Figure 2. Plasma cells promote osteoclastogenesis in a RANKL-dependent manner.

Bone marrow plasma cells (CD3^–Gr1^–CD138⁺B220^– cells) or B cells (CD19⁺ cells) were cocultured with osteoclast precursor cells for 5 days. (A) Tnfsf11 (left) and Prdm1 (encoding Blimp1) (right) mRNA expression of the bone marrow plasma cells and B cells before the coculture (n = 4). (B and C) Osteoclast formation after the coculture of osteoclast precursor cells derived from untreated DBA1/J mice with bone marrow plasma cells or B cells from arthritic DBA1/J mice (n = 3–6). The number of TRAP⁺ multinucleated (more than 3 nuclei) cells (MNCs) is shown. Scale bar: 100 μm. (D and E) Osteoclast formation after the coculture of osteoclast precursor cells prepared from splenocytes from Tnfsf11^Δ/Δ mice with bone marrow plasma cells or B cells from arthritic DBA1/J mice (D, n = 3–4) or Mb1-Cre Tnfsf11^fl/Δ mice (E, n = 3–5). (F) The numbers of pre–/pro–B cells (IgM^–B220^mid), immature B cells (IgM⁺B220^mid), mature B cells (IgM⁺B220^hi), plasmablasts (CD3^–Gr1^–CD138⁺CD267⁺B220⁺), and plasma cells (CD3^–Gr1^–CD138⁺CD267⁺B220^–) in the bone marrow under physiological and arthritic conditions (n = 5–9). All data are expressed as the mean ± SEM. *P < 0.05; **P < 0.01; ***P < 0.001 by unpaired Student’s t test (A), 1-way ANOVA with the Holm-Sidak multiple-comparison test (B, D, and E), or 2-way ANOVA with the Holm-Sidak multiple-comparison test (F). NS, not significant.