RIAM (Rap1-interacting adaptor molecule) regulates complement-dependent phagocytosis

Phagocytosis mediated by the complement receptor CR3 (also known as integrin α_Mß₂ or Mac-1) is regulated by the recruitment of talin to the cytoplasmic tail of the ß₂ integrin subunit. Talin recruitment to this integrin is dependent on Rap1 activation. However, the mechanism by which Rap1 regulates this event and CR3-dependent phagocytosis remains largely unknown. In the present work, we examined the role of the Rap1 effector RIAM, a talin-binding protein, in the regulation of complement-mediated phagocytosis. Using the human myeloid cell lines HL-60 and THP-1, we determined that knockdown of RIAM impaired α_Mß₂ integrin affinity changes induced by stimuli fMLP and LPS. Phagocytosis of complement-opsonized RBC particles, but not of IgG-opsonized RBC particles, was impaired in RIAM knockdown cells. Rap1 activation via EPAC induced by 8-pCPT-2′-O-Me-cAMP resulted in an increase of complement-mediated phagocytosis that was abrogated by knockdown of RIAM in HL-60 and THP-1 cell lines and in macrophages derived from primary monocytes. Furthermore, recruitment of talin to ß₂ integrin during complement-mediated phagocytosis was reduced in RIAM knockdown cells. These results indicate that RIAM is a critical component of the phagocytosis machinery downstream of Rap1 and mediates its function by recruiting talin to the phagocytic complement receptors.     

Effect of insulin on immunological phagocytosis by macrophages

Summary It was shown that, in physiological concentrations, insulin enhances, in vitro, the immunological phagocytosis of sensitized sheep erythrocytes by cultured mouse peritoneal macrophages. Insulin seems to stimulate macrophage phagocytosis as a cholinomimetic agonist by increasing the intracellular levels of cyclic GMP.Acknowledgments. This investigation was supported by a grant from the National Council for Cientific and Tecnological Development (CNPq), Rio de Janeiro, Brazil.     

Effects of plant lectins on cellular defense reactions of ascidian hemocytes

The effects of plant lectins on the three cellular defense reactions of hemocytes of the solitary ascidian,Halocynthia roretzi (hemocyte aggregation, phagocytosis, and an allogenic reaction), were investigated. Concanavalin A inhibited aggregation, while wheat germ agglutinin and ricin inhibited the allogenic reaction. Neither of the lectins showed inhibitory effects on phagocytosis, but ricin promoted phagocytosis. These effects of the lectins were diminished by the addition of sugars specific for the respective lectins. These results strongly suggest that different surface carbohydrates are involved in the recognition mechanisms of threeH. roretzi cellular defense reactions.     

Role of serum components in the binding and phagocytosis of oxidatively damaged erythrocytes by autologous mouse macrophages

To investigate the role of autologous serum components in the recognition of damaged cells by macrophages, we examined the binding and phagocytosis of damage oxidatively damaged red blood cells with Cu2+ and ascorbate (oxRBCs) by autologous resident mouse peritoneal macrophages. The binding of oxRBCs by macrophages was independent of the presence of serum. However, phagocytosis by macrophages increased with serum concentration, and macrophages showed little ingestion of oxRBCs in a serum-free medium. Macrophages neither bound nor appreciably ingested native RBCs (before oxidation) in either the absence or presence of autologous serum. Mouse macrophages ingested significantly more native as well as oxRBCs in the presence of heat-inactivated fetal calf serum than in the presence of heat-inactivated mouse serum. Pretreated oxRBCs with normal serum were rarely ingested by macrophages in a serum-free medium. Phagocytosis of oxRBCs was significantly inhibited by depletion of IgG or calcium from serum, by heat inactivation of complement, or by antiserum against mouse C3. These results demonstrate that serum components such as IgG, C3, and calcium are involved in phagocytosis of oxRBCs by autologous macrophages.     

The effect of corticotropin-releasing factor and pro-opiomelanocortin-derived peptides on the phagocytosis of molluscan hemocytes

The effect of corticotropin-releasing factor (CRF) and pro-opiomelanocortin (POMC)-derived peptides on hemocyte phagocytosis in two molluscs,Planorbarius corneus andViviparus ater was studied. The peptides and related fragments examined are those which have been shown to influence hemocyte motility in the two species. The results obtained revealed that the effects on phagocytosis are not directly correlated with previous findings on cell motility. Furthermore, the mode of action of an individual peptide could be species-specific and dose-dependent. The relationships between peptides, locomotion and phagocytosis in these molluscs are discussed.     

Are rat alveolar macrophages capable of phagocytizing pollen grains?]

Plane-tree pollen grains were incubated in vitro with alveolar macrophages from inbred Rats, and the possibility of phagocytosis was investigated. No phagocytosis was observed even after 48 hrs incubation. But alveolar cells were bound to pollen grains generally at the apertures. This binding did not require the Fc receptor on the macrophage membrane.     

Membrane interiorization by phagocytosing macrophages — an ultrastructural morphometric approach

Summary Stereological methods have been used to quantify selected membrane compartments of normal and activated rat peritoneal macrophages, before and after phagocytosis of latex beads. Despite being rounder, activated cells are more efficient phagocytes: 30 min after latex challenge they suffer a greater nett depletion of plasma membrane and sequester more and larger phagocytic vacuoles. However, phagocytosis of latex is not the major route of membrane interiorization.We wish to thank Professor R. Barer for his advice and criticism. The work was undertaken by L.O. as a research project in partial fulfilment of requirements for a B.Sc. degree in Human Biology and Anatomy, University of Sheffield.     

Functions of the testicular gland of blenniid fish: Structural and histochemical investigations

Summary We investigated the functions of the testicular glands of blenniid fishes by fine-structural and histochemical methods. These glands function in the differentiation and nutrition of germ cells, in the secretion of sialomucins, in phagocytosis of germ cells, and in lipid storage.     

Circulating Trypanosoma cruzi from the same cloned population show differences in the ability to infect cells and to cause lethal infection in mice

Two subpopulations of circulating parasites displaying different abilities to infect mammalian cells and to cause lethal infection when inoculated into normal mice were demonstrated in the blood of mice acutely infected with T. cruzi. Parasites of one subpopulation rapidly penetrated mouse fibroblasts and were readily phagocytized by normal mouse peritoneal macrophages whereas parasites of the other subpopulation showed little ability to invade non-phagocytic cells and resisted phagocytosis. Inoculation of organisms of this latter population into mice resulted in infections with lower parasitemias and longer time to death as compared to controls inoculated with organisms from a population containing both types of parasites. When a population of parasites containing both types of trypanosomes was cultured in acellular medium at 28 degrees C a decrease in the number of parasites was noted to occur in the initial days of culture. This decrease was not noted when parasites of the subpopulation of trypanosomes resistant to phagocytosis were cultured similarly.     

Binding of ferritin-lectin conjugates to C-type virus in intact cells.

Ferritin-Ricin II and Ferritin-Concanavalin A bound to budding as well as mature C-type viral particles. No differencies in binding between the viral coat and adjacent plasma membrane were detected with either lectin conjugate. Aggregation of viral particles by lectin conjugates was observed, and linking of virus to the plasma membrane resulted in phagocytosis of viral particles.     

Fluid and protein clearance in the rat endometrium. Part II: Ultrastructural evidence for the presence of alternative, non-lymphatic clearance mechanisms in the rat endometrium

In the rat endometrium, resident macrophages and exudate phagocytes ensure proteolysis by means of phagocytosis, macro- and micropinocytosis. Using exogenous tracer particles no ultrastructural evidence could be obtained for the occurrence of endometrial prelymphatics. It is suggested that the free tissue fluid may be drained via the fenestrated (probably venous) blood capillaries.     

Close association of erythrocytes with surface of late mouse blastocysts: SEM analysis

Summary SEM analysis of preimplantation mouse blastocysts reveals closely associated red blood cells on involuted surfaces of trophoblasts, an indication of the capability for initial phases of phagocytosis at an early developmental stage.Acknowledgment. This study was supported by NICHD grant HD-06234 and NIH grant RR-05384. Author for reprint requests.     

Elektronenmikroskopische Beobachtungen an den Hülsenarteriolen in der Milz des Hundes

Summary The endothelial cells of sheathed arterioles of dog spleen were found to contain an abundance of intracytoplasmic filaments about 80 Å in diameter. The endothelium is surrounded by a fenestrated clastin skeleton. The sheath cells show signs of phagocytosis. A possible vasomotor function of the endothelial cells is discussed.     

A possible preferential inhibition of chemotaxis of polymorphonuclear neutrophils by a chemical modification.

The modification of neutrophils with amino group blocking reagents of different chemical specificities showed that dansyl chloride caused inhibition of chemotaxis without suppression of random movement. Dansylated neutrophils, like control cells, ingested bacteria. Neither the stimulated cyanide-insensitive respiration, nor lactate production during phagocytosis, was affected significantly by dansylation as compared with the inhibition of directed movement.     

A possible preferential inhibition of chemotaxis of polymorphonuclear neutrophils by a chemical modification

Summary The modification of neutrophils with amino group blocking reagents of different chemical specificities showed that dansyl chloride caused inhibition of chemotaxis without suppression of random movement. Dansylated neutrophils, like control cells, ingested bacteria. Neither the stimulated cyanide-insensitive respiration, nor lactate production during phagocytosis, was affected significantly by dansylation as compared with the inhibition of directed movement.     

Differences in phagocytic activity of methacrylate copolymer particles in normal and stimulated macrophages

Summary Methacrylate copolymer particles were found to be optimal for a study of phagocytosis in normal and stimulated macrophages, and, after their simple coating with antiserum, for a specific cell labelling with minimal spontaneous adhesion to the cell surface.     

Close association of erythrocytes with surface of late mouse blastocysts: SEM analysis

SEM analysis of preimplantation mouse blastocysts reveals closely associated red blood cells on involuted surfaces of trophoblasts, and indication of the capability for initial phases of phagocytosis at an early developmental stage.     

Fluid and protein clearance in the rat endometrium. Part II: Ultrastructural evidence for the presence of alternative,non-lymphatic clearance mechanisms in the rat endometrium

Summary In the rat endometrium, resident macrophages and exudate phagocytes ensure proteolysis by means of phagocytosis, macro-and micropinocytosis. Using exogenous tracer particles no ultrastructural evidence could be obtained for the occurrence of endometrial prelymphatics. It is suggested that the free tissue fluid may be drained via the fenestrated (probably venous) blood capillaries.Supported by a grant from the Nationaal Fonds voor Wetenschappelijk Onderzoek-Fonds voor Geneeskundig Wetenschappelijk Onderzoek (Belgium).     

Prostaglandin production by human polymorphonuclear leucocytes during phagocytosis in vitro

Summary Human polymorphonuclear leukocytes were found to be able to synthetize and release substantial amounts of PGE₂, when stimulated by a phagocytic stimulus such as zymosan particles coated with complement. Hydrocortisone, at a concentration of 10^–5 M, which proved to be effective in other biological systems, failed to inhibit phagocytosis and PG release.