Immunoglobulin G (IgG)-induced RANKL expression in peripheral blood monocytes and osteoclast differentiation. (A) After peripheral blood CD14+ monocytes were cultured with 0 to 20 mg/mL of intravenous immunoglobulin (IVIg) for 72 h, the expression of RANKL mRNA was determined using real-time PCR. The expression of RANKL mRNA increased at 1.0 mg/mL of IVIg. (B) Peripheral blood CD14+ monocytes were pretreated with anti-CD64, anti-CD32, or anti-CD16 for 1 h and were cultured with 1 mg/mL of IVIg for 72 h. The expression of RANKL mRNA was determined using real-time PCR. The expression of RANKL mRNA decreased after inhibition of FcγRI, FcγRIIa, and FcγRIIb. (C) CD14+ monocytes, which were isolated from peripheral blood, were cultured with 25 ng/mL of M-CSF and 0 to 1.0 mg/mL of IVIg. After 21 days of culture, TRAP-positive multinucleated cells were counted and bone resorbing function was assessed. TRAP+ multinucleated osteoclasts were differentiated from the monocytes and bone resorbing function was induced by IVIg, however, the effect was smaller than that of CRP. The figures represent one of three independent experiments (original magnification: 200×). The data represents the mean ± SEM for three independent experiments; *
P <0.05, **
P <0.01. CRP, C-reactive protein; FcγR, Fcgamma receptors; M-CSF, macrophage colony-stimulating factor; RANKL, receptor activator of nuclear factor kappa-B ligand; SEM, standard error of the mean; TRAP, tartrate-resistant acid phosphatase.