Immunohistochemical identification of osteoclasts and multinucleated macrophages

•Both multinucleated macrophages and osteoclasts were found to express CD68.•Giant cells and multinucleated cells expressed CD13 and CD14 but did not express GrB, Ki67 or CD56.•Osteoclasts do not express the macrophage-associated antigens GrB and Ki67.•Giant cells are formed from osteoclast precursors of mononuclear phagocyte.

Osteoclasts are bone-resorbing multinuclear cells derived from hematopoietic stem cells which are specialised to carry out lacunar bone resorption. The immunophenotype of giant cell-containing bone lesions in a wide range of osteoclast-like giant cells was similarly assessed. Both multinucleated macrophages and osteoclasts were found to express CD68. Multinucleated macrophages, but not osteoclasts, expressed GrB and Ki67. CD13+/CD14+/CD68+/GrB−/Ki67−/CD56− all giant-cell lesions noted in giant cells of bone. Giant cells have an osteoclast phenotype in most giant cell-rich lesions of bone, which do not express the macrophage-associated antigens GrB and Ki67. Our results indicate that they are formed from osteoclast precursors of mononuclear phagocyte.