Objective: Higher incidence of osteopenia and osteoporosis underlie increased rates of fragility fracture in HIV infection. B cells are a major source of osteoprotegerin (OPG), an inhibitor of the key osteoclastogenic cytokine receptor activator of nuclear factor-κB ligand (RANKL). We previously showed that higher B-cell RANKL/OPG ratio contributes to HIV-induced bone loss. T-cell OPG production in humans, however, remains undefined and the contribution of T-cell OPG and RANKL to HIV-induced bone loss has not been explored.
Design: We investigated T-cell OPG and RANKL production in ART-naive HIV-infected and uninfected individuals in relation to indices of bone loss in a cross-sectional study.
Methods: T-cell RANKL and OPG production was determined by intracellular staining and flow cytometry, and plasma levels of bone resorption markers were determined by ELISA.
Results: We demonstrate for the first time in-vivo human T-cell OPG production, which was significantly lower in HIV-infected individuals and was coupled with moderately higher T-cell RANKL production, resulting in a significantly higher T-cell RANKL/OPG ratio. T-cell RANKL/OPG ratio correlated significantly with BMD-derived z-scores at the hip, lumbar spine and femur neck in HIV-infected individuals with CD4 T-cell counts at least 200 cells/μl but not in those with lower counts.
Conclusion: Our data suggest that T cells may be a physiologically relevant source of OPG and T-cell RANKL/OPG imbalance is associated with HIV-induced bone loss in CD4 T-cell-sufficient patients. Both B and T lymphocytes may thus contribute to HIV-induced bone loss.