Expression of tyrosine kinase receptors Tie-1 and Tie-2 in giant cell tumor of the tendon sheath: a possible role in synovial proliferation.

We have recently demonstrated that Tie-1 and Tie-2 are expressed in synovial cells from rheumatoid arthritis (RA). To elucidate the possible involvement of Tie receptors in synovial proliferation, we analyzed their expression by immunostaining in five cases of giant cell tumor of tendon sheath (GCTTS), which represents a proliferating lesion of synovial cells. Strong immunoreactivity for both Tie-1 and Tie-2, regardless of the individual patient's profile, was observed in all cases of GCTTS. Six sets of double immunohistochemical stainings for Tie-1/Tie-2 and fibronectin, CD68, or CD34 were carried out to determine the phenotype of Tie-1 and Tie-2-positive tumor components. In these studies, both Tie-1 and Tie-2 immunoreactivity were widely observed in the fibronectin-positive fibroblastic and the CD68-positive histiocytic mononuclear cells, as well as in the osteoclast-like giant cells. In tumor vasculature, Tie receptors were expressed in the CD34-positive endothelial cells possessing proliferating cell nuclear antigen (PCNA) immunoreactivity. We also evaluated the correlation of Tie-1/Tie-2 expression and proliferating cells in GCTTS by using double staining of Tie-1/Tie-2 together with PCNA. Overexpression of PCNA immunoreactivity was frequently found in Tie receptors-positive cells with no obvious differences in the expression pattern of Tie-1 and Tie-2. These findings suggest the possible involvement of Tie receptors in the pathogenesis of GCTTS other than solely via their involvement in angiogenesis and subsequent vascularization. It was demonstrated that Tie-2 immunoreactivity was restricted to the fibroblastic, but not histiocytic, phenotype in RA synovium, suggesting different regulatory control of Tie-2 expression in GCTTS and RA synovium. Overexpression of Tie receptors in GCTTS may imply a biological role for these receptors in synovial proliferation.