ObjectiveTo test the hypothesis that the effects of intravenous injection of latex particles would demonstrate the contribution of phagocytosis by mononuclear phagocytes to the development of Escherichia coli-induced acute lung injury in neutropenic guinea pigs.DesignProspective, controlled, experimental study. Intravenously injected the latex particles into 41 guinea pigs to investigate the contribution of the phagocytosis in acute lung injury.SubjectsForty-one guinea pigs.InterventionsForty-one guinea pigs were divided into five experimental groups: a saline group (n equals 9); an endotoxin group (n equals 10) receiving 2 mg/kg of intravenous E. coli endotoxin; a latex group (n equals 7) receiving 2 times 109/kg of intravenous polystyrene latex (mean diameter 3.19 micro meter); an endotoxin plus latex group (n equals 8); and an E. coli group (n equals 7) receiving 2 times 109live E. coli/kg.Measurements and Main ResultsThe lung wet/dry ratio was increased in the live E. coli-treated guinea pigs (6.71 plus minus 0.16 [SEM], p less than .01) as compared with the saline control (5.40 plus minus 0.16), whereas the ratio was not increased in the endotoxin (5.52 plus minus 0.14) or latex (5.58 plus minus 0.20) groups. However, the lung wet/dry ratio was greater in the endotoxin plus latex group (6.11 plus minus 0.16, p less than .05) than in the saline control. The125I albumin lung tissue/plasma ratio was greater in the E. coli (2.00 plus minus 0.29, p less than .01) and endotoxin plus latex (0.84 plus minus 0.12, p less than .05) groups than in the saline group (0.18 plus minus 0.07), whereas no increases were observed in the endotoxin group (0.22 plus minus 0.10) and the latex (0.34 plus minus 0.13) group. More than 40% of the injected radiolabeled latex was observed to have accumulated in the reticuloendothelial system (liver and spleen), in both the saline control (40.1 plus minus 2.3%, n equals 4) and endotoxin (57.3 plus minus 6.8%, n equals 5) groups, with 2.6 plus minus 1.5% and 3.1 plus minus 1.7% in the lungs for the saline control and the endotoxin groups, respectively. The percent deposition of radiolabeled latex in the liver was greater in the endotoxin group (51.7 plus minus 3.8%, p less than .05) than in the saline group (37.6 plus minus 5.9%).ConclusionsThese findings suggest that, in neutropenic guinea pigs: a) the combination of endotoxin and latex particles induces acute lung injury; and b) the phagocytic properties of mononuclear phagocytes in the reticuloendothelial system augment endotoxin-induced pulmonary responses and may play a role in the development of live E. coli-induced acute lung injury.(Crit Care Med 1996; 24:1034-1040)