T-cell–deficient nude mice display decreased baseline BMD and increased bone resorption, concurrent with decreased total BM OPG, and B-cell–specific OPG production. (A) BMD was determined in WT mice at the total body, spine, and femurs, 12 weeks of age (black bars) and 16 weeks of age (white bars), and in nude mice at 12 weeks of age (vertical lines) and 16 weeks (horizontal lines) of age. Data are presented as mean ± SD of 29 nude mice and 18 WT mice. *P ≤ .001 relative to age-matched WT. Percentage changes (Δ) between nude and WT mice at 12 and 16 weeks are indicated above the appropriate bars. (B) μCT reconstructions showing reduced trabecular and cortical structure of representative tibias in nude mice relative to WT. (C) Increased biochemical indices of bone resorption (CTx) were observed in the serum of nude mice compared with WT. *P < .05; n = 9 mice per group. (D) Decreased OPG production by BM derived from nude mice compared with WT (ELISA). (E) Decreased OPG production by purified IgM⁺ B cells from nude mice relative to WT, quantitated in 48-hour–conditioned medium by ELISA; n = 6 mice per group. *P ≤ .01. (F) Real-time RT-PCR quantitation of OPG and RANKL mRNA expression in WT and nude mice. Mean ± SD of 3 independent WT and nude mice. *P < .01.