MULTINUCLEATED CELLS IN PIGMENTED VILLONODULAR SYNOVITIS AND GIANT-CELL TUMOR OF TENDON SHEATH EXPRESS FEATURES OF OSTEOCLASTS

Pigmented villonodular synovitis (PVNS) and the histologically related lesion giant cell tumor of tendon sheath (GCTTS) are idiopathic, prol iferative lesions that can induce osteolysis and formation of bone cys ts, These lesions contain two predominant cell types: mononuclear poly hedral cells and multinucleated cells (MNCs). Previous studies demonst rated that the mononuclear cells exhibit phenotypic features consisten t with derivation from a monocyte/macrophage lineage. The cell lineage of the MNCs and their relationship to osteoclasts are not known. To c haracterize the MNCs in these lesions and to establish the relationshi p of these MNCs to osteoclasts, histological sections from six cases o f PVNs and two cases of GCTTS were studied, Mononuclear cells expresse d CD14 and HLA-DR, in keeping with their relationship to cells of the monocyte/macrophage lineage, Characterization of the MNCs revealed fea tures associated with an osteoclast phenotype, Seven of the eight spec imens contained MNCs that were intensely tartrate-resistant acid phosp hatase positive approximately 5% of the mononuclear cells were tartrat e-resistant acid phosphatase positive and these tended to surround MNC s, MNCs in both lesions reacted strongly with the 23C6 monoclonal anti body that recognizes the alpha V beta(3) integrin (the vitronectin rec eptor), as did several mononuclear cells surrounding the MNCs, Most MN Cs did not express CD14 or HLA-DR, Expression of-receptors for calcito nin, a marker for osteoclasts, was detected ora MNCs after incubation of sections with I-125-labeled salmon calcitonin and emulsion autoradi ography, MNCs in four of six PVNS and two of two GCTTS samples demonst rated specific calcitonin binding Expression of mRNA for calcitonin re ceptor was confirmed in all cases by reverse transcriptase polymerase chain reaction, These results demonstrate that MNCs in PVNS and GCTTS express phenotypic features of authentic osteoclasts and suggest that osteoclast-like multinucleated cells can arise in synovial soft tissue s remote from bone.