CD154 expression is differentiation dependent and restricted to the megakaryocyte phenotype. (A) Relative CD154 mRNA expression in K562 cells driven to megakaryocyte or erythrocyte differentiation with PMA or hemin, respectively. (B) Kinetics of CD154 mRNA expression in PMA-differentiated CMK cells. After 96 hours of PMA exposure, the CMK cells were harvested, washed, and replated in fresh medium in the absence of PMA and allowed to incubate an additional 48 hours (96 + 48). The bars represent means plus or minus the standard error from 3 independent experiments. (C) Micrographs of CMK cells after the described treatment. Original magnification 250× for all panels.