Localization of receptors and early events of phagocytosis in the macrophage

Characterization of patocytosis: endocytosis into macrophage surface-connected compartments

Previously, we described a unique macrophage endocytosis pathway in which aggregated low density lipoproteins and microcrystalline cholesterol induce and enter a labyrinth of membrane-bound compartments that remain connected to the cell surface. We now show that certain types of non-lipid particles such as polystyrene microspheres and colloidal gold also induce and enter macrophage surface-connected compartments (SCC), a process we call patocytosis. A common property among particles that stimulate patocytosis is their hydrophobic nature. Both aggregated LDL and microcrystalline cholesterol that we showed previously to stimulate patocytosis are hydrophobic. We now show that hydrophobic polystyrene microspheres and gold particles but not their hydrophilic counterparts triggered patocytosis. Uptake by patocytosis was limited to hydrophobic polystyrene microsphere particles less than 0.5 micron in diameter. Hydrophobic polystyrene microspheres greater than this size entered macrophages by phagocytosis. Actin-independent capping of hydrophobic polystyrene microspheres on the plasma membrane preceded actin-dependent uptake of the microspheres into SCC. Sequential rounds of microsphere uptake into SCC over two successive days could occur. There was some mixing of initial and subsequently accumulated microspheres in SCC. SCC formed from plasma membrane invaginations that connected with spaces created by unfolding of stacks of internal microvilli. Microsphere transport from plasma membrane invaginations into these spaces was inhibited by primaquine. Patocytosis is a unique endocytic process in macrophages triggered by small hydrophobic particles that provides a mechanism to sequester large amounts of these materials within a labyrinth of SCC.

Aberrant differentiation of neuroepithelial cells in developing mouse brains subsequent to retinoic acid exposure in utero

All-trans-retinoic acid induced 2 types of disorganized neuroepithelium, localized and continuous, in the exencephaly of 9-day-old mouse embryos exposed to 60 or 40 mg/kg for 27 to 30 hr in utero. The localized effect appeared as a protuberance in the wall of the telencephalon and thick neural folds in the mesencephalon with the discontinuity of the apical terminal sheet. The continuous disorganization was seen from the olfactory placode to the myelencephalon with rosettes of cells and many dense bodies in the neuroepithelium. Ultrastructurally, cells in the localized disorganizations showed swelling of Golgi complexes, coated vesicles, and rough endoplasmic reticulum resulting in degeneration. The continuous disorganizations consisted of undifferentiated homogeneous cells in which the nuclei exhibited expansion of nucleolar granular portions and coagulated heterochromatin, and cytoplasm showed monosomal dispersion. In both types of disorganized neuroepithelium, junctional complexes were seen focally at the apical side or apical processes of the rosette, with few or no microfilament bundles. A layer of microfilaments at the base of the neuroepithelial cells in controls, just above the basal lamina, was not present in the monosome dispersed cytoplasm. In the neuroepithelium of controls, one phagosome was seen in the perinuclear region in 0.8% of the cells examined, whereas in the experimental neuroepithelium 2 or more phagosomes were seen in a cell, and phagocytosis occurred by pseudopods. These findings suggest that all-trans-retinoic acid induces not only cytotoxicity but also dedifferentiation in the neuroepithelial cells leading to more cell death, which activates the phagocytosis. These lesions in the neuroepithelium may be a cause of exencephaly.

Effects of bile acids and endotoxin on the function and morphology of cultured hamster Kupffer cells

The mechanisms of hepatic reticuloendothelial cell dysfunction in obstructive jaundice were investigated using cultured hamster Kupffer cells. The introduction of free bile acids, cholic acid (CA) at concentrations over 2 mM and chenodeoxycholic acid (CDCA) over 1 mM inhibited colloidal carbon pinocytosis. CA and CDCA at concentrations over 0.5 mM inhibited IgG-coated sheep red blood cell phagocytosis. With the application of conjugated bile acid and endotoxin at concentrations over 50 micrograms/ml, endocytic function was inhibited. With bile acids, a dose-dependent increase in the concentration of beta-glucuronidase occurred in the culture medium, and with endotoxin a time-dependent increase in beta-glucuronidase was noted. Bile acids produced alterations in cell organelles before destruction of the cell membrane. The presence of endotoxin led to the appearance of large vacuoles in the cytoplasm. These observations suggest that bile acids and endotoxin inhibit Kupffer cells by different mechanisms. We tentatively conclude that bile acids rather than endotoxin influence Kupffer cells in vivo.

Mechanisms of phagocytosis of Mycobacterium leprae and other mycobacteria by human oligodendroglial cells

The mechanisms by which human oligodendroglial cells, KG-1-C cells, phagocytose mycobacteria, especially Mycobacterium leprae, were studied. The ability of glial cells to phagocytose M. leprae was inhibited by azide, dinitrophenol (inhibitors of oxidative phosphorylation), and iodoacetamide but not fluoride (both are inhibitors of glycolysis). Thus, the energy metabolism dependency is somewhat different from that of peritoneal macrophages and polymorphonuclear leukocytes, the phagocytic capacities of which are mainly dependent on glycolysis. Phagocytosis of M. leprae by KG-1-C cells was markedly suppressed by a microfilament inhibitor (cytochalasin B) but not microtubule inhibitors (colchicine and vinblastine), as with macrophages. The phagocytosis of M. leprae by KG-1-C cells was dependent on the lipid and somewhat on the sugar ligands of the organism. Moreover, the phagocytosis of a given mycobacterium by KG-1-C cells correlated well with its hydrophobicity, thus revealing the importance of some lipid moieties on the surface of bacteria in the establishment of rigid binding interaction of bacteria with KG-1-C cells, before the onset of engulfment. Electric charge of a given microorganism did not correlate with its phagocytosis by KG-1-C cells.

Fibronectin, complement and immunoglobulins in serum after surgery

In recent years it has been suggested that fibronectin is a non-specific opsonic protein of significance in host resistance against septic complications following trauma and surgery. The aim of the present study was to investigate the fluctuations in serum levels of fibronectin, immunoglobulins IgG and IgM, and complement factors C3 and C4 postoperatively. Serum samples were obtained pre-operatively and at different intervals postoperatively in 72 patients admitted for elective surgical procedures on the alimentary tract, the heart and the hip joint. The mean pre-operative fibronectin values were 257 +/- 79 micrograms/ml. The lowest values (166 +/- 65 micrograms/ml) were found immediately after the operation, followed by an increase which did not reach pre-operative levels within 120 h. Five patients who developed postoperative complications and 14 patients with malignant disease did not differ significantly either in their pre- or postoperative fibronectin levels, compared with the whole group. The lowest fibronectin levels seen were also significantly above the concentrations necessary to promote binding of gelatinized test particles to macrophages and monocytes in vitro. There was a significant decrease in C3, C4 and IgG levels postoperatively whereas IgM levels were unaltered. The observed reduction did not extend below the lower normal levels for these proteins. The probable mechanism behind the reduction in serum levels seems to be a sequestration at the site of tissue injury. The postoperative reduction in circulating fibronectin levels has probably no implications for host resistance against septic complications. When sequestered into the site of injury, it may, however, be of significance for normal wound healing, due to its cell-matrix interactions.

The mechanisms of cell death and phagocytosis in the early chick lens morphogenesis: a scanning electron microscopy and cytochemical approach

The cell surface characteristics of degenerating cells and phagocytes, as well as the participation of lysosomes in the cell death process associated with the early embryogenesis of chick lens rudiment, were studied by means of scanning electron microscopy and cytochemically using the Gomori-beta-glycerophosphate method for acid phosphatase. The prospective dying columnar epithelial cells lose their apical and basal processes and become rounded. The rounded, isolated, dying cells initially show a rough surface with some cytoplasmic constrictions followed by progressive break-up into several pitted fragments. Coincident with the loss of the columnar cell shape, acid phosphatase is localized within the Golgi apparatus and autophagic vacuoles which progressively increase in size. In contrast, the isolated dying cells and fragments do not show significant acid phosphatase activity. The role of lysosomes in this degenerative process is discussed. Neighboring epithelial cells phagocytose the dead cell fragments, becoming nonspecialized phagocytes. These consist of columnar epithelial cells and free cells which have migrated from the lens epithelium. Two mechanisms of internalization are observed. The most frequent mechanism takes place in both the columnar epithelial cells and the free cells, and consists of the progressive engulfment of the fragments into craters of the cell surface. The other mechanism is only detected in the free cells and takes place by pseudopod engulfment. We suggest that both phagocytic procedures could be related to the degree of intercellular connection. The presence of phagocytic internalization by crater formation in the epithelial cells could be a mechanism preserving the epithelial stability, which is necessary for a normal morphogenesis. Small microprocesses binding the surface of the phagocyte and the fragment are present prior to the internalization process. In the lens stalk and in the space located between the ectoderm and the lens vesicle, there are some cells displaying migratory characteristics. This fact suggests that an active migration of epithelial cells from the lens stalk could account for the process of detachment of lens vesicle from the ectoderm. The free cells appear to undergo an in situ progressive degeneration.

Properties of a macrophage cell line transformed by simian virus 40. Morphological changes related to cell functions

A mouse macrophage clone (line nH-1) transformed by simian virus 40 (SV40) was examined by electron microscopy. In the growing phase of the cultures, NH-1 cells were non-phagocytic and SV40 T antigen-positive, and contained a large number of filament sheaths within their pseudopodia. In the late stationary phase, they became phagocytic, SV40 T antigen-negative and contained a filamentous network within their psudopodia. In addition, NH-1 cells in the late stationary phase were very similar to normal macrophages in other morphological properties.

The structure of the glycocalyx of the golden hamster's peritoneal macrophages following antigen stimulation

Electon-microscopy was used to study the glycocalyx of peritoneal macrophages from hamsters with transplanted melanotic and amelanotic tumours, and from control animals. The growth of transplantable melanomas in hamsters was found to cause a reduction in the amount of the material stainable with ruthenium red on the surface of the macrophages, as well as changes in the structure of the glycocalyx. The changes were more marked in the case of amelanotic melanomas.

Cell death and phagocytosis in the neuroepithelium of the developing retina. A TEM and SEM study

Phagocytosis by neuroepithelial cells independent of the presence of pseudopodes is observed as the main mechanism of elimination of physiologically degenerating cells during the early development of the retina in the chick embryo.

Kinetics of phagocytosis of Chlamydia psittaci by mouse fibroblasts (L cells): separation of the attachment and ingestion stages

The kinetics of phagocytosis of Chlamydia psittaci (6BC) by monolayers of mouse fibroblasts (L cells) was studied with an assay that distinguished between the attachment and ingestion phases of phagocytosis. At multiplicities of 10 and 100 50% infectious doses (ID50) per L cell, virtually all of the inoculated C. psittaci had been attached and ingested after 60 min at 37 degrees C. At multiplicities of 500 to 5,000 ID50 per L cell, the initial rates of attachment and ingestion of C. psittaci to L cells increased with the multiplicity of infection, but phagocytosis stopped even though many chlamydial cells remained free in suspension and readily available for attachment to the host-cell monolayers. Phagocytosis probably ceased because the L cells were injured when they took up large numbers of chlamydial cells. This injury prevented direct determination of the number of potential binding sites for C. psittaci on each L cell. However, this number is large enough to make the rates of chlamydial attachment and ingestion predominantly dependent on the multiplicity of infection.

Differences in the mode of phagocytosis with Fc and C3 receptors in macrophages

Mouse macrophages, activated in vivo or in vitro, were made to internalize sheep erythrocytes opsonized with IgG or IgM and complement. Scanning electron microscopy and transmission electron microscopy were performed at various times after the transfer of the cultures from conditions favoring attachment to conditions favoring internalization. The receptors for Fc and C3 were distributed randomly over the macrophage surface with the exception of the extreme periphery, were Fc receptors were more abundant. The E-IgG were ingested by means of thin membrane extensions rising from the macrophage surface and enclosing the opsonized particles tightly in a cup-like structure protruding from the macrophage surface. Only afterwards were the covered particles drawn into the cell body proper. The E-IgMC were seen to sink directly into the macrophage cytoplasm without apparent involvement of membrane extensions. Experiments with cytochalasin B suggested that microfilaments were essential for the phagocytosis by Fc but much less important with the C3 receptor.