Erythroblasts and Myelocytes

S1, E6: Red Blood Cell gets lost again and finds herself in her birthplace, the Red Bone Marrow. She reminisces on being a young Erythroblast being trained by a Macrophage on how to be a Red Blood. Once, when she was an Erythroblast, she was attacked by a bacterium, and was rescued by a Myelocyte. In the present, a cancer cell attacks a normal cell.