RAPID IMAGING OF EXPERIMENTAL-INFECTION WITH TECHNETIUM-99M-DTPA AFTER ANTI-DTPA MONOCLONAL-ANTIBODY PRIMING

Antibodies accumulate nonspecifically in infectious foci due to the lo cally increased vascular permeability, This study describes a method o f infection imaging in which Tc-99m-DTPA (diethylenetriaminepentaaceti c acid) is trapped at the target by a previously administered anti-DTP A monoclonal antibody, DTIn1. Methods: Rats with Staphylococcus aureus -infected calf muscle were injected intravenously with DTIn1. Two to 2 4 hr after the DTIn1 injection, Tc-99m-DTPA was injected intravenously . In separate experiments, excess DTIn1 was cleared from the circulati on 2 hr after injection with bovine serum albumin (BSA)-DTPA-In, galac tosylated BSA-DTPA-In, goat antimouse IgG or avidin. Additionally, the effect of DTIn1 dose on Tc-99m-DTPA abscess uptake was determined in a three-step protocol. The distribution of the radiolabels was studied by gamma counting of dissected tissue and gamma camera imaging, Resul ts: Priming with DTIn1 resulted in specific retention of Tc-99m-DTPA i n the abscess. Such Tc-99m-DTPA abscess uptake was not dependent on th e interval between the DTIn1 and the Tc-99m-DTPA injection: Optimal Tc -99m-DTPA abscess uptake was already achieved within a 2-hr time span between the DTIn1 and DTPA injections, However, relatively high Tc-99m -DTPA background was observed due to slowly clearing DTIn1-Tc-99m-DTPA complexes. Background reduction with various agents had a prominent e ffect on DTIn1 as well as Tc-99m-DTPA biodistribution. The best reduct ion was obtained using BSA-DTPA-In. Optimal Tc-99m-DTPA abscess uptake in the three-step protocol was obtained at higher DTIn1 doses (>100 m u g). Conclusion: Infectious foci in a rat model can be imaged earlier with extremely low background levels after priming with DTIn1, follow ed by BSA-DTPA-In and imaging with Tc-99m-DTPA, as compared with direc tly labeled IgG.