M-CSF-responsive immortal macrophages are a new model for studying macrophage function

We generated non-senescent, macrophage colony stimulating factor (M-CSF) dependent macrophages from murine fetal livers. These fetal liver macrophages (FLM-M) resemble bone marrow macrophage (BMM) morphology and express similar macrophage surface markers as BMM. In comparison to granulocyte monocyte-colony stimulating factor (GM-CSF) derived FLM (FLM-G), FLM-M have higher surface expression of CD11b, CD68, CD14 and CD64, and lower expression of CD11c. BMM, FLM-M and FLM-G all produce TNFa and IL-6 in response to lipopolysaccharide activation. BMM and FLM-M cells have similar phagocytic properties with 99.3% of BMM and FLM-M actively phagocytosing opsonized sheep erythrocytes and a phagocytic efficiency of 0.9. The average number of internalized erythrocytes per cell was higher (13.1±10.0) in BMM than in FLM-M (7.6±2.9). FLM-G had fewer actively phagocytic cells (86%), lower phagocytic efficiency (0.7) and fewer internalized erythrocytes per macrophage (4.2±2.1) than BMM or FLM-M. Principal component analysis and hierarchical clustering demonstrated mRNA expression profiles were more similar between BMM and FLM-M cells than FLM-G. Transcriptome comparison to the ImmGen tissue atlas shows cultured BMM and FLM-M cluster with macrophage progenitors and bone marrow macrophages. In conclusion, FLM-M cell cultures share major morphological, phenotypic and functional properties of BMM except for senescence, and can be an effective substitute to BMM. These new cells will facilitate study of macrophage biology by enabling experiments requiring long-term culture or genetic modifications. Overall design: Comparison of 3 different murine macrophage cell cultures.