Induction of TRAP-positive cells by RANKL in the presence of FL.
Bone marrow cells were incubated for 6 hours at 3 × 105cells/mL. Nonadherent cells (3 × 104/well) were then incubated in RANKL (100 ng/mL) and FL for 6 days before the assessment of (A) TRAP-positive cell numbers and (B) total cell numbers. Figures are mean ± SEM of 6 cultures per variable. Cultures in which M-CSF (50 ng/mL) replaced FL were included for comparison. No TRAP cells developed in cultures to which RANKL had not been added. *P < .05 versus no FL/M-CSF. (C, D) Formation of TRAP-positive cells capable of bone resorption by RANKL and FL. Nonadherent bone marrow cells were incubated with RANKL (100 ng/mL) and FL (100 ng/mL) for 6 days (for TRAP staining) or 10 days for bone resorption. (C) Two strongly TRAP-positive mononuclear cells, and several TRAP-negative cells (no counterstain). (D) Three small excavations (arrows) produced by cells incubated in RANKL and FL. Excavations were never seen in cultures from which RANKL was omitted.
