m-CSF-1R expression in RA-resistant APL cells. (A) Northern blotting was used to examine m-CSF-1R levels in response to RA and TNF. m-CSF-1R levels were observed to increase in response to RA in only UF-1 and MR2 cells within 72 hours of treatment. The combination of TNF and RA induced a large increase in m-CSF-1R levels in all RA-resistant cells undergoing monocytic differentiation but not in UF-1 cells. (B) FACS analysis showing heightened cell surface expression of m-CSF-1R in response to 3-day treatments with TNF and RA. Percentages indicate positive staining.