Fig. 1

B cells are located close to osteoblasts in bones from RA mice. a Frozen sections of knees from 6-m-old TNF-Tg and WT mice were H&E stained (upper panels) and adjacent sections (lower panels) were subjected to IF with anti-B220 Ab for B cells (red) and anti-osteocalcin (OCN) Ab for OBs (green). White arrows= B cell aggregates. Bar = 200 μm. b ALP staining (left-hand panel) and an adjacent section (middle panel and right panel at higher magnification) stained for B cells and OBs. Yellow arrows: inflammatory cells. Blue arrows: OBs. Bar = 50 μm. c Images of long bones from the above mice in a show B cells and OBs along the endosteum of cortical bone of a TNF-Tg mouse. Bar = 25 μm. d B220+ B cell area/tissue area (%) in long bone marrow (BM) and SB areas from TNF-Tg mice were measured on B220 IF-stained sections. *p < 0.05 vs. BM. e μCT analysis and morphometric data of femoral SB volume. *p < 0.05 vs. WT. f Frozen sections of knees from Ctl and CIA mice 2 weeks after the onset of CIA were subjected to IF with anti-B220 and anti-OCN Abs. White arrows = B cell aggregate. Bar = 200 μm. The quantification of OCN+ area/tissue area (%) (g) and B220+ B cell area/tissue area (%) (h) in SB area from the above mice in f. *p < 0.05 vs. Ctl. 5–8 mice and their controls were included in each experiment. All of these experiments were repeated at least once. Representative images and quantifications in the panels come from one independent experiment. All error bars represent s.e.m. Two-tailed unpaired Student’s t-test was performed