Early hematopoietic factors induce APRIL expression in myeloid precursor cells. (A) Human HSCs were induced to differentiate in granulocytes or erythrocytes. (Left) CD13 and CD16 expression on cells at the end of a granulocyte differentiation culture. Percentages of cells in each subset are indicated. (Right) APRIL secretion determined by ELISA in culture supernatants. The results are representative of 3 independent experiments. (B) HSCs were induced to differentiate with the indicated cytokines (S, SCF; T, TPO; F, FLT3-L; G, G-CSF; I, IL-3). The production of APRIL (nanograms per 10⁵ cells) at day 8 is shown. Data are representative of 3 independent experiments.