Steps Of Phagocytosis Research Articles

'Phagocytosis' of Sendai Virus by Model Membranes

Sendai viruses were attached to liposomes (vesicular model membranes) at 0 to 4 degrees C, and were then incubated at 37 degrees C. Liposomes made of phosphatidylcholine, cholesterol and gangliosides enveloped the viruses at 37 degrees C to give a picture that resembles the ingestion step of phagocytosis. Virus particles were enveloped only by liposomes that contained gangliosides which serve as Sendai virus receptors.

Bactericidal and Opsonic Properties of C4-Deficient Guinea Pig Serum

Abstract The bactericidal and opsonic properties of serum obtained from a strain of guinea pigs totally lacking in hemolytically active or antigenically detectable C4 were studied and compared to serum from normal guinea pigs and those heterozygous for C4 deficiency. Bactericidal activity against two strains of E. coli was present in C4-deficiency serum; however, the latent period was prolonged and the rate was slower when compared to that in normal or heterozygous sera. C4-deficient serum bactericidal activity could be restored to normal by mixing with normal serum or by adding partially purified C4 from human serum. Treatment of both C4-deficient and normal serum with heat (56°C for 30 min), 0.04 M EDTA, and zymosan abolished bactericidal activity, whereas 0.03 M hydrazine treatment impaired but did not completely destroy the activity of both sera. C4-deficient serum promoted phagocytosis of S. aureus, type 25 pneumococci, E. coli and C. albicans but kinetic studies employing 14C labeled bacteria indicated that ingestion rates were slower than in normal or heterozygous serum. Prior incubation of pneumococci in serum established that opsonization was the rate-limiting step in phagocytosis of these organisms and that this was significantly diminished from normal in C4-deficient serum. Normal opsonization could be restored by the addition of as few as 10 units of partially purified guinea pig C4. Treatment with heat, EDTA and zymosan abolished opsonization in both normal and C4-deficient sera. Hydrazine treatment diminished the opsonic activity of normal serum against pneumococci but did not significantly affect C4-deficient serum pneumococcal opsonization. These observations are consistent with the operation of an alternate pathway for activation of late complement components necessary for bacterial opsonization and killing by serum, but suggest that participation of C4 presumably through the classic C1,4,2,3–9 sequence might be necessary for maximal rates of activity. In addition, the results of studies using the various complement inhibitors offer support for the participation of heat labile factors, divalent cations and zymosan and hydrazine inhibitable components in the alternate pathway. Finally, both normal and C4-deficient guinea pigs were found to be highly resistant to intraperitoneal administration of high doses of type 25 pneumococci or E. coli used in the in vitro studies. Limited studies of the effects of intravenous challenge with pneumococci likewise revealed no striking impairment in the survival of the C4-deficient animals, suggesting that by utilization of the alternate pathway the host defenses are adequately maintained in vivo.

Uptake of aldehyde-treated erythrocytes by L2 cells: Inhibition by anti-red cell antibody or by coating the erythrocytes with purified proteins

Aldehyde-treated erythrocytes were taken up by mouse L2 cells grown on glass in MEM-10% fetal calf serum. Uptake was inhibited by anti-red cell rabbit serum or by IgG obtained from immune serum. Antiserum was inhibitory when either added to ingestion medium or used to pretreat the erythrocytes. Qualitative observations showed that the attachment of red cells to L2 cells was also decreased. Non-immune serum and non-immune IgG were not inhibitory. Inhibitory activity was sharply reduced by absorption with homologous erythrocytes but not with heterologous red cells or with L2 cells, indicating that the effect of antiserum was immunologically specific. Digestion of the immune IgG with pepsin decreased the inhibitory activity two fold, whereas digestion with papain led to a twenty fold decrease in activity. Thus, L2 cells, unlike macrophages, do not have surface receptors for antigen-bound immunoglobulin. Uptake of aldehyde-red cells coated with ovalbumin, plasma albumin or hemoglobin was likewise reduced when compared to that of non-coated erythrocytes. It is suggested that antibody, or the purified proteins, either mask the red cell surface sites that interact with the L2 surface or otherwise modify the particle surface so as to inhibit the attachment step of phagocytosis.

The dissociation of the attachment and ingestion phases of phagocytosis by macrophages

A procedure is described for the separate examination of the attachment and ingestion stages of particle uptake by peritoneal macrophages. This system makes use of the unique properties of aldehyde treated red blood cells (GRC). “Attachment”, expressed at GRC/macrophage, increased linearly with the GRC load, was temperature dependent and did not require the presence of added serum or divalent cations. “Percentage ingestion”, defined as ingested GRC/total ingested and attached, decreased with load but remained constant within a range of 0.5–2.0 GRC/macrophage. Ingestion was also temperature dependent, but required the presence of serum and divalent cations. Differences in the behaviour of attachment and ingestion toward temperature were also noted. These results support the discrete nature of the attachment and ingestion steps in phagocytosis by macrophages.

Nutritive phagocytosis in animal cells

Nutritive phagocytosis in the hydroid Clava squamata was studied with the electron microscope, using carbon particles of 0.6 μ as an indicator. An early step in phagocytosis is the transformation, in many cells, of the free border from a type with cylindrical microvilli to one with a complicated system of cytoplasmic folds. Particles fixed at the actual stage of ingestion are found (a) between two cytoplasmic folds, (b) between a fold and a relatively straight portion of the cell surface, or (c) in a depression of an otherwise straight portion of the cell surface. Ingested carbon particles were always found enclosed by a membrane, with a layer of moderate electron density between the carbon particle and the membrane. The ingested carbon particles are localized apically in small vesicles each containing one particle (interpreted as primary phagocytic vesicles) or at deeper levels of the cell, in larger vesicles containing many carbon particles (interpreted as secondary phagocytic vesicles). Other cytoplasmic changes during phagocytosis relate to the distribution of mitochondria and the occurence and distribution of flattened vesicles of a characteristic appearance.