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Archived Comments for: The quest for a biomarker of circulating osteoclast precursors

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  1. Response to Editorial by C Ritchlin...

    John Hamilton, University of Melbourne

    22 July 2009

    We agree with Dr. Ritchlin that our in vitro demonstration that human osteoclast precursors are within the proliferative monocyte subpopulation must be interpreted with caution; we also support his comments that the importance of the proliferative subset in rheumatoid and psoriatic arthritis should be examined. As a point of clarification, the presence and surface phenotyping of this immature proliferative subset in the blood of many donors, as well as the suggestion of its possible relevance to inflammatory/autoimmune conditions, have been reported in a number of previous publications from our laboratory [1-5]. Also, those interested are referred to a recent publication where human osteoclasts could be generated, and potentially in large numbers, from a precursor population derived in turn from hemopoietic stem cells [6].

    Dr Ritchlin also raises important questions as to whether the proliferative monocyte subpopulation expresses higher cell surface levels of c-Fms to account for the increased proliferative capacity and whether it expresses a unique surface marker(s). We have not been able to observe any differential expression of c-Fms and no unique surface marker has yet been found, although there is evidence that the subpopulation has altered expression of certain myeloid markers compared with other monocyte populations [5]. As Dr. Ritchlin states, the quest for such a marker(s) on osteoclast precursors should continue so that they can be better characterized.

    1. Cheung DL, Hamilton JA: Regulation of human monocyte DNA synthesis by colony-stimulating factors, cytokines, and cyclic adenosine monophosphate. Blood 1992, 79(8):1972-1981.
    2. Finnin M, Hamilton JA, Moss ST: Characterization of a CSF-induced proliferating subpopulation of human peripheral blood monocytes by surface marker expression and cytokine production. J Leukoc Biol 1999, 66(6):953-960.
    3. Finnin M, Hamilton JA, Moss ST: Direct comparison of the effects of CSF-1 (M-CSF) and GM-CSF on human monocyte DNA synthesis and CSF receptor expression. J Interferon Cytokine Res 1999, 19(4):417-423.
    4. Moss ST, Hamilton JA: Proliferation of a subpopulation of human peripheral blood monocytes in the presence of colony stimulating factors may contribute to the inflammatory process in diseases such as rheumatoid arthritis. Immunobiology 2000, 202(1):18-25.
    5. Clanchy FI, Holloway AC, Lari R, Cameron PU, Hamilton JA: Detection and properties of the human proliferative monocyte subpopulation. J Leukoc Biol 2006, 79(4):757-766.
    6. Way KJ, Dinh H, Keene MR, White KE, Clanchy FI, Lusby P, Roiniotis J, Cook AD, Cassady AI, Curtis DJ et al: The generation and properties of human macrophage populations from hemopoietic stem cells. J Leukoc Biol 2009, 85(5):766-778.

    Competing interests

    None declared