Antigenic role of stress-induced catalase of Salmonella typhimurium in cell-mediated immunity

Abstract

The ability of the H2O2-induced catalase of Salmonella typhimurium to induce cell-mediated immunity against S. typhimurium infection in mice was examined. When exponentially growing cells of S. typhimurium were treated with 20 μM H2O2, the cells resisted killing by 1 mM H2O2 and showed the induction of a new species of catalase in addition to the constitutively produced one. Two molecules of catalases in S. typhimurium were isolated from mutant strains: H2O2-induced catalase (catalase II, 320 kDa), from a regulatory gene-deficient oxyR1 mutant, and constitutive catalase (catalase I, 350 kDa), from a katG gene-deleted mutant. When mice were inoculated with a sublethal dose of live cells, an intensive protective immunity (100% survival at 3 weeks) after challenge with a virulent strain associated with the delayed-type footpad hypersensitivity (DTH) reactions to both catalase I and catalase II was induced. Conversely, mice immunized with formalin-killed virulent S. typhimurium did not elicit protective immunity or DTH to either catalase. When mice were immunized with catalase I or catalase II, an enhanced protection (to a certain extent: 50% survival at 3 weeks) was induced in mice immunized with catalase II associated with DTH which did not cross-react with catalase I but not in those given catalase I. These results suggest that H2O2-induced stress proteins, including catalase II, are the dominant antigens for cell-mediated immunity in live cells of S. typhimurium and that a burst of such stress proteins in live salmonellae in phagocytes is responsible for the induction of cell-mediated immunity that is largely involved in the protection of susceptible mice against Salmonella infection.