Neutralization of either the m-CSF-1R or its ligand negates CD14 induction in response to TNF and RA. Cytofluorimetric analysis of CD14 levels on RA-resistant APL cells in response to treatment with RA and TNF. UF-1 cells were treated for 3 days, while others were treated for 5. Antibodies and reagents were replenished at day 3 of the 5-day treatments. The synergy observed between ATRA and TNF observed 5 days after treatment was ablated on addition of neutralizing antibodies to m-CSF-1R or m-CSF. The antibodies did not decrease CD11b levels in UF-1. Control experiments using rabbit immunoglobulin G (rIgG) antibodies showed very little effect on CD14 expression.