SOLUBLE FORMS OF THE HIGH-AFFINITY FIBROBLAST GROWTH-FACTOR RECEPTOR IN HUMAN VITREOUS FLUID

Purpose. Fibroblast growth factor-binding proteins (FGF-BPs) have been identified recently in blood and other biologic fluids and have been shown to be identical to a truncated form of the high-affinity cell su rface FGF receptor. The authors examined the hypothesis that FGF-BPs a lso are present in human vitreous fluid. Methods. Vitreous fluid obtai ned from 12 patients tvas incubated overnight with heparin-Sepharose, FGF-2 heparin-Sepharose, and wheat germ agglutinin (WGA)-Sepharose, a lectin known to bind to high-affinity FGF receptors. The precipitated proteins were characterized by immunoblotting using two FGF receptor a ntibodies raised to either the extracellular domain of FGFR-1 or the i ntracellular domain of FGFR-1. Results. A 70- to 85-kd FGF-BP was dete cted in the vitreous in each of the 12 eyes examined. A 55-kd FGF-BP w as detected in six of the samples. Both the 70- to 85-kDa and the 55-k Da proteins were precipitated by FGF-2 heparin-Sepharose but not by he parin-Sepharose alone, suggesting that the interaction was dependent o n thepresence of FGF-2. The proteins bound avidly to WGA-Sepharose. We stern blot analysis revealed that the proteins were recognized by an a ntibody raised to the extracellular domain of the high-affinity FGF re ceptor but not by an antibody raised to the intracellular domain of th e FGF receptor, indicating they are likely to be truncated portions of the extracellular domain of the high-affinity FGF receptor. Conclusio ns. Vitreous fluid contains 70- to 85-kd and 55-kd FGF-BPs that have b iochemical and immunologic characteristics similar to the extracellula r domain of the high-affinity FGF receptor. These naturally occurring FGF-BPs may sequester free FGF in the vitreous cavity and may modulate the biologic activity of FGF in vitreoretinal diseases.