Toll-like receptor 2 and 4 surface expressions on human monocytes are modulated by interferon-gamma and macrophage colony-stimulating factor.

Human Toll-like receptor 2 (TLR2) and TLR4 are recently identified receptors. TLR4 was shown to be the main protein involved in recognizing Gram-negative bacteria, whereas TLR2 is apparently the key factor in responses to other types of microbial pathogens. We examined regulations of TLR2 and TLR4 surface expressions in human peripheral blood monocytes by interferon-gamma (IFN-gamma) and macrophage colony-stimulating factor (M-CSF). IFN-gamma up-regulated both TLR2 and TLR4, but enhanced the surface expression, on human peripheral blood monocytes of TLR4 more than that of TLR2. On the other hand, M-CSF up-regulated both TLR2 and TLR4 surface expression on human peripheral blood monocytes, with no change in the ratio of TLR2/TLR4 surface expression. These results indicate that IFN-gamma enhances receptors involved in the response to Gram-negative bacteria more than those involved in responses to other types of microbial pathogens, whereas M-CSF enhances the receptor response to Gram-negative bacteria in the same manner as to other types of microbial pathogens.