Helicobacter pylori manipulates B cell responses, favouring the differentiation of regulatory T cells via cell contact-dependent mechanisms.

Regulatory T cells (Tregs) play a critical role in the persistence and pathogenesis of Helicobacter pylori infection. However, the mechanisms by which Tregs expand during the infection remain poorly understood. Regulatory B cells (Bregs) have been identified as Treg-inducing, but their role in H. pylori infection is unclear. Flow cytometry was used to characterise Bregs and Tregs in peripheral blood from H. pylori infected and uninfected patients, gastric lymphocytes were analysed by immunohistochemistry. An in vitro B-T cell coculture system was employed to evaluate murine and human Treg differentiation. Higher frequencies of CD19+IL-10+ Bregs (median 85% increase; p=0.007) and CD4+CD25hi Tregs (129% increase; p=0.048) were present in the peripheral blood of infected patients. An association was found between numbers of Pax5+ B cells and Foxp3+ Tregs (p<0.0001) in the infected gastric mucosa, and B and T cells were in close proximity. H. pylori directly activated murine B cells in vitro to produce >6-fold higher IL-10 concentrations (p<0.04), with enhanced CD25hiFoxp3+ Treg differentiation (p<0.001). Similar results were found with human B cells. Generation of Tregs was unaffected by anti-IL-10 neutralising antibody, but frequencies of Tregs were halved when B and T cells were separated by a membrane (p<0.05). VacA and CagA virulence factors did not influence the response. In conclusion, H. pylori induced Breg responses in vitro, promoting Treg expansion, via B-T cell contact and soluble factors other than IL-10. Increased frequencies and proximity of these cell populations in the infected gastric mucosa suggests this mechanism could potentially occur in vivo.