Enzymatic modifications of immunoglobulins alter pro-osteoclastogenic properties. IgG from individual patients with and without BD (n = 7-11 in each group) were treated with neuraminidase (A-B) and galactosidase (C-D) to reduce sialylation and galactosylation, respectively, and then added to preosteoclasts for 2 to 4 days before the number of TRAP-positive cells with ≥3 nuclei was counted. (E-F) IgG from patients with and without BD were treated with UDP-galactose to increase galactosylation and added to preosteoclasts for 2 to 4 days before the number of TRAP-positive cells with ≥3 nuclei was counted. The number of mature osteoclasts was evaluated by using TRAP stain. Data presented in panels A-F are relative to RANKL control. P values determined by Wilcoxon matched-pairs signed rank test. Symbols: purple diamond, sialic acid; yellow circle, galactose; blue square, GlcNAc; green circle, mannose; red triangle, fucose. ns, not significant.