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Abstract

Infection with the bacterium Helicobacter pylori (H. pylori) is the main cause for gastric cancer (GC) and although approximately half of the world population is infected, only 3 5% develop the neoplasia. Globally, this makes GC the fifth most commonly diagnosed cancer and fourth most common cause of death from cancer. In order to enable efficient screening for GC, identifying individuals at risk is desirable, which could be achieved by measuring antibody responses against H. pylori. So far, serological associations between GC and H. pylori have mainly been described for an overall infection or for well-known virulence factors, but did not show sufficiently strong associations to achieve a relevant stratification for GC risk. The aim of this thesis was to identify further H. pylori antigens, which could be used to enhance GC risk stratification. For this purpose, I generated H. pylori microarrays presenting a multitude of antigens in parallel. A pilot study was conducted probing 245 different H. pylori antigens with sera from non-cardia gastric cancer (NCGC) patients and healthy controls. I was able to confirm the well-known association between NCGC and antibodies against the Cytotoxin-associated gene A (CagA) and described a new association between NCGC and antibodies against the Helicobacter outer membrane porin A (HopA). In a next step, I expanded the antigen repertoire of the H. pylori microarrays to a total of 1,833 non-redundant antigens by including additional H. pylori strains from different countries to account for the genetic variety of the bacterium. H. pylori multi strain microarrays were probed with sera from the cross-sectional Shanxi study (58 cases and 58 controls) and the prospective Linxian General Population Nutrition Intervention Trial (119 cases and 119 controls), both samples in Northern China. Subsequently, I selected 22 H. pylori antigens to be further validated using high-throughput multiplex serology. To enable this, I expressed the selected H. pylori antigens as GST-X-TAG fusion proteins and measured respective antibody responses in >1,600 samples derived from participants of two Chinese studies. Associations between NCGC and antibodies against individual H. pylori proteins were examined by logistic regression analyses. Thereby, I confirmed HopA as new serological NCGC marker which performed comparable to the widely used CagA. The other new H. pylori antigens individually did not show a consistent association with NCGC between the analyzed studies. However, a combinational approach could potentially enable the generation of enhanced GC risk models. Future studies should address the clinical applicability of the newly identified markers to potentially promote secondary prevention of GC.