Biodistribution of 111In-labelled IgG and IgM in experimental infection

SUMMARYBoth the protein used and the conjugation method are factors which may be relevant for targeting infection with In-labelled proteins. In this study, human immunoglobulin G (IgG), conjugated to either DTPA or LiLo, and LiLo conjugated human immunoglobulin M (IgM) were evaluated. In rats with Staphylococcus aureus calf muscle infection, biodistribution was determined 6, 24 and 48 h after the injection of In-DTPA-IgG, In-LiLo-IgG or In-LiLo-IgM. Absolute abscess uptake of In-LiLo-IgG was significantly higher than that of In-DTPA-IgG (P < 0.05). Since blood clearance of In-LiLo-IgG was initially significantly slower (P < 0.01), the higher abscess uptake did not result in higher abscess-to-background ratios. In-LiLo-IgG accumulated to a greater extent in the liver (P < 0.001). In-DTPA-IgG showed higher uptake in the kidneys and bone marrow (P < 0.001 and P < 0.01, respectively). Although decreasing over time, In-LiLo-IgM showed reasonable abscess uptake and rapid blood clearance, resulting in higher abscess-to-background ratios compared with In-LiLo-IgG (P < 0.01). However, liver and spleen uptake were three- to four-fold higher than that of In-LiLo-IgG (P < 0.001). Compared with DTPA-conjugation, chelation with LiLo has a minor influence on abscess targeting of In-labelled IgG. However, differences in blood clearance and organ uptake do occur. In-LiLo-IgM shows high relative accumulation in abscesses as well as high liver and spleen uptake. In-LiLo-IgM appears promising for imaging infection outside the trunk region.