Imaging and assessment of regional clearances of indium-111 labelled circulating immune complexes in humans.

The in vivo function of the reticulo-endothelial system in humans is currently studied by the blood clearance of 51Cr labeled RBC sensitized with IgG anti-Rh. By replacing 51Cr by 111In we developed a method which allows imaging and assessment of clearances of circulating immune complexes (CIC) by individual organs. Nine normal subjects were studied successively with 51Cr labelled CIC and 111In-labelled CIC by blood sampling and sequential imaging. Time activity curves were obtained over spleen, liver, heart lungs and kidneys. The blood clearance values were similar with 111In (T1/2 +/- SD = 23.4 min +/- 6.4 min) and 51 Cr (T1/2 = 22.9 min +/- 5.8 min). The blood clearance derived from the time activity curve obtained over the cardiac area (T1/2 = 26.6 min +/- 8.4 min) was not significantly different from that obtained by blood sampling. Most of the CIC were taken up by the spleen with a T1/2 of 20.3 min +/- 4.1 min. Although hepatic uptake was observed in all subjects, it was lower than that of the spleen and CIC were subsequently released from the liver in five of the nine patients. The spleen/liver ratio increased with time, reaching a plateau averaging 24.0 +/- 5.8 within 80 min in all subjects. CIC imaging allows, by a non-invasive procedure, the computation of CIC blood clearance and the estimation of the respective role of spleen and liver in phagocytic function.