Osteoclast activated FoxP3+ CD8+ T-cells suppress bone resorption in vitro.
BACKGROUND
Osteoclasts are the body's sole bone resorbing cells. Cytokines produced by pro-inflammatory effector T-cells (T(EFF)) increase bone resorption by osteoclasts. Prolonged exposure to the T(EFF) produced cytokines leads to bone erosion diseases such as osteoporosis and rheumatoid arthritis. The crosstalk between T-cells and osteoclasts has been termed osteoimmunology. We have previously shown that under non-inflammatory conditions, murine osteoclasts can recruit naïve CD8 T-cells and activate these T-cells to induce CD25 and FoxP3 (Tc(REG)). The activation of CD8 T-cells by osteoclasts also induced the cytokines IL-2, IL-6, IL-10 and IFN-γ. Individually, these cytokines can activate or suppress osteoclast resorption.


RESULTS
To determine the net effect of Tc(REG) on osteoclast activity we used a number of in vitro assays. We found that Tc(REG) can potently and directly suppress bone resorption by osteoclasts. Tc(REG) could suppress osteoclast differentiation and resorption by mature osteoclasts, but did not affect their survival. Additionally, we showed that Tc(REG) suppress cytoskeletal reorganization in mature osteoclasts. Whereas induction of Tc(REG) by osteoclasts is antigen-dependent, suppression of osteoclasts by Tc(REG) does not require antigen or re-stimulation. We demonstrated that antibody blockade of IL-6, IL-10 or IFN-γ relieved suppression. The suppression did not require direct contact between the Tc(REG) and osteoclasts.


CONCLUSIONS
We have determined that osteoclast-induced Tc(REG) can suppress osteoclast activity, forming a negative feedback system. As the CD8 T-cells are activated in the absence of inflammatory signals, these observations suggest that this regulatory loop may play a role in regulating skeletal homeostasis. Our results provide the first documentation of suppression of osteoclast activity by CD8 regulatory T-cells and thus, extend the purview of osteoimmunology.
Department of Molecular Microbiology and Immunology, Saint Louis University School of Medicine, St. Louis, Missouri, United States of America.
Zachary S
ZS
Buchwald
Jennifer R
JR
Kiesel
Richard
R
DiPaolo
Meghana S
MS
Pagadala
Rajeev
R
Aurora
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001862:Bone Resorption / Q000276:immunology / Q000503:physiopathology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D016207:Cytokines / Q000276:immunology; D017931:DNA Primers / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D008213:Lymphocyte Activation / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009500:Neutralization Tests; D010010:Osteoclasts / Q000378:metabolism / Q000502:physiology*; D053245:RANK Ligand; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000911:Antibodies, Monoclonal; D016207:Cytokines; D017931:DNA Primers; D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; D053245:RANK Ligand; C505689:Tnfsf11 protein, mouse; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins