Proliferative response of infected clones to Epo or IL-6. Cells from different G418-resistant clones grown in IL-6 were washed and 5 × 10⁴ cells/mL were grown in MEM containing 500 μg/mL of G418, 10% FCS, and 1 U/mL rhEpo (solid symbols) or 10% P388D1 conditioned medium (open symbols) or without growth factor (✙ and ○) as described in the Materials and Methods. E1 (squares) and E2 (triangles) are Epo-R–expressing TEPC clones.