Comparison of neutrophil and capillary diameters and their relation to neutrophil sequestration in the lung

Abstract

Neutrophils [polymorphonuclear leukocytes (PMNs)] are sequestrated in the lung capillary bed because PMNs are delayed with respect to red blood cells (RBCs) as they pass through these microvessels. The present study examines circulating PMN size in relation to the distribution of capillary segment diameters in human, dog, and rabbit lungs and compares the shape of PMNs in suspension to that found within the pulmonary capillaries. The data show that 61, 67, and 38% of the capillary segments are narrower than the mean diameter of spherical PMNs in the rabbit, dog, and human, respectively. They also show that PMNs deform from a spherical to an ellipsoid shape in the pulmonary capillaries of all three species. These findings are consistent with previous studies showing that the pulmonary circulation restricts the passage of PMNs through the lungs and suggest that PMNs are delayed because they must deform to pass through restrictions encountered in the pulmonary capillary bed. We conclude that the discrepancy between PMN and pulmonary capillary size and the decreased deformability of PMNs with respect to RBCs are major determinants of the delay that PMNs experience with respect to RBCs in the pulmonary circulation.

The expression of adhesion molecules in cigarette smoke-induced airways obstruction

“…This is followed by firm adhesion via the CD11/CD18 on leucocytes to the ICAMs on endothelium, preparing the cell for emigration. In the pulmonary microvessels, this initial tethering step is unnecessary because leucocytes are trapped in pulmonary capillaries due to their relatively larger size compared to pulmonary capillary segments [18]. We discerned no clear differences in the expression of the endothelial-associated selectins between pulmonary and bronchial vessels in the present studies.…”

Unique Structural Features That Influence Neutrophil Emigration Into the Lung

“…Approximately 50% of the capillary segments are narrower than the mean diameter of a spherically shaped neutrophil. This size discrepancy forces neutrophils to deform and assume a "sausage" shape as they enter and squeeze through narrow capillary segments (55,102) (Fig. 3).…”

“…The tethering mechanisms required to capture neutrophils from flowing blood in larger vessels are apparently not necessary in the alveolar capillary bed. The diameters of spherical neutrophils (6 -8 m) are larger than the diameters of many capillary segments (2-15 m), and ϳ50% of the capillary segments would thereby require neutrophils to change their shape to pass through (55,82,104,166). Given the large number of capillary segments through which a neutrophil must pass (often Ͼ50), most neutrophils must change shape during transit from arteriole to venule.…”

“…Given the large number of capillary segments through which a neutrophil must pass (often Ͼ50), most neutrophils must change shape during transit from arteriole to venule. Morphometric analysis of neutrophils in the alveolar capillary beds revealed significant deviation from spherical shape (55,82). Computational models of the capillary bed describing flow, hematocrit, pressure gradients, and the effects of deformation on the capillary transit times of neutrophils support the concept that the structure of the capillary bed and the deformation of neutrophils are critical under normal conditions (110).…”

Invited review: Relationship between cattle transport, immunity and respiratory disease

“…The major mechanism behind the neutrophil-mediated tissue damage in the respiratory tract is thought to be due to the massive infiltration of cells during an immune challenge; it has also been suggested that the state, in combination with simply the presence, of neutrophils in the tissue is important to their destructive potential (Haslett et al, 1989). In fact, neutrophils may become sequestered in the pulmonary vasculature by several mechanisms (Doerschuk et al, 1993;Burns et al, 2001), mainly because the size of the capillaries in the lungs is smaller than the diameter of neutrophils themselves. This may increase the length of time that the neutrophils are in contact with pulmonary tissue.…”