The catalase katA gene of Helicobacter pylori encodes an antioxidant enzyme to protect the bacteria from environmental toxic oxygen species. In this study, the baculovirus-insect cell expression system was used to express the full-length katA gene from the Taiwanese H. pylori TW-34 strain. Three lipidopteran insect cell lines (Sf9, Sf21, High5) were evaluated to produce the recombinant catalase (KatA) using serum-containing and serum-free media. Large-scale production and purification of the recombinant KatA protein was achieved in a 2-1 bioreactor and through the use of immobilized metal affinity chromatography (IMAC). Human gastric carcinoma AGS cells were co-cultured with H. pylori and the presence of the purified KatA protein resulted in a significant decrease in the apoptotic bodies observed in AGS cells. Our present study is the first report to demonstrate the functionality of recombinant KatA protein expressed in baculovirus-infected insect cells to protect human gastric cell apoptosis against H. pylori insults. (C) 2004 Elsevier Inc. All rights reserved.