Neural differentiation-associated generation of microglia-like phagocytes in murine embryonal carcinoma cell line

We have characterized microglia-like cells which appeared at late stages of neural differentiation of the P19 line of embryonal carcinoma cells. The microglia-like cells arose as round cells on top of a bed layer in mixed cultures of retinoic acid-treated P19 cells. The period of initial appearance of these cells coincided with that of the disappearance of neurons, and the generation of these cells persisted thereafter. The P19-derived microglia-like cells morphologically resembled ameboid microglia, and some of these cells took the form of resting microglia. These cells, both in enriched cultures and in mixed cell cultures, showed phagocytic activity towards latex beads. Most of the P19-derived microglia-like cells in enriched cultures reacted with an antibody against Mac-1, a macrophage surface marker, whereas only the round cells on top of the bed layer showed positive Mac-1 immunoreactivity in a mixed P19 culture. Moreover, the microglia-like cells contained non-specific esterase, an enzyme marker for macrophages. These cells showed apparent morphological changes in response to macrophage colony stimulating factor secreted by cultured L929 cells. The above characteristics of the microglia-like cells derived from P19 cells are similar to those of brain microglia in primary culture. The generation of microglia-like cells from P19 cells during neural differentiation may provide insights into the origin and life cycle of brain microglia.