Measurement of the pulmonary vascular granulocyte pool

Radiolabelled leucocytes in human pulmonary disease

INTRODUCTION

Radionuclides for leucocyte kinetic studies have progressed from non-gamma emitting cell-labelling radionuclides through gamma emitting nuclides that allow imaging of leucocyte kinetics, to the next goal of positron emission tomography (PET).

SOURCES OF DATA

Mostly the authors' own studies, following on from studies of the early pioneers.

AREAS OF CONTROVERSY

From early imaging studies, it appeared that the majority of the marginated granulocyte pool was located in the lungs. However, later work disputed this by demonstrating the exquisite sensitivity of granulocytes to ex vivo isolation and labelling, and that excessive lung activity is artefactual.

AREAS OF AGREEMENT

Following refinement of labelling techniques, it was shown that the majority of marginated granulocytes are located in the spleen and bone marrow. The majority of leucocytes have a pulmonary vascular transit time only a few seconds longer than erythrocytes. The minority showing slow transit, ~5% in healthy persons, is increased in systemic inflammatory disorders that cause neutrophil priming and loss of deformability. Using a range of imaging techniques, including gamma camera imaging, whole-body counting and single photon-emission computerized tomography, labelled granulocytes were subsequently used to image pulmonary trafficking in lobar pneumonia, bronchiectasis, chronic obstructive pulmonary disease and adult respiratory distress syndrome.

GROWING POINTS

More recently, eosinophils have been separated in pure form using magnetic bead technology for the study of eosinophil trafficking in asthma.

AREAS TIMELY FOR DEVELOPING RESEARCH

These include advancement of eosinophil imaging, development of monocyte labelling, development of cell labelling with PET tracers and the tracking of lymphocytes.

Real-time differential tracking of human neutrophil and eosinophil migration in vivo

BACKGROUND

Hitherto, in vivo studies of human granulocyte migration have been based on indiscriminate labeling of total granulocyte populations. We hypothesized that the kinetics of isolated human neutrophil and eosinophil migration through major organs in vivo are fundamentally different, with the corollary that studying unseparated populations distorts measurement of both.

METHODS

Blood neutrophils and eosinophils were isolated on 2 separate occasions from human volunteers by using Current Good Manufacturing Practice CD16 CliniMACS isolation, labeled with technetium 99m-hexamethylpropyleneamine oxime, and then reinfused intravenously. The kinetics of cellular efflux were imaged over 4 hours.

RESULTS

Neutrophils and eosinophils were isolated to a mean purity of greater than 97% and greater than 95%, respectively. Activation of neutrophils measured as an increase in their CD11b mean fluorescence intensity in whole blood and after isolation and radiolabeling was 25.98 ± 7.59 and 51.82 ± 17.44, respectively, and was not significant (P = .052), but the mean fluorescence intensity of CD69 increased significantly on eosinophils. Analysis of the scintigraphic profile of lung efflux revealed exponential clearance of eosinophils, with a mean half-life of 4.16 ± 0.11 minutes. Neutrophil efflux was at a significantly slower half-life of 13.72 ± 4.14 minutes (P = .009). The migration of neutrophils and eosinophils was significantly different in the spleen at all time points (P = .014), in the liver at 15 minutes (P = .001), and in the bone marrow at 4 hours (P = .003).

CONCLUSIONS

The kinetics of migration of neutrophils and eosinophils through the lung, spleen, and bone marrow of human volunteers are significantly different. Study of mixed populations might be misleading.

Why the spleen is a very rare site for metastases from epithelial cancers

It is not known why metastases from epithelial cancers are rare in the spleen, yet common in the other major organs of the reticuloendothelial system in which, like the spleen, leucocytes display a prolonged physiological intravascular transit time. Another unresolved issue that at first seems unrelated to splenic metastases is the inconsistency between the concept of physiological granulocyte disposal through granulocyte ageing and the observation that granulocytes leave the blood in an exponential fashion (half-time 7 h), which implies random disposal. Intravascular granulocytes pass through the spleen with an exponential distribution of transit times (mean 10 min). The spleen is highly active in physiological granulocyte destruction so it is suggested that the variation in times of exposure to the splenic microenvironment converts the age-dependent granulocyte destruction observed ex vivo into the random process observed in vivo, probably through exposure to apoptosis-inducing signals. This leads to the second hypothesis, which is that cancer cells fail to survive in the spleen as a result of these pro-apoptotic signals.

Measuring whole-body neutrophil redistribution using a dedicated whole-body counter and ultra-low doses of 111Indium

BACKGROUND

There is increasing interest in the 'homing' of neutrophils to bone marrow. The aim of this study was to measure the whole-body redistribution of (111) In using a whole-body counter following the administration of ultra-small activities of (111) In-labelled neutrophils.

METHODS

The detectors of a dedicated whole-body counter were fitted with lead collimators. Whole-body (111) In distribution was recorded at 45 min, 24 h, and 2, 4, 7 and 10 days after administration of (111) In-labelled neutrophils (0·29-0·74 MBq) in eight healthy non-smokers, five healthy smokers, eight patients with inactive bronchiectasis, three with asthma and nine with chronic obstructive pulmonary disease (COPD).

RESULTS

Intravascular 45-min (111) In-labelled neutrophil recovery was not significantly different between groups, ranging from 33 (SD 8%) in healthy smokers to 45 (14%) in healthy non-smokers (P > 0·05). Peaks were identified on the whole body count profile corresponding to the chest, upper abdomen (liver/spleen) and pelvis (bone marrow). (111) In distribution changed between 45 min and 24 h and then remained stable thereafter. Peak chest counts increased ∼ 1·5-fold between 45 min and 24 h, whereas upper abdominal peak counts decreased by ∼ 25% with no significant inter-group differences. The increment in pelvic counts (∼ 2·7-fold) was similar between groups, except COPD patients, in whom it was 2·04 (0·35; P < 0·02 vs. healthy participants).

CONCLUSIONS

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.

Pulmonary involvement and allergic disorders in inflammatory bowel disease

Inflammatory bowel disease (IBD) has been associated with either clinical or subclinical airway and parenchymal lung involvement and interstitial lung complications. Several studies have reported that atopy has a high prevalence in IBD patients. Overlapping allergic disorders seem to be present in both the respiratory and gastrointestinal systems. The purpose of this review is to update clinicians on recent available literature and to discuss the need for a highly suspicious approach by clinicians.

Kinetic analysis of pulmonary neutrophil retention in vivo using the multiple-indicator-dilution technique

Multiple-indicator-dilution experiments were performed in the lungs of 13 anesthetized dogs by simultaneous bolus injection of 111In-labeled neutrophils, 51Cr-labeled red blood cells, and Evans blue-labeled albumin. Concomitant counts of unlabeled neutrophils were similar in pulmonary artery and aortic blood samples, demonstrating a dynamic balance across the lungs in the physiological state. Outflow profiles of labeled neutrophils were analyzed on the basis of a recirculatory pharmacokinetic model of labeled albumin. The outflow profiles of the recovered neutrophils were composed of a throughput component of circulating neutrophils and a component of reversibly marginated neutrophils. They were interpreted by a model incorporating neutrophil margination (transfer coefficient = 0.195 +/- 0.081 s-1), rapid demargination (0.054 +/- 0.027 s-1), and transfer to a slow marginated pool (0.023 +/- 0.018 s-1). It will be interesting to apply the analysis in future studies aimed at determining whether it could be a useful research tool to investigate the interactions between the pulmonary endothelium and neutrophils in physiological and diseased states.

Feasibility of scintigraphy in exercise-induced pulmonary haemorrhage detection and quantification: preliminary studies

We hypothesised that scintigraphic imaging of the lungs following injection of 99mTc labelled red blood cells (99mTc-RBC) in the exercising horse might enable exercise-induced pulmonary haemorrhage (EIPH) quantification. Ideally, to favour detection of bleeding, circulating 99mTc-RBC not involved in the haemorrhage should be removed from the circulation quickly. Altering RBC during labelling to stimulate splenic uptake of 99mTc-RBC may encourage this. In order to investigate this hypothesis, 99mTc-RBC distribution was followed for 1 h in 2 groups of horses. Group 1 was injected i.v., at rest, with radioactive nondenatured RBC (99mTc-NDRBC); Group 2 received labelled RBC partly denatured by heating (99mTc-HDRBC). In Group 2, splenic uptake was higher at all times and radioactivity in the lung was proportionally higher and decreased less quickly than in Group 1. Hence, the time-consuming 99mTc-HDRBC labelling technique did not demonstrate any advantage over the easier 99mTc-NDRBC labelling procedure. Additionally, the feasibility of scintigraphic visualisation of a small amount of pulmonary bleeding was confirmed with the following trial: using an endoscope, a radioactive solution mimicking 50 ml of bleeding was deposited at the usual site of EIPH in a live horse. The radioactivity recorded in that area was compared to the one obtained in the same region in Group 1 and 2. The activity measured 20 min post endoscopy corresponded to 33% of the activity obtained in Group 1 vs. 8% in Group 2 at that timing. Once again, there was no advantage of using 99mTc-HDRBC vs. 99mTc-NDRBC. These results demonstrated that small amounts of bleeding might potentially be detected with scintigraphy; they also suggest that the limiting factor for detecting small amounts of bleeding may be the level of lung background radioactivity.

Bimodal granulocyte transit time through the human lung demonstrated by deconvolution analysis

The lungs are an important site of granulocyte pooling. The aim of the study is to quantify pulmonary vascular granulocyte transit time using deconvolution analysis, as has previously been performed to measure pulmonary red cell transit time. Granulocyte and red cell studies were performed in separate groups of patients. Both cell types were labelled with Tc-99m, which for granulocyte labelling was complexed with hexamethylpropyleneamine oxime (HMPAO). The red cell impulse response function (IRF) was monoexponential with a median transit time of 4.3 s. The granulocyte IRF was biexponential in 19 of 22 subjects, 18 of whom had systemic inflammation (inflammatory bowel disease, systemic vasculitis or graft-vs-host disease) and four were controls without inflammatory disease. The median transit time of the fast component ranged from 20 to 25 s and of the slow component 120-138 s in the four patient groups. The fraction of cells undergoing slow transit correlated significantly with (a) mean granulocyte transit time and (b) the fraction showing shape change in vitro. We conclude that granulocyte transit time through the pulmonary circulation is bimodal and that shape-changed (activated) cells transit more slowly that non-activated cells. The size of the fraction undergoing slow transit is closely related to mean granulocyte transit time and is an important determinant of the size of the pulmonary vascular granulocyte pool.