Seeligeriolysin O, a Cholesterol-Dependent Cytolysin ofListeria seeligeri, Induces Gamma Interferon from Spleen Cells of Mice

Seeligeriolysin O (LSO), one of the cholesterol-dependent cytolysins produced by Listeria seeligeri, shows 80% homology to listeriolysin O (LLO) produced by Listeria monocytogenes at the amino acid sequence level. In addition to cytolytic activity, LLO has been shown to exhibit cytokine-inducing activity. In order to determine whether LSO is also capable of exhibiting these two different activities, we constructed a recombinant full-length LSO (rLSO530) and a noncytolytic truncated derivative with a C-terminal deletion (rLSO483) and compared these molecules with recombinant LLO. The cytolytic rLSO530 molecule could induce gamma interferon (IFN-gamma) production in spleen cells when the cytolytic activity was blocked by treatment with cholesterol. The noncytolytic truncated rLSO483 molecule also induced IFN-gamma production. Anti-LLO polyclonal antibody inhibited not only LLO-induced IFN-gamma production but also LSO-induced IFN-gamma production. Both NK cells and CD11b(+) cells were required for LSO-induced IFN-gamma production. Among the various cytokines expressed in CD11b(+) cells, interleukin-12 (IL-12) and IL-18 appeared to be essential. We concluded that LSO exhibits the same biological activity as LLO.