Biological characterization of human bone tumors. X. The proliferation behavior of macrophages as compared to fibroblastic cells in malignant fibrous histiocytoma and giant cell tumor of bone.

Seven giant cell tumors of bone and four malignant fibrous histiocytomas were studied immunohistochemically with different monoclonal antibodies to the mononuclear phagocyte system (MPS), to HLA-DR antigens, and to a proliferation-associated nuclear antigen (KI-67), in order to clarify the role of macrophages in these tumors. A part of the mononuclear cells stained positive with antibodies against the MPS. Antibody 25-F-9 against mature tissue macrophages showed the strongest reaction. The osteoclast-like giant cells also stained positive with this antibody. Fibroblast-like stromal cells, however, showed negative reactions to all antibodies against MPS cells. A double-labeling immunohistological technique was used to detect the proliferating cell population in these tumors. The fibroblast-like cells that were negative for MPS markers, were positively labeled with the monoclonal antibody Ki-67 against a proliferation-associated nuclear antigen, whereas a negative reaction to Ki-67 was seen in cells positive with antibodies to the MPS. These results support the concept that macrophages are a reactive population in these tumors, whereas the fibroblast-like mesenchymal cells are the proliferating tumor cells.