Bone Abstracts

Background: Osteoclasts are unique multinucleated cells that originate from the fusion of monocytes. They are the only cells known to be capable of bone resorption. Interestingly, the foreign body multinucleated giant cell (FBGC) arises from the same lineage as the osteoclast, and they share numerous similar characteristics, among which the expression of tartrate resistant acid phosphatase (TRAcP). Yet, it is not known whether the FBGC has the capacity to resorb bone.

Objective: To compare the bone resorptive capacity of two different populations of multinucleated cells i.e. the osteoclast and the FBGC.

Methods: CD14⁺ monocytes were isolated from human blood. Differentiation of CD14⁺ cells into osteoclasts was induced by M-CSF and RANK-L, and for the differentiation into FBGC, M-CSF, IL-4 and IL-13 was added. Cells were seeded on bones slices. After 25 days the cells were fixed and stained for activity of TRAcP and the nuclei were stained with 4′,6-diamidino-2-phenylindool (DAPI). To analyze bone resorption, the bone slices were stained with coomassie brilliant blue.

Results: High and similar numbers of multinucleated cells were seen both in the osteoclast and in the FBGC cultures. The multinucleated FBGCs however, proved to be much larger and also the number of nuclei per cell was much higher. Bone resorption was very extensive in the osteoclast cultures; almost the entire surface of the bone slices were resorbed. In sharp contrast herewith, a complete absence of resorption was apparent in the FBGC cultures.

Conclusion: In spite of the same precursor and an obvious mulitnuclearity, there is an essential difference between both populations. The FBGCs were considerably larger and had a higher number of nuclei compared to the osteoclast culture. The most important difference was that, in contrast to osteoclasts, FBGC do not have the capacity to resorb bone.