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Our results suggest that osteoblastic cells or a subpopulation of these cells may have immune functions in bone. Further studies in which immune functions are assessed will be needed to test this hypothesis.

Background/Aims: Osteoblasts are classically considered to play an important role during bone tissue development, and to be involved in the formation of mineralized bone matrix. Recent reports have suggested that they can also exert some activities directly associated with the immune system (cytokine synthesis and antigen presentation). Moreover, some authors have found antigens on osteoblast-like cells normally expressed by other cells with a common origin in bone marrow.Methods: We isolated and cultured human osteoblast-like lines and studied their antigenic phenotype with flow cytometry using monoclonal antibodies against antigens associated with hematopoietic cells.Results: Cultured cells expressed CD34, but were negative for CD45. B cell antigens CD20 and CD23 and myelomonocytic antigens CD11b, CD13, and CD16 were detected. Expression of CD3, CD14, CD15 and CD68 was negative, whereas CD25 expression was positive. CD56, an antigen expressed on NK cells, was positive. These cells were CD10, CD44, CD54, CD80, CD86 and HLA-DR positive, as previously described. An antigen specific to follicular dendritic cells was also observed on cultured osteoblast-like cells.Conclusions: The antigenic phenotypes of human osteoblast-like cells and FDC are similar. These data suggest that osteoblasts may be functionally related to certain dendritic cells and may play an additional role in bone tissue to that classically assigned.