DIFFERENTIAL REGULATION OF TNF-ALPHA 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 alp ha (TNF-alpha) in anti-listeria immunity, we have investigated TNF-alp ha production by macrophages after they ingested live LLO-producing co mpared to LLO-non-producing bacteria, We used two genetically engineer ed strains of Listeria that differed only in their ability (Ly+) or in ability (Ly-) to produce LLO, Ly+ and Ly- caused the same kinetics of increased mRNA abundance for TNF-alpha during the first 90 min after p hagocytosis, However, only Ly+ caused sustained transcription of TNF-a lpha mRNA, and this may account for the increased release of TNF-alpha . The transcriptional inhibitor 5,6-dichloro-1-beta-D-ribofuranosylben zimidazole (DRB) prevented the sustained abundance of cytokine mRNA 20 h after ingestion of Ly+. In addition, nuclear run-on assays indicate d sustained transcription of TNF-alpha genes only after ingestion of L y+. LLO itself was not responsible for the ability of Ly+ to stimulate the sustained transcription of the TNF-alpha genes, Instead, LLO may allow Listeria to survive within macrophages so that other bacterial p roducts cause sustained TNF-alpha gene transcription, Both Ly+ and Ly- produced molecules, isolated by 50% ammonium sulfate, that induced cy tokine production, In conclusion, we now report that Ly+ causes sustai ned transcription of the TNF-alpha gene and production of TNF-alpha by macrophages in vitro, We speculate that the TNF-alpha may activate en dothelium and thus allow the recruitment of T cells to sites of infect ion, This may contribute to the ability of only LLO-producing Listeria to induce protective immunity.