Published online Mar 28, 2015. doi: 10.3748/wjg.v21.i12.3636
Peer-review started: September 12, 2014
First decision: October 29, 2014
Revised: December 1, 2014
Accepted: January 16, 2015
Article in press: January 16, 2015
Published online: March 28, 2015
Core tip: Persistent inflammation of the stomach induced by Helicobacter pylori (H. pylori) can have consequences on the rest of the body. Despite the vigorous innate and adaptive immune response against the bacterium, H. pylori escape and evade host responses by a variety of mechanisms. Low tryptophan levels and increased concentrations of its degradation product, kynurenine, may be directly involved in diminished T-cell responsiveness to antigenic stimulation in cancer. H. pylori seropositive colorectal cancer patients with significantly higher kynurenine/tryptophan and reduced nitric oxide suggested that H. pylori might support immune tolerance leading to cancer development, even in patients without an apparent upper gastrointestinal tract disease.