Helicobacter pylori is a Gram-negative spiral shaped bacterium that can colonize the mucous layer of human gastric epithelium. The organism, one of the most common chronic bacterial infections of humans, is associated with chronic active gastritis and is implicated in peptic ulceration and gastric cancer. Disease outcome depends on many factors, including bacterial genotype and host physiology, genotype and dietary habits. Relatively little is known about the response of the human host to H. pylori infection. The aim of our study was to identify changes in gene expression in human gastric epithelial cells in-vitro upon infection with H. pylori using high-density cDNA array hybridization.

KATO III gastric epithelial cells were cultured with H. pylori or no bacterium as control. mRNA, isolated at 0 minutes, 45 minutes, 3 hours and 24 hours post-infection, was used as a template for the synthesis of radioactively labelled 1st strand cDNA for hybridization to high-density gridded arrays of PCR-amplified cDNA clone inserts immobilized on nylon membranes. The arrays included a non-redundant version of the human IMAGE Consortium cDNA array (46,302 clones), a redundant spleen cDNA library (12,288 clones), a custom “inflammatory gene set” and Clontech Atlas grids. Hybridization signals were captured by phosphorimaging and image analysis performed using a GW proprietary PC-based software (DGENT). Differentially expressed sequences were confirmed by a second hybridization.

Analysis of the hybridized cDNA arrays identified many genes to be differentially expressed. Sequence analysis revealed more than 200 genes of known function and 60 novel genes/ESTs being differentially expressed. This included sequences encoding growth factors/receptors, cytokines/receptors, apoptosis proteins, oncoproteins and transcription factors. Subsequent RT-PCR of human gastric biopsy samples showed that several of these genes are also differentially expressed in vivo (for example p23/histamine releasing factor, amphiregulin and a novel gene hprg1).

The identification of a large number of H. pylori host response genes by cDNA array hybridization demonstrates the usefulness of this technology. Also, the cell culture in vitro model has shown correlations with human in vivo infection. Further in vivo gene expression studies and characterization of the genes/pathways involved will improve our understanding of the host response to infection and may aid vaccine development for this important pathogen.