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Figure S1. Effect of recombinant IL-4 on osteoclast precursor cells derived from WT or Stat6-/- mice in the RANKL-M-CSF system. (A) Microphotographs and (B) quantification of the formation of TRAP+ cells in the RANKL-M-CSF system and the bone resorption assay. 1 or 10 ng/ml IL-4 was added to the culture system on day 0 (at the same time as RANKL) or 1 d later (on day 1). The cells were stained with TRAP and the bone-resorbing activity was evaluated. TRAP+ MNCs were not formed in WT cells when IL-4 was added on day 0, but Stat6-/- cells were completely resistant to the inhibitory effects of IL-4. Although TRAPdim MNCs were formed when IL-4 was added on day 1, these cells did not have bone-resorbing activity. The TRAP+ MNCs formed in Stat6-/- cells could resorb bone, indicating that IL-4 inhibits osteoclastogenesis and induces macrophage polykarions weakly positive for TRAP through Stat6.