NR8383 Cells Research Articles

Characterization of a rat alveolar macrophage cell line that expresses a functional mannose receptor.

The mannose receptor is a single polypeptide transmembrane glycoprotein expressed on the surface of macrophages that binds and internalizes soluble and particulate ligands. Physiological ligands for this receptor are pathogens, such as mycobacteria, and extracellular acid hydrolases and peroxidases. Expression of the mannose receptor is tightly linked to the functional state of the macrophage: the receptor appears during differentiation, is increased by macrophage deactivating agents, and is reduced in the presence of macrophage activating agents. Studies of the mechanisms underlying these regulatory processes have been hampered by the lack of a stable cell line that expresses a functional and appropriately regulated mannose receptor. In this study we describe expression and modulation of the mannose receptor by the rat alveolar cell line NR8383. Similar amounts of the mannose receptor ligand horseradish peroxidase were internalized by both NR8383 cells and alveolar macrophages. In addition, NR8383 cells expressed immunoreactive mannose receptor protein and mannose receptor mRNA as detected by Northern analysis. Regulation studies showed that mannose receptor expression was regulated at the levels of activity, protein, and mRNA in NR8383 cells similarly to regulation in primary rat macrophages. In addition, NR8383 cells could be successfully transfected with a luciferase reporter gene, providing the transfectable, mannose receptor-positive macrophage cell line. These results support the hypothesis that NR8383 cells potentially represent the best current macrophage cell line for studying various aspects of macrophage function, and are particularly critical in studies of regulation of the mannose receptor, a key receptor in host defense and immune regulation.

Activation of rat macrophages by Betafectin PGG-glucan requires cross-linking of membrane receptors distinct from complement receptor three (CR3).

PGG-glucan (Betafectin) is a soluble, highly purified yeast (1,3)-beta-glucan with broad anti-infective and immunomodulatory activities. These studies evaluated the ability of PGG-glucan to directly elicit O2- and tumor necrosis factor alpha (TNF-alpha) production by rat leukocytes in vitro. Particulate beta-glucan stimulated O2- production by the rat NR8383 alveolar macrophage cell line and resident rat peritoneal macrophages, but soluble PGG-glucan did not. In contrast, presentation of PGG-glucan to cells after covalent immobilization to a plastic surface caused a direct stimulation of O2- and TNF-alpha production. The O2- response of rat leukocytes to immobilized PGG-glucan was inhibited by soluble PGG-glucan, indicating that cellular responses to both immobilized and soluble PGG-glucan occur via common cell surface receptors. Because complement receptor type three (CR3) has been proposed as a beta-glucan receptor on human leukocytes, NR8383 cells were evaluated for the presence of CR3. Indirect immunofluorescence and flow cytometric analysis showed that despite being responsive to both particulate and immobilized beta-glucans, NR8383 cells expressed no detectable CR3. These results indicate that the beta-glucan receptors on NR8383 cells are not CR3 and suggest that physical presentation plays an important role in inducing pro-inflammatory leukocyte responses to PGG-glucan.

Alveolar macrophage cell line is not activated by exposure to polymeric microspheres

An in vitro cell culture model based on a rat alveolar macrophage (AM) cell line, NR8383, was used to determine if poly( l-lactide) (PLA) microspheres prepared by the precipitation with a compressed antisolvent (PCA) method can be taken up by AMs and activate AMs. To examine cellular uptake of microspheres, microspheres were labeled with rhodamine 6G. Using fluorescence microscopy, the uptake of microspheres by NR8383 cells was followed as a function of time, microsphere concentration, and susceptibility to lysosomotropic agents. To determine if microspheres can activate NR8383 cells, the oxidative burst and production of TNF- α by NR8383 cells following microsphere treatment was measured. Uptake of microspheres by NR8383 cells was dependent on microsphere concentration and appeared to occur via endocytosis, as uptake was significantly inhibited by the putative lysosomotropic agents, ammonium chloride and chloroquine. Furthermore, the microspheres do not appear to activate NR8383 cells, since microsphere exposure results in negligible oxidative burst and TNF- α production in NR8383. Microspheres prepared by the PCA method hold great potential in targeting drugs to AMs and, therefore, may be of utility for the treatment of diseases in which AMs play an important role, such as tuberculosis (TB).

Effect of melatonin on activated macrophage TNF, IL-6, and reactive oxygen intermediates.

Melatonin has recently been investigated as a biological response modifier in sepsis and hypovolemic shock. Although melatonin is reported to influence a variety of inflammatory and immune responses, evidence supporting its effects on important macrophage-derived mediators is incomplete. This study was designed to determine whether melatonin alters the release TNF, IL-6, and reactive oxygen intermediates by activated macrophages. TNF and IL-6 bioactivity in LPS-stimulated Wistar rat alveolar macrophage and RAW 264.7 cell culture supernatants were unchanged by pretreatment with melatonin. Similarly, macrophage production of reactive oxygen intermediates, including H2O2 and superoxide anion, were unaffected by melatonin pretreatment. PMA-stimulated H2O2 production was determined in rat alveolar macrophages and RAW 264.7 cells. Superoxide anion generation was determined in the rat alveolar macrophage NR8383 cell line. Melatonin, at concentrations ranging from 10(-7) to 10(-4) M, does not alter LPS-stimulated TNF and IL-6, or PMA-stimulated H2O2 and superoxide anion production by the macrophage populations studied. These observations are in contrast to previous reports. Further studies are necessary to determine whether melatonin indirectly influences macrophage function by actions on nonmacrophage cell populations.

Functional characterization of recombinant rat macrophage inflammatory protein-1 alpha and mRNA expression in pulmonary inflammation.

Chemokines are important inflammatory mediators that function by activating and recruiting leukocytes to an inflamed tissue. We have recently cDNA cloned the rat chemokine macrophage inflammatory protein-1 alpha (MIP-1 alpha) (1). In the present study, we characterize the biological function of recombinant MIP-1 alpha protein and describe expression of its mRNA both in vitro and in a rat model of lung inflammation. In vitro rat rMIP-1 alpha protein was chemotactic for both polymorphonuclear leukocytes (PMNs) and macrophages with maximal activity at 50 nM for both cell types. In in vivo studies, we found that intratracheal instillation of 1 and 5 micrograms of rMIP-1 alpha resulted in a significant (P < 0.05) influx of cells, primarily monocytes/macrophages, into the airspace of the lungs after 6 h. Mean numbers of lavagable PMNs were not elevated significantly (P < 0.05) for either dose of MIP-1 alpha. As a model of inflammation, rats were intratracheally instilled with 0.1 mg/kg bacterial lipopolysaccharide (LPS). Bronchoalveolar lavage (BAL) was performed 3 h later. Instillation of LPS resulted in an acute neutrophilia, but no significant change in lavagable macrophages. BAL cells from control animals (saline instilled) displayed no basal mRNA expression of either MIP-1 alpha or MIP-2 (positive control). In contrast, both MIP-1 alpha and MIP-2 mRNA levels increased markedly in BAL cells from rats instilled with LPS. The rat alveolar macrophage cell line (NR8383) also showed increased MIP-1 alpha mRNA levels in response to LPS (10 micrograms/ml) with a maximal increase after 6-8 h. The induction of MIP-1 alpha mRNA expression by LPS in NR8383 cells was attenuated by cotreatment with the antioxidants N-acetylcysteine and dimethylsulfoxide, suggesting that the induction of MIP-1 alpha mRNA by LPS is mediated via the generation of reactive oxygen species. We conclude that MIP-1 alpha is a potent chemoattractant for macrophages in vivo, and its mRNA expression in macrophages and BAL cells in response to inflammatory stimuli suggests a fundamental role in acute pulmonary inflammation.

Regulation of cytosolic free Ca2+ in cultured rat alveolar macrophages (NR8383)

Ca2+ mobilization in the rat alveolar macrophage cell line NR8383 was examined with the Ca2+-sensitive fluorescent probe Fura-2. ATP and norepinephrine elicited a 108 and 46% increase, respectively, in cytosolic free Ca2+ concentration ([Ca2+]i). Acetylcholine, nicotine, isoproterenol, substance P, and vasoactive intestinal polypeptide did not alter [Ca2+]i. Inositol 1,4,5-trisphosphate (IP3) formation was also activated by ATP. The carbohydrate-rich cell wall preparation, zymosan, induced a gradual [Ca2+]i, increase only in the presence of external Ca2+, but did not activate IP3 formation. This increase was abolished by laminarin and by removal of extracellular Ca2+, suggesting that the [Ca2+]i increase was activated by beta-glucan receptors and mediated by Ca2+ influx. This influx was significantly reduced by SKF96365, but not by nifedipine, (omega-conotoxin GVIA, (omega-agatoxin IVA, or flunarizine. These results suggest that release of intracellular Ca2+ in NR8383 cells is regulated by P2-purinoceptors and that zymosan causes Ca2+ influx via a receptor-operated pathway.

Serotype-dependent induction of pulmonary neutrophilia and inflammatory cytokine gene expression by reovirus.

Reovirus type 3 Dearing (T3D) causes a prominent neutrophil influx, substantially greater than seen with reovirus type 1 Lang (T1L) in a rat model of viral pneumonia. We sought to measure reovirus-mediated increases in chemokine mRNA expression in pulmonary cells. We found that the neutrophilia induced by T1L and T3D infection in vivo correlated directly with increased levels of chemokine mRNA expression in T3D-infected compared with those of T1IL-infected lungs. In vitro, reovirus-infected normal alveolar macrophages (AMs) and the rat AM cell line NR8383 expressed greater levels of macrophage inflammatory protein 2, KC, and tumor necrosis factor alpha mRNA. A synergism between reovirus and lipopolysaccharide was also detected for macrophage inflammatory protein 2 and KC mRNA expression. Tumor necrosis factor protein secretion was also increased to a greater extent by T3D than by T1L in primary rat AMs and the NR8383 cells. We conclude that the virus-mediated inflammatory cytokine induction suggests a role for these cytokines in the neutrophil influx observed in the rat reovirus pneumonia model.

The effects of cyclosporine and dexamethasone on an alveolar macrophage cell line (NR8383).

Lung infections are a major source of morbidity and mortality in recipients of lung transplants. Prominent among the pathogens that cause pneumonias in these subjects are gram-negative bacilli, particularly Pseudomonas strains. One important reason that bacteria infect the lungs of these patients is that pulmonary defenses are impaired by the drugs used to prevent transplant rejection. Using a rat alveolar macrophage cell line (NR8383), we measured the effects of exposure (24 hr) to cyclosporine and dexamethasone (DEX) on the ability of these cells to (1) kill Pseudomonas aeruginosa (Pa); (2) produce H2O2; and (3) release tumor necrosis factor. We found that the bactericidal activity against unopsonized or opsonized Pa of NR8383 cells was unaltered by CsA (0.1, 0.5, or 1 micrograms/ml), DEX (10(-6) M), or CsA + DEX (0.5 micrograms/ml + 10(-6) M, respectively). Likewise, LPS-induced TNF release, and zymosan A and Pa-induced H2O2 production were unaltered by CsA (0.1 or 1 microgram/ml). In contrast, H2O2 production and TNF release were decreased by about 50% and 90%, respectively, by DEX exposure (10(-6) M). Thus, while DEX but not CsA decreased TNF release and H2O2 production in NR8383 cells, bactericidal activity against Pa was unaffected. One explanation for these results is that decreases in TNF or H2O2 of the magnitude we observed do not impair bactericidal activity against Pa; however, an alternative explanation is that Pa are killed by NR8383 cells through other mechanisms. Interpretation of these results must take into consideration the fact that macrophages from different species and tissues may respond differently to various stimuli.

Resistance of mucoid Pseudomonas aeruginosa to nonopsonic phagocytosis by alveolar macrophages in vitro.

A unique, recently described rat alveolar macrophage cell line (NR8383) was used to study the interaction of the pulmonary immune system with a mucoid cystic fibrosis isolate of Pseudomonas aeruginosa (SRM-3), its nonmucoid revertant (SRM-3R), and a non-cystic fibrosis isolate (PAO-1). Strain SRM-3 was cultivated in a chemostat system to allow maintenance of an entirely mucoid population. The alveolar macrophage response to the mucoid and nonmucoid strains of P. aeruginosa was determined by visually quantitating phagocytosis in acridine orange-stained monolayers and measuring the induction of an oxidative burst as indicated by chemiluminescence and H2O2 production. In all experiments, fewer than 2% of the NR8383 cells engulfed the mucoid SRM-3 isolate, while SRM-3R and PAO-1 were phagocytized by 15 and 41%, respectively. Opsonization by normal serum (complement) provided minimal phagocytic enhancement of these strains, whereas specific anti-P. aeruginosa antibody slightly elevated phagocytic responses to strains with nonmucoid phenotypes while providing a sevenfold increase in uptake of SRM-3. Chemiluminescent and H2O2 responses were comparable with the levels of phagocytosis observed, with very little or no response to the mucoid strain SRM-3. The data indicate that the strains with mucoid phenotypes are refractile to ingestion and that studies which describe ingestion of mucoid strains were likely measuring ingestion of revertants. Alginic acid (2 mg/ml) was found to inhibit stimulation of macrophage response to the opsonized and unopsonized nonmucoid strain PAO-1.