Use of 111-Indium-labelled autologous eosinophils to establish the in vivo kinetics of human eosinophils in healthy subjects

Eosinophils are the major cellular effectors of allergic inflammation and represent an important therapeutic target. Whilst the genesis and activation of eosinophils has been extensively explored, little is known about their intravascular kinetics or physiological fate. This study was designed to determine the intravascular lifespan of eosinophils, their partitioning between circulating and marginated pools, and sites of disposal in healthy individuals. Using autologous, minimally manipulated 111-Indium-labelled leukocytes with blood sampling, we measured the eosinophil intravascular residence time as 25.2 hours (compared to 10.3 hours for neutrophils) and demonstrated a substantial marginated eosinophil pool. Gamma camera imaging studies using purified eosinophils demonstrated initial retention in the lungs, with early re-distribution to the liver and spleen, and evidence of re-circulation from a hepatic pool. This work provides the first in vivo measurements of eosinophil kinetics in healthy volunteers and shows that 111-Indium-labelled-eosinophils can be used to monitor the fate of eosinophils non-invasively.