Sf. Vaneeden et al., POLYMORPHONUCLEAR LEUKOCYTES RELEASED FROM THE BONE-MARROW PREFERENTIALLY SEQUESTER IN LUNG MICROVESSELS, Microcirculation, 4(3), 1997, pp. 369-380
Objective: A hallmark of the systemic response to an inflammatory stim
ulus is the release of polymorphonuclear leukocytes (PMNs) from the bo
ne marrow. This study was designed to measure the release of PMNs from
the bone marrow and to determine their sequestration in the lung afte
r an intravenous injection of either endotoxin (n = 5) or saline (n =
5). Methods and Results: The thymidine analogue 5'-bromo-2-deoxyuridin
e (BrdU) was used to pulse label dividing PMNs in the bone marrow of r
abbits (n = 13), and immunohistochemistry and morphometry were used to
detect the release of BrdU-labeled PMNs into the circulation and to d
etermine their sequestration in the lung. Endotoxin treatment caused a
drop in the circulating PMN counts (3.3 +/- 0.08 at baseline to 0.12
+/- 0.02 x 10(9)/L at 1 hour after endotoxin), which was followed by a
neutrophilia at 8 hours (6.3 +/- 1.1 x 10(9)/L, p < 0.01), an increas
e in circulating band cells (0.12 +/- 0.01 at baseline to 2.18 +/- 0.4
x 1(9)/L at 8 hours, p < 0.001), and an increase in the percentage of
BrdU-labeled PMNs (0.01% +/- 0.004% at baseline to 26.1% +/- 3.2% at
8 hours, p < 0.001). Endotoxemia caused an arteriovenous difference in
BrdU-labeled PMNs across the lung (35.9% +/- 2.9% versus 26.1% +/- 3.
1%, mixed venous versus arterial. p < 0.02). Morphometric studies show
ed that endotoxin caused sequestration of PMNs in the lung (2.2 +/- 0.
4 versus 1.0 +/- 0.2 x 10(10), endotoxin versus saline, p < 0.03) with
preferential retention of BrdU-labeled PMNs (0.79 +/- 0.21 versus 0.0
39 +/- 0.016 x 10(10), endotoxin versus saline, p < 0.05). The percent
age of BrdU-labeled PMNs in the alveolocapillary walls was higher than
in circulating blood (64.01% +/- 4.3% versus 26.1% +/- 3.2%, p < 0.01
) in the endotoxin group. In vitro filtration of cells through 5-mm po
re size filters showed that circulating BrdU-labeled PMNs, 8 hours aft
er endotoxin, were preferentially retained in the filters (p < 0.01).
Conclusions: We conclude that endotoxemia stimulates the bone marrow t
o release mature and immature PMNs. Compared to PMNs released from the
bone marrow during normal turnover, these PMNs are less deformable an
d preferentially sequester in the lung microvessels.