Cholera Toxin Inhibits Tumor Necrosis Factor Secretion By Human Monocytes and Alveolar Macrophages

Abstract

Tumor necrosis factor-α (TNF) is a pro-inflammatory cytokine which has a strong influence in destructive, inflammatory, and fibrotic lung disorders. Monocytes and alveolar macrophages (AM) are effective producers of TNF when stimulated with lipopolysaccharide (LPS) or Mycoplasma fermentans (MP). We tested the hypothesis that a cholera toxin (CT)-sensitive G protein is involved in the secretion of TNF. Both AM and monocytes were stimulated with LPS or MP both with and without CT. Supernatants were harvested and examined by bioassay for TNF activity. The results of the TNF bioassay revealed marked inhibition of LPS-and MP-induced TNF secretion in both populations of cells when preincubated with CT. This inhibition was seen in freshly isolated AM and overnight incubation. In monocytes, however, the cells became refractory to stimulation by LPS or MP following overnight incubation. Next we examined the kinetics of CT inhibition of TNF production in both AM and monocytes by adding CT at various times following stimulation of the cells. Both cell types had a similar time course for CT inhibition of TNF secretion. Finally, we examined mRNA for TNFa by Northern Blot analysis in monocytes treated with LPS both with and without CT. No inhibition of TNF mRNA was observed in LPS-stimulated monocytes treated with CT. These findings indicate that TNF secretion by both AM and monocytes can be inhibited by cholera toxin (CT), thus implicating the Gsα protein in TNF secretion by these cells.