Regulatory B and T cells in Helicobacter pylori infection

In the human gastric mucosa, an inflammatory response stimulated by H. pylori infection can lead to gastric cancer and peptic ulcer disease. Expression of the i1 active variant of Vacuolating Cytotoxin A (VacA) by the colonising bacterial strain has been identified as an independent risk factor for disease. VacA skews the adaptive immune response towards a regulatory phenotype to promote persistent H. pylori colonisation. In H. pylori-infected individuals, regulatory T cells (Tregs), which suppress inflammation through mechanisms including interleukin-10 (IL-10) production, are thought to play a role in protection against extra-gastric diseases such as multiple sclerosis and oesophageal cancer. IL-10 is an immunomodulatory cytokine which is expressed by several immune cell types including regulatory B cells (Bregs), whose role in H. pylori infection is unclear. Blood was donated by uninfected and infected patients, and those who underwent successful eradication of their H. pylori infection. A flow cytometry antibody panel was developed to quantify the relative frequencies of peripheral blood Bregs and Tregs, and investigate differences according to H. pylori status. Mice were also infected with H. pylori to determine VacA i1 versus i2 differences in the induced regulatory B and T cell frequencies. Stool samples were collected from patients to develop a VacA i-region PCR-based diagnostic test. Results showed that compared to during H. pylori infection, the proportion of IL-10-producing Tregs in the peripheral blood of patients declined after successful eradication therapy. A pilot study in mice revealed B lymphocytes to be another important source of IL-10, and the population expanded after H. pylori infection. In a study of H. pylori-positive, H. pylori-negative and H. pylori-eradicated patients, there were no significant differences in peripheral blood Breg or IL-10+ Breg frequencies. Data from an expanded mouse study using blood and spleen showed that VacA variants in a colonising H. pylori strain did not induce differences in Breg or Treg frequencies 9 weeks after wildtype or mutant H. pylori SS1 infection. The H. pylori 16S gene was successfully detected in stool DNA samples and could be used to determine infection status, but the development of a vacA i-region PCR-based typing stool test was unsuccessful. Previous work in the research group has identified how Treg frequencies are associated with H. pylori infection and disease. While Bregs are capable of producing IL-10 after stimulation, their role in H. pylori infection in mice and humans appears to be limited. The consistency of peripheral blood Treg frequencies in patients from their infected state until two years post-eradication is a start to understanding whether H. pylori-induced extra-gastric protection may also be maintained after eradication. While stool remains a promising resource for non-invasively diagnosing H. pylori infection worldwide, there are strong concerns about contamination and reproducibility which are unlikely to be overcome for use in a clinical setting