The organ uptake of intravenously injected particles was examined in 13 species. All animals were injected intravenously with 198Au colloid and magnetic iron oxide particles. Vascular clearance kinetics of198Au colloid was similar in all species. Pulmonary uptake of 198Au colloid ranged from 17 to 60% in sheep, calves, pigs, and cats but was <1.1% in monkeys, hyraxes, rabbits, guinea pigs, rats, mice, and chickens. For iron oxide particles, pulmonary uptake ranged from 80 to 99% in sheep, calves, pigs, goats, and cats and 15 to 18% in hamsters, hyraxes, and monkeys and was <10% in rabbits, chicken, mice, rats, and guinea pigs. In all species, the bulk of the remainder of particle uptake was in the liver. Pulmonary intravascular macrophages are the cellular site of lung uptake in calves, cats, pigs, goats, and sheep, whereas monocytes and neutrophils predominate in other species. Kupffer cells were the site of uptake in the liver. Our data show marked species differences in the fate of circulating particles; ruminants, pigs, and cats have extensive pulmonary localization due to phagocytosis by pulmonary intravascular macrophages.

Gadolinium (Gd) suppresses reticuloendothelial functions in vivo by unknown mechanisms. In vitro exposure of rat alveolar macrophages to GdCl3.6H20 caused cell death, as measured by trypan blue permeability, in both dose- and time-dependent fashions. Even a 10-min exposure to Gd caused significant cell death by 24 h. The morphology of Gd-treated cells, pyknosis and karyorrhexis prior to loss of membrane integrity, suggested apoptosis. Upon flow cytometric examination, Gd-treated propidium iodide-excluding cells demonstrated light scatter changes characteristic of apoptotic cells (decreased forward and increased right angle scatter). Gel electrophoresis of DNA from Gd-treated macrophages clearly showed the ladder pattern unique to apoptotic cells. Electron-dense structures containing Gd were observed via electron spectroscopic imaging within phagosomes and also within nuclei (associated with condensed chromatin). Gadolinium, endocytosed by macrophages and distributed to nuclei, causes apoptosis of macrophages in vitro.

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Pulmonary intravascular macrophages (PIMs) are an extensive population of mature phagocytic cells adherent to the pulmonary capillary endothelium in selected species. They are not prevalent in lungs of commonly studied laboratory animals, such as rodents, and thus have only been recently appreciated. However, their potential role in host defense and acute lung injury has attracted interest, since a number of studies have demonstrated pulmonary localization of circulating particles, microbes, and endotoxin by PIMs. Those animal species, such as ruminants, that provide useful models of pathogen (or endotoxin)-induced acute lung injury demonstrate rapid pulmonary uptake of bacteria by PIMs. Inflammatory mediators released by activated PIMs may initiate the process and provoke accumulation of neutrophils and platelets. This review summarizes the morphological characteristics of PIMs and their species distribution. The role of these members of the mononuclear phagocyte system, both beneficial and potentially pathogenic, is reviewed. The question of whether PIMs have a role in acute lung injury in humans is also discussed.

Reovirus serotype 1 (Lang) can be conjugated with rhodamine B or fluorescein isothiocyanate in a way that preserves viral infectivity. We have used epifluorescence microscopy to detect individual vnirions bound to the surface ofcells and to follow in real time the early stages of reovirus infection in living cells. Following uptake of the virus into endocytic vesicles, the movement of these vesicles can be observed readily. The vesicle movement is inhibited by nocodazole or colchicine, consistent with previous fldings that the movement of intracellular vesicles is often microtubule-based.Epifluorescence microscopy has become one of the essential tools in biology. A major attribute of this technique is its sensitivity: as few as 50 fluorescent molecules in a cubic micrometer can be detected (1). In contrast to electron microscopy, epifluorescence microscopy can be readily adapted to experiments with living cells (1). With the advent of highly sensitive detection systems including improved photographic film and video cameras that can image aggregates offewer than 20 fluorescent molecules, the time seemed ripe for an attempt to detect a single animal virus particle by light microscopy.Fluorescently labeled viruses have been used in other ways to study virus-host interactions. Epstein-Barr virus conjugated with fluorescein isothiocyanate (FITC) has been used to examine the specificity of binding to cellular receptors (2), and FITC diphosphate-conjugated influenza virus has been used to study viral uncoating in endosomes (3). However, it has not been established whether each individual fluorescent particle represents a single virion or an aggregate of several virions; nor have fluorescently labeled viruses been used for studies in a living cell system.Based on the size of most animal viruses and the detection systems available, we estimated that -500 molecules of rhodamine B per virion might be sufficient for detection. Reovirus serotype 1 (Lang) was chosen for these studies because it grows to high titer in cell culture, is relatively stable at high pH, and is therefore more likely t6 survive the conditions of dye conjugation (2). We report here that individual virions of reovirus conjugated with Rither rhodamine or fluorescein can be observed on-the surface of infected L cells at early times after inoculation and that endocytic vesicles containing small cluste~is of virions can be seen moving inside cells in a manner consistent with the translocation of organelles along microtubules. MATERIALS AND METHODSCells and Virus. Mouse L cells (fibroblasts) were grown on glass coverslips or in spinner cultures in "completed MEM" containing Joklik's modified Eagle's medium (Irvine Scientific) supplemented with 2.5% fetal bovine serum (HyClone), 2.5% neonatal bovine serum (Biocell Laboratories), 0.3% glutamine, and 1% penicillin/streptomycin solution (Irvine Scientific).Plaque-purified reovirus serotype 1 (Lang) was used for conjugation. The virus was purified by sonication and Freon extraction (4, 5). The virus was ...