Update on the immunologic basis of Helicobacter pylori gastritis.

PURPOSE OF REVIEW: Helicobacter pylori is a ubiquitous bacterial pathogen that has evolved to chronically infect the gastric mucosal surface, evade host immune clearance, and cause peptic ulcer disease or gastric neoplasia in a significant minority of infected individuals. Understanding the colonization, persistence, and virulence determinants of the bacterium as well as the innate and adaptive immune responses of the host are critically important if we are to develop novel treatment strategies for eradication of infection and prevention of H. pylori-induced gastroduodenal disease. RECENT
FINDINGS: Substantial progress has been made in understanding the role of CagA in altering gastric epithelial cell signaling pathways. Intracellular CagA has been shown to activate the Ras/MEK/ERK mitogen activated protein kinase cascade and to associate with epithelial tight-junction scaffolding protein ZO-1. CagA was shown to regulate cellular responses and possibly contribute to gastritis by phosphorylation-dependent pathways. A phosphorylation-independent mechanism for CagA intracellular effects has also been proposed. The potential for CagA to disrupt the apical junctional barrier and for the outer membrane protein oipA to promote IL-8 secretion and gastric inflammation have also been explored. A number of different mechanisms by which H. pylori escapes and evades host immune attack to cause chronic indolent inflammation have been uncovered. Meanwhile, the examination and development of new adjuvants and vaccine delivery mechanisms to induce mucosal immune responses against key bacterial antigens has been a continuing focus of investigation in both animal and human studies.
SUMMARY: H. pylori induces gastritis through production of a variety of antigens, virulence factors, and soluble mediators. The bacterium also dysregulates, disarms, and evades host immune responses to maintain chronic colonization of the gastric mucosa. Understanding the mechanisms of its growth and survival in the human stomach are essential for the development of an effective vaccine and other novel eradication strategies.