The gut bacterium Helicobacter pylori can cause gastritis and cancer when introduced into adults but can be pro-tolerogenic in neonates. In the Journal of Clinical Investigation, Müller and colleagues identify the mechanism by which H. pylori infection can engender tolerance. Both in vivo and in vitro, H. pylori suppresses the activation of dendritic cells (DCs) in a contact-dependent way, which leads to a 'semi-mature' state. These semi-mature DCs are poor antigen-presenting cells and also convert naive effector cells into Foxp3+ regulatory T cells (Treg cells). These Treg cells in turn suppress an experimental model of asthma, a finding consistent with some results obtained with humans showing amelioration of autoimmune disease associated with H. pylori infection. The ability of DCs exposed to H. pylori to elicit Treg cells is entirely dependent on their production of interleukin 18 and intact signaling via its receptor in the target T cells.

J. Clin. Invest. 122, 1082–1096 (2012)