Tc-99(m)-HIG accumulates in the synovial tissue of rats with adjuvant arthritis by binding to extracellular matrix proteins

Our objective was to investigate the mechanism of accumulation of Tc-99(m)-labelled non-specific polyclonal human immunoglobulin (Tc-99(m)-HIG) in inflamed synovial tissue (ST) in an experimental animal model of arthritis. Following Tc-99(m)-HIG scintigraphy, the in vivo localization of Tc-99(m)-HIG in the ST of knee joints of rats with adjuvant arthritis was studied using immunohistochemical techniques. In addition, the in vitro binding of Tc-99(m)-HIG to extracellular matrix proteins was analysed by means of immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). After Tc-99(m)-HIG scintigraphy, Tc-99(m)-HIG was detected in the ST of rats with adjuvant arthritis. Tc-99(m)-HIG was diffusely distributed and not bound to cells. In vitro incubation of Tc-99(m)-HIG on the ST of rats with adjuvant arthritis revealed binding of Tc-99(m)-HIG to inflamed, but not to non-inflamed, ST. In addition, specific binding of Tc-99(m)-HIG to fibronectin, fibrin, collagen type I and III was demonstrated by ELISA. We conclude that the accumulation of Tc-99(m)-HIG in inflamed ST can be explained by the binding of Tc-99(m)-HIG to extracellular matrix proteins.