Neutrophil phagocytosis during endotoxin-induced lung injury

Depressed neutrophil (PMN) phagocytosis in patients with ARDS may contribute to the known increased incidence of pulmonary sepsis. To evaluate changes in phagocytosis, circulating PMNs from normal rats were compared to circulating and alveolar PMNs (obtained by bronchoalveolar lavage, BAL) from rats after 72 hr of endotoxin infusion (LPS-Rx)-induced acute lung injury. Since phagocytosis correlates with adherence, PMN adherence to coverslips and to a standard nylon wool column was also measured. PMN adherence to nylon wool was 65% for control, 77% for circulating LPS-Rx, and 20% for BAL PMNs. As a measure of phagocytosis the PMNs were incubated for 30 min with opsonized fluorescent (FITC) tagged yeast. Total PMN with yeast were 95.4 +/- 2.1% for control; 96.4 +/- 1.8% for circulating LPS-Rx; and 78.7 +/- 7.8% (P less than 0.05 compared to control) for BAL PMNs. Total numbers of yeast particles per 100 PMN are 270 +/- 64 for control, 300 +/- 42 for circulating LPS-Rx, and 170 +/- 45 (P less than 0.05 compared to control) for BAL PMN. Conclusions: (1) Intraalveolar (BAL) PMNs have decreased adherence; (2) nonadherent PMNs have decreased uptake of yeast; (3) BAL PMNs, overall, have a significantly decreased uptake of yeast; (4) this depression in BAL PMN phagocytosis may partially explain the known decreased rate of bacterial clearance in injured lungs and the increased risk of pulmonary sepsis with adult respiratory distress syndrome.