title: Activated T lymphocytes suppress osteoclastogenesis by diverting early monocyte/macrophage progenitor lineage commitment towards dendritic cell differentiation through down-regulation of receptor activator of nuclear factor-kappaB and c-Fos.
abstract: Activated T lymphocytes either stimulate or inhibit osteoclastogenesis from haematopoietic progenitors in different experimental models. To address this controversy, we used several modes of T lymphocyte activation in osteoclast differentiation--mitogen-pulse, anti-CD3/CD28 stimulation and in vivo and in vitro alloactivation. Osteoclast-like cells were generated from non-adherent immature haematopoietic monocyte/macrophage progenitors in murine bone-marrow in the presence of receptor activator of nuclear factor (NF)-kappaB ligand (RANKL) and monocyte-macrophage colony-stimulating factor (M-CSF). All modes of in vivo and in vitro T lymphocyte activation and both CD4(+) and CD8(+) subpopulations produced similar inhibitory effects on osteoclastogenesis paralleled by enhanced dendritic cell (DC) differentiation. Osteoclast-inhibitory effect was associated with T lymphocyte activation and not proliferation, and could be replaced by their culture supernatants. The stage of osteoclast differentiation was crucial for the inhibitory action of activated T lymphocytes on osteoclastogenesis, because the suppressive effect was visible only on early osteoclast progenitors but not on committed osteoclasts. Inhibition was associated specifically with increased granulocyte-macrophage colony-stimulating factor (GM-CSF) expression by the mechanism of progenitor commitment toward lineages other than osteoclast because activated T lymphocytes down-regulated RANK, CD115, c-Fos and calcitonin receptor expression, and increased differentiation towards CD11c-positive DC. An activated T lymphocyte inhibitory role in osteoclastogenesis, confirmed in vitro and in vivo, mediated through GM-CSF release, may be used to counteract activated bone resorption mediated by T lymphocyte-derived cytokines in inflammatory and immune disorders. We also demonstrated the importance of alloactivation in osteoclast differentiation and the ability of cyclosporin A to abrogate T lymphocyte inhibition of osteoclastogenesis, thereby confirming the functional link between alloreaction and bone metabolism.
authors.affiliation: Department of Physiology and Immunology, University of Zagreb School of Medicine, Zagreb, Croatia. dgrcevic@mef.hr
authors.forename: D
authors.initials: D
authors.lastname: Grcević
authors.forename: I K
authors.initials: IK
authors.lastname: Lukić
authors.forename: N
authors.initials: N
authors.lastname: Kovacić
authors.forename: S
authors.initials: S
authors.lastname: Ivcević
authors.forename: V
authors.initials: V
authors.lastname: Katavić
authors.forename: A
authors.initials: A
authors.lastname: Marusić
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000276:immunology / Q000502:physiology; D016572:Cyclosporine / Q000494:pharmacology; D003713:Dendritic Cells / Q000166:cytology*; D015536:Down-Regulation / Q000276:immunology; D005260:Female; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000502:physiology*; D007959:Lymphocyte Culture Test, Mixed; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D053245:RANK Ligand / Q000378:metabolism; D053246:Receptor Activator of Nuclear Factor-kappa B / Q000378:metabolism; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000378:metabolism; D018003:Receptors, Calcitonin / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D007166:Immunosuppressive Agents; D016760:Proto-Oncogene Proteins c-fos; D053245:RANK Ligand; D053246:Receptor Activator of Nuclear Factor-kappa B; D018003:Receptors, Calcitonin; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D016572:Cyclosporine; D016186:Receptor, Macrophage Colony-Stimulating Factor