Systemic tumor necrosis factor alpha mediates an increase in peripheral CD11bhigh osteoclast precursors in tumor necrosis factor alpha-transgenic mice.
OBJECTIVE
To investigate the mechanisms whereby tumor necrosis factor alpha (TNFalpha) increases osteoclastogenesis in vivo.


METHODS
TNFalpha-transgenic (TNF-Tg) and wild-type mice injected with TNFalpha 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 TNFalpha antagonist, was used to block TNFalpha activity in vivo. The effects of TNFalpha 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 CD11b(high) population and contained both c-Fms- and c-Fms+ cells. The increased number of OCPs correlated with the initiation of detectable TNFalpha in serum and the onset of inflammatory arthritis in TNF-Tg mice. Etanercept eliminated the increase in peripheral OCPs. TNFalpha did not affect proliferation, survival, or differentiation of CD11b(high) 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 CD11b(high) OCPs in spleen after 3 days of multiple injections.


CONCLUSIONS
Systemic TNFalpha 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 TNFalpha 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.
Li
Ping
P
University of Rochester Medical Center, Rochester, New York 14642, USA. Lianping_Xing@URMC.Rochester.Edu.
Schwarz
Edward M
EM
O'Keefe
Regis J
RJ
Ma
Lin
L
Looney
R John
RJ
Ritchlin
Christopher T
CT
Boyce
Brendan F
BF
Xing
Lianping
L
D000818:Animals; D018501:Antirheumatic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001854:Bone Marrow Cells / Q000166:cytology / Q000502:physiology; D039481:CD11b Antigen / Q000235:genetics*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D000068800:Etanercept; D007074:Immunoglobulin G / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D010010:Osteoclasts / Q000166:cytology / Q000502:physiology*; D018124:Receptors, Tumor Necrosis Factor; D013154:Spleen / Q000166:cytology; D013234:Stem Cells / Q000166:cytology / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics*
D018501:Antirheumatic Agents; D039481:CD11b Antigen; D007074:Immunoglobulin G; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D000068800:Etanercept