IMAGING OF FOCAL SITES OF INFLAMMATION IN RHESUS-MONKEYS WITH TC-99M-LABELED HUMAN POLYCLONAL IGG

The biological behavior of human polyclonal immunoglobulin G (IgG) rad iolabeled with Tc-99m via a nicotinyl hydrazine derivative, was evalua ted in Rhesus monkeys. Tc-99m-IgG and In-111-MACROSCINT(R) DTPA-IgG we re co-administered to Rhesus monkeys with focal sites of sterile infla mmation and scintillation camera images were acquired at 6 and 19 h af ter injection. The biodistribution of the two antibody preparations we re similar, however, small differences were detected: Tc-99m-IgG > In- 111-IgG in spleen and lung; Tc-99m-IgG < In-111-IgG in bone and skelet al muscle. A linear correlation of the tissue-to-blood ratios of Tc-99 m- and In-111-labeled IgG was observed at both times (r(2) > 0.98). Th e slopes of the regression lines were not significantly different from unity: 6 h-0.982 +/- 0.018; 19 h 1.0334 +/- 0.0226. Also, at both 6 a nd 19 h after injection, the target-to-background ratios (T/B) for the sites of inflammation were remarkably similar for In-111 and Tc-99m. These studies establish that human polyclonal IgG labeled with Tc-99m via a nicotinyl hydrazine modified intermediate is equivalent to In-11 1-MACROSCINT(R) DTPA-IgG for imaging focal sites of inflammation in mo nkeys.