selectin. 1F11 could partly compete with SZ21 in a binding to platelet surface. In addition, 1F11 inhibited platelet aggregation induced by adenosine diphosphate, but had no effect on platelet P-selectin expression or Thromboxane B(2) production of platelets. These results indicate that H. pylori ureB antibody could cross-react with human platelet GP IIIa and partly inhibit platelet aggregation. UreB may be a crucial component of H. pylori involved in the pathogenesis of a subset of ITP.

Screening and identification of a novel B-cell neutralizing epitope from Helicobacter pylori UreB

Urease plays a crucial role in the survival and pathogenesis of Helicobacter pylori (H. pylori), and antibody neutralizing the urease activity may be implicated for the protection against H. pylori infection. Previously, a neutralizing monoclonal antibody (MAb) 6E6 against UreB of H. pylori was developed. In this work, we try to identify the B-cell epitope recognized by neutralizing MAb 6E6. Following screening a series of truncated proteins of UreB, an epitope was primarily localized in the aa 200-230 of UreB. Subsequently, we screened the overlapping synthetic peptides covering the aa 200-230 and identified a novel B-cell epitope (U(211-225), IEAGAIGFKIHEDWG) that was recognized by specific MAb 6E6. The newly identified epitope may help understanding of the protective immunity against H. pylori and be implicated for vaccine development.

Oral vaccination with liposome-encapsulated recombinant fusion peptide of urease B epitope and cholera toxin B subunit affords prophylactic and therapeutic effects against H. pylori infection in BALB/c mice

A new fusion peptide CtUBE of cholera toxin B subunit and Helicobacter pylori urease B subunit epitope was expressed in Escherichia coli. With this fusion peptide, an oral liposome vaccine against H. pylori infection was prepared and evaluated in BALB/c mice. Based on the results of urease tests, quantitation of culturable bacteria colonies in mice stomachs and histological identification of gastritis, the mice were protected significantly after intragastric vaccination with this CtUBE liposome vaccine, which increased the content levels of specific anti-urease serum IgG and mucosal IgA for both prophylactic and therapeutic vaccination protocols. These results showed that the fusion peptide CtUBE retained immunogenicity and could be used as antigen in the development of an oral vaccine against H. pylori infection.

The current status of Helicobacter pylori vaccines: a review

Helicobacter pylori, a Gram-negative flagellate bacterium that infects the stomach of more than half of the global population, is regarded as the leading cause of chronic gastritis, peptic ulcer disease, and even gastric adenocarcinoma in some individuals. Although the bacterium induces strong humoral and cellular immune responses, it can persist in the host for decades. It has several virulence factors, some of them having vaccine potential as judged by immunoproteomic analysis. A few vaccination studies involving a small number of infected or uninfected humans with various H. pylori formulations such as the recombinant urease, killed whole cells, and live Salmonella vectors presenting the subunit antigens have not provided satisfactory results. One trial that used the recombinant H. pylori urease coadministered with native Escherichia coli enterotoxin (LT) demonstrated a reduction of H. pylori load in infected participants. Although extensive studies in the mouse model have demonstrated the feasibility of both therapeutic and prophylactic immunizations, the mechanism of vaccine-induced protection is poorly understood as several factors such as immunoglobulin and various cytokines do not contribute to protection. Transcriptome analyses in mice have indicated the role of nonclassical immune factors in vaccine-induced protection. The role of regulatory T cells in the persistence of H. pylori infection has also been suggested. A recently developed experimental H. pylori infection model in humans may be used for testing several new adjuvants and vaccine delivery systems that have been currently obtained. The use of vaccines with appropriate immunogens, routes of immunization, and adjuvants along with a better understanding of the mechanism of immune protection may provide more favorable results.

Ex vivo visualization of Helicobacter pylori using an endocytoscopic probe

Observation of microorganisms by endoscopy has been technically difficult. In this study, we tried to visualize bacteria during endoscopic examination to provide a powerful tool for a diagnosis of gastrointestinal infection. We observed the bacterium Helicobacter pylori, cultured ex vivo, using a novel ultra-high "magnified endoscopy" system ("endocytoscopy" prototype, Olympus Medical Systems). Cultures were prepared from gastric mucus obtained from three gastric ulcer patients. H. pylori in the supernatant of the culture medium were observed directly by endocytoscopy. Staphylococcus aureus and red blood cells were used as controls. H. pylori in the culture medium were observed directly by endocytoscopy, and recorded using a video recorder. Live, moving bacteria can be visualized and recorded ex vivo using this new "endocytoscopy" technology.

Inflammation, immunity, vaccines for Helicobacter infection

The reason why some individuals remain Helicobacter pylori infected for life but without any symptoms while others develop severe diseases is only partially clarified. Presumably, it depends on multifactorial interactions among host immunologic and physiologic factors, bacterial virulence determinants, and environmental influences modulating the host response. Much effort has been made to identify host genetic factors that may explain an individual susceptibility of the host to H. pylori infection. The identification of H. pylori determinants and the elucidation of their role in modifying the host immune responses were further delineated. The ability of H. pylori to overcome the defense mechanisms on mucosal surfaces as well as to modulate the immune response by interfering with host recognition and transduction systems has been shown. Also new bacterial anti-inflammatory defense systems have been described. Findings in experimental animal models and humans with natural H. pylori infection suggested a double role of regulatory T cells in the course of H. pylori infection: protecting the infected host against excessive gastric inflammation and, in contrast, promoting bacterial colonization.

Implications for induction of autoimmunity via activation of B-1 cells by Helicobacter pylori urease

Besides various gastroduodenal diseases, Helicobacter pylori infection may be involved in autoimmune disorders like rheumatoid arthritis (RA) or idiopathic thrombocytopenic purpura. Such autoimmune disorders are often associated with autoreactive antibodies produced by B-1 cells, a subpopulation of B lymphocytes. These B-1 cells are mainly located in the pleural cavity or mucosal compartment. The existence of H. pylori urease-specific immunoglobulin A (IgA)-producing B cells in the mucosal compartment and of their specific IgM in the sera of acutely infected volunteers suggests the possibility that urease stimulates mucosal innate immune responses. Here, we show for the first time that purified H. pylori urease predominantly stimulates the B-1-cell population rather than B-2 cells, which produce antigen-specific conventional antibodies among splenic B220(+) B cells. The fact that such stimulation of B-1 cells was not affected by the addition of polymyxin B indicates that the effect of purified H. pylori urease was not due to the contamination with bacterial lipopolysaccharide. Furthermore, the production of various B-1-cell-related autoreactive antibodies such as IgM-type rheumatoid factor, anti-single-stranded DNA antibody, and anti-phosphatidyl choline antibody was observed when the splenic B cells were stimulated with purified H. pylori urease in vitro. These findings suggest that H. pylori components, urease in particular, may be among the environmental triggers that initiate various autoimmune diseases via producing autoreactive antibodies through the activation of B-1 cells. The findings shown here offer important new insights into the pathogenesis of autoimmune disorders related to H. pylori infection.