title: Inhibition of antigen presentation and T cell costimulation blocks PTH-induced bone loss.
abstract: T cells are required for continuous parathyroid hormone (cPTH) treatment to induce bone loss as they sensitize stromal cells to PTH through CD40 ligand (CD40L), a surface molecule of activated T cells. Since CD40L expression is a feature of activated T cells, we investigated whether antigen (Ag)-mediated T cell activation is required for PTH to exert its catabolic activity. We report that inhibition of Ag presentation through silencing of either class I or class II MHC-T cell receptor (TCR) interaction prevents the cortical bone loss induced by in vivo cPTH treatment. We also show that the bone loss and the stimulation of bone resorption induced by cPTH treatment are prevented by CTLA4-Ig, an inhibitor of T cell costimulation approved for the treatment of rheumatoid arthritis. Since inhibition of antigen-driven T cell activation by blockade of either TCR signaling or T cell costimulation is sufficient to silence the catabolic activity of cPTH, antigen-presenting cells and T lymphocyte interactions therefore play a critical role in the mechanism of action of PTH.
authors.affiliation: Department of Medicine, Emory University, Atlanta, Georgia, USA.
authors.forename: Brahmchetna
authors.initials: B
authors.lastname: Bedi
authors.forename: Jau-Yi
authors.initials: JY
authors.lastname: Li
authors.forename: Francesco
authors.initials: F
authors.lastname: Grassi
authors.forename: Hesham
authors.initials: H
authors.lastname: Tawfeek
authors.forename: M Neale
authors.initials: MN
authors.lastname: Weitzmann
authors.forename: Roberto
authors.initials: R
authors.lastname: Pacifici
mesh_terms: D000069594:Abatacept; D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000378:metabolism; D001862:Bone Resorption / Q000139:chemically induced* / Q000517:prevention & control*; D001842:Bone and Bones / Q000187:drug effects / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D005260:Female; D018796:Immunoconjugates / Q000494:pharmacology* / Q000627:therapeutic use; D007166:Immunosuppressive Agents / Q000494:pharmacology / Q000627:therapeutic use; D008213:Lymphocyte Activation / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010281:Parathyroid Hormone / Q000009:adverse effects*; D013601:T-Lymphocytes / Q000187:drug effects* / Q000276:immunology
chemical_list: D018796:Immunoconjugates; D007166:Immunosuppressive Agents; D010281:Parathyroid Hormone; D000069594:Abatacept
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