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.