Activation of FosER increases the propensity of M1 cells to be induced for differentiation by IL-6. Cells were treated as indicated, and after 3 days the morphology of at least 300 cells on May-Grunwald-Giemsa-stained cytospin smears was determined as detailed in “Materials and methods” (photomicrographs; original magnification, × 400). The proportion of immature blast cells, cells at intermediate monocyte stage, and mature macrophages was calculated. NT indicates not treated. Data presented are an average (± SD) of at least 3 experiments.