RETENTION OF TC-99M IN INFECTIOUS FOCI IN RATS AFTER RELEASE FROM TC-99M LABELED HUMAN NONSPECIFIC POLYCLONAL IMMUNOGLOBULIN-G - A DUAL-LABEL STUDY WITH HYDRAZINONICOTINAMIDO AND IMINOTHIOLANO IMMUNOGLOBULIN

In an effort to contribute to the understanding of the mechanism of up take of technetium-99m labelled non-specific polyclonal human immunogl obulin G (hIgG) in inflammatory lesions we compared the tissue distrib ution of double-labelled Tc-99m-hydrazinonicotinamido (HYNIC) hIgG-C-1 4 and Tc-99m-iminothiolano hIgG-C-14 in groups of five Wistar rats wit h a Staphylococcus aureus infection of the left calf muscle between 2 h p.i. and 24 h p.i. The stability of the two double-labelled hIgG pre parations was evaluated in vitro and in plasma in vivo by high-perform ance liquid chromatography (HPLC) analysis. At 24 h after injection of Tc-99m-HYNIC-hIgG-C-14 the abscess uptake of Tc-99m (1.5% ID/g+/-0.2% ID/g) was significantly higher (P<0.01) than the C-14 uptake (1.0% ID /g+/-0.1% ID/g). After injection of Tc-99m-iminothiolano hIgG-C-14 no significant difference (P=0.08) was found between the abscess uptake o f the two radionuclides at 24 h p.i. (Tc-99m: 0.8% ID/g+/-0.1% ID/g; C -14: 0.90% ID/g+/-0.09% ID/g), HPLC analysis of plasma samples reveale d release of Tc-99m from both double-labelled immunoglobulin preparati ons. This phenomenon was more pronounced for iminothiolano hIgG than f or HYNIC hIgG (43% vs 18%), in most tissues other than abscesses signi ficant differences were also found between the Tc-99m and the correspo nding C-14 uptake. Our results demonstrate that the chemical form in w hich Tc-99m is bound to hIgG severely influences its release from hIgG and its retention in infections.