Toxoplasma gondiiInhibits Toll-Like Receptor 4 Ligand-Induced Mobilization of Intracellular Tumor Necrosis Factor Alpha to the Surface of Mouse Peritoneal Neutrophils

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Abstract
Neutrophils are well-known to rapidly respond to infection through chemotactic infiltration at sites of inflammation, followed by rapid release of microbicidal molecules, chemokines, and proinflammatory cytokines. For tumor necrosis factor alpha (TNF-α), we recently found that neutrophils contain intracellular pools of the cytokine and display the capacity to upregulate transcriptional activity of the gene during lipopolysaccharide (LPS) stimulation. We now show that triggering of mouse peritoneal neutrophils with Toll-like receptor 2 (TLR2), TLR4, and TLR9 ligands, but not ligands of TLR3, induces upregulation of surface membrane TNF-α. However, neutrophils infected with the protozoanToxoplasma gondiidisplayed an inability to respond fully in terms of TLR ligand-induced increases in membrane TNF-α expression. Infected neutrophils failed to display decreased levels of intracellular TNF-α upon LPS exposure. In contrast to intermediate inhibitory effects in nontreated neutrophils,T. gondiiinduced a complete blockade in LPS-induced surface TNF-α expression in the presence of the protein synthesis inhibitor cycloheximide. Despite these inhibitory effects, the parasite did not affect LPS-induced upregulation of TNF-α gene transcription. Collectively, the results show thatToxoplasmaprevents TLR ligand-triggered mobilization of TNF-α to the neutrophil surface, revealing a novel immunosuppressive activity of the parasite.