Enhancement of colony-stimulating-factor--dependent clonal growth of murine macrophage progenitors and their phagocytic activity by retinoic acid

The effect of retinoic acid (RA) on the colony-stimulating-factor-dependent clonal growth of myeloid progenitors was assessed in semisolid agar cultures of mouse bone marrow cells using L-cell-conditioned medium that gave rise to macrophage colonies, granulocyte colonies, and mixed macrophage-granulocyte colonies and clusters. RA was found to enhance the overall formation of myeloid colonies (about 50%) and clusters in 7-day cultures. The increase was due to an enhanced formation of macrophage colonies (70-250%) and clusters which reached a maximal value at about 3 microM RA. In 4-day cultures, the effect of RA on macrophage colony formation was biphasic with a maximal enhancement at 10 nM. RA suppressed granulocyte-colony formation in 4-day cultures. RA increased the phagocytic activity of bone-marrow-derived macrophages at all stages of differentiation and/or maturation in culture. The Fc-receptor-mediated erythrophagocytosis as well as the phagocytosis of heat-killed yeast cells (HK-yeast) and starch particles increased by RA treatment in a dose-dependent manner, reaching an increase of 100-200% of the activity expressed in the absence of RA. Peritoneal exudate macrophages likewise exhibited an increased phagocytic response to a variety of particles, at both physiological and pharmacological concentrations of RA. Expression of an RA-mediated increase in phagocytic activity required a prolonged incubation with RA (greater than 19 hr). The data suggest that RA may be of physiological relevance in the regulation of proliferation and function of hemopoietic cells. Therapeutic doses of RA may potentiate macrophage proliferation and function, elements that are crucial at all phases of the various defense mechanisms that the organism possesses.     

Effect of insulin and isoproterenol on macrophage phagocytic activity

To reveal the influence of cyclic adenosine monophosphate (cAMP) on the completion of the phagocytosis of salmonellae, the influence of insulin and isoproterenol on the phagocytic activity of peritoneal macrophages obtained from mice infected with S. typhimurium strains differing in virulence was studied in vitro. The study showed that isoproterenol, while increasing the intracellular content of cAMP, suppressed the bactericidal properties of macrophages with respect to salmonellae, whereas insulin decreased the level of cAMP in the cells and thus facilitated more rapid and complete digestion of ingested bacteria irrespective of their virulence.     

Suppressing action of splenic cells on macrophage phagocytic activity]

The culture media withdrawn from 18-hour cultures of live spleen cells suppressed the phagocytic activity of peritoneal macrophages in mice. The level of suppression, as estimated for an equal number of spleen cells, varied in individual animals, which seemed to be connected with the level of normal infection in the animals. In the process of development of Ehrlich's carcinoma in mice suppressors were produced in the spleen in an increased amount, but only in connection with the total increase in the number of spleen cells, and not due to the selective accumulation of suppressor cells.     

Inhibition of macrophage phagocytic activity by selective sensitization to alloantigens of the H-2 system

The action exerted by selective sensitizations to alloantigens coded by the Major Histocompatibility System of the mouse, H-2, on the phagocytic ability of the mouse peritoneal macrophages has been studied. The results suggest that when immunizations are performed between completely incompatible animals for the H-2k haplotype, after the third immunization the total number of macrophages able to carry out phagocytosis decreases very significantly. When the incompatibilities, however, are due to the left half of the H-2 system or to minor histocompatibility antigens, such an inhibition does not appear.     

Hemolymph cells of fleas and their phagocytic activity

The present paper concerns 4 groups of haemolymph cells of fleas (proleukocytes, leukocytes, trophic cells and oenocytoids), results of observations on their phagocytic activity during parenteral infection of insects with bacteria, bacilli, and cells' response to the infection with Microsporidia.     

Effect of orexin-A on phagocytic activity of peritoneal macrophage in starved rats

The aim of this study was to investigate the effect of fasting-induced orexin-A (OXA) on inflammation and macrophage phagocytic activity. Fifty six male wistar rats were fasted for 36 h to stimulate OXA synthesis. In 24 rats, air pouches were induced subcutaneously in the intrascapular area. After (6 h) carrageenan injection into the pouches, the contents of the air pouches were removed. The exudate volume, protein content and cell count were measured. After the determination of fasting on inflammation, the peritoneal macrophages were collected from 32 rats to investigate the effect of fasting-induced OXA on macrophage phagocytic activity. Plasma OXA levels were markedly higher in fasted rats compared with control rats. The phagocytic capability of peritoneal macrophages was obtained as a percentage of phagocytosing macrophages and number of phagocytosed particles per cell. In spite of increased blood OXA level SB-334867, selective orexin type 1 receptor antagonist (10 mg/kg) did not change phagocytic activity of peritoneal macrophages. These findings indicate that 36 h fasting-induced OXA has no significant effect to phagocytosis of peritoneal macrophages.     

Augmentation of macrophage growth-stimulating activity of lipids by their peroxidation

Previously, we reported that some kinds of lipids (cholesterol esters, triglycerides, and some negatively charged phospholipids) that are constituents of lipoproteins or cell membranes induce growth of peripheral macrophages in vitro. In this paper, we examined the effect of peroxidation of lipids on their macrophage growth-stimulating activity because lipid peroxidation is observed in many pathological states such as inflammation. When phosphatidylserine, one of the phospholipids with growth-stimulating activity, was peroxidized by UV irradiation, its macrophage growth-stimulating activity was augmented in proportion to the extent of its peroxidation. The activity of phosphatidylethanolamine was also increased by UV irradiation. On the other hand, phosphatidylcholine or highly unsaturated free fatty acids, such as arachidonic acid and eicosapentaenoic acid, did not induce macrophage growth irrespective of whether they were peroxidized. The augmented activity of UV-irradiated phosphatidylserine was not affected by the coexistence of an antioxidant, vitamin E or BHT. These results suggest that some phospholipids included in damaged cells or denatured lipoproteins which are scavenged by macrophages in vivo may induce growth of peripheral macrophages more effectively when they are peroxidized by local pathological processes.     

Intracellular glutathione status regulates mouse bone marrow monocyte-derived macrophage differentiation and phagocytic activity

Although a redox shift can regulate the development of cells, including proliferation, differentiation, and survival, the role of the glutathione (GSH) redox status in macrophage differentiation remains unclear. In order to elucidate the role of a redox shift, macrophage-like cells were differentiated from the bone marrow-derived monocytes that were treated with a macrophage colony stimulating factor (M-CSF or CSF-1) for 3 days. The macrophagic cells were characterized by a time-dependent increase in three major symptoms: the number of phagocytic cells, the number of adherent cells, and the mRNA expression of c-fms, a M-CSF receptor that is one of the macrophage-specific markers and mediates development signals. Upon M-CSF-driven macrophage differentiation, the GSH/GSSG ratio was significantly lower on day 1 than that observed on day 0 but was constant on days 1-3. To assess the effect of the GSH-depleted and -repleted status on the differentiation and phagocytosis of the macrophages, GSH depletion by BSO, a specific inhibitor of the de novo GSH synthesis, inhibited the formation of the adherent macrophagic cells by the down-regulation of c-fms, but did not affect the phagocytic activity of the macrophages. To the contrary, GSH repletion by the addition of NAC, which is a GSH precursor, or reduced GSH in media had no effect on macrophage differentiation, and led to a decrease in the phagocytic activity. Furthermore, we observed that there is checkpoint that is capable of releasing from the inhibition of the formation of the adherent macrophagic cells according to GSH depletion by BSO. Summarizing, these results indicate that the intracellular GSH status plays an important role in the differentiation and phagocytosis of macrophages.     

Monocyte and macrophage heterogeneity

Heterogeneity of the macrophage lineage has long been recognized and, in part, is a result of the specialization of tissue macrophages in particular microenvironments. Circulating monocytes give rise to mature macrophages and are also heterogeneous themselves, although the physiological relevance of this is not completely understood. However, as we discuss here, recent studies have shown that monocyte heterogeneity is conserved in humans and mice, allowing dissection of its functional relevance: the different monocyte subsets seem to reflect developmental stages with distinct physiological roles, such as recruitment to inflammatory lesions or entry to normal tissues. These advances in our understanding have implications for the development of therapeutic strategies that are targeted to modify particular subpopulations of monocytes.     

Translocation of VP1686 upregulates RhoB and accelerates phagocytic activity of macrophage through actin remodeling

Here, we report that Vibrio parahaemolyticus induces a rapid remodeling of macrophage actin and activates RhoB GTPase. Mutational analysis revealed that the effects depend on type III secretion system 1 regulated translocation of a V. parahaemolyticus effector protein, VP1686, into the macrophages. Remodeling of actin is shown to be necessary for increased bacterial uptake followed by initiation of apoptosis in macrophages. This provides evidence for functional association of the VP1686 in triggering an eat-me-and-die signal to the host.     

ICAM-1 facilitates alveolar macrophage phagocytic activity through effects on migration over the AEC surface

We postulate that intercellular adhesion molecule-1 (ICAM-1) on type I alveolar epithelial cells (AEC) facilitates phagocytic activity of alveolar macrophages (AM) in the alveolus. When wild-type and ICAM-1-deficient mice were inoculated intratracheally with FITC-labeled microspheres, AM phagocytosis of beads (after 1 and 4 h) was significantly reduced in ICAM-1-/- mice compared with controls. To focus on ICAM-1-mediated interactions specifically involving AM and AEC, rat AM were placed in culture with rat AEC treated with neutralizing anti-ICAM-1 F(ab')(2) fragments. Blocking ICAM-1 significantly decreased the AM phagocytosis of beads. Planar chemotaxis of AM over the surface of AEC was also significantly impaired by neutralization of AEC ICAM-1. ICAM-1 in rat AEC is associated with the actin cytoskeleton. Planar chemotaxis of AM was also significantly reduced by pretreatment of the AEC monolayer with cytochalasin B to disrupt the actin cytoskeleton. These studies indicate that ICAM-1 on the AEC surface promotes mobility of AM in the alveolus and is critically important for the efficient phagocytosis of particulates by AM.     

Photo-enhancement of macrophage phagocytic activity via Rac1-mediated signaling pathway: Implications for bacterial infection

Phagocytosis and the subsequent destruction of invading pathogens by macrophages are indispensable steps in host immune responses to microbial infections. Low-power laser irradiation (LPLI) has been found to exert photobiological effects on immune responses, but the signaling mechanisms underlying this photobiomodulation of phagocytosis remains largely unknown. Here, we demonstrated for the first time that LPLI enhanced the phagocytic activity of macrophages by stimulating the activation of Rac1. The overexpression of constitutively activated Rac1 clearly enhanced LPLI-induced phagocytosis, whereas the overexpression of dominant negative Rac1 exerted the opposite effect. The phosphorylation of cofilin was involved in the effects of LPLI on phagocytosis, which was regulated by the membrane translocation and activation of Rac1. Furthermore, the photoactivation of Rac1 was dependent on the Src/PI3K/Vav1 pathway. The inhibition of the Src/PI3K pathway significantly suppressed LPLI-induced actin polymerization and phagocytosis enhancement. Additionally, LPLI-treated mice exhibited increased survival and a decreased organ bacterial load when challenged with Listeria monocytogenes, indicating that LPLI enhanced macrophage phagocytosis in vivo. These findings highlight the important roles of the Src/PI3K/Vav1/Rac1/cofilin pathway in regulating macrophage phagocytosis and provide a potential strategy for treating phagocytic deficiency via LPLI.     

Stimulation of phagocytic function by factors inhibiting leukocyte and macrophage migration in humans

Fractions containing macrophage migration inhibition factor (MIF) and leucocyte migration inhibition factor (LIF) were obtained using Sephadex G-200 filtration from supernatant fluids of human lymphocyte cultures stimulated by PHA. The fractions were tested for the ability to affect migration and phagocytic activity of target cells. Peripheral blood leucocyte migration capacity was inhibited by the fraction with the molecular mass of 60,000-70,000 D (LIF), while migration activity of mouse peritoneal exudate cells was suppressed by the fraction with the molecular mass of 20,000-30,000 D (MIF). MIF- and LIF-containing fractions increased almost three-fold Fc-receptor-mediated phagocytic activity of neutrophils.     

A macrophage receptor for (mannose/glucosamine)-glycoproteins of potential importance in phagocytic activity

Lung macrophages, in the absence of serum factors in vitro, strongly bound and ingested yeast cells ($\text{Candida}\text{krusei}$ and zymosan). Binding was temperature-and calcium-dependent, and was inhibited by the presence of D-mannose, D-glucosamine, horseradish peroxidase and beta-glucuronidase. Pretrypsinization of the macrophages also prevented binding of yeast cells. Binding was not affected by D-mannitol, D-glucose, D-galactose nor L-fucose. I suggest that macrophage binding of yeast cells is mediated by a mannose/glucosamine receptor on the cell membrane. This receptor may be responsible for opsosin-independent phagocytosis of activators of the alternative complement pathway and, as well, the phagocyte-dependent clearance of certain lysosomal enzymes.     

Electrophysiology of phagocytic membranes: intracellular K+ activity and K+ equilibrium potential in macrophage polykaryons

The role of K⁺ as current carrier during the slow membrane hyperpolarizations (SH) elicited by iontophoretic Ca²⁺ injections into macrophage polykaryons is studied. The intracellular K⁺ activity (a_K) and the K⁺ equilibrium potential (E_K) are measured using ion-sensitive microelectrodes. The mean value of a_K is 84 ± 5 mM in a culture medium containing 5.3 mM K⁺, but increases to 100 ± 8 mM when the extracellular K⁺ concentration is raised to 30.3 mM. Under the same conditions the values of E_K obtained from the Nernst equation are −81 ± 2 mV and −40 ± 2 mV, respectively. The reversal potentials (E_R) of the SH are calculated from changes observed in transmembrane potential and input resistance, according to an equivalent model based only on passive ionic fluxes. The mean E_R values obtained are −74 ± 8 mV in the presence of low K⁺ concentration and −37 ± 3 mV for the high K⁺ medium. These values are significantly smaller than the estimated E_K for the corresponding situations. Evidence for the existence of an electrogenic (Na⁺ + K⁺)-ATPase activity is also presented. The evidence indicates that an increase in the membrane potassium permeability can account for about 90% of the total permeability change occurring during the SH.     

Identification of two macrophage populations by flow cytometry monitoring of oxidative burst and phagocytic functions

Two populations of phagocytic cells from trehalose dimycolate-elicited mouse peritoneal cells are demonstrated by flow cytofluorometry, using two fluorescent probes excited at the same wavelength (488 nm). Liposomes containing diethylenetriaminepentaacetate daunorubicin conjugate (maximum emission wavelength: 590 nm) allow the discrimination of phagocytes and non-phagocytic cells. Among the phagocytes, an activated population is revealed by a cell-associated fluorescence of the oxidation product of dichlorofluorescein diacetate (maximum emission wavelength: 520 nm).     

Anti-interferon globulin inhibits macrophage phagocytic enhancement in vivo by tilorone or Newcastle disease virus

Administration of the interferon inducers tilorone or Newcastle disease virus to mice enhances the in vitro uptake of opsonized erythrocytes (EA) by peritoneal macrophages. To evaluate the role of induced interferon (IF) in the macrophage stimulation, sheep anti-IF, or control globulins were given to mice prior to and after the administration of the inducers. Both IF titers and uptake of EA by macrophages were reduced by anti-IF but not by control globulin. In contrast, phagocytic stimulation by a lipopolysaccharide, a weak IF inducer, was unaffected by the anti-IF globulin. The results indicate that endogenously generated type I IF may participate in the control of macrophage function in vivo.