Delayed ontogeny of APRIL expression by BM cells. The expression of mRNA IL-6 (A), BAFF (B), and APRIL (C) was evaluated by quantitative real-time RT-PCR on fresh BM cells and on BMSCs from 2-week-old, 4-week-old, and adult mice. Results include data generated with a pool of 6 to 7 individual mice (total BM cells) or 5 independent cultures of a pool of 10 mice (enriched BMSCs). *P < .05. (D) BMSCs (5 × 10⁴) from adult and 2-week-old mice were stained in chamber slides with IIID3 antibody as described in “APRIL immunostaining.” (E) BMSCs (5 × 10⁴) from adult mice were stained in chamber slides with IIID3 antibody and anti–Mac-1 antibody as described in “APRIL immunostaining.”