ULTRASTRUCTURAL AND IMMUNOCYTOCHEMICAL STUDY OF THE PULMONARY INTRAVASCULAR MACROPHAGES OF ESCHERICHIA-COLI LIPOPOLYSACCHARIDE-TREATED SHEEP

Background: Pulmonary intravascular macrophages (PIMs) of sheep, cattl e, goats, and horses have a novel heparin-sensitive chain of globules, called a surface coat, on their plasma membrane. The globules are arr anged at a distance of 32-39 nm from the plasma membrane of PIMs. Intr avascular nonbiological tracer particles complex with these globules p rior to their endocytosis by the PIMs. Methods: We conducted a prelimi nary in vivo time-course study in sheep to investigate responses of th e coat globules to a single dose of Escherichia coil lipopolysaccharid e (E, coli LPS). Six sheep (6-9 months of age) were used in this study , and five of them were intravenously injected with E. coli (1 mu g/kg body weight) and euthanised at 3, 8, 10, 30, and 180 min (n = 1 each) after treatment. One sheep injected with saline solution served as th e control. Acid phosphatase (AcPase) cytochemistry and immunocytochemi stry using a polyclonal antibody were employed to localize secretory a ctivity and E. coli LPS respectively in the PIMs. Results: The surface coat of PIMs disappeared rapidly following the LPS administration. Es cherichia coli LPS micelles and coat globules were colocalized as a co mplex in the endosomes of PIMs. At 8-10 min following the treatment, e ndosomal and the other membranes were disrupted, and the LPS was ident ified in cytoplasm and nuclear matrix of PIMs simultaneously with the development of pulmonary interstitial edema, Progression of AcPase rea ctivity along the nucleus-Golgi complex axis coupled with intense buil dup of coated transport vesicles within 30 min of the LPS injection su ggested enhanced biosynthetic activity in the PIMs. Conclusions: This study provides initial data on the sensitivity of the coat globules an d their possible role in the endocytosis of E. coli LPS by the PIMs. R apid biosynthetic activation of PIMs concurrent with loss of the coat and treatment with the LPS probably results in the secretion of inflam matory substances and contributes to the enhanced susceptibility of sh eep to endotoxin-induced lung pathology. (C) 1997 Wiley-Liss, Inc.