Abstract
Increased retention of activated neutrophils in the lungs contributes to endothelial cell injury. However, characterization of the morphological changes that occur in neutrophils during activation in the pulmonary microcirculation has not been fully determined in vivo. Therefore, the present study was designed to determine structural and cytochemical properties of neutrophils in situ in pulmonary arterioles and alveolar capillaries during the infusion of zymosan-activated plasma (ZAP) or plasma (control) in anesthetized sheep. Quantitative morphological methods showed that ZAP infusion caused significant retention of neutrophils in alveolar capillaries [2.19 +/- 0.40 (SD) x 10(8) neutrophils/ml of capillary blood volume] and pulmonary arterioles (1.02 +/- 0.46 x 10(8) neutrophils/ml of arterial blood volume) compared with plasma infusion (1.03 +/- 0.15 and 0.30 +/- 0.10 x 10(8) neutrophils/ml, respectively; P < 0.05). Harmonic mean diameter of ZAP-activated neutrophils in situ (7.19 +/- 0.44 microns) was significantly greater than the diameter of neutrophils in plasma-treated sheep (6.29 +/- 0.17 microns; P < 0.05). Neutrophil cross-sectional area (54 +/- 3 microns2) and volume (248 +/- 27 microns3) in situ in alveolar capillaries were also significantly greater in ZAP-treated sheep than in control sheep (41 +/- 4 microns2 and 184 +/- 9 microns3, respectively; P < 0.05). Similarly, microvascular neutrophils in ZAP-treated sheep were vacuolated and elongated, filamentous actin was redistributed peripherally, and the cells were degranulated. We conclude that during ZAP infusion, neutrophils become enlarged and degranulated in pulmonary microvessels, especially in alveolar capillaries. The structural and cytochemical changes that occur are consistent with the hypothesis that neutrophil activation is accompanied by alterations in neutrophil physical properties, alterations that may facilitate retention and contribute to endothelial cell injury.
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