Neutrophil Activation and Lung Injury Associated with Chronic Endotoxemia in Rabbits

Abstract

Chronic endotoxemia produces emphysematous lung destruction in several animal models. The present study was designed to examine changes in the polymorphonuclear leukocytes (PMN) and the lung parenchyma of rabbits that received either saline (control, n = 6) or Escherichia coli endotoxin (LPS, n = 6) 2–3 times weekly for 15 to 28 weeks. Peripheral blood was collected just before and after each intravenous injection and lung tissue was processed at the end of the experiment. PMN myeloperoxidase was stained with diaminobenzidine tetrahydrochloride (DAB)—H₂O₂, and CD11/CD18 was detected with immunogold. The changes in the PMN and the lung parenchyma were quantitatively analyzed. The results show that each dose of LPS produced an initial fall, followed by a rise in the circulating mature and immature PMN cell counts. Repealed doses of LPS induced PMN activation, degranulation, and an increase in the mean thickness of the alveolar wall (control, 4.1 ± 0.2; LPS, 5.1 ± 0.5; p < .05) at 28 weeks without evidence of alveolar septa destruction. Morphometric analysis of intravascular PMN showed an increase in the volume (V) of myeloperoxidase-containing azurophil granules (control, 6.1 ± 1.3 μm³; LPS, 13.1 ± 2.8 μm³; p < .05); a trend for a decrease in the V of specific granules (control, 15.8 ± 3.4 μm³; LPS, 10.2 ± 1.5 μm³; p = .09); an increase in the V of the cytoplasm (control, 37.3 ± 6.4 μm³; LPS, 54.5 ± 7.1 μm³; p < .05); and an increase in CD11/CD18 expressed as the number of gold particles per micrometer of cell surface membrane (G/μm) (control, 7.5 ±1.4 G/μm; LPS, 18.1 ± 7.8 G/μm; p < .05). The results indicate that chronic endoxemia in rabbits accelerates the release of PMN from the bone marrow, enhances the retention of both mature and immature activated PMN in the pulmonary microvessels, and causes alveolar wall thickening rather than emphysematous lung destruction.

Key Words:

• de-granulation
• emphysema
• endotoxemia
• neutropenia
• neutrophilia
• PMN activation
• rabbits