Formation of multinucleated cells with osteoclast precursor features in human cord monocytes cultures

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Abstract
A common lineage between monocytes and osteoclasts has been suggested but not yet proved, and an osteoclast precursor might be an immature cell of the monocyte‐macrophage family. We therefore compared the ability of cord blood and adult monocytes in long‐term culture to differentiate toward osteoclasts. Both adult and cord monocytes were cultured for 3 weeks in the presence of 20% horse serum. The proportion of multinucleated cells formed was influenced by 1,25(OH)2D3 in cord, but not in adult monocyte cultures: 10−9M 1,25(OH)2D3 increased multinucleated cells from 13 ± 2 to 26 ± 1% of total cells in cord monocyte cultures. The formation of multinucleated cells in cord monocyte cultures, in the presence of 10−9 M 1,25(OH)2D, was decreased by salmon calcitonin (dose dependently from 10−8 to 10−6 M) and increased by 1—34 parathormone (100 ng/ml). None of these hormones induced any modification of the proportion of multinucleated cells formed in adult monocytes culture. Specific antigens on the membrane of the cells obtained after 3 weeks culture in the presence of 10−9 M 1,25(OH)2D3 were assessed by immunocytochemistry. The respective proportion of adult and cord labeled cells was 64 ± 11 vs. 63 ± 6% with Leu M5 (specific for monocyte) and 68 ± 7 vs. 30 ± 10% (P45Ca from devitalized 45Ca‐prelabeled rat calvaria; they did not form an acidic extracellular compartment, as assessed by acridine orange fluorescence, and there was no ultrastructural evidence of a brush border at the interface with bone. In conclusion, cord blood monocytes in long‐term culture do not form mature osteoclasts. However, in contrast to adult monocytes, some acquire, in culture, characteristics of osteoclast precursors: sensitivity to osteotropic hormones and expression of an osteoclast membrane‐specific antigen.

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