Osteoimmunology: Interactions of the Bone and Immune System
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Osteoimmunology: Interactions of the Bone and Immune System Joseph Lorenzo, Mark Horowitz and Yongwon Choi Endocr. Rev. 2008 29:403-440 originally published online May 1, 2008; , doi: 10.1210/er.2007-0038 To subscribe to Endocrine Reviews or any of the other journals published by The Endocrine Society please go to: http://edrv.endojournals.org//subscriptions/ Copyright © The Endocrine Society. All rights reserved. Print ISSN: 0021-972X. Online 0163-769X/08/$20.00/0 Endocrine Reviews 29(4):403–440 Printed in U.S.A. Copyright © 2008 by The Endocrine Society doi: 10.1210/er.2007-0038 Osteoimmunology: Interactions of the Bone and Immune System Joseph Lorenzo, Mark Horowitz, and Yongwon Choi Department of Medicine and the Musculoskeletal Institute (J.L.), The University of Connecticut Health Center, Farmington, Connecticut 06030; Department of Orthopaedics (M.H.), Yale University School of Medicine, New Haven, Connecticut 06510; and Department of Pathology and Laboratory Medicine (Y.C.), The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104 Bone and the immune system are both complex tissues that that the other system has on the function of the tissue they are respectively regulate the skeleton and the body’s response to studying. This review is meant to provide a broad overview of invading pathogens. It has now become clear that these organ the many ways that bone and immune cells interact so that a systems often interact in their function. This is particularly better understanding of the role that each plays in the devel- true for the development of immune cells in the bone marrow opment and function of the other can develop. It is hoped that and for the function of bone cells in health and disease. Be- an appreciation of the interactions of these two organ systems cause these two disciplines developed independently, inves- will lead to better therapeutics for diseases that affect either tigators in each don’t always fully appreciate the significance or both. (Endocrine Reviews 29: 403–440, 2008) I. Introduction X. Role of the Immune System in Bone Disease: the Birth of II. The Origins of Bone Cells Osteoimmunology A. Osteoclasts XI. Role of Immune Cells in Estrogen-Withdrawal-Induced B. Osteoblasts Bone Loss III. Role of Osteoblasts in Hematopoiesis XII. Modulation of Immunity by the RANKL-RANK-OPG IV. Role of Osteoblasts in Bone Marrow Cell Transplantation Axis V. B Lymphocyte Differentiation XIII. Toll-Like Receptors, Inflammation, and Osteoimmunology A. PU.1 B. Early B cell factor (Ebf) C. Pax5 I. Introduction VI. Role of Megakaryocytes in Bone Turnover VII. Cytokines and Local Immune Cell Factors as Regulators ONE IS A COMPLEX organ with multiple functions. It of Bone Cell Functions B provides structural integrity for the body, it is the site A. Receptor activator of nuclear factor-B ligand of hematopoiesis, and it is a storehouse for calcium and (RANKL), receptor activator of nuclear factor-B (RANK), and osteoprotegerin (OPG) First Published Online May 1, 2008 B. RANKL-RANK mediated signals for osteoclast Abbreviations: AIRE, Autoimmune regulator; BMP, bone morpho- differentiation genic protein; BMSC, bone marrow stromal cells; BSAP, B-cell specific C. Costimulation in RANKL-induced osteoclast activation activation protein; CD40L, CD40 ligand; Ebf, early B cell factor; Eph, erythropoietin-producing hepatocyte kinase; FasL, Fas li- differentiation ␥ ␥ D. Macrophage colony-stimulating factor gand; FcR , Fc receptor ; G-CSF, granulocyte colony-stimulating factor; GCV, ganciclovir; GM-CSF, granulocyte M-CSF; HSC, hematopoietic E. Additional colony stimulating factors stem cell(s); IFN, interferon; IgH, Ig heavy; ITAM, immunoreceptor F. Interleukin-1 tyrosine-based activation motif; LIF, leukemia inhibitory factor; LPS, G. Tumor necrosis factor lipopolysaccharide; M-CSF, macrophage colony-stimulating factor; H. Additional TNF superfamily members MITF, microphthalmia-associated transcription factor; MK, megakaryo- cyte(s); MMP, matrix metalloproteinase; MyD88, myeloid differentia- I. Interleukin-6 J. Additional interleukin-6 family members tion factor 88; NF- B, nuclear factor B; OCL, osteoclast-like cell(s); OPG, osteoprotegerin; OSCAR, osteoclast-associated receptor; OVX, ovariec- K. Interleukin-7 tomy; Pax, paired box; PI3K, phosphatidylinositide-3-kinase; PIR-A, L. Interleukin-8 and other chemokines paired Ig-like receptor A; PLC, phospholipase-C; RANK, receptor ac- M. Interleukin-10 tivator of NF-B; RANKL, RANK ligand; ROS, reactive oxygen species; N. Interleukin-12 SCF, stem cell factor; SIRP 1, signal regulatory protein 1; TCR, T-cell O. Interleukin-15 receptor; TH, T-helper; TLR, Toll-like receptor; TPO, thrombopoietin; P. Interleukin-17 and interleukin-23 TRAF, TNF receptor-associated factor; TRAIL, TNF-related apoptosis inducing ligand; TREM-2, triggering receptor expressed by myeloid Q. Interleukin-18 cells-2; TRIF, Toll/IL-1 receptor domain-containing adaptor inducing R. Interferons interferon-; XHIM, X-liked hyper IgM. S. Additional cytokines Endocrine Reviews is published by The Endocrine Society (http:// VIII. Regulation of Osteoblasts by Immune Cells and Cytokines www.endo-society.org), the foremost professional society serving the IX. Role of Osteoclasts in Regulating Osteoblasts endocrine community. 403 404 Endocrine Reviews, June 2008, 29(4):403–440 Lorenzo et al. • Osteoimmunology phosphorus (1). Likewise, the immune system is complex pression of surface antigens that separate these two cell types and provides organisms with protection from invading (8, 9). Mononuclear cells, which can differentiate into oste- pathogens (2). Multiple overlapping and interacting mech- oclast-like cells (OCL) in a variety of in vitro culture systems, anisms have evolved to regulate both systems. Interactions are present in the bone marrow and the peripheral blood (10, between bone and immune cells are now well described. It 11). has become apparent that to explain the phenotype of many The availability of multiple antibodies recognizing cell in vivo models with abnormal bone metabolism, one can no surface molecules, which are expressed on hematopoietic longer view either system in isolation. Rather, to understand cells (12–15), has allowed the identification of bone marrow their function, they must be viewed as a single integrated peripheral blood and spleen cell populations that can form system. Examples of recently identified interactions of bone OCL in vitro. Studies from multiple laboratories have iden- and immune cells include the findings: 1) that cells related to tified several candidate populations with the ability to form osteoblasts, which form bone, are critical regulators of the OCL in coculture with stromal cells, when cultured alone in hematopoietic stem cell (HSC) niche from which all blood liquid medium or when cultured in methylcellulose. In ex- and immune cells derive; and 2) that osteoclasts, which are periments performed before the identification of receptor the cells that resorb bone, appear to share a common origin activator of nuclear factor (NF)-B ligand (RANKL), which with the myeloid precursor cells that also gives rise to mac- is the critical cytokine that regulates osteoclast formation rophages and myeloid dendritic cells. It has also been shown (16), investigators relied on coculture of various fractions of in vitro that cells that are relatively far along in their differ- cells (generally from bone marrow) with stromal or osteo- entiation toward antigen-presenting dendritic cells retain the blastic cells (17). In these assays, cells were stimulated to ability to form mature bone-resorbing osteoclasts (3). Finally, induce osteoclastogenesis by treatment with a stimulator of over the last 30 yr, it has become well established that mul- resorption like 1,25 OH2 vitamin D3 or PTH. Interestingly, tiple soluble mediators of immune cell function including these assays require cell-cell interaction between osteoblastic cytokines, chemokines, and growth factors also regulate os- and osteoclastic cells because OCL did not form in these teoblast and osteoclast activity (4). It is likely that immune cultures if the two cell types were separated by a membrane cells and cytokines are critically responsible for the changes (18). The majority of these early studies focused on myeloid in bone turnover and bone mass that occur in postmeno- lineage cells. They demonstrated that rodent cells expressing pausal osteoporosis and inflammatory conditions such as mature macrophage markers, which were isolated from the rheumatoid arthritis, periodontal disease, or inflammatory bone marrow or spleen, gave rise to OCL when they were bowel disease. cocultured with bone marrow stromal cells (BMSC) (19). The regulation of bone by hematopoietic and immune cells Muguruma and Lee (20) identified an osteoclast progenitor serves a variety of functions. It is likely that developing population in murine bone marrow that was negative for hematopoietic cells regulate bone turnover and maintain the mature markers of B lymphocytes (CD45R/B220), granulo- marrow cavity by interacting with osteoblasts and oste- cytes (Gr-1), macrophages (CD11b/Mac-1), and erythroid oclasts during normal bone development (5). Conversely, cells (Ter-119). This population did not express Sca-1, which during inflammatory states either locally produced or cir- is a marker that is found on HSC but was positive for the culating cytokines, which are the products of activated im- progenitor marker CD117/c-kit (20). These