Systemic tumor necrosis factor α mediates an increase in peripheral CD11bhigh osteoclast precursors in tumor necrosis factor α–transgenic mice

P Li, EM Schwarz, RJ O'Keefe, L Ma… - … : Official Journal of …, 2004 - Wiley Online Library
P Li, EM Schwarz, RJ O'Keefe, L Ma, RJ Looney, CT Ritchlin, BF Boyce, L Xing
Arthritis & Rheumatism: Official Journal of the American College …, 2004Wiley Online Library
Objective To investigate the mechanisms whereby tumor necrosis factor α (TNFα) increases
osteoclastogenesis in vivo. Methods TNFα‐transgenic (TNF‐Tg) and wild‐type mice injected
with TNFα were studied. In vitro osteoclastogenesis assays, monocyte colony‐forming
assays, and fluorescence‐activated cell sorting were performed using splenocytes,
peripheral blood mononuclear cells (PBMCs), and bone marrow cells to quantify and
characterize osteoclast precursors (OCPs). Etanercept, a TNFα antagonist, was used to …
Objective
To investigate the mechanisms whereby tumor necrosis factor α (TNFα) increases osteoclastogenesis in vivo.
Methods
TNFα‐transgenic (TNF‐Tg) and wild‐type mice injected with TNFα were studied. In vitro osteoclastogenesis assays, monocyte colony‐forming assays, and fluorescence‐activated cell sorting were performed using splenocytes, peripheral blood mononuclear cells (PBMCs), and bone marrow cells to quantify and characterize osteoclast precursors (OCPs). Etanercept, a TNFα antagonist, was used to block TNFα activity in vivo. The effects of TNFα on proliferation, apoptosis, and differentiation of OCPs were assessed using 5‐bromo‐2′‐deoxyuridine labeling, annexin V staining, and reverse transcriptase–polymerase chain reaction.
Results
OCP numbers were increased 4–7‐fold in PBMCs and spleen, but not in bone marrow of TNF‐Tg mice. The OCPs in spleen were in the CD11bhigh population and contained both c‐Fms− and c‐Fms+ cells. The increased number of OCPs correlated with the initiation of detectable TNFα in serum and the onset of inflammatory arthritis in TNF‐Tg mice. Etanercept eliminated the increase in peripheral OCPs. TNFα did not affect proliferation, survival, or differentiation of CD11bhigh splenocytes in vivo or in vitro, but caused a rapid increase in CD11b+ cells in blood within 4 hours of a single injection and an accumulation of CD11bhigh OCPs in spleen after 3 days of multiple injections.
Conclusion
Systemic TNFα induces a marked increase in circulating OCPs that is reversible by anti‐TNF therapy and may result from their mobilization from bone marrow. Our findings provide a new mechanism whereby TNFα stimulates osteoclastogenesis in patients with inflammatory arthritis, suggesting that CD11b+ PBMCs could be used to evaluate a patient's potential for erosive disease and the efficacy of anti‐TNF therapy.
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