The effects of B and T cells on bone are mediated by several key cytokine regulators of bone metabolism (11, 18), including the inflammatory cytokines tumor necrosis factor-α (TNF-α) and interferon-γ, which have been implicated in bone loss in RA, periodontitis, postmenopausal osteoporosis, and HIV (30). The gene discussed is TNF; the disease is periodontitis.