Major human pathogen Helicobacter pylori (Hp) can colonize the gastric mucosa causing inflammation and being of potential risk for gastric cancer development but the contribution of fibroblasts to the pathogenesis of Hp in the stomach has been little studied. Normal stroma contains few fibroblasts, especially myofibroblasts, but their number rapidly increases in the reactive stroma surrounding inflammatory region and neoplastic tissue. We determined the effect of coincubation of cultured rat gastric fibroblasts with alive Hp on the transdifferentiation of fibroblasts into myofibroblasts associated with Hp-induced inflammation and neoplasia. Gastric mucosal samples were harvested from 8-week-old Spraque-Dowley rats and cultured to obtain the sub-confluent fibroblasts. The isolated fibroblasts were infected with 1 x 10(9) of live Hp (ATCC 700824, cagA+, vacA+) per dish and incubated in humidified atmosphere for 3, 24 and 48 hours. At respective times, fibroblasts were harvested and the expression of mRNA for α-smooth muscle actin (SMA), hypoxia inducible factor (HIF)-1α, collagen I, heat shock protein (HSP)-70, heme oxygenase (HO)-1, Bax and Ki67 transcripts was determined by RT-PCR with specific primers. Hp increased the transdifferentiation of fibroblasts into myofibroblasts as reflected by the time-dependent overexpression of mRNA for α-SMA. The increased expression of HIF-1α and collagen I was observed in fibroblasts co-cultured with Hp. The expression of HSP70 which was negligible in isolated fibroblasts incubated with vehicle (saline) showed time-dependent 2-3 fold increase in those incubated with Hp. The HO-1 mRNA was strongly expressed in rat gastric fibroblasts without or with the co-incubation with Hp. The mRNA for Bax was progressively downregulated within the time of incubation while no significant changes in expression of proliferation marker Ki67 were recorded. We conclude that Hp-induced transdifferentiation of fibroblasts into myofibroblasts involves an increased expression of the early carcinogenic marker HIF-1α, and inhibition of proapoptotic Bax expression, and 2) the overexpression of HSP70 and the unchanged expression HO-1 and Ki67 probably represent the enhanced protective activity of Hp-infected fibroblasts to maintain their own integrity under inflammatory action of this bacteria and its cytotoxins.