Summary The antigenic phenotype, ultrastructure and bone resorbing ability of mononuclear and multinucleated giant cells of four giant cell tumour of tendon sheath (GCTTS) lesions was assessed. Both the giant cells and the mononuclear cells exhibted the antigenic phenotype of cells of the monocyte/macrophage lineage. The giant cells, unlike osteoclasts, did not respond morphologically to calcitonin and showed ultrastructural and immunophenotypic features of macrophage polykaryons. However (Wood et al., 1988), and do not support the concept that the lesion is a form of xanthoma or benign fibrous histiocytoma (Rosai, 1981).There have been several recent studies on the nature of giant cells in giant cell lesions of bone and soft tissue which have used bone resorption as an operational or functional criterion to determine whether tumour-associated giant cells present in a pathological lesion are osteoclasts (Athanasou et al., 1983;Flanagan & Chambers, 1988;Flanagan & Chambers, 1989
Materials and methodsBovine parathyroid hormone (PTH) (2,500 U mg ')was provided by Dr J. Zanelli (National Institute for Biological Standards, London, UK) and dissolved (230 IU ml-') in 1 ml 0.001 % acetic acid in distilled water containing 1 mg ml1' of bovine serum albumin (Sigma, UK) (BSA). Salmon calcitonin (CT) was donated by Armour Pharmaceuticals, Eastbourne, UK (4,450 IU mg-1) and dissolved (1 mg ml') in 0.05% NaCl and 0.2% sodium acetate in distilled water containing 1 mg ml-' of BSA. Prostaglandin E2 (Sigma) (PGE2) was dissolved (10-2 M) in alcohol. 1,25-Dihydroxy vitamin D3 [1, was donated by Roche products (Welwyn Garden City, UK) and dissolved (10-2 M) in alcohol. Interleukin-1 (IL-1) was kindly provided by Dr J. Saklatvala and dissolved (200 ng ml-') in RPMI.Four GCTTS lesions were examined. These were from the left index finger of a 37 year old female, the right index finger of a 58 year old male and the right and left middle fingers of a 45 year old male. In all cases, part of the lesion was fixed in formalin and processed routinely. For transmission electron microscopy, tiny samples of tissue were fixed in 4%phosphate buffered glutaraldehyde for 6 h, then post-fixed_in 2% buffered osmium tetroxide for 2 h. Tissue was dehydrated in graded alcohol, treated with propylene oxide and embedded in epoxy resin (EMix). Thin sections were stained with uranyl acetate and lead citrate, and examined in a Jeol 100 CX electron microscope. Samples of the tumour were also snap-frozen in liquid nitrogen and then stored at -220C for cytostate sectioning. Several antigenic determinants were sought in cryostat sections of the lesions after the application of monoclonal antibodies listed in Table I. These antibodies were derived from the Third and Fourth Workshops on Human Leucocyte Differentiation Antigens (Hogg & Horton, 1987;Knapp et al., 1989). Immunohistochemistry was performed using an indirect immunoperoxidase technique (Gatter et al., 1984).Preparation of isolated macrophages and macrophage polykaryons The remainder of the tissue was...