Listeriolysin negative mutants of Listeria monocytogenes specifically stimulate T-lymphocytes mediating protection and granulomatous inflammation.

The ability of several listeriolysin O negative mutants of the virulent EGD strain of Listeria monocytogenes to activate specific T cell responses in vitro and in vivo was determined. A T cell line and a derived clone specific for Listeria monocytogenes, strain EGD, which are able to adoptively transfer protection and granuloma formation were examined. Specificity testing showed no difference between listeriolysin positive and negative strains to induce proliferation of the T cell lines and clones. Similar results were obtained when we examined T cell mediated granuloma formation in the livers of mice previously immunized with viable bacteria. Granulomatous inflammation could be elicited by i.v. application of heat killed bacteria of listeriolysin positive as well as of negative bacteria. Thus, the expression of the heat induced 60KD listeriolysin protein is not a prerequisite for the stimulation of Listeria-specific T lymphocytes mediating protection and granuloma formation.