Eosinophils are the major cellular effectors of allergic inflammation and represent an important therapeutic target. Although the genesis and activation of eosinophils have been extensively explored, little is known about their intravascular kinetics or physiological fate. This study was designed to determine the intravascular life span of eosinophils, their partitioning between circulating and marginated pools, and sites of disposal in healthy persons. Using autologous, minimally manipulated 111-Indium-labeled leukocytes with blood sampling, we measured the eosinophil intravascular residence time as 25.2 hours (compared with 10.3 hours for neutrophils) and demonstrated a substantial marginated eosinophil pool. ␥ camera imaging studies using purified eosinophils demonstrated initial retention in the lungs, with early redistribution to the liver and spleen, and evidence of recirculation from a hepatic pool. This work provides the first in vivo measurements of eosinophil kinetics in healthy volunteers and shows that 111-Indium-labeled eosinophils can be used to monitor the fate of eosinophils noninvasively. (Blood. 2012;120(19):4068-4071) IntroductionEosinophils play a key role in allergic inflammation 1 and represent an important therapeutic target in asthma and other allergic diseases. They have the capacity to release histotoxic substances, including granule proteins, inflammatory cytokines, and reactive oxygen metabolites, which cause bronchoconstriction, epithelial damage, hyper-responsiveness, and airway remodeling. [2][3][4][5][6] Much is known about the cellular mechanisms regulating the development and maturation of eosinophils, their release from the bone marrow, and the processes involved in their recruitment, activation, and clearance during allergic inflammation. 7-11 By contrast, very little is known about the physiology of circulating eosinophils in humans. Because of the relative scarcity of eosinophils in the blood of healthy persons (range, 0.0-0.4 ϫ 10 9 /L), previous attempts to study eosinophil kinetics have been restricted to patients with hypereosinophilia, 12-14 hampered by label reuse after pulse injection of 3 H-thymidine, 15 or relied on autoradiographs developed Ͼ 500 days. 16 We have used 111-Indiumlabeled mixed leukocytes with postinjection isolation of eosinophils to ascertain their intravascular life span, and subsequently purified 111-Indium-labeled autologous eosinophils with ␥ camera imaging to assess organ-specific trafficking in vivo. We have demonstrated an intravascular lifespan for circulating eosinophils exceeding 24 hours and revealed extensive intravascular margination of these cells, together with evidence of recirculation from a hepatic pool. Methods ParticipantsHealthy male and female adults with normal lung function and eosinophil counts (range, 0.02-0.38 ϫ 10 9 /L) gave written informed consent in accordance with the Declaration of Helsinki. The study was approved by Cambridgeshire Research Ethics Committee (09/H0308/119) and the Administration of Radioactive Substan...

In patients with COPD, sequential SPECT showed increased lung accumulation of (99m)Tc-labelled neutrophils, while whole-body counting demonstrated subsequent higher losses of (111)In-labelled neutrophils in patients who continued to smoke. Sequential SPECT as a means of quantifying neutrophil migration deserves further evaluation.

Assuming neutrophils are distributed only between blood, liver, spleen and bone marrow, the data suggest that marrow pools 25% and destroys 67% of circulating neutrophils, rising in COPD to 40% and 80%, respectively, possibly as a result of the effects on marrow of chronic hypoxaemia.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Very little is known about the physiology of P‐glycoprotein (P‐gp) expression in the lungs. • Ex vivo evidence based on resected lung tissue suggests that pulmonary P‐gp is upregulated by cigarette smoke, but there are no in vivo studies to date. WHAT THIS STUDY ADDS • The novel observation that healthy cigarette smokers have a delayed pulmonary elimination rate of inhaled 99mTc‐sestamibi, a P‐gp substrate, provides for the first time a potential method for quantifying functional pulmonary P‐gp expression that may inform about drug therapy by inhalation as well as provide a non‐invasive, quantitative, human biomarker for assessing P‐gp modulators. AIM To explore inhaled technetium‐99m‐labelled hexakis‐methoxy‐isobutyl isonitrile (99mTc‐sestamibi) for quantifying pulmonary P‐glycoprotein (P‐gp) expression. METHODS The elimination rate from the lungs of 99mTc‐sestamibi was recorded scintigraphically for 30 min following inhalation as an aerosol in healthy smokers, nonsmokers and patients with lung disease. RESULTS 99mTc‐sestamibi elimination rates [% min−1 (SD; P vs. healthy nonsmokers)] were: healthy nonsmokers, 0.43 (0.083); healthy smokers, 0.19 (0.056; P < 0.001); chronic obstructive pulmonary disease patients, 0.26 (0.077; P < 0.001). Elimination rates in three patients with interstitial lung disease were not accelerated. CONCLUSION Cigarette smoke upregulates lung P‐gp. 99mTc‐sestamibi elimination in normal smokers could be used to test new P‐gp modulators. The findings also have implications for inhaled drug delivery.