Bonus question of 5 point :
You have isolated a population of blood cells by Fluorescence Activated Cell Sorting (FACS). If you grow these cells in culture in the presence of the factor GM-CSF, the cells differentiate into macrophages. If you grow the cells in the presence of the factor Erythropoietin, the cells die. If you grow the cells in the presence of both GMCSF and Erythropoietin, the cells differentiate into red blood cells.
All of the following COULD be true, EXCEPT: