Just How Big is the Pulmonary Granulocyte Pool?

Abstract

1. It is widely believed that a large fraction of the blood granulocyte population is located in the pulmonary circulation. 2. Evidence in favour of this belief is based on several independent and complementary techniques including studies of granulocyte deformability in relation to pulmonary capillary diameter, isolated perfused lungs, direct videomicroscopic observations, cellular and capillary morphometry, physiological studies and labelled blood cell kinetics. 3. Inconsistencies in this body of evidence can be identified and traced in many cases to doubts concerning the physiological integrity of labelled granulocytes. 4. In addition to the lungs, other regions of the body undoubtedly pool granulocytes, and there is good quantitative evidence, based mainly on clinical studies, pointing to the liver, bone marrow and especially the spleen. 5. Clinical studies, furthermore, have generally not supported major granulocyte pooling in the lung, except in association with systemic inflammatory diseases, such as inflammatory bowel disease and systemic vasculitis. 6. Compromises based on technical considerations permit reconciliation of the literature, and an overall whole-body model of granulocyte distribution is proposed with which all the existing data are broadly compatible.

The Pathogenic Involvement of Neutrophils in Acute Respiratory Distress Syndrome and Transfusion-Related Acute Lung Injury

“…They are the most common type of granulocytes and constitute more than half of all circulating leukocytes. In healthy adults, around 36% of all PMNs are residing in the circulation, and of the total number of PMNs around 28%, both circulating and non-circulating, are suggested to be present in the pulmonary pool [15,16]. The number of PMNs in the pulmonary pool is subject to change upon systemic inflammatory conditions.…”

Neutrophils: Molecules, Functions and Pathophysiological Aspects

“…In the absence of inflammation, the marginating pool, better called "physiological regional granulocyte pool" (Peters, 1998), comprises granulocytes transiently arrested in narrow, mainly pulmonary, capillaries. This physiological retention of neutrophils in capillaries appears to be a mechanical process due to the stiffness of neutrophils-as compared with the high deformability of erythrocytes (Downey et al, 1990)-and does not involve cell adhesion (Doyle et al, 1997;Mizgerd et al, 1996;Yamaguchi et al, 1997;Yoder et al, 1990).…”

The pathogenesis of transfusion‐related acute lung injury (TRALI)

“…The increased transit time also accounts for the significant neutrophil accumulation ('marginated pool') in the lungs (Doerschuk, 1999). The pulmonary circulation contains about 28% of the blood neutrophil pool that is available on demand for host defence against bacterial infections (Peters, 1998).…”