Differential regulation of TNF-α production by listeriolysin-producing versus nonproducing strains of Listeria monocytogenes

Only Listeria monocytogenes that produce listeriolysin O (LLO) elicit protective immunity. Given the importance of tumor necrosis factor cc (TNF-α) in anti-Listeria immunity, we have investigated TNF-α production by macrophages after they ingested live LLO-producing compared to LLO-nonproducing bacteria. We used two genetically engineered strains of Listeria that differed only in their ability (Ly+) or inability (Ly-) to produce LLO. Ly+ and Ly- caused the same kinetics of increased mRNA abundance for TNF-α during the first 90 min after phagocytosis. However, only Ly+ caused sustained transcription of TNF-α mRNA, and this may account for the increased release of TNF-α. The transcriptional inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) prevented the sustained abundance of cytokine mRNA 20 h after ingestion of Ly+. In addition, nuclear run-on assays indicated sustained transcription of TNF-α genes only after ingestion of Ly+. LLO itself was not responsible for the ability of Ly+ to stimulate the sustained transcription of the TNF-α genes. Instead, LLO may allow Listeria to survive within macrophages so that other bacterial products cause sustained TNF-α gene transcription. Both Ly+ and Ly- produced molecules, isolated by 50% ammonium sulfate, that induced cytokine production. In conclusion, we now report that Ly+ causes sustained transcription of the TNF-α gene and production of TNF-α by macrophages in vitro. We speculate that the TNF-α may activate endothelium and thus allow the recruitment of T cells to sites of infection. This may contribute to the ability of only LLO-producing Listeria to induce protective immunity.