Induction of Toll-like receptor 4 in granulocytic and monocytic cells differentiated from HL-60 cells

Toll-like receptor 4 (TLR4) is the main protein expressed on the cell surfa ce and is an essential receptor for Lipopolysaccharide (LTS) signalling in human peripheral blood leucocytes. We examined TLR4 expression and the func tional response to LPS in retinoic acid-treated HL-60 cells (HL-60-derived granulocytic cells) and interferon-gamma -treated HL-60 cells (HL-60-derive d monocytic cells). Slight TLR4 expression was induced in HL-60-derived gra nulocytic cells, while strong induction was seen in HL-60-derived monocytic cells. LPS induced interleukin 1 beta (IL-1 beta) production and TLR4 expr ession in HL-60-derived monocytic cells, but not HL-60-derived granulocytic cells. These data indicate different responses to LPS in the cells. TLR4 s urface expression paralleled LPS-induced phagocytosis and TLR4-neutralizing antibody partially inhibited LPS-induced IL-8 production in HL-60-derived monocytic cells, but not in HL- 60-derived granulocytic cells. These result s suggest that HL-60-derived monocytic cells are partially activated via TL R4, but that HL-60-derived granulocytic cells are not activated via TLR4.