The stomach pathogen Helicobacter pylori is present in approximately half the global population and is the leading cause of gastric cancer. This bacterium has developed various strategies to supress host immune responses and establish a chronic infection. We hypothesised that one strategy may be via membranous nanoparticles, known as extracellular vesicles (EVs), which are released by bacteria and that play an important role in communication with the host. To identify factors in H. pylori EVs that modulate host immune responses, we used H. pylori EVs to prime human peripheral blood mononuclear cells (PBMCs) from healthy volunteers (n=9). PBMCs were then activated with the T cell mitogen, concanavalin A (ConA), and cytokine responses measured by ELISA. PBMCs that had been primed with EVs produced reduced levels of the pro-inflammatory cytokine IFN-g to ConA stimulation than unprimed cells (p < 0.05). By screening EVs from different H. pylori mutant strains, we identified two factors with immunosuppressive activity. One of these factors was a soluble lytic transglycosylase (SLT) that is involved in peptidoglycan turnover in the bacterial cell wall, resulting in the shedding of peptidoglycan fragments that are sensed by the innate immune protein, nucleotide-binding oligomerisation domain-containing protein 1 (NOD1). We found that splenocytes from Nod1-/- mice produced reduced levels of the anti-inflammatory cytokine IL-10 when stimulated with H. pylori EVs from either WT or slt strains (p < 0.05). Unexpectedly, we also found that H. pylori slt mutants exhibit morphological defects with membrane bulging, a finding that has not been reported previously. Taken together, we propose that peptidoglycan associated with H. pylori EVs is a factor capable of contributing to the suppression of host immune responses and allowing bacterial persistence in the human stomach.