Intraperitoneal lipopolysaccharide-induced neutrophil sequestration in the lung microvasculature is due to a factor produced in the peritoneal cavity

Introduction

Intraperitoneal injection of Gram-negative lipopolysaccharide (LPS) results in a profound decrease in circulating leukocyte counts with a significant increase in neutrophil sequestration in the lung microvasculature as measured by lung myelo-peroxidase levels. Mice made deficient in toll-like receptor 4 (TLR4) are resistant to LPS challenges. Furthermore, it has been demonstrated that the systemic effects of LPS are due to parenchymal, possibly endothelial, cells and not due to bone marrow-derived cells, such as leukocytes.

Methods

C57B/6 mice were anesthetized and sacrificed. Peritoneal lavage using 3 ml PBS followed by a gentle abdominal massage for 1 minute was performed. Lavage fluid was aspirated and centrifuged to concentrate the peritoneal cells. Cells were then treated with normal saline or 10 μg LPS. The treated peritoneal cells were then injected into the peritoneal cavities of TLR4-deficient mice (C57B/10ScNJ) for a duration of 4 hours. Measured outcomes included circulating leukocyte counts and lung myeloperoxidase (MPO) levels.

Results

Normal saline-treated control C57B/6 mice had circulating counts of 6.38 ± 0.56 million cells/ml, and the MPO levels in normal saline-treated peritoneal cells transferred into C57B/6 mice were 5.80 ± 0.73 units. Normal saline-treated peritoneal cells of C57B/6 mice injected into TLR4-deficient mice resulted in circulating counts of 5.18 ± 0.22 million cells/ml and MPO levels of 4.23 ± 0.73 units. LPS-treated control C57B/6 mice had circulating counts of 1.94 ± 0.22 million cells/ml, and the MPO levels in LPS-treated peritoneal cells transferred into C57B/6 mice were 16.52 ± 4.3 units. LPS-treated peritoneal cells of C57B/6 mice injected into TLR4-deficient mice resulted in circulating counts of 2.48 ± 0.44 million cells/ml and MPO levels of 12.06 ± 1.74 units. The liver endothelium was the only organ activated in this model. Furthermore, this process of LPS-treated, peritoneal cell-induced neutrophil sequestration in the lung microvasculature was found to be independent of mast cells and NKT cells.

Conclusion

An as yet to be identified factor, or factors, produced from the peritoneal lavage cells, can produce neutrophil sequestration in the lung microvasculature.