Effect of cytokines and lipopolysaccharide on CD14 antigen expression in human monocytes and macrophages

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Abstract
The 52 kD myeloid membrane glycoprotein CD14 represents the receptor for complexes of lipopolysaccharide (LPS) and LPS binding protein (LBP); it is involved in LPS induced tumor necrosis factor‐alpha production. Expression of CD14 increases in monocytes differentiating into macrophages, and it is reduced by rIFNg in monocytes in vitro. In the present study CD14 membrane antigen expression was investigated in cultures of human mononuclear leucocytes (PBL), in elutriated, purified monocytes, and in blood monocyte derived Teflon cultured macrophages. Cells were incubated for 15 or 45 h with rIL‐1, rIL‐2, rIL‐3, rIL‐4, rIL‐5, rIL‐6, rTNFa, rGM‐CSF, rM‐CSF, rTGFb1, rIFNa, lipopolysaccharide (LPS), and, as a control, rIFNg. The monoclonal antibodies Leu‐M3 and MEM 18 were used for labelling of CD14 antigen by indirect immunofluorescence and FACS analysis of scatter gated monocytes or macrophages. IFNg concentrations were determined in PBL culture supernatants by ELISA. rIFNa and rIL‐2 reduced CD14 in 15 and 45 h PBL cultures, an effect mediated by endogenous IFNg, since it was abolished by simultaneous addition of an anti‐IFNg antibody. rIFNa and rIL‐2 were ineffective in purified monocytes or macrophages. rIL‐4 strongly reduced CD14 in PBL and purified monocytes after 45 h, whereas in macrophages the decrease was weak, although measurable after 15 h. The other cytokines investigated did not change CD14 antigen expression. Cycloheximide alone reduced CD14, but when added in combination with rIFNg the effect on CD14 downregulation was more pronounced. The effect of rIFNg on CD14 in PBL cultures was dose‐dependently inhibited by rIL‐4 and this inhibition is probably due to an IL‐4 mediated blockade of IFNg secretion. LPS at a low dose increased CD14, at a high dose it produced a variable decrease of CD14 in PBL, which was probably due to LPS induced IFNg secretion. LPS strongly enhanced CD14 in 45 h cultures of purified monocytes. The results, showing that CD14 antigen expression is upregulated by LPS and downregulated by rIFNg and rIL‐4, suggest that the LPS‐LBP receptor is involved in the feedback response of IFNg and IL‐4 to LPS stimulation.