Gastric infection, as well as inflammation, caused by Helicobacter pylori, activates the production of cytokines and chemokines by mononuclear cells; interleukin-8 (IL-8) is one of the major inflammatory chemokines. Since H. pylori does not invade mucosal tissue, we observed the effect of the water extract of H. pylori (HPE), containing shed factors, on the production of IL-8 by human peripheral blood monocytes and the human monocyte cell line THP-1. HPE-treatment induced activation of the mitogen-activated protein kinases (MAPKs) ERK (extracellular signal-regulated kinase), p38 and JNK (c-Jun N-terminal kinase), an effect which was not dependent on the presence of the cag pathogenicity island. p38 MAPK activation was sustained. The specific inhibitors, U0126 (for ERK1/2 signalling) and SB203580 (for p38 MAPK signalling), both abrogated IL-8 secretion from HPE-treated THP-1. Dominant-negative mutants of the upstream kinases MEK1 (MAPK/ERK kinase 1), MKK (MAPK kinase) 6 and MKK7 also inhibited IL-8 secretion, pointing to a role of all three MAPKs in HPE-mediated IL-8 release. The inhibitory effects of polymyxin B and anti-CD14 antibody suggested that the effect of HPE on MAPKs was mediated by H. pylori lipopolysaccharide (LPS). By analysis of IL-8-promoter-driven luciferase gene expression, we observed that the effects of HPE-induced nuclear factor-kappaB (NF-kappaB) activation and MAPK signalling were mediated at the level of the IL-8 promoter. While ERK1/2 activation could be linked to enhanced DNA binding of activator protein-1 (AP-1), p38 MAPK signalling did not affect AP-1 DNA binding. Taken together, these results provide the first evidence that LPS from H. pylori stimulates IL-8 release from cells of the monocytic lineage through activation of NF-kappaB and signalling along MAPK cascades. The stimulation of MAPK signalling in macrophages by LPS of H. pylori amplifies the inflammatory response associated with gastric H. pylori infection and needs to be taken into consideration when developing therapeutics based on these signalling pathways.