Mycoplasma fermentans inhibits tumor necrosis factor α-induced apoptosis in the human myelomonocytic U937 cell line

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Abstract
Mycoplasma fermentans (M. fermentans) was shown to be involved in the alteration of several eukaryotic cell functions (i.e. cytokine production, gene expression), and was suggested as a causative agent in arthritic diseases involving impaired apoptosis. We investigated whether M. fermentans has a pathogenic potential by affecting tumor necrosis factor (TNF)-induced apoptosis in the human myelomonocytic U937 cell line. A significant reduction in the TNF-induced apoptosis (60%) was demonstrated upon either infection with live M. fermentans or by stimulation with non-live M. fermentans. To investigate the mechanism of M. fermentans antiapoptotic effect, the reduction of mitochondrial transmembrane potential ( m) and the protease activity of caspase-8 were measured. In the infected cells, the reduction of m was inhibited (75%), and a 60% reduction of caspase-8 activity was measured. In conclusion, M. fermentans significantly inhibits TNF-induced apoptosis in U937 cells, and its effect is upstream of the mitochondria and upstream of caspase-8.