Mononuclear phagocyte progenitor cells derived from femoral and tibial bone marrow are propagated in the presence of M-CSF. This macrophage growth factor is secreted by L929 cells and is used in the form of L929 cell conditioned medium. The progenitor cells proliferate and differentiate through monoblast, promonocyte and monocyte stages before maturing to macrophages. At this time the cells become firmly adherent to the culture vessel.
