B-lineage cells are a major source of OPG production in the BM and spleen. (A) OPG secretion by total BM white cells or the B-cell fraction contained therein was quantitated by ELISA. Mean ± SD of triplicates. Data are representative of more than 6 independent experiments. (B) Relative OPG transcription was quantitated by RT-PCR in total BM white cells or B-cell fraction contained therein. Data are presented as mean ± SD of 3 independent mice per group. (C) OPG production by equivalent numbers (1 × 10⁷ cells) of purified BM B-cell precursors, immature B cells, mature B cells, and plasma cells. (D) B-lineage cell composition as a percentage of total nucleated BM cells. (E) Actual concentration of OPG secreted by specific B-lineage cells per 10⁷ total nucleated BM cells. The total OPG production was 134 ± 26.1 pg/mL/10⁷ total white BM cells. (F) OPG production by equivalent numbers of mature spleen B cells was quantitated relative to plasma cells and non–B-lineage cells (non-B cell). (G) Spleen B-cell composition as a percentage of total nucleated spleen cells. (H) Percentage spleen OPG production for each cell population in the spleen. Mean ± SD of 2 independent experiments measured in triplicate. *P < .05 relative to unstimulated. (I) Comparison of OPG production by equivalent numbers of mature B cells derived from BM, peripheral blood (PB), lymph nodes (LN), or spleen (SP). BM from 5 independent mice was measured in triplicate. *P < .001 relative to BM (ANOVA). (J) OPG production by mature splenic B cells stimulated in vitro with CD40L (500 ng/mL) and/or anti-IgM activating antibody (5 ng/mL).