TNF- has numerous biological activities including induction of chemokine expression, and is involved in many gastric injuries. C-C chemokines (MCP-1 and MIP-1) and C-X-C chemokines (MIP-2 and CINC-2) mediate chemotaxis of monocytes and neutrophils, respectively. We examined the roles of TNF- and dynamics of chemokine expression in gastric ulceration including ulcer recurrence and indomethacin-induced injury. Rats with healed chronic gastric ulcers received intraperitoneal TNF- to induce ulcer recurrence. Some rats were given neutralizing antibodies against neutrophils or MCP-1 together with TNF-. In a separate experiment, rats were orally administered 20 mg/kg indomethacin with or without pretreatment with pentoxifylline (an inhibitor of TNF- synthesis) or anti-MCP-1 antibody. TNF- (1 µg/kg) induced gastric ulcer recurrence after 48 hours, which was completely prevented by anti-neutrophil antibody. TNF- increased the number of macrophages and MCP-1 mRNA expression in scarred mucosa from 4 hours, whereas it increased myeloperoxidase activities (marker of neutrophil infiltration) and mRNA expression of MIP-2 and CINC-2 from 24 hours. Anti-MCP-1 antibody inhibited leukocyte infiltration with reduction of the levels of C-X-C chemokines, and prevented ulcer recurrence. Indomethacin treatment increased TNF-/chemokines mRNA expression from 30 minutes, and induced macroscopic erosions after 4 hours. Pentoxifylline inhibited the indomethacin-induced gastric injury with reduction of neutrophil infiltration and expression of chemokine (MCP-1, MIP-2 and CINC-2). Anti-MCP-1 antibody also inhibited the injury and these inflammatory responses, but did not affect TNF- mRNA expression. In conclusion, increased MCP-1 triggered by TNF- may play a key role in gastric ulceration, by regulating leukocyte recruitment and chemokine expression.