BIODISTRIBUTION OF IN-111-LABELED IGG AND IGM IN EXPERIMENTAL-INFECTION

Both the protein used and the conjugation method are factors which may be relevant for targeting infection with In-111-labelled proteins. In this study, human immunoglobulin G (IgG), conjugated to either DTPA o r LiLo, and LiLo conjugated human immunoglobulin M (IgM) were evaluate d. In rats with Staphylococcus aureus calf muscle infection, biodistri bution was determined 6, 24 and 48 h after the injection of In-111-DTP A-IgG, In-111-LiLo-IgG or In-111-LiLo-IgM. Absolute abscess uptake of In-111-LiLo-IgG was significantly higher than that of In-111-DTPA-IgG (P < 0.05). Since blood clearance of In-111-LiLo-IgG was initially sig nificantly slower(P < 0.01), the higher abscess uptake did not result in higher abscess-to-background ratios. In-111-LiLo-IgG accumulated to a greater extent in the Liver (P < 0.001). In-111-DTPA-IgG showed hig her uptake in the kidneys and bone marrow (P < 0.001 and P < 0.01, res pectively). Although decreasing over time, In-111-LiLo-IgM showed reas onable abscess uptake and rapid blood clearance, resulting in higher a bscess-to-background ratios compared with In-111-LiLo-IgG (P < 0.01). However, liver and spleen uptake were three- to four-fold higher than that of In-111-LiLo-IgG (P < 0.001). Compared with DTPA-conjugation, c helation with LiLo has a minor influence on abscess targeting of In-11 1-labelled IgG. However, differences in blood clearance and organ upta ke do occur. In-111-LiLo-IgM shows high relative accumulation in absce sses as well as high Liver and spleen uptake. In-111-LiLo-IgM appears promising for imaging infection outside the hunk region.