IL-4 inhibition of TNF-α–induced osteoclastogenesis. Bone marrow cells from wild-type and STAT6^-/- animals were cultured with rmM-CSF (100 ng/mL) for 3 days. Subsequently, RANKL (150 ng/mL) ± rmIL-4 (10 ng/mL) or rmTNF (20 ng/mL) ± rmIL-4 (10 ng/mL) was added to the BMM, keeping the concentration of M-CSF (100 ng/mL) constant until the end of the experiment 3 days later. Cells were fixed and stained for TRAP activity. TRAP stain; original magnification, × 10.