Experimental Bacterial Pneumonia in Rabbits: Polymorphonuclear Leukocyte Margination and Sequestration in Rabbit Lungs and Quantitation and Kinetics of51Cr-Labeled Polymorphonuclear Leukocytes inE. coli-Induced Lung Lesions

Abstract

A relationship between the circulating and marginal polymorphonuclear leukocyte (PMN) pools was documented using ⁵¹Cr-labeled leukocytes as a marker. ⁵¹Cr-leukocytes marginating in the lungs were found to decrease following a first-order exponential decline, while ⁵¹Cr radioactivity accumulated in the liver and the spleen. Intravenously administered endotoxin caused a rapid selective disappearance of PMNs from the circulation. The percentage of infused ⁵¹Cr cells disappearing was equal to the percentage of disappearance of host cells. The PMNs were found to sequester in the lungs, with peak sequestration of labeled cells occurring 5 min after an endotoxin challenge. Over the next 25 min the ⁵¹Cr radioactivity in the lungs declined. Large numbers of PMNs, probably newly derived from the bone marrow, were observed histologically to be sequestered in the lung vasculature 90 min after an endotoxin dose, while the early sequestration of circulating leukocytes could not be assessed histologically. Pulmonary inflammatory lesions were induced selectively with Escherichia coli in the left lower lobes of rabbits, leaving the right lower lobes as intrinsic controls. PMN-accumulation into the lesions was quantitated using ⁵¹Cr-labeled blood leukocytes. With the aid of ¹²⁵l-labeled E. coli, a logarithmic dose-response relationship was found between the number of E. coli and of PMNs. Over a 6-hr period circulating PMNs were found to accumulate in a lesion in the left lower lobe, whereas in the control right lower lobe, leukocyte radioactivity declined. These findings were confirmed with the aid of lavages of the right and left lungs. Two peaks of PMN-accumulation were found by studying leukocyte kinetics: a larger peak between 0 and 6 hr and a smaller peak 18-24 hr after instillation of the microorganisms. Histologic studies confirmed the accumulation of leukocytes, and by 3 weeks showed a complete resolution of the lesions.