title: Interleukin 18 inhibits osteoclast formation via T cell production of granulocyte macrophage colony-stimulating factor.
abstract: IL-18 inhibits osteoclast (OCL) formation in vitro independent of IFN-gamma production, and this was abolished by the addition of neutralizing antibodies to GM-CSF. We now establish that IL-18 was unable to inhibit OCL formation in cocultures using GM-CSF-deficient mice (GM-CSF -/-). Reciprocal cocultures using either wild-type osteoblasts with GM-CSF -/- spleen cells or GM-CSF -/- osteoblasts with wild-type spleen cells were examined. Wild-type spleen cells were required to elicit a response to IL-18 indicating that cells of splenic origin were the IL-18 target. As T cells comprise a large proportion of the spleen cell population, the role of T cells in osteoclastogenesis was examined. Total T cells were removed and repleted in various combinations. Addition of wild-type T cells to a GM-CSF -/- coculture restored IL-18 inhibition of osteoclastogenesis. Major subsets of T cells, CD4+ and CD8+, were also individually depleted. Addition of either CD4+ or CD8+ wild-type T cells restored IL-18 action in a GM-CSF -/- background, while IL-18 was ineffective when either CD4+ or CD8+ GM-CSF -/- T cells were added to a wild-type coculture. These results highlight the involvement of T cells in IL-18-induced OCL inhibition and provide evidence for a new OCL inhibitory pathway whereby IL-18 inhibits OCL formation due to action upon T cells promoting the release of GM-CSF, which in turn acts upon OCL precursors.
authors.affiliation: St. Vincent's Institute of Medical Research and The University of Melbourne, Department of Medicine, St. Vincent's Hospital, Fitzroy, Victoria 3065, Australia.
authors.forename: N J
authors.initials: NJ
authors.lastname: Horwood
authors.forename: N
authors.initials: N
authors.lastname: Udagawa
authors.forename: J
authors.initials: J
authors.lastname: Elliott
authors.forename: D
authors.initials: D
authors.lastname: Grail
authors.forename: H
authors.initials: H
authors.lastname: Okamura
authors.forename: M
authors.initials: M
authors.lastname: Kurimoto
authors.forename: A R
authors.initials: AR
authors.lastname: Dunn
authors.forename: T
authors.initials: T
authors.lastname: Martin
authors.forename: M T
authors.initials: MT
authors.lastname: Gillespie
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000096:biosynthesis* / Q000235:genetics; D007369:Interferon Inducers / Q000494:pharmacology*; D020382:Interleukin-18; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects*; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism
chemical_list: D016207:Cytokines; D007369:Interferon Inducers; D020382:Interleukin-18; D016178:Granulocyte-Macrophage Colony-Stimulating Factor