Polymorphisms in Toll-like receptors 1, 2, 5, and 10 are associated with predisposition to Helicobacter pylori infection

New Promising Routes in Peptic Ulcers: Toll-like Receptors and Semaphorins

Peptic ulcers (PU) are one of the commonest yet problematic diseases found to be existing in the majority of the population. Today, drugs from a wide range of therapeutic classes are available for the management of the disease. Still, the complications of the condition are difficult to tackle and the side effect profile is quite a concern. The literature indicates that Toll-like receptors (TLRs) and Semaphorins (SEMAs) have been under study for their various pharmacological actions over the past few decades. Both these signalling pathways are found to regulate immunological and inflammatory responses. Moreover, receptors and signalling molecules from the family of TLRs and SEMAs are found to have bacterial recognition and antibacterial properties which are essential in eradicating Helicobacter pylori (H. pylori), one of the major causative agents of PU. Our understanding of SEMAs, a class of proteins involved in cell signalling, is relatively less developed compared to TLRs, another class of proteins involved in the immune response. SEMAs and TLRs play different roles in biological processes, with SEMAs primarily involved in guiding cell migration and axon guidance during development, while TLRs are responsible for recognizing pathogens and initiating an immune response. Here, in this review, we will discuss in detail the signalling cascade of TLRs and SEMAs and thereby understand its association with PU for future therapeutic targeting. The review also aims at providing an overview of the study that has been into exploring the role of these signalling pathways in the management of PU.

The role of toll-like receptors in immune tolerance induced by Helicobacter pylori infection

Helicobacter pylori (H. pylori) is a gram-negative, microaerobic bacterium that colonizes the gastric mucosa in about half of the world's population. H. pylori infection can lead to various diseases. Chronic infection by H. pylori exposes the gastric mucosa to bacterial components such as lipopolysaccharide (LPS), outer membrane vesicles (OMVs), and several toxic proteins. Infected with H. pylori activates the release of pro-inflammatory factors and triggers inflammatory responses that damage the gastric mucosa. As the only microorganism that permanently colonizes the human stomach, H. pylori can suppress host immunity to achieve long-term colonization. Toll-like receptors (TLRs) play a crucial role in T-cell activation, promoting innate immune responses and immune tolerance during H. pylori infection. Among the 10 TLRs found in humans, TLR2, TLR4, TLR5, and TLR9 have been thoroughly investigated in relation to H. pylori-linked immune regulation. In the present review, we provide a comprehensive analysis of the various mechanisms employed by different TLRs in the induction of immune tolerance upon H. pylori infection, which will contribute to the research of pathogenic mechanism of H. pylori.

Masking of typical TLR4 and TLR5 ligands modulates inflammation and resolution by Helicobacter pylori

Helicobacter pylori is a paradigm of chronic bacterial infection and is associated with peptic ulceration and malignancies. H. pylori uses specific masking mechanisms to avoid canonical ligands from activating Toll-like receptors (TLRs), such as lipopolysaccharide (LPS) modification and specific flagellin sequences that are not detected by TLR4 and TLR5, respectively. Thus, it was believed for a long time that H. pylori evades TLR recognition as a crucial strategy for immune escape and bacterial persistence. However, recent data indicate that multiple TLRs are activated by H. pylori and play a role in the pathology. Remarkably, H. pylori LPS, modified through changes in acylation and phosphorylation, is mainly sensed by other TLRs (TLR2 and TLR10) and induces both pro- and anti-inflammatory responses. In addition, two structural components of the cag pathogenicity island-encoded type IV secretion system (T4SS), CagL and CagY, were shown to contain TLR5-activating domains. These domains stimulate TLR5 and enhance immunity, while LPS-driven TLR10 signaling predominantly activates anti-inflammatory reactions. Here, we discuss the specific roles of these TLRs and masking mechanisms during infection. Masking of typical TLR ligands combined with evolutionary shifting to other TLRs is unique for H. pylori and has not yet been described for any other species in the bacterial kingdom. Finally, we highlight the unmasked T4SS-driven activation of TLR9 by H. pylori, which mainly triggers anti-inflammatory responses.

Linking dysbiosis to precancerous stomach through inflammation: Deeper than and beyond imaging

Upper gastrointestinal endoscopy is considered the gold standard for gastric lesions detection and surveillance, but it is still associated with a non-negligible rate of missing conditions. In the Era of Personalized Medicine, biomarkers could be the key to overcome missed lesions or to better predict recurrence, pushing the frontier of endoscopy to functional endoscopy. In the last decade, microbiota in gastric cancer has been extensively explored, with gastric carcinogenesis being associated with progressive dysbiosis. Helicobacter pylori infection has been considered the main causative agent of gastritis due to its interference in disrupting the acidic environment of the stomach through inflammatory mediators. Thus, does inflammation bridge the gap between gastric dysbiosis and the gastric carcinogenesis cascade and could the microbiota-inflammation axis-derived biomarkers be the answer to the unmet challenge of functional upper endoscopy? To address this question, in this review, the available evidence on the role of gastric dysbiosis and chronic inflammation in precancerous conditions of the stomach is summarized, particularly targeting the nuclear factor-κB (NF-κB), toll-like receptors (TLRs) and cyclooxygenase-2 (COX-2) pathways. Additionally, the potential of liquid biopsies as a non-invasive source and the clinical utility of studied biomarkers is also explored. Overall, and although most studies offer a mechanistic perspective linking a strong proinflammatory Th1 cell response associated with, but not limited to, chronic infection with Helicobacter pylori, promising data recently published highlights not only the diagnostic value of microbial biomarkers but also the potential of gastric juice as a liquid biopsy pushing forward the concept of functional endoscopy and personalized care in gastric cancer early diagnosis and surveillance.

No evidence for a causal link between Helicobacter pylori infection and nonalcoholic fatty liver disease: A bidirectional Mendelian randomization study

Although clinical studies have shown the possible relationship between Helicobacter pylori (H. pylori) infection and the development of nonalcoholic fatty liver disease (NAFLD), their causal relationship is still unknown. This bidirectional Mendelian randomization (MR) study aimed to investigate the causal link between H. pylori infection and NAFLD. Two previously reported genetic variants SNPs rs10004195 and rs368433 were used as the instrumental variables (IVs) of H. pylori infection. The genetic variants of NAFLD were extracted from the largest genome-wide association study (GWAS) summary data with 1,483 cases and 17,781 controls. The exposure and outcome data were obtained from the publicly available GWAS dataset. Then, a bidirectional MR was carried out to evaluate the causal relationship between H. pylori infection and NAFLD. In addition, the GWAS data were also collected to explore the causal relationship between H. pylori infection and relevant clinical traits of NAFLD, including triglycerides, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), fasting blood glucose (FBG), and body mass index (BMI). Genetically predicted H. pylori infection showed no association with NAFLD both in FinnGen GWAS (OR, 1.048; 95% CI, 0.778-1.411; value of p = 0.759) and the GWAS conducted by Anstee (OR, 0.775; 95% CI, 0.475-1.265; value of p = 0.308). An inverse MR showed no causal effect of NAFLD on H. pylori infection (OR,0.978;95% CI, 0.909-1.052; value of p = 0.543). No significant associations were observed between H. pylori infection and the levels of triglycerides, LDL-C, HDL-C, or FBG, while H. pylori infection was associated with an increase in BMI. These results indicated that there was no genetic evidence for a causal link between H. pylori and NAFLD, suggesting that the eradication or prevention of H. pylori infection might not benefit NAFLD and vice versa.

Innate-Immunity Genes in Obesity

The main functions of adipose tissue are thought to be storage and mobilization of the body’s energy reserves, active and passive thermoregulation, participation in the spatial organization of internal organs, protection of the body from lipotoxicity, and ectopic lipid deposition. After the discovery of adipokines, the endocrine function was added to the above list, and after the identification of crosstalk between adipocytes and immune cells, an immune function was suggested. Nonetheless, it turned out that the mechanisms underlying mutual regulatory relations of adipocytes, preadipocytes, immune cells, and their microenvironment are complex and redundant at many levels. One possible way to elucidate the picture of adipose-tissue regulation is to determine genetic variants correlating with obesity. In this review, we examine various aspects of adipose-tissue involvement in innate immune responses as well as variants of immune-response genes associated with obesity.

The role of toll-like receptors in peptic ulcer disease

Helicobacter pylori (HP) is the primary etiologic factor that induces events in the immune system that lead to peptic ulcers. Toll-like receptors (TLRs) are an important part of the innate immune system, as they play pivotal roles in pathogen-associated molecular pattern (PAMP) recognition of HP as well host-associated damage-associated molecular patterns (DAMPs). Recent advancements such as COX-2 production, LPS recognition through TLR2, CagL, and CagY protein of HP activating TLR5, TLR9 activation via type IV secretion system (T4SS) using DNA transfer, TLR polymorphisms, their adaptor molecules, cytokines, and other factors play a significant role in PUD. Thus, some novel PUD treatments including Chuyou Yuyang granules, function by TLR4/NF-κB signaling pathway suppression and TNF-α and IL-18 inhibition also rely on TLR signaling. Similarly glycyrrhetinic acid (GA) treatment activates TLR-4 in Ana-1 cells not via TRIF, but via MYD88 expression, which is significantly upregulated to cure PUD. Therefore, understanding TLR signaling complexity and its resultant immune modulation after host-pathogen interactions is pivotal to drug and vaccine development for other diseases as well including cancer and recent pandemic COVID-19. In this review, we summarize the TLRs and HP interaction; its pathophysiology-related signaling pathways, polymorphisms, and pharmaceutical approaches toward PUD.

The Role of Toll-Like Receptor-2 in Clostridioides difficile Infection: Evidence From a Mouse Model and Clinical Patients

Background

Clostridioides difficile is the leading cause of nosocomial infectious diarrhea. Toll-like receptors (TLRs) are the major components of innate immunity that sense pathogens. The relationship between TLRs and C. difficile infection (CDI) was analyzed in clinical patients and a mouse model.

Materials and Methods

A prospective investigation was conducted in medical wards of Tainan Hospital, Ministry of Health and Welfare, Tainan, Taiwan, from January 2011 to January 2013. Adult patients were followed up for the development of CDI. Single nucleotide polymorphisms (SNPs) of TLR2 and TLR4 were analyzed to assess the relationship between genetic polymorphisms and the development of CDI. A mouse model of CDI was used to investigate the pathogenic role of TLRs in CDI, TLR2 and TLR4 knockout (Tlr2-/- and Tlr4-/-) mice.

Results

In the prospective study, 556 patients were enrolled, and 6.5% (36) of patients, accounting for 3.59 episodes per 1000 patient-days, developed CDI. Of 539 patients with available blood samples, the TLR2 rs3804099 polymorphism was more often noted in those with CDI than in those without CDI (64.5% vs. 46.1%; P = 0.046) but was not significant in multivariate analysis. Because the TLR2 rs3804099 polymorphism was moderately associated with CDI, the role of TLR2 and TLR4 was further evaluated in a mouse model. Both Tlr2-/- and Tlr4-/- mice showed more severe CDI disease than wild-type mice in terms of body weight change and fecal content five days after oral challenge with C. difficile. Furthermore, Tlr2-/- mice suffered from more severe disease than Tlr4-/- mice, as evidenced by stool consistency, cecum weight, and survival rate.

Conclusion

The TLR2 rs3804099 polymorphism is marginally associated with the development of CDI, and the pathogenic role of TLR2 is further supported by a mouse model.

Association of toll-like receptor 4, 5 and 10 polymorphisms with Helicobacter pylori-positive peptic ulcer disease in a center in Jordan

BACKGROUND

Helicobacter pylori infection is widespread, affecting about 50% of the global population. Polymorphisms in host genes such as the toll-like receptor 4 (TLR4) might affect the susceptibility and severity of infection and treatment success.

OBJECTIVE

Investigate the susceptibility and severity of H pylori infection with host TLR4 (rs11536889, rs4986790, rs200109652, rs10759932), TLR5 (rs5744174, rs2072493, rs746250566), TLR10 (rs559182335, rs10004195) polymorphisms.

DESIGN

Analytical, cross-sectional.

SETTING

Endoscopy clinic at tertiary care center.

PATIENTS AND METHODS

Genomic DNA was extracted from formalin-fixed paraffin-embedded tissues collected from H pylori-infected patients and healthy individuals. The single nucleotide polymorphisms (SNPs) within the targeted TLR genes were genotyped to assess the genetic association of various SNPs with disease severity.

MAIN OUTCOME MEASURES

Effect of genotype distribution on H pylori infection.

SAMPLE SIZE

250 peptic ulcer patients and 217 controls.

RESULTS

The TLR10 genotype showed no significant association with H pylori infection except for rs10004195 (T>A) (P=.002). The genotype frequency of Rs5744174 in TLR5 had a significant association with the presence of H pylori infection (P=.046, OR=0.52). Except for gender (P=.022), there were no significant associations between clinical and demographic variables and SNPs relating to the severity of the H pylori infections.

CONCLUSIONS

Our findings are consistent with differences in severity of H pylori infection due to TLR SNPs in different ethnic groups. Understanding differences in genetic susceptibility could help in classifying patients and matching patients with various treatment options on a genetic basis.

LIMITATIONS

Lack of H pylori pathogenicity features assessment.

CONFLICTS OF INTEREST

None.

Vaccine development against Helicobacter pylori: from ideal antigens to the current landscape

Introduction: The interest of the world scientific community for an effective vaccine against Helicobacter pylori infection arises from its high prevalence and association with many diseases. Moreover, with an immunological response that is not always effective for the eradication of the bacteria and an increasing antibiotic resistance in the treatment of this infection, the search for a vaccine and new therapeutic modalities to control this infection is urgent.Areas covered: We bring an overview of the infection worldwide, discussing its prevalence, increasing resistance to antibiotics used in its therapy, in addition to the response of the immune system to the infection registered so far. Moreover, we address the most used antigens and their respective immunological responses expected or registered up to now. Finally, we address the trials and their partial results in development for such vaccines.Expert opinion: Although several studies for the development of an effective vaccine against this pathogen are taking place, many are still in the preclinical phase or even without updated information. In this sense, taking into account the high prevalence and association with important comorbidities, the interest of the pharmaceutical industry in developing an effective vaccine against this pathogen is questioned.