Alzahrani, Shatha
(2024)
Investigating links between the immune response and Helicobacter pylori-mediated disease outcomes.
PhD thesis, University of Nottingham.
Abstract
Background: Helicobacter pylori is the primary cause of chronic gastritis and peptic ulcer disease and a significant risk factor for gastric adenocarcinoma. Numerous studies have reported the role of cytokines in the pathogenesis of gastric inflammation during H. pylori infection and disease outcomes are more likely with virulent strains that carry the Cytotoxin Associated Gene Pathogenicity Island (cag PAI). Interleukin-16 (IL-16) is a multifunctional cytokine implicated in various chronic inflammatory conditions, such as inflammatory bowel disease, asthma, and rheumatoid arthritis. Elevated IL-16 levels have previously been observed in the serum of gastric cancer patients compared to healthy controls. However, the connection between IL-16 production and H. pylori infection remained unclear. A comprehensive study profiling plasma cytokine levels across different stages of gastric cancer prognosis, including non-atrophic gastritis, atrophic gastritis, intestinal metaplasia, and gastric cancer could provide insights into the correlation between cytokines and disease progression and their potential as biomarkers for gastric cancer. Previous research demonstrated H. pylori's ability to induce IL-16 production in gastric epithelial cell lines. Since monocytes and dendritic cells are among the first cells to encounter H. pylori after it breaches the gastric epithelial barrier, the effect of H. pylori and its virulence factors on IL-16 production in these cells has not been explored.
Aims; A key objective of this thesis was to measure IL-16 concentrations in plasma samples from H. pylori-positive and negative patients and to investigate potential links between IL-16 and H. pylori-mediated gastro-duodenal disease. The study explored relationships between serum IL-16 and colonization by more virulent cagA-positive H. pylori strains, associations with gender and smoking status, the presence and severity of histopathological changes in the gastric mucosa, oesophageal diseases, and the impact of H. pylori eradication therapy and other co-expressed inflammatory cytokines. Additionally, the thesis aimed to explore the effects of H. pylori infection and its virulence factors, and bile metabolites, on cytokine production by monocytes and dendritic cells. Another significant aim was to understand differential cytokine expression concerning gastric cancer progression and their potential as biomarkers for the disease.
Materials and Methods; Gastric biopsy and plasma samples were collected from H. pylori-infected and non-infected patients, including those who had received successful eradication therapy for the infection. IL16 mRNA and plasma IL-16 levels were measured using RT-qPCR and a commercial ELISA kit respectively.
cag PAI-negative H. pylori, cag PAI-positive H. pylori, and isogenic virulence factor mutants co-cultured with human peripheral blood monocytes, monocyte-derived dendritic cells, and THP-1 and KG-1 cell lines for 24 hours. IL-6, IL-10 and IL-16 cytokines were measured by ELISA and flow cytometry.
320 plasma samples were collected from H. pylori-infected and uninfected patients with various gastric conditions, including non-atrophic gastritis, atrophic gastritis, intestinal metaplasia, and gastric cancer. Concentrations of cytokines and chemokines (including IL-1β, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-16, IL-17, IL-18, IL-23, CCL2, CCL3, CXCL10, IFN-γ, and TNF-α) were measured using multiplex assays from Mesoscale Discovery (MSD).
Results: IL-16 was detected in all plasma samples, from both H. pylori-infected and uninfected patients, with wide variation in both groups, and there were no significant differences. IL-16 levels were not significantly associated with gender, age, or smoking status, nor did they differ based on whether the colonizing strain was cagA-positive or negative. No link was found between IL-16 concentration and histopathological changes in the gastric mucosa, or oesophageal diseases, and there were no significant differences in plasma IL-16 levels before and after H. pylori eradication. The results showed that H. pylori virulence factors did not alter cytokine production by monocytes and dendritic cells. Interestingly, GC patients exhibited a significant reduction in IL-16 plasma levels compared to individuals with gastritis, peptic ulcer disease, and healthy controls. This outcome contradicts a previous study that reported elevated IL-16 serum concentrations in GC patients relative to healthy controls, likely due to different patient recruitment criteria. This finding's reliability was further substantiated by similar results from another ethnic group, a Mexican patient population, which showcased a reduction in both IL-16 and IL-18 plasma levels in GC patients compared to those with non-atrophic gastritis, atrophic gastritis, and intestinal metaplasia.
Conclusion: This comprehensive study analyzed various sample types, including plasma, gastric tissue, cell lines, and peripheral blood monocytes, utilizing techniques such as ELISA, MSD, RT-qPCR, and Flow Cytometry. Participants were categorized as healthy controls, H. pylori-infected and uninfected patients, individuals with different gastric conditions, and those from diverse ethnic backgrounds. The study considered multiple parameters potentially influencing plasma IL-16 levels, including age, gender, smoking status, cagA status, and oesophageal disorders. The study concluded that H. pylori infection does not affect IL-16 cytokine levels.
A suggested correlation between IL-16 and IL-18 cytokines in the context of gastric cancer presents a novel research avenue. Both interleukins could be components of a larger immune regulatory network. Disruption in this network might lead to inadequate tumor control. Further research should be conducted to explore how IL-16 and IL-18 interact and influence each other in the context of cancer immunology. Investigating the combined roles of IL-16 and IL-18 can provide deeper insights into their contributions to immune response modulation.
Actions (Archive Staff Only)
 |
Edit View |
Tools
Tools
