Murine Bone Marrow Macrophages Research Articles

Interleukin 4, interferon-gamma, and prostaglandin E impact the osteoclastic cell-forming potential of murine bone marrow macrophages.

Interleukin 4 (IL-4) is an immune cytokine that inhibits bone resorption in mice and suppresses osteoclastic cell formation in vitro through an undefined mechanism. In this report, we have established the cellular identity of the IL-4 target cell using a variety of bone marrow/stromal cell coculture methods. Initially, we found that the majority of IL-4's inhibition of osteoclastic cell formation was due to its effect on bone marrow cells, not stromal cells. Consequently, bone marrow macrophages were used as osteoclastic cell progenitors after they had been transiently exposed to IL-4 (48 h), before the addition of stromal cells, 1,25-dihydroxyvitamin D3, and dexamethasone. In this circumstance, IL-4 impaired subsequent osteoclastic cell formation, suggesting that the macrophage may be potentially targeted by many factors known to influence osteoclast formation. Consequently, we discovered that interferon-gamma (IFN gamma), prostaglandin E (PGE), and cell-permeant cAMP analogs also impacted osteoclastic cell formation when used to selectively treat bone marrow macrophages. IFN gamma suppressed osteoclastic cell formation, whereas PGE and cAMP analog treatment led to the formation of significantly enlarged osteoclastic cells. Importantly, PGE antagonized the inhibitory effects of both IL-4 and IFN gamma on the osteoclastic cell-forming potential of bone marrow macrophages. Collectively, these findings establish bone marrow macrophages as osteoclastic cell precursors with the degree of their commitment to the osteoclast pathway sensitive to the effects of soluble mediators, including IL-4, IFN gamma, and PGE.

Rabies virus replication in primary murine bone marrow macrophages and in human and murine macrophage-like cell lines: implications for viral persistence.

To determine whether rabies viruses replicate in macrophage or macrophage-like cells, several human and murine macrophage-like cell lines, as well as primary cultures of murine bone marrow macrophages, were incubated with the Evelyn-Rokitnicki-Abelseth (ERA) virus and several different street rabies viruses (SRV). ERA rabies virus replicated well in human monocytic U937 and THP-1 cells and murine macrophage IC-21 cells, as well as primary cultures of murine macrophages. Minimal replication was detected in murine monocytic WEHI-3BD- and PU5-1R cells, and ERA virus did not replicate in murine monocytic P388D1 or J774A.1 cells. A tissue culture-adapted SRV of bat origin also replicated in IC-21 and U937 cells. Non-tissue culture-adapted SRV isolated from different animal species, particularly bats, replicated minimally in U937, THP-1, IC-21 cells and primary murine bone marrow macrophages. To determine whether rabies virus replication is dependent upon the state of differentiation of the macrophage-like cell, human promyelocytic HL-60 cells were differentiated with 12-O-tetradecanoylphorbol-13-acetate (TPA). ERA rabies virus replicated in the differentiated HL-60 cells but not in undifferentiated HL-60 cells. Persistent infections were established in macrophage-like U937 cells with ERA rabies virus and SRV, and infectious SRV was isolated from adherent bone marrow cells of mice that had been infected 96 days previously. Virus harvested from persistently infected U937 cells and the adherent bone marrow cells had specifically adapted to each cell. This specificity was shown by the inability of the viruses to infect macrophages other than U937 cells and primary bone marrow macrophages, respectively. Virus titers of the persistently infected U937 cells fluctuated with extended cell passage. After 30 passages, virus released from the cells had lost virulence as shown by its inability to kill intracranially inoculated mice. However, the avirulent virus released from the persistently infected cells was more efficient in infecting and replicating in naive U937 cells than the virus which was used to establish the persistent infection. These results suggest that macrophages may serve as reservoirs of infection in vivo, sequestering virus which may subsequently be activated from its persistent state, resulting in clinical infection and death.

Prostaglandin E 2 induces up-regulation of murine macrophage β-endorphin receptors

Cultured murine bone marrow macrophages specifically bound 125I-labeled β-endorphin. Binding was displaceable by 100 times molar excess of full-length β-endorphin but was insensitive to the opioid receptor antagonist, naloxone. Binding was inhibited by β-endorphin's C-terminal tetrapeptide, lys-lys-gly-glu, but not by the truncated N-terminal 27 amino acid fragment, indicating that binding of β-endorphin to this receptor is dependent on its C-terminus. Macrophages incubated for 24 h with 10 −8–10 −5 M prostaglandin E 2 showed a dose-dependent increase in β-endorphin binding, implying receptor up-regulation. This was also observed in response to the phosphodiesterase inhibitor, isobutylmethylxanthine, indicating that regulation of these receptors may be mediated through a cAMP-dependent process. This is the first demonstration that β-endorphin receptor expression can be positively regulated.

Chapter 15: Immunoelectron Microscopy of Endosomal Trafficking in Macrophages Infected with Microbial Pathogens

This chapter discusses immunoelectron microscopy of endosomal trafficking in macrophages infected with microbial pathogens. Immunoelectron microscopy provides a powerful tool for the elucidation of intracellular trafficking pathways that can either deliver or remove material from the microbe-containing vacuole. The results provide information about the relative position of the compartment within the endosomal network and the extent to which the pathogen has induced “aberrant” behavior in its host vacuole. This chapter outlines some approaches that have been used for the analysis of murine bone marrow macrophages infected with either Leishmania or Mycobacterium. The relative pathogenicity of the microbe to its host cell must be considered in the design of these experiments. Both Leishmania and Mycobacterium form extremely stable interactions with the host cell, and it is feasible to establish longer-term experiments examining infections from the point of initial infection up to two weeks later. The biotin–streptavidin interaction is examined to detect the trafficking of a range of different ligands or fluid phase markers in infected macrophages.

The specific recognition by macrophages of CD8+,CD45RO+ T cells undergoing apoptosis: a mechanism for T cell clearance during resolution of viral infections.

During viral infections, CD8+,CD45RO+ T populations expand. These primed cells express abundant levels of cytoplasmic granules that contain perforin and TIA-1. Recent work has suggested that the majority of this CD8+ population downregulates Bcl-2 protein expression and is destined to undergo apoptosis. In this study we have investigated the elimination of these apoptotic CD8+ T cells by both human monocyte-derived and murine bone marrow macrophages. We have found that these phagocytes recognize and ingest both apoptotic CD8+ and CD4+ T cells using an alpha v beta 3 (vitronectin receptor)/CD36/thrombospondin recognition system, with the same receptors being used in the recognition of apoptotic neutrophils. These data provide new evidence for a mechanism that enables the clearance of greatly increased populations of CD8+ effector cells which are found during viral infections. This enables cellular homeostasis to occur in the host upon resolution of viral diseases in vivo.

Presentation of exogenous antigens by macrophages: analysis of major histocompatibility complex class I and II presentation and regulation by cytokines

There is an antigen presenting cell (APC) in the lymphoid organs capable of presenting exogenous antigen (Ag) with major histocompatibility complex (MHC) class I molecules. This study was initiated to isolate clones of these APC to definitively establish their phenotype and to further study their properties. Murine bone marrow macrophages (BM M psi) were immortalized by overexpression myc and raf oncogenes. Five BM M psi cell lines were generated that are phagocytic and expressed at their surface M psi differentiation Ag. All five cell lines processed and presented exogenous ovalbumin (OVA) with MHC class I molecules. They all presented OVA-linked to a phagocytic substrate 10(2)-10(4)-fold more efficiently than soluble Ag. Clonal isolates of two of the M psi cell lines had an identical phenotype and functional properties as the uncloned lines. These results definitively establish that M psi are APC with the capacity of presenting exogenous Ag with MHC class I molecules. Interferon (IFN)-gamma interleukin-4, granulocyte-macrophage colony stimulating factor and lipopolysaccharide either alone or in combination induced little or no augmentation and in some cases decreased presentation of exogenous OVA with MHC class I. In contrast, all of M psi activating factors increased MHC class I expression. Moreover, IFN-gamma increased the presentation of cytosolic OVA, demonstrating differences between the presentation of cytosolic Ag versus exogenous Ag with MHC class I. Finally, some lines constitutively processed and presented exogenous OVA with MHC class II while others only presented after stimulation with IFN-gamma. These results demonstrate that the pathways involved in the presentation of exogenous Ag with MHC class I and class II are independently regulated and that a cloned cell is capable of presenting exogenous Ag through both pathways.

Production and action of cytokines in space

B6MP102 cells, a continuously cultured murine bone marrow macrophage cell line, were tested for secretion of tumor necrosis factor-α and Interleukin-1 during space flight. We found that B6MP102 cells secreted more tumor necrosis factor-α and interleukin-1 when stimulated in space with lipopolysaccharide than controls similarly stimulated on earth. This compared to increased secretion of interferon-beta and -gamma by lymphocytes that was measured on the same shuttle flights. Although space flight enhanced B6MP102 secretion of tumor necrosis factor-α, an experiment on a subsequent space flight (STS-50) found that cellular cytotoxicity, mediated by tumor necrosis factor-α, was inhibited.

IL-7 stimulates CSF-induced proliferation of murine bone marrow macrophages and Mac-1+ myeloid progenitors in vitro.

The role of IL-7 as an important stimulator of the growth of B and T cell precursors, as well as mature T cells, is well established. In contrast, the role of IL-7 in myelopoiesis has not been characterized thoroughly, and thus, IL-7 has been regarded as a lymphoid lineage-restricted cytokine. However, we have recently reported that IL-7 enhanced CSF-induced myeloid proliferation of primitive murine hematopoietic (Lin-Sca-1+) progenitors, whereas IL-7 did not affect significantly the proliferation of a population of more mature (Lin-) progenitors. The present study was initiated to investigate further whether IL-7 might affect CSF-induced proliferation of subpopulations of committed myeloid progenitors as well as mature bone marrow macrophages. IL-7 enhanced macrophage colony-stimulating factor (CSF-1)-induced colony formation of single bone marrow macrophages 90%, whereas IL-7 alone had no effect. Furthermore, IL-7, in a concentration-dependent manner, increased the proliferation of mononuclear cells expressing the Mac-1 Ag (Mac-1+ mononuclear cells (MNC); CD11b) up to fivefold in response to CSF-1, granulocyte macrophage-CSF (GM-CSF), or IL-3. In contrast, no effect of IL-7 was observed on Mac-1- MNC. The synergistic effect of IL-7 on Mac-1+ MNC was caused by an increase in macrophage colonies (CFU-M) and mixed granulocyte-macrophage colonies (CFU-GM), whereas the total number of granulocyte colonies (CFU-G) was not affected. This suggests that IL-7 can provide proliferative signals to Mac-1+ progenitors with a macrophage potential, but not to progenitors committed to pure granulocyte differentiation.

CSF‐1 stimulates nucleoside transport in S1 macrophages

We have examined nucleoside transport (NT) in a cell line derived from primary day 7 murine bone marrow macrophages (S1 macrophages) in response to the macrophage growth factor, colony-stimulating factor 1 (CSF-1). Adenosine and uridine transport in quiescent S1 macrophages occurred primarily by two facilitated diffusional routes, one that was sensitive and one that was relatively resistant to the inhibitor nitrobenzylthioinosine (NBMPR). Addition of CSF-1 to quiescent cultures resulted in increased adenosine and uridine transport with biphasic kinetics with respect to the cell cycle. Basal NT activity was elevated (about twofold) within 15 min of CSF-1 addition, returned to near basal levels by 1 h, and then increased again (three- to fourfold) 8-12 h later, returning again to basal levels by 48 h post CSF-1 stimulation. We propose that the large increase in NT activity at 8-12 h corresponded with the time when cultures synchronously began to enter the S phase of the cell cycle. In addition to these changes in the absolute rates, the proportions of NBMPR-sensitive and NBMPR-insensitive transport also change after CSF-1 addition. Quiescent cultures exhibited primarily NBMPR-insensitive transport while logrithmically growing cultures exhibited primarily NBMPR-sensitive nucleoside transport activity. The increase in the NBMPR-sensitive component of the transport process paralleled a similar increase in the number of high-affinity NBMPR binding sites, suggesting that the mechanism for upregulating NBMPR-sensitive NT activity involves increases in the number of NBMPR-sensitive transporter sites. Interestingly, we were unable to detect Na(+)-dependent concentrative uptake of adenosine, uridine, or formycin-B either in the S1 macrophage cell line or in primary (day 7) murine macrophages. Thus these bone marrow derived macrophages did not display the characteristically large Na(+)-dependent transport systems observed by others in peritoneal macrophages, implying that these two populations of macrophages are, indeed, functionally distinct.

Regulation of macrophage alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein by lipopolysaccharide and interferon-gamma.

alpha 2-Macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2M-R/LRP) is a broad specificity receptor that may function in lipoprotein metabolism, proteinase regulation, and growth factor regulation. In this study, we demonstrated that alpha 2M-R/LRP expression in macrophages can be markedly decreased by LPS and by IFN-gamma. Regulation of alpha 2M-R/LRP in RAW 264.7 cells was demonstrated at the mRNA, antigen, and receptor-function levels. In receptor-function studies, the decrease in alpha 2M-R/LRP expression was detected as a 90% decrease in the Bmax or maximum receptor binding capacity for activated alpha 2M after treatment with LPS or IFN-gamma. Western blot analysis of whole cell lysates demonstrated significant loss of alpha 2M-R/LRP heavy-chain. Northern blot analysis of poly(A)+ RNA revealed a marked decrease in alpha 2M-R/LRP mRNA after treatment with LPS (79% decrease) or IFN-gamma (70% decrease). Other cytokines, including tumor necrosis factor-alpha, transforming growth factor-beta-1, and interleukin-6 did not regulate alpha 2M-R/LRP. The ability of LPS and IFN-gamma to regulate alpha 2M-R/LRP was confirmed in experiments with primary cultures of murine bone marrow macrophages. These studies demonstrate that macrophage alpha 2M-R/LRP is subject to significant downregulation by physiologically significant cytokines and signaling macromolecules.

Characterization of the ets oncogene family member, fli-1.

The recently cloned fli-1 gene is a member of the ets oncogene family that is preferentially expressed in hematopoietic cells. It is a target of dysregulation by Friend leukemia virus insertion and translocation in Ewing's sarcoma and neuroepithelioma. In this report, we have studied the function and regulation of both murine and human fli-1. Analysis of the human and mouse fli-1 proteins showed that fli-1 binds to specific DNA sequences highly related to m-ets-2 binding sites. Methylation protection experiments showed that fli-1 and m-ets-2 contacted the same nucleotides in two different binding sites. The fli-1 protein was shown to be a transcriptional activator in co-transfection studies. Stimulation of murine bone marrow macrophages by mediators of inflammation, such as lipopolysaccharide, phorbol 12-myristate 13-acetate, interleukin-1, and interferon-gamma resulted in the reduced expression of fli-1 mRNA. fli-1 was only expressed in a defined subset of human erythroleukemia cell lines.

Granulocyte-macrophage colony stimulating factor in autologous bone marrow transplantation: augmentation of graft versus tumor effect via antibody dependent cellular cytotoxicity.

Several immunomodulatory approaches have been explored with the aim of inducing a graft versus tumor effect (GVT) in autologous bone marrow transplantation (ABMT). Granulocyte-macrophage colony stimulation factor (GM-CSF) has been reported to induce antibody dependent cellular cytotoxicity (ADCC) via stimulation of peripheral blood neutrophils, lymphocytes, and monocytes. We investigated the role of GM-CSF in inducing ADCC via bone marrow (BM) macrophages against murine and human tumor cells both in vitro and vivo. Our data shows that stimulation of murine BM macrophages with GM-CSF induced a potent ADCC against a murine melanoma in vitro. Treatment of tumor bearing mice with a combination of GM-CSF and antibody against melanoma resulted in a significant reduction in the dissemination of melanoma both in a nontransplant as well as in a transplantation setting. Adoptive transfer of BM macrophages obtained from animals undergoing treatment with GM-CSF plus antibody significantly reduced the spread of tumor in secondary recipients; this effect was seen only in mice undergoing bone marrow transplantation. GM-CSF treatment of human BM macrophages induced a significant ADCC against a human melanoma and a lymphoma in vitro, as well as against a human lymphoma implanted in nude mice. Treatment with GM-CSF alone or with antibody alone was ineffective in controlling the dissemination of tumors both in transplantation as well as in nontransplant situations. These observations indicate that treatment with GM-CSF plus tumor specific monoclonal antibodies after ABMT may induce a GVT effect and bring about the eradication of residual disease.

Different populations of macrophages use either the vitronectin receptor or the phosphatidylserine receptor to recognize and remove apoptotic cells.

One of the key features associated with programmed cell death in many tissues is the phagocytosis of apoptotic bodies by macrophages. Removal of apoptotic cells occurs before their lysis, indicating that these cells, during the development of apoptosis, express specific surface changes recognized by macrophages. We have compared the mechanisms by which four different macrophage populations recognize apoptotic cells. Murine macrophages elicited into the peritoneal cavity with either of two different phlogistic agents were able to phagocytose apoptotic cells. This phagocytosis was inhibited by phosphatidylserine (PS), regardless of the species (human or murine) or type (lymphocyte or neutrophil) of the apoptotic cell. In contrast, the murine bone marrow macrophage, like the human monocyte-derived macrophage, utilized the vitronectin receptor, an alpha v beta 3 integrin, for the removal of apoptotic cells, regardless of their species or type. That human macrophages are capable, under some circumstances, of recognizing PS on apoptotic cells was suggested by the observation that PS liposomes inhibited phagocytosis by phorbol ester-treated THP-1 cells. These results suggest that the mechanism by which apoptotic cells are recognized and phagocytosed by macrophages is determined by the subpopulation of macrophages studied.

Staphylococcus aureus and derived exotoxins induce nuclear factor kappa B-like activity in murine bone marrow macrophages.

Heat-killed gram-positive Staphylococcus aureus as well as S. aureus-derived exotoxins B and toxic shock syndrome toxin 1 can induce nuclear factor kappa B (NF-kappa B)-like activity in murine bone marrow macrophages. The induction of NF-kappa B-like activity in murine macrophages by S. aureus was as effective as induction by tumor necrosis factor alpha (TNF-alpha) or lipopolysaccharides (LPS) and was observed in macrophages derived from LPS-sensitive and LPS-resistant mice. Stimulation of macrophages with S. aureus but not with the exotoxins resulted in the accumulation of TNF-alpha in the culture medium. The induction of NF-kappa B-like activity by S. aureus, however, clearly preceded TNF-alpha secretion and was not inhibited by a neutralizing serum against TNF-alpha. In addition, pretreatment of macrophages with the protein synthesis inhibitor cycloheximide or dexamethasone, which prevented the secretion of TNF-alpha from macrophages, did not interfere with the induction of NF-kappa B-like activity by S. aureus. This findings reveal the existence of bacterial components other than LPS which can induce NF-kappa B-like activity in susceptible cells.

Characterization and partial purification of a high molecular weight tumoricidal activity secreted by murine bone marrow macrophages.

Cultured murine bone marrow-derived macrophage (BMM phi) can be induced to secrete tumoricidal activity in vitro when activated with recombinant IFN-gamma and bacterial lipopolysaccharide (LPS). We have analyzed this activity for tumor specificity, relationship to tumor necrosis factor-alpha (TNF-alpha), serine proteases, and reactive nitrogen intermediates, and partially purified this activity by high pressure liquid chromatography. Cytolytic activity was recovered in conditioned culture supernatants of serum-free cultivated BMM phi treated with a combination of IFN-gamma and LPS but was not inducible by either stimulant alone. It selectively affected tumor cells of murine as well as human origin irrespective of sensitivity towards recombinant murine TNF-alpha (r-muTNF-alpha), but did not significantly affect non-tumorigenic cells of either species. It was inactivated by 56 degrees C, trypsin, and neuraminidase treatment, but could not be inhibited by neutralizing antibodies against r-muTNF-alpha or serine protease inhibitors. Tumoricidal activity was purified approximately 10-fold by gel filtration and eluted as a major peak with a Mr of 170 kDa, containing a single predominant protein band of approximately 170 kDa on SDS-PAGE analysis, which is shown to be a disulfide linked glycoprotein heterodimer of 110 and 58 kDa subunits (gp170). Expression of this glycoprotein was strongly dependent on activation of BMM phi by a combination of IFN-gamma and LPS but was only marginally induced by either stimulant alone. Furthermore, the level of gp170 expression was quantitatively correlated with the tumoricidal activity of BMM phi culture supernatants, whereas no such correlation was found with respect to the amount of secreted TNF-alpha or reactive nitrogen intermediates. These data demonstrate that activated murine BMM phi secrete a tumoricidal activity, which is not related to TNF-alpha, serine proteases, or reactive nitrogen intermediates, but is closely associated with a 170 kDa glycoprotein composed of two subunits with Mr's of 110 and 58 kDa.

Monomeric IgG2a promotes maturation of bone-marrow macrophages and expression of the mannose receptor.

The macrophage mannose receptor, a 172-kDa lineage-specific glycoprotein, partakes in nonopsonin-mediated phagocytosis by recognition of terminal mannose residues on targeted particles. Because appearance of the receptor progresses with monocyte/macrophage differentiation, its expression is indicative of the maturational state of the cell. Monomeric IgG2a and IgG2b up-regulate mannose-receptor surface expression and biosynthesis by murine bone-marrow macrophage precursors as much as 7- to 12-fold in a dose-dependent manner. IgG2a accelerates macrophage mannose-receptor expression by several days during in vitro bone-marrow differentiation; however, treated and control cells ultimately express equivalent levels of receptor. Moreover, the effect is independent of cell cycle or ambient levels of colony-stimulating factor 1. The coinduction of another maturation-dependent lineage-specific antigen, F4/80, and the fact that macrophage precursors respond to IgG2a only within the first day of culture, indicate that the targeted cell is an early myelomonocytic precursor, responsive only during a short, early developmental window. The effect is specific for immunoglobulin molecules of the IgG2a and IgG2b subclasses and probably involves an Fc gamma-receptor signal-transduction pathway but not macrophage priming or activation. Most importantly, a paracrine mechanism of immunoglobulin-mediated bone-marrow macrophage differentiation is suggested by experiments in which basal levels of mannose-receptor expression are reduced by continual removal of B-cell-generated IgG from marrow cultures. Thus, IgG2a and IgG2b prompt mannose-receptor synthesis and bone-marrow macrophage differentiation and may, therefore, play a role in the regulation of macrophage differentiation in host defense.

IFN-gamma induces the expression of the genes for MHC class II I-A beta and tumor necrosis factor through a protein kinase C-independent pathway.

The mechanism of gene expression for the MHC I-A beta and TNF genes was studied in murine bone marrow macrophages. The treatment of macrophages with PMA stimulated the expression of TNF, but not I-A beta, suggesting that the TNF gene is responsive to activators of protein kinase C whereas the I-A beta gene is not. The treatment of macrophages with IFN-gamma led to an increase in the level of RNA for both TNF and I-A beta. The increase in expression of I-A beta and TNF, induced by IFN-gamma, was blocked by naphthalenesulfonamide or phenothiazine (trifluoperazine) but was not affected by the addition of isoquinolinesulfonamide or sphingosine. These results suggest that the induced expression of I-A beta and TNF by IFN-gamma is mediated by a pathway that is protein kinase C independent. This was supported by the finding that calcium ionophores were also able to induce the gene expression of both TNF and I-A beta. We observed that when both IFN-gamma and PMA were added to the macrophages, the level of RNA for TNF increased to a higher level than the level seen when either agent alone was added to the cells. In contrast, the addition of both IFN-gamma and PMA to macrophages had an inhibitory effect on the expression of the I-A beta gene. These results further emphasize the complex nature of gene regulation during the activation of macrophages.

Uptake of liposomes by cultured mouse bone marrow macrophages: influence of liposome composition and size

A wide range of liposome compositions have previously been examined in vivo for their ability to affect the uptake of liposomes into cells of the reticuloendothelial (RE, mononuclear phagocyte) system (Allen, T.M. and Chonn, A. (1987) FEBS Lett. 223, 42–46; Allen et al. (1989) Biochim. Biophys. Acta 981, 27–35). In this study we have examined the ability of cultured murine bone marrow macrophages to endocytose liposomes of various compositions and have looked for correlations between the in vivo and the in vitro observations. Compounds which substantially decreased RE uptake of liposomes in vivo, such as monosialoganglioside (G M1) and a novel synthetic lipid derivative of polyethyleneglycol (PEG-PE), also greatly decreased liposome uptake by bone marrow macrophages in a concentration-dependent manner. Lipids which increase bilayer rigidity, such as sphingomyelin (SM) and cholesterol (CHOL), decreased both in vivo and in vitro uptake of liposomes. Likewise, positive correlations were observed between the in vivo behavior of liposomes containing phosphatidylserine (PS) or various gangliosides and the ability of these liposomes to be taken up by bone marrow macrophages. Total liposome uptake by macrophages increased with incubation time at 37°C while very little liposome association with the macrophages was observed at 4°C. Liposome uptake increased with liposome concentration and for liposomes composed of egg phosphatidylcholine (PC) uptake plateaued at 40 nmol lipid per mg cell protein. There was an inverse correlation between liposome size of extruded large unilamellar vesicles and their uptake by macrophages.

Macrophages produce somnogenic and pyrogenic muramyl peptides during digestion of staphylococci

Muramyl peptides have a variety of biological effects in mammals, including enhancement of the immune response, sleep, and body temperature. Although mammals lack biosynthetic pathways for muramyl peptides, they are found in mammals and are well known as components of bacterial cell walls. This suggests that phagocytic mammalian cells digest bacterial cell walls and produce biologically active muramyl peptides. Staphylococcal cell walls were radioactively labeled during growth of the bacteria. During the digestion of these radiolabeled bacteria, murine bone marrow macrophages produced low-molecular-weight substances that coeluted chromatographically with the radioactive cell wall marker. Further separation of these substances using reversed-phase high-performance liquid chromatography resulted in the isolation of substances with high specific biological activity. Intracerebroventricular injection of rabbits with these substances induced an increase in slow-wave sleep and body temperature and a suppression of rapid-eye-movement sleep. The characteristics of the biological responses and the chromatographic behavior of the active components are consistent with those of muramyl peptides. The ability of macrophages to tailor muramyl peptides from peptidoglycan may provide an amplification step for the immune response. Muramyl peptides released by macrophages may also act as mediators for various facets of the acute phase response elicited by bacterial infections such as fever and sleep.

Murine bone marrow macrophage colony-forming units response to radiation + 40–42°C: Potential implications for combined total body irradiation and hyperthermia

Murine bone marrow macrophage colony-forming units response to radiation + 40–42°C: Potential implications for combined total body irradiation and hyperthermia