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 microM 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.