Reversible phagocytosis in rabbit polymorphonuclear leukocytes

Detoxification of bacterial lipopolysaccharides (endotoxins) by a human neutrophil enzyme

Lipopolysaccharides in the cell walls of Gram-negative bacteria elicit toxic as well as potentially beneficial inflammatory responses in animals. It is now reported that tissue toxicity caused by lipopolysaccharides is preferentially reduced by an enzymatic activity in human neutrophils. Acyloxyacyl hydrolysis removes fatty acyl chains that are linked to the hydroxyl groups of 3-hydroxytetradecanoyl residues in the bioactive lipid A moiety of the lipopolysaccharides. Maximal acyloxyacyl hydrolysis reduced lipopolysaccharide tissue toxicity, as measured in the dermal Shwartzman reaction, by a factor of 100 or more. In contrast, the ability of the deacylated lipopolysaccharides to stimulate B lymphocytes to divide was decreased only by a factor of 12. It is suggested that during tissue invasion by Gram-negative bacteria acyloxyacyl hydrolysis may be a defense mechanism that reduces the toxicity of lipopolysaccharides while preserving some of their potentially beneficial inflammatory and immune stimuli.

Phagocytosis of latex particles by leucocytes. I. Dependence of phagocytosis on the size and surface potential of particles

A series of latex particles, having different sizes and surface structures, were prepared and the dependence of phagocytosis of latex particles by leucocytes on the particle size and surface potential was investigated by measuring the oxygen consumption of leucocytes. Most of the phagocytic behaviour in the initial stages can be explained by susceptibility of particles to heterocoagulation i.e. attachment of small particles (latex particles) onto large particles (leucocytes) by the colloidal attractive force between the two kinds of particles. Specific behaviour for fine particles seems to be attributed to the contribution of steric stabilization by the hydrated layer on the particle surface and to the inability for the leucocytes to recognize very fine particles as foreign materials.

Endocytosis in Entamoeba histolytica. Evidence for a unique non-acidified compartment

Our studies on endocytosis in Entamoeba histolytica trophozoites suggest that there are two vacuolar compartments in this organism. The first compartment consists of large vacuoles (greater than 2 microns diameter). As measured by the fluid phase markers, fluorescein isothiocyanate (FITC)-dextran and horseradish peroxidase (HRP), this compartment is a rapid equilibrium with the external milieu and is constantly exchanging (1-2 h) its contents with the external medium. The contents of these vacuoles are not acidified. This together with the absence of degradation of fluid phase markers clearly differentiates these vacuoles from lysosomes of eucaryotes. By labeling externally disposed peptides on the surface membrane of trophozoites with 125I, we could show that the surface membrane was rapidly internalized over a 2-h period and then reached a plateau. All major 125I surface proteins, with the exception of a set of peptides in the 40,000 molecular weight range, were interiorized and approximately 60% of the total radiolabel were found to be in the internal membrane fraction at any given time. The kinetics of this process were similar to those for the uptake of fluid phase markers and are best explained by cycling of the surface membrane into the vacuolar compartment(s) and then back to the cell surface. The second vacuolar compartment consisted of small vesicles (less than 2 microns diameter) with acidified contents as indicated by acridine orange uptake. The endocytic nature of these vesicles was shown by their slow (days) labeling with FITC-dextran, and spectral analysis of internalized FITC-dextran confirmed that this second compartment is acidified (pH 5.2).

Exocytosis of zymosan particles by human phagocytes

The kinetics of human leucocyte phagocytosis and exocytosis of fluorescein-isothiocyanate (FITC)-labelled zymosan particles were studied by flow cytometry (FCM). The leucocytes rapidly associated with zymosan particles, and internalization was confirmed by a fluorescence quenching technique. For incubation periods longer than about 60 min, exocytosis of ingested particles was observed. All human phagocytes ejected zymosan particles. The rate of exocytosis was about 1 particle per phagocyte per h, and was independent of the number of internalized particles. Exocytosis was dependent on temperature and glucose, but did not require Ca++ and Mg++ ions. Phagocytosis and exocytosis occurred concurrently, and phagocytosis accelerated ejection of previously internalized particles. The exocytosed particles were partially degraded by the phagocytes, and rephagocytosis of ejected zymosan particles was slower than the uptake of control particles. Phagocytes undergoing exocytosis remained intact during the 210 min examined. The findings indicate a heretofore neglected vector in the interaction of prey and phagocytosing cells.

Cytoplasmic lipid droplets as the possible eventual cellular fate of active forms of cyclosporin

The activity of cyclosporins can be defined with regard to their ability to inhibit the proliferation of susceptible lymphoblastoid cell clones. All active cyclosporins cause the emergence of highly refringent globular bodies, independently of cell susceptibility to cyclosporin. Cyclosporins devoid of proliferation-inhibition capability do not cause such alterations in cell morphology. The use of dansylated active cyclosporins suggests that within a few hours of treatment in vitro, most if not all cyclosporin is contained within those globular bodies. By using cytochemical methods allowing differential staining, we show here that these cyclosporin-containing structures are neither normal mitochondria (shown by use of rhodamine 123) nor normal lysosomes (shown by use of acridine orange under stringent staining conditions) but most probably lipid droplets (shown by use of perylene and various dansylated hydrophobic probes).

Biological activity, lipoprotein-binding behavior, and in vivo disposition of extracted and native forms of Salmonella typhimurium lipopolysaccharides

Although phenol-extracted gram-negative bacterial lipopolysaccharides (LPS) have been used to study the properties of endotoxins for many years, nothing is known about the behavior of native (unextracted) LPS in vivo. Accordingly, we have compared extracted and native forms of LPS with regard to their biological activity, their ability to bind to plasma high density lipoproteins (HDL), and their fate after intravenous injection into rats. The LPS of Salmonella typhimurium G-30 were labeled with [(3)H]galactose, and whole bacteria, bacterial outer membranes, outer membrane fragments (harvested from the bacterial culture supernatant), and phenol extracts of the bacteria were prepared. After defining the LPS, phospholipid, and protein composition of these preparations, we compared the activity of the LPS in phenol extracts and membrane fragments in two assays. In both the limulus lysate assay and the rabbit pyrogen test, the LPS in phenol extracts were slightly more potent than the LPS in membrane fragments. We next studied the ability of the LPS in each preparation to bind to rat lipoproteins in vitro, and each preparation was then injected intravenously into rats for measurements of LPS-HDL binding and tissue uptake in vivo. Two patterns of lipoprotein binding were observed. Less than 25% of the LPS in both outer membranes and whole bacteria bound to HDL in vitro. When the outer membranes and whole bacteria were injected into rats, their LPS again bound poorly to HDL and they were rapidly removed from plasma into the liver and spleen. In contrast, >50% of the LPS in both culture supernatant membrane fragments and phenol-water extracts bound to HDL in vitro. When these preparations were injected into rats, approximately 50% of the LPS in the membrane fragments and phenol-water extracts bound to HDL and remained in the plasma over the 10-min study period. Moreover, the LPS in these preparations accumulated in the ovary and the adrenal gland, two tissues that use HDL-cholesterol for hormone synthesis. Binding to HDL thus greatly influenced the plasma half-life and tissue uptake of both extracted and native LPS. We conclude that extraction of S. typhimurium LPS with phenol does not significantly alter the biological activity or the lipoprotein binding behavior of the LPS and that the in vivo fates of phenol-extracted and membrane fragment LPS are essentially identical. The results thus provide important support for many previous studies that have used phenol-extracted LPS to mimic the activities of native LPS in vivo. However, the only native LPS that resembled the behavior of extracted LPS were the LPS that had been shed from the bacteria in fragments of membrane that had reduced amounts of protein and phospholipid. Removal of LPS from other outer membrane constituents, whether by chemical extraction or by a natural process of surface shedding, thus alters the behavior of the LPS; the most important feature of this alteration appears to be the ability of these LPS to bind readily to HDL.

The respiratory burst of phagocytic cells is associated with a rise in vacuolar pH

Neutrophil leukocytes are the body's major defence against bacteria, which they phagocytose and kill. It has been found that phagocytosis and killing are accompanied by a dramatic rise in non-mitochondrial respiration; and that the efficiency of killing is impaired in the absence of oxygen. It is also impaired in neutrophils from patients with chronic granulomatous disease (CGD), where the respiratory burst is absent. This has been difficult to reconcile with their normal content of granule proteins that kill bacteria in vitro. Indeed, CGD cells are essentially normal both morphologically and constitutionally except that they lack a functional very low potential cytochrome b (b-245), which is a component of the oxidase system responsible for the respiratory burst of normal cells. Activation of the oxidase is associated with the generation of various reduced oxygen species which have been widely thought to be responsible for the killing of phagocytosed microorganisms either directly, or by acting as substrates for myeloperoxidase-mediated halogenation. We report here, however, that a major consequence of the defective function of this oxidase in neutrophils and monocytes from CGD patients is an absence of the normal initial rise, and an unusually rapid and extensive fall in pH which is itself associated with the impairment of the killing and digestion of intracellular staphylococci.

Mechanisms of exocytosis in phagocytic inflammatory cells. Parke-Davis Award Lecture

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Polarization of endocytosis and receptor topography on cultured macrophages

In the 1774.2 macrophage cell line, microtubule disassembly by colchicine causes the polarization of membrane functions ane structure. Colchicine-treated cells develop a bulge or protuberance that is bordered by microvillous membrane. The protuberance is the site of concanavalin A cap formation. The fluid pinocytosis of horseradish peroxidase and of fluorescein- and rhodamine-conjugated high molecular-weight dextrans, the adsorptive pinocytosis of concanavalin A, and the concentration and phagocytosis at 37 degrees C of a range of phagocytic particles (IgG- and complement-opsonized erythrocytes, complement-opsonized zymosan, latex shpres, albumin-stabilized oil droplets) are all similarly restricted to the protuberance. A reduction in the rate of dextran pinocytosis, determined by fluorimetry, and reductions in phagocytic rates for oil emulsion and IgG-opsonized erythrocytes accompany the polarization of endocytic activity in colchicine-trated 1774.2 macrophages. Membrane receptors for phagocytic particles are not confined to the protuberance but rather may display their own unique topographical asymmetry. The inherent topography of receptors was inferred from particle distribution under conditions that limit particle-receptor redistribution (after labeling at 4 degrees C or a very brief incubation at 37 degrees C). Under these restrictive conditions, latex binding sites were detected over the whole membrane whereas receptors for IgG-opsonized erythrocytes, aggregated IgG, complement-opsonized erythrocytes, and complement-opsonized zymosan were excluded from the protuberance. Thus, functional (endocytosis) and structural (inherent receptor distribution) analyses of membrane topography define different patterns of asymmetry in protuberant cells. The asymmetry induced in 1774.2 macrophages by colchicine is highly analogous to the functional and structural polarity of epithelial cells. Exploration of this analogy may provide insight into the development of polarized epithelia and, more generally, into mechanisms by which specialized areas of membrane are established.