CD154 mRNA expression in primary hematopoietic progenitor cells and megakaryocytes. (A) Relative CD154 mRNA levels in primary human CD34⁺ hematopoietic progenitor cells, the CD41-negative and CD41-positive cell populations after in vitro differentiation as described in “In vitro differentiation of human CD34⁺ and mouse LSK hematopoietic progenitor cells.” (B) Relative CD154 mRNA expression in mouse hematopoietic stem cells (LSK), the CD41-positive and -negative cell populations after in vitro differentiation, and primary CD41-positive and -negative cells isolated from mouse bone marrow. The bars represent means plus or minus the standard error from 3 independent experiments.