pylori-infected individuals [38], especially in children [39]. H. pylori is capable of actively skewing T-cell

responses towards Alisertib cost a regulatory phenotype, thereby suppressing Th17-driven immunity and facilitating persistence [40,41]. The proposed mechanisms involve the interaction of H. pylori with DCs, which upon in vitro exposure to the bacteria appear to preferentially prime Treg over Th17 responses [40] and fail to produce pro-inflammatory cytokines [41]. An additional mechanism of immune escape was suggested by Sayi et al. [8], who showed that preferential ligation of the anti-inflammatory TLR-2, as opposed to other TLRs, by Helicobacter PAMPs may favor immunoregulatory over effector responses. TLR-2−/− mice are better able than wild-type mice to control Helicobacter infection, but as a consequence develop accelerated gastric immunopathology [8]. The functions of two novel players with immunoregulatory properties were recently elucidated with respect to their involvement in H. pylori persistence [14,42]. In addition to olfactomedin discussed already [14], the activation of a novel protease-activated

receptor, PAR-1, was shown by Wee et al. [42] to limit H. pylori-associated gastritis by interfering with pro-inflammatory cytokine production. PAR-1−/− animals were better able than wild type to control the infection, JQ1 molecular weight but also exhibited more severe gastritis and higher H. pylori-specific serum titers, implying that PAR-1 activation serves to protect the host against excessive immunopathology [42]. Lewis et al. [43] explored the molecular mechanism of arginase II-mediated immune evasion in macrophages and examined the effects of arginase II gene targeting on H. pylori colonization and H. pylori-associated

gastritis [44]. H. pylori induced arginase medchemexpress II expression in macrophages; the pharmacological inhibition of arginase activity increased NO production by infected macrophages via enhancing iNOS translation, resulting in increased killing of H. pylori [43]. Consistent with a role for arginase II in the intracellular depletion of L-arginine and a concomitant reduction in NO-mediated bacterial killing, Arg2−/− mice expressed higher levels of iNOS and cleared H. pylori more efficiently than wild-type mice [44]. The first weeks and months of life are characterized by a default inclination of the neonatal immune system to induce peripheral Treg cells upon antigenic stimulation [45]. Arnold et al. [46] examined the effects of early-life H. pylori acquisition on disease outcome. In a murine model of cagPAI+ infection, neonatally infected mice developed immunological tolerance to H. pylori, which manifested in higher bacterial loads, decreased serum titers and local cytokine responses, and a strongly reduced risk of developing gastric cancer precursor lesions later in life [46]. It is tempting to speculate that the reported inverse correlation between H.