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Polymorphonuclear leukocytes released from the bone marrow preferentially sequester in lung microvessels
S F van Eeden1, Y Kitagawa, M E Klut
1University of British Columbia, Pulmonary Research Laboratory, St. Paul's Hospital, Vancouver, Canada.
Objective:
A hallmark of the systemic response to an inflammatory stimulus is the release of polymorphonuclear leukocytes (PMNs) from the bone marrow. This study was designed to measure the release of PMNs from the bone marrow and to determine their sequestration in the lung after an intravenous injection of either endotoxin (n = 5) or saline (n = 5).
Methods And Results:
The thymidine analogue 5'-bromo-2-deoxyuridine (BrdU) was used to pulse label dividing PMNs in the bone marrow of rabbits (n = 13), and immunohistochemistry and morphometry were used to detect the release of BrdU-labeled PMNs into the circulation and to determine 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 increase 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 showed 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 0.039 +/- 0.016 x 10(10), endotoxin versus saline, p < 0.05). The percentage 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 pore size filters showed that circulating BrdU-labeled PMNs, 8 hours after endotoxin, were preferentially retained in the filters (p < 0.01).
Conclusions:
We conclude that endotoxemia stimulates the bone marrow to release mature and immature PMNs. Compared to PMNs released from the bone marrow during normal turnover, these PMNs are less deformable and preferentially sequester in the lung microvessels.
Insights
Endotoxemia prompts the bone marrow to release polymorphonuclear leukocytes (PMNs). These PMNs are less deformable and preferentially sequester in lung microvessels, impacting inflammatory responses.
Area of Science:
- Immunology
- Hematology
- Pulmonary Medicine
Background:
- Polymorphonuclear leukocytes (PMNs) are critical in the systemic inflammatory response.
- The release of PMNs from bone marrow is a hallmark of inflammation.
- Understanding PMN sequestration in the lungs is vital for inflammatory disease research.
Purpose of the Study:
- To quantify PMN release from bone marrow following endotoxin administration.
- To determine the extent of PMN sequestration within the lung microvasculature.
- To investigate the characteristics of endotoxin-induced PMN release and lung sequestration.
Main Methods:
- Utilized 5'-bromo-2-deoxyuridine (BrdU) to label dividing PMNs in rabbit bone marrow.
- Employed immunohistochemistry and morphometry to track BrdU-labeled PMNs in circulation and lung.
- Measured circulating PMN counts, band cells, and arteriovenous differences across the lung.
Main Results:
- Endotoxin induced a transient drop in circulating PMNs, followed by neutrophilia and increased band cells.
- A significant increase in BrdU-labeled PMNs was observed in circulation and preferentially sequestered in the lung.
- Endotoxin-treated rabbits showed higher percentages of BrdU-labeled PMNs in alveolocapillary walls and impaired deformability.
Conclusions:
- Endotoxemia stimulates the bone marrow to release both mature and immature PMNs.
- These endotoxin-induced PMNs exhibit reduced deformability compared to normally released PMNs.
- Preferential sequestration of these less deformable PMNs occurs within the lung microvasculature.