PAR2 promotes vaccine-induced protection against Helicobacter infection in mice

Strategies of Helicobacter pylori in evading host innate and adaptive immunity: insights and prospects for therapeutic targeting

Helicobacter pylori (H. pylori) is the predominant pathogen causing chronic gastric mucosal infections globally. During the period from 2011 to 2022, the global prevalence of H. pylori infection was estimated at 43.1%, while in China, it was slightly higher at approximately 44.2%. Persistent colonization by H. pylori can lead to gastritis, peptic ulcers, and malignancies such as mucosa-associated lymphoid tissue (MALT) lymphomas and gastric adenocarcinomas. Despite eliciting robust immune responses from the host, H. pylori thrives in the gastric mucosa by modulating host immunity, particularly by altering the functions of innate and adaptive immune cells, and dampening inflammatory responses adverse to its survival, posing challenges to clinical management. The interaction between H. pylori and host immune defenses is intricate, involving evasion of host recognition by modifying surface molecules, manipulating macrophage functionality, and modulating T cell responses to evade immune surveillance. This review analyzes the immunopathogenic and immune evasion mechanisms of H. pylori, underscoring the importance of identifying new therapeutic targets and developing effective treatment strategies, and discusses how the development of vaccines against H. pylori offers new hope for eradicating such infections.

A Deep Insight Into Regulatory T Cell Metabolism in Renal Disease: Facts and Perspectives

Kidney disease encompasses a complex set of diseases that can aggravate or start systemic pathophysiological processes through their complex metabolic mechanisms and effects on body homoeostasis. The prevalence of kidney disease has increased dramatically over the last two decades. CD4⁺CD25⁺ regulatory T (Treg) cells that express the transcription factor forkhead box protein 3 (Foxp3) are critical for maintaining immune homeostasis and preventing autoimmune disease and tissue damage caused by excessive or unnecessary immune activation, including autoimmune kidney diseases. Recent studies have highlighted the critical role of metabolic reprogramming in controlling the plasticity, stability, and function of Treg cells. They are also likely to play a vital role in limiting kidney transplant rejection and potentially promoting transplant tolerance. Metabolic pathways, such as mitochondrial function, glycolysis, lipid synthesis, glutaminolysis, and mammalian target of rapamycin (mTOR) activation, are involved in the development of renal diseases by modulating the function and proliferation of Treg cells. Targeting metabolic pathways to alter Treg cells can offer a promising method for renal disease therapy. In this review, we provide a new perspective on the role of Treg cell metabolism in renal diseases by presenting the renal microenvironment、relevant metabolites of Treg cell metabolism, and the role of Treg cell metabolism in various kidney diseases.

Gastric Subserous Vaccination With Helicobacter pylori Vaccine: An Attempt to Establish Tissue-Resident CD4+ Memory T Cells and Induce Prolonged Protection

Tissue-resident memory T (Trm) cells are enriched at the sites of previous infection and required for enhanced protective immunity. However, the emergence of Trm cells and their roles in providing protection are unclear in the field of Helicobacter pylori (H. pylori) vaccinology. Here, our results suggest that conventional vaccine strategies are unable to establish a measurable antigen (Ag)-specific memory cell pool in stomach; in comparison, gastric subserous injection of mice with micro-dose of Alum-based H. pylori vaccine can induce a pool of local CD4+ Trm cells. Regional recruitment of Ag-specific CD4+ T cells depends on the engagement of Ag and adjuvant-induced inflammation. Prior subcutaneous vaccination enhanced this recruitment. A stable pool of Ag-specific CD4+ T cells can be detected for 240 days. Two weeks of FTY720 administration in immune mice suggests that these cells do not experience the recirculation. Immunohistochemistry results show that close to the vaccination site, abundant CD4+T cells locate on epithelial niches, independent of lymphocyte cluster. Paradigmatically, Ag-specific CD4+ T cells with a phenotype of CD69+CD103- are preferential on lymphocytes isolated from epithelium. Upon Helicobacter infection, CD4+ Trm cells orchestrate a swift recall response with the recruitment of circulating antigen-specific Th1/Th17 cells to trigger a tissue-wide pathogen clearance. This study investigates the vaccine-induced gastric CD4+ Trm cells in a mice model, and highlights the need for designing a vaccine strategy against H. pylori by establishing the protective CD4+ Trm cells.

IL-22-induced antimicrobial peptides are key determinants of mucosal vaccine-induced protection against H. pylori in mice

Despite the recent description of the mucosal vaccine-induced reduction of Helicobacter pylori natural infection in a phase 3 clinical trial, the absence of immune correlates of protection slows the final development of the vaccine. In this study, we evaluated the role of interleukin (IL)-22 in mucosal vaccine-induced protection. Gastric IL-22 levels were increased in mice intranasally immunized with urease+cholera toxin and challenged with H. felis, as compared with controls. Flow cytometry analysis showed that a peak of CD4+IL-22+IL-17+ T cells infiltrating the gastric mucosa occurred in immunized mice in contrast to control mice. The inhibition of the IL-22 biological activity prevented the vaccine-induced reduction of H. pylori infection. Remarkably, anti-microbial peptides (AMPs) extracted from the stomachs of vaccinated mice, but not from the stomachs of non-immunized or immunized mice, injected with anti-IL-22 antibodies efficiently killed H. pylori in vitro. Finally, H. pylori infection in vaccinated RegIIIβ-deficient mice was not reduced as efficiently as in wild-type mice. These results demonstrate that IL-22 has a critical role in vaccine-induced protection, by promoting the expression of AMPs, such as RegIIIβ, capable of killing Helicobacter. Therefore, it can be concluded that urease-specific memory Th17/Th22 cells could constitute immune correlates of vaccine protection in humans.

Role of Inflammatory Monocytes in Vaccine-Induced Reduction of Helicobacter felis Infection

Despite the proven ability of immunization to reduce Helicobacter infection in mouse models, the precise mechanism of protection has remained elusive. In this study, we evaluated the role of inflammatory monocytes in the vaccine-induced reduction of Helicobacter felis infection. We first showed by using flow cytometric analysis that Ly6C(low) major histocompatibility complex class II-positive chemokine receptor type 2 (CCR2)-positive CD64(+) inflammatory monocytes accumulate in the stomach mucosa during the vaccine-induced reduction of H. felis infection. To determine whether inflammatory monocytes played a role in the protection, these cells were depleted with anti-CCR2 depleting antibodies. Indeed, depletion of inflammatory monocytes was associated with an impaired vaccine-induced reduction of H. felis infection on day 5 postinfection. To determine whether inflammatory monocytes had a direct or indirect role, we studied their antimicrobial activities. We observed that inflammatory monocytes produced tumor necrosis factor alpha and inducible nitric oxide synthase (iNOS), two major antimicrobial factors. Lastly, by using a Helicobacter in vitro killing assay, we showed that mouse inflammatory monocytes and activated human monocytes killed H. pylori in an iNOS-dependent manner. Collectively, these data show that inflammatory monocytes play a direct role in the immunization-induced reduction of H. felis infection from the gastric mucosa.

Protease-activated receptor 1 suppresses Helicobacter pylori gastritis via the inhibition of macrophage cytokine secretion and interferon regulatory factor 5

Chronic gastritis from Helicobacter pylori infection is a major factor in the development of gastric adenocarcinoma. Factors that regulate gastritis severity are important in determining which individuals are susceptible to H. pylori-associated disease. Although protease-activated receptor 1 (PAR1) has been identified as one such host factor, its mechanism of action is unknown. Using chimeric mice, we demonstrated that PAR1-mediated protection against H. pylori gastritis requires bone marrow-derived cells. Analyses of the gastric mucosa revealed that PAR1 suppresses cellular infiltration and both T helper type 1 (Th1) and T helper type 17 (Th17) responses to infection. Moreover, PAR1 expression was associated with reduced vaccine-mediated protection against H. pylori. Analyses of H. pylori-stimulated macrophages revealed that PAR1 activation suppressed secretion of interleukin (IL)-12 and IL-23, key drivers of Th1 and Th17 immunity, respectively. Furthermore, PAR1 suppressed interferon regulatory factor 5 (IRF5), an important transcription factor for IL-12 and IL-23, both in the infected mucosa and following bacterial stimulation. PAR1 suppression of IRF5 and IL-12/23 secretion by macrophages provides a novel mechanism by which the host suppresses the mucosal Th1 and Th17 response to H. pylori infection. Dysregulation of this process is likely an important factor in the susceptibility of some individuals to H. pylori-associated disease.

Regulation of epithelial cell tight junctions by protease-activated receptor 2

A layer of epithelial cells prevents the invasion of bacteria and the entry of foreign substances into the underlying tissue. The disruption of epithelial tight junctions initiates and exacerbates inflammation. However, the precise mechanism underlying the disruption of the epithelial tight junction remains unclear. The activation of protease-activated receptor 2 (PAR2) by serine proteases produced by some bacteria and mast cells contributes to inflammation in many tissues. In the present study, we tested the hypothesis that PAR2 activation affects the structure and function of tight junctions in Madin-Darby canine kidney (MDCK) cells. Although the application of a PAR2-activating peptide, PAR2-AP, from the apical side of MDCK cells failed to modify the transepithelial resistance (TER), its application from the basal side markedly suppressed the TER. In 3-dimensional cultures of MDCK cells expressing the mCherry-tagged PAR2, a lateral localization of PAR2 was observed. The application of PAR2-AP from the basal side changed the localization of the tight junctional protein, zonula occludin-1. Furthermore, PAR2-AP induced the phosphorylation of p38 MAP kinase. A p38 MAP kinase inhibitor, SB202190, inhibited PAR2-AP-induced changes in TER. Our results suggest that the activation of PAR2 leads to the disruption of tight junctions and increases the barrier permeability through the activation of p38 MAPK, which may cause the initiation and exacerbation of inflammation.

Immune responses to Helicobacter pylori infection

Helicobacter pylori (H. pylori) infection is one of the most common infections in human beings worldwide. H. pylori express lipopolysaccharides and flagellin that do not activate efficiently Toll-like receptors and express dedicated effectors, such as γ-glutamyl transpeptidase, vacuolating cytotoxin (vacA), arginase, that actively induce tolerogenic signals. In this perspective, H. pylori can be considered as a commensal bacteria belonging to the stomach microbiota. However, when present in the stomach, H. pylori reduce the overall diversity of the gastric microbiota and promote gastric inflammation by inducing Nod1-dependent pro-inflammatory program and by activating neutrophils through the production of a neutrophil activating protein. The maintenance of a chronic inflammation in the gastric mucosa and the direct action of virulence factors (vacA and cytotoxin-associated gene A) confer pro-carcinogenic activities to H. pylori. Hence, H. pylori cannot be considered as symbiotic bacteria but rather as part of the pathobiont. The development of a H. pylori vaccine will bring health benefits for individuals infected with antibiotic resistant H. pylori strains and population of underdeveloped countries.

Why can't we make an effective vaccine against Helicobacter pylori?

Helicobacter pylori is a major human pathogen that colonizes the stomach and is the lead etiological agent for several pathologies. An effective vaccine against these bacteria would be invaluable for protecting against gastric adenocarcinoma. However, the development of such a vaccine has stalled and the field has progressed little in the last decade. In this review, the authors provide an opinion on key problems that are preventing the development of a H. pylori vaccine. Primarily, this involves the inability to produce a completely protective immune response. The knock-on effects of this include a loss of industry investment. Overcoming these problems will likely involve defeating the immune-evasion defenses of H. pylori, in particular the mechanism(s) by which it evades antibody-mediated attack.

Toward drugs for protease-activated receptor 2 (PAR2)

PAR2 has a distinctive functional phenotype among an unusual group of GPCRs called protease activated receptors, which self-activate after cleavage of their N-termini by mainly serine proteases. PAR2 is the most highly expressed PAR on certain immune cells, and it is activated by multiple proteases (but not thrombin) in inflammation. PAR2 is expressed on many types of primary human cells and cancer cells. PAR2 knockout mice and PAR2 agonists and antagonists have implicated PAR2 as a promising target in inflammatory conditions; respiratory, gastrointestinal, metabolic, cardiovascular, and neurological dysfunction; and cancers. This article summarizes salient features of PAR2 structure, activation, and function; opportunities for disease intervention via PAR2; pharmacological properties of published or patented PAR2 modulators (small molecule agonists and antagonists, pepducins, antibodies); and some personal perspectives on limitations of assessing their properties and on promising new directions for PAR2 modulation.

Helicobacter pylori in gastric malignancies

Helicobacter pylori infection remains common worldwide and is significantly associated with gastric adenocarcinoma and gastric mucosa-associated lymphoid tissue (MALT)lymphoma. This article reviews recent developments in the field of H. pylori with an emphasis on mechanisms of carcinogenesis, and the bacterial, environmental and host factors that may alter risk of developing gastric cancer or gastric MALT lymphoma. The topic of eradication of H. pylori to prevent the development of malignancy and the possibility of a vaccine against H. pylori are also explored.

Helicobacter spp. other than H. pylori

Significant advances have been made over the last 12 months in the understanding of the biology of non-H. pylori Helicobacter species (NHPH). Several studies have investigated the association between NHPH and human disease, including Crohn's disease, lithiasis, liver disease, coronary disease, gastritis, and pyoderma gangrenosum-like ulcers. Novel Helicobacter taxa were identified in new vertebrate hosts, and new methodologies in the fields of identification of Helicobacter spp. and evaluation of antibiotic resistance were described. The genome of the first human-derived gastric NHPH strain (Helicobacter bizzozeronii CIII-1) was sequenced, and several studies elucidated functions of different genes in NHPH. A number of important investigations regarding pathogenesis and immunopathobiology of NHPH infections have been published including the description of a new urease in Helicobacter mustelae. Finally, the effects of the gut microbiota and probiotics on NHPH infections were investigated.