title: Intracellular growth of Listeria monocytogenes as a prerequisite for in vivo induction of T cell-mediated immunity.
abstract: The in vivo induction of T cell-mediated immunity was studied by infecting mice with two genetically closely related mutants from Listeria monocytogenes, differing only with respect to the secretion of an active SH-dependent hemolysin. It is shown that even minute doses of hemolytic bacteria capable of growing in host tissues easily induced the expression of T cell-mediated immunity, as estimated by the level of delayed sensitivity, adoptive protection and long-lasting immunological memory. On the contrary, nonhemolytic bacteria unable to multiply in host tissues totally failed to initiate the expression of T cell-mediated immunity in vivo. This failure was even observed when mice were repeatedly infected by high doses of nonhemolytic bacteria, allowing to maintain a significant amount of viable bacteria for several days in host tissues. These results mean that the presence of viable bacteria at a significant level in the host is not sufficient per se to induce detectable T cell clonal expansion in the in vivo setting, implying that the process of bacterial growth inside macrophages is required to initiate in vivo the expression of T cell-mediated immunity.
mesh_terms: D000818:Animals; D000942:Antigens, Bacterial / Q000032:analysis; D004306:Dose-Response Relationship, Immunologic; D006460:Hemolysin Proteins / Q000502:physiology; D007111:Immunity, Cellular; D008089:Listeria monocytogenes / Q000235:genetics / Q000254:growth & development / Q000276:immunology*; D008088:Listeriosis / Q000276:immunology*; D008264:Macrophages / Q000276:immunology / Q000382:microbiology; D051379:Mice; D009154:Mutation; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000942:Antigens, Bacterial; D006460:Hemolysin Proteins