Figure 4.

IL-3 promotes infection of early megakaryocyte-lineage cells. Bone marrow cells from transgenic mice were grown in media supplemented with SCF, TPO, and IL-3 (A and C) or with SCF and TPO (B and D). Cells were infected with RCAS-AP after 5 days in culture and stained for HPAP expression 48 hr after infection. Wright-Giemsa stains demonstrate numerous mature megakaryocytes when IL-3 is not in the growth media (B), whereas mature megakaryocytes are rare when IL-3 is present (A). Likewise, infected, HPAP-expressing mature megakaryocytes are readily apparent only when IL-3 is not in the growth media (C and D).