Rapid imaging of experimental infection with technetium-99m-DTPA after anti-DTPA monoclonal antibody priming.

UNLABELLED Antibodies accumulate nonspecifically in infectious foci due to the locally increased vascular permeability. This study describes a method of infection imaging in which 99mTc-DTPA (diethylenetriaminepentaacetic acid) is trapped at the target by a previously administered anti-DTPA monoclonal antibody. DTIn1. METHODS Rats with Staphylococcus aureus-infected calf muscle were injected intravenously with DTIn1. Two to 24 hr after the DTIn1 injection, 99mTc-DTPA was injected intravenously. In separate experiments, excess DTIn1 was cleared from the circulation 2 hr after injection with bovine serum albumin (BSA)-DTPA-In, galactosylated BSA-DTPA-In, goat antimouse IgG or avidin. Additionally, the effect of DTIn1 dose on 99mTc-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. RESULTS Priming with DTIn1 resulted in specific retention of 99mTc-DTPA in the abscess. Such 99mTc-DTPA abscess uptake was not dependent on the interval between the DTIn1 and the 99mTc-DTPA injection: Optimal 99mTc-DTPA abscess uptake was already achieved within a 2-hr time span between the DTIn1 and DTPA injections. However, relatively high 99mTc-DTPA background was observed due to slowly clearing DTIn1-99mTc-DTPA complexes. Background reduction with various agents had a prominent effect on DTIn1 as well as 99mTc-DTPA biodistribution. The best reduction was obtained using BSA-DTPA-In. Optimal 99mTc-DTPA abscess uptake in the three-step protocol was obtained at higher DTIn1 doses (> 100 micrograms). CONCLUSION Infectious foci in a rat model can be imaged earlier with extremely low background levels after priming with DTIn1, followed by BSA-DTPA-In and imaging with 99mTc-DTPA, as compared with directly labeled IgG.