Peptidoglycans promotes human leukemic THP-1 cell apoptosis and differentiation.

The innate immune system coordinates the inflammatory response to pathogens. To do so, its cells must discriminate self from non-self utilizing receptors that identify molecules synthesized exclusively by microbes. Toll- like receptors have a crucial role in the detection of microbial infection in mammals and insects. In mammals, they have evolved to recognize conserved products unique to microbial metabolism. These include lipopolysaccharide (LPS), lipotechoic acids, and peptidoglycans (PGN). We show here that TLRs, including TLR2, are expressed on the THP-1 human leukemia cell line. Activation of TLR2 signaling in THP-1 by PGN induces the synthesis of various soluble factors and proteins including interleukin-1β, interleukin-8 and TNF-α and apoptosis of THP-1 with PGN dose and time dependence. Moreover , in this study we show that PGN induces apoptosis of THP-1 cells in a TNF-α-dependent manner. These findings indicate that TLR2 signaling results in a cascade leading to tumor apoptosis and differentiation, which may suggest new clinical prospects using TLR2 agonists as cytotoxic agents in certain cancers.