Differentiation of Macrophage Precursors to Cells with LAK Activity under the Influence of CSF-1 and High Dose IL-2

Mouse macrophage precursor cells with natural killer (NK) like activity, derived from in vitro culture of light-fraction-bone marrow cells in the presence of colony-stimulating factor 1 (CSF-1) and low dose IL-2, were incubated with high dose (1000 U/ml) IL-2. After 3 days of incubation, cells had developed from NK like (killing Yac-1 but not P815) into LAK-like (killing both YAC-1 and P815) effector cells. Morphological studies revealed that LAK activity occurred at the time when macrophage precursors with NK like activity containing few cytoplasmic granules had further differentiated into cells with abundant azurophilic granules in their cytoplasma. Proliferation of macrophage-precursor derived NK/LAK-like cells was dependent on the presence of colony-stimulating factor, generation of cytoplasmic granules was induced by IL-2 in a dose dependent way. Flow cytometric analysis showed that macrophage precursor-derived LAK effectors were positive for NK 1.1 but almost negative for F4/80. When the same starting cell population was cultured in the presence of 200 U/ml Interferon gamma (IFN gamma), proliferation was completely stopped and within 3-4 days all cells differentiated into mature macrophages expressing F4/80. In context with our previous data, we describe here a continuum of development from agranular macrophage precursors to granular cells with NK-like activity and further to cells with LAK activity under the influence of CSF-1 as growth factor and IL-2 as granule- and cytotoxicity-inducing factor.