The present invention provides methods for diagnosing and treating Helicobacter pylori infection by using a monoclonal antibody to detect Helicobacter pylori neutrophil-activating protein (HP-NAP) and inhibit the activity thereof. The monoclonal antibody is an anti-FLAG antibody that binds to a specific epitope on HP-NAP for the detection of HP-NAP in its native form or denatured form. Furthermore, the present invention uses the anti-FLAG antibody to block HP-NAP-induced production of reactive oxygen species by human neutrophils. Thus, the present invention can be applied in clinical diagnosis of Helicobacter pylori infection as well as treatment of the infection via inhibiting Helicobacter pylori-induced inflammation.
