H. pylori seropositive patients with AIP showed significantly lower antibody responses to 3 antigens (Cagδ, CagA, HP0231) and patients with chronic pancreatitis to 9 (Cad, Cagδ, CagA, CagM, HP0305, HpaA, HyuA, Omp, and VacA) compared to H. pylori seropositive patients with other gastrointestinal tract cancers as a reference, with there being a significant increase of antibody reactivities to VacA in H. pylori seropositive patients with AIP and NapA in those with pancreatic cancer. This evidence concerns the gene OMP and pancreatic neoplasm.