Species and immunoglobulin preparation related effects on the biodistribution of technetium-99m-labelled immunoglobulin G in a baboon model

Technetium-99m-labelled immunoglobulin G (99mTc-IgG) is a convenient and useful radio-pharmaceutical for the scintigraphic detection of inflammatory foci. However, unfavourable physiological biodistribution patterns such as high activities in the liver and especially in the kidneys impede the efficacy of this agent. This report describes biodistribution studies in the baboon model of various thiol reduction-mediated 99mTc-labelled immunoglobulins, including human IgG preparations (Sandoglobulin and Sigma: gamma-globulins prepared from Cohn fractions II and III) as well as baboon IgG preparations (Sigma: gamma-globulins prepared from Cohn fractions II and III and IgG isolated from the serum obtained from specific animals). The biodistribution studies demonstrated differences in kidney concentration, i.e. human IgG (Sandoglobulin) > baboon IgG (cross-over animal experiments with IgG isolated from the serum of the different animals) > human IgG (Sigma) approximately baboon IgG (Sigma) approximately baboon IgG (own IgG isolated from the serum of a specific animal, labelled with 99mTc and reinjected). Differences in liver concentration were also observed: human IgG (Sandoglobulin) < human IgG (Sigma) approximately baboon IgG (Sigma) approximately baboon IgG (own IgG) approximately IgG (cross-over). Characteristic were the relatively high activities in the liver and kidneys compared to those in other organs with high blood supply, and a relatively high retention in the blood pool.