Ultrastructure of pulmonary alveolar macrophages in peroral exposure to nitrosodimethylamine

The data of electron microscopic studies of alveolar macrophages obtained by lung lavage in intact random bred white rats and in rats 3, 12 and 24 hours after a single intraperitoneal administration of nitrosodimethylamine (NDMA) at a toxic dose of 30 mg/kg are presented. It is shown that the activation of macrophages takes place within the first hours after exposure. Later such destructive effects as autolysis, fatty dystrophy, "dark" type destruction, nuclear fragmentation, etc., resulting in cellular death and disintegration can appear. The data obtained can serve the basis for the application of lung alveolar macrophages in estimating the harmful effect of different chemical environmental factors.     

Morphological changes in pulmonary alveolus macrophages as affected by alcohol and nitrosodimethylamine

Comparative electron microscopic studies of lung alveolar macrophage (LAM) ultrastructure (with their surface architectonics) were performed in transmission and scan regimen in 3 groups of animals: in intact rats and in rats 12 and 24 hours after a single intragastric administration of nitrosodimethylamine at a concentration of 30 mg/kg in one case and of 50% ethanol (2 ml per 100 g animal weight) in the other case. The transformation of cytoplasmic excrescences, manifested in their diminution, twisting and fusion resulted in the formation of fold-hilly LAM surface. The data obtained may be used for the elaboration of criteria for the assessment of environmental effects of toxic factors.     

Poly(I):poly(C)-enhanced alveolar and peritoneal macrophage phagocytosis: quantification by a new method utilizing fluorescent beads

Phagocytosis is an important immune function to quantify. This immune response may be modulated by exposure to biological response modifiers or by exposure to pollutants. A new technique for quantifying nonspecific phagocytosis of alveolar and peritoneal macrophages in the same animal has been developed that utilizes fluorescent polystyrene beads. When incorporated into inhalation studies, this technique can be used to determine whether the toxic effect of an inhaled pollutant is local (effect on alveolar macrophages), systemic (effect on peritoneal macrophages), or both local and systemic. This method results in a determination of both the level of phagocytosis (the percentage of phagocytic macrophages) and the macrophage specific activity (the number of beads phagocytized per macrophage). This method also allows a determination of adherence by quantifying the number of particles in contact with, but not phagocytized by, the macrophage. Macrophage preparations were incubated with fluorescent beads for 2 hr and cyto-centrifuged onto a glass slide. Fluorescent beads present on the slide or cell-associated but not ingested by phagocytosis were removed by immersing the slide containing the macrophage preparation in methylene chloride for 15-30 sec. Fluorescent beads ingested by phagocytosis were then easily quantified with a fluorescence microscope. This technique was used to assess the baseline levels of phagocytosis for rat alveolar and peritoneal macrophages from the same animal and the kinetics and level of enhanced phagocytosis for alveolar and peritoneal macrophages after injection with the interferon inducer polyinosinate-polycytidylate (poly(I):poly(C)). The kinetics of enhanced alveolar and peritoneal macrophage phagocytosis by poly(I):poly(C) were similar; however, stimulated phagocytic levels of peritoneal macrophages never reached the phagocytic activity observed for the resident, highly phagocytic alveolar macrophages. This elevated phagocytic activity is most likely due to interferon stimulated by particulate matter in the large volume of air processed by the lungs and is important for host defense against a number of different inhaled microorganisms.     

Hyaluronic acid-degrading enzymes in rat alveolar macrophages and in alveolar fluid: stimulation of enzyme activity after oral treatment with the immunomodulator RU 41740

RU 41740 (Biostim) is an immunomodulator clinically used for the treatment of chronic bronchitis and recurrent pulmonary infections. In these diseases large amounts of mucus are produced which congest the bronchi. A major glycosaminoglycan constituent of this mucus is hyaluronic acid, one of the largest molecules in nature; its metabolic degradation is carried out by 3 acid hydrolases: hyaluronidase, beta-N-acetylglucosaminidase, and beta-glucuronidase. In the lung these enzymes are especially synthesized and active in alveolar macrophages. It was thus interesting to study the effect of RU 41740 administration on the hyaluronic acid-degrading activity of these cells. This compound was given by gastric gavage to rats and the activities of lung alveolar macrophage and alveolar fluid hyaluronidase, beta-N-acetylglucosaminidase, beta-glucuronidase, and acid phosphatase as a lysosomal marker were determined. The effect on macrophage proliferation was also examined. The results obtained showed that: (1) unstimulated alveolar macrophages display the remarkable property, compared with other cell types, that hyaluronidase activity is about equally distributed between the inside and the outside of the cell; (2) RU 41740 administration increases the total activity of the 4 enzymes studied in the alveolar macrophages without inducing any increase in the number of macrophages; (3) the intracellular activities of beta-N-acetylglucosaminidase and beta-glucuronidase are markedly increased, whereas intracellular hyaluronidase activity is not changed. However, in the extracellular fluid only hyaluronidase activity is highly increased; (4) even the lysosomal marker enzyme acid phosphatase has only its intracellular activity increased. This would suggest the possibility that other lysosomal enzymes may also be increased by this immunomodulator.(ABSTRACT TRUNCATED AT 250 WORDS)     

Surface tension influences cell shape and phagocytosis in alveolar macrophages

The effect of surface tension on alveolar macrophage shape and phagocytosis was assessed in vivo and in vitro. Surface tension was regulated in vivo by conditionally expressing surfactant protein (SP)-B in Sftpb-/- mice. Increased surface tension and respiratory distress were produced by depletion of SP-B and were readily reversed by repletion of SP-B in vivo. Electron microscopy was used to demonstrate that alveolar macrophages were usually located beneath the surfactant film on the alveolar surfaces. Reduction of SP-B increased surface tension and resulted in flattening of alveolar macrophages on epithelial surfaces in vivo. Phagocytosis of intratracheally injected fluorescent microbeads by alveolar macrophages was decreased during SP-B deficiency and was restored by repletion of SP-B in vivo. Incubation of MH-S cells, a mouse macrophage cell line, with inactive surfactant caused cell flattening and decreased phagocytosis in vitro, findings that were reversed by the addition of sheep surfactant or phospholipid containing SP-B. SP-B controls surface tension by forming a surfactant phospholipid film that regulates shape and nonspecific phagocytic activity of alveolar macrophages on the alveolar surface.     

Characterization of mononuclear phagocyte subpopulations in the human lung by using monoclonal antibodies: changes in alveolar macrophage phenotype associated with pulmonary sarcoidosis

Current concepts of pulmonary sarcoidosis suggest that the alveolar macrophage plays a central role in the pathogenesis of the disease. To help define the population of alveolar macrophages in sarcoidosis, we compared the surface phenotype of alveolar macrophages from patients with sarcoidosis and from normal individuals by using monoclonal antibodies (63D3, OKM1, M phi P-9, M phi S-1, 61D3, and M phi S-39) that detect surface antigens on cells of monocyte/macrophage lineage. Although almost all blood monocytes expressed surface antigens detected by each of these antibodies, only a minority of normal alveolar macrophages expressed the same surface antigens (p less than 0.05, each comparison). However, in sarcoidosis, the percentage of alveolar macrophages expressing these surface antigens was increased (p less than 0.05, each comparison with normal alveolar macrophages). Several findings supported the conclusion that the increased expression of these monocyte-lineage surface antigens on sarcoid alveolar macrophages resulted from increased recruitment of monocytes to the lung in sarcoidosis and not from abnormal "activation" of alveolar macrophages. First, alveolar macrophages expressing these antigens had an immature morphology. Second, in vitro cultivation of blood monocytes and alveolar macrophages in the presence of immune and inflammatory mediators, including mediators known to be present in the lung in sarcoidosis, did not prevent the loss of expression of monocyte-lineage surface antigens from monocytes or induce reexpression of monocyte-lineage surface antigens on alveolar macrophages. Third, the expression of monocyte-lineage surface antigens was only increased on sarcoid macrophages from patients whose lower respiratory tract contained an increased number of T lymphocytes, cells known to release monocyte chemotactic factor in sarcoidosis. Consistent with the knowledge that corticosteroids usually suppress the alveolitis of active sarcoidosis, when the expression of alveolar macrophage surface antigens was evaluated before and during therapy, the percentage of alveolar macrophages expressing monocyte-lineage surface antigens returned to normal after 1 to 3 mo of therapy.(ABSTRACT TRUNCATED AT 400 WORDS)     

The expression of Fc gamma receptors on the surface of macrophages activated by a vaccinal strain of Yersinia pestis

The expression of Fc gamma R on the surface of macrophages in the process of antiplague immunity formation is analyzed. The stud is performed on the alveolar and peritoneal macrophages obtained from intact and immunized guinea pigs in different periods after vaccination (the 1st, 7th, 14th and 21st day). It is established that during the formation of the antiplague immunity there occurs activation of macrophages which is accompanied by an increase of the Fc gamma R expression on the outer surface of the membrane both of peritoneal and alveolar macrophages and the pattern of response of these cells to the interaction with the vaccine strain of the plague microbe changes. The Fc gamma R expression heterogeneity of certain macrophage populations is revealed both in an intact and in immune organism as well as different pattern of the intact alveolar and peritoneal macrophage response during the interaction with the vaccine strain of the antiplague microbe. These differences are levelled in the process of the antiplague immunity formation.     

Macrophages mediate lung inflammation in a mouse model of ischemic acute kidney injury

Serum IL-6 is increased in acute kidney injury (AKI) and inhibition of IL-6 reduces AKI-mediated lung inflammation. We hypothesized that circulating monocytes produce IL-6 and that alveolar macrophages mediate lung inflammation after AKI via chemokine (CXCL1) production. To investigate systemic and alveolar macrophages in lung injury after AKI, sham operation or 22 min of renal pedicle clamping (AKI) was performed in three experimental settings: 1) systemic macrophage depletion via diphtheria toxin (DT) injection to CD11b-DTR transgenic mice, 2) DT injection to wild-type mice, and 3) alveolar macrophage depletion via intratracheal (IT) liposome-encapsulated clodronate (LEC) administration to wild-type mice. In mice with AKI and systemic macrophage depletion (CD11b-DTR transgenic administered DT) vs. vehicle-treated AKI, blood monocytes and lung interstitial macrophages were reduced, renal function was similar, serum IL-6 was increased, lung inflammation was improved, lung CXCL1 was reduced, and lung capillary leak was increased. In wild-type mice with AKI administered DT vs. vehicle, serum IL-6 was increased. In mice with AKI and alveolar macrophage depletion (IT-LEC) vs. AKI with normal alveolar macrophage content, blood monocytes and lung interstitial macrophages were similar, alveolar macrophages were reduced, renal function was similar, lung inflammation was improved, lung CXCL1 was reduced, and lung capillary leak was increased. In conclusion, administration of DT in AKI is proinflammatory, limiting the use of the DTR-transgenic model to study systemic effects of AKI. Mice with AKI and either systemic mononuclear phagocyte depletion or alveolar macrophage depletion had reduced lung inflammation and lung CXCL1, but increased lung capillary leak; thus, mononuclear phagocytes mediate lung inflammation, but they protect against lung capillary leak after ischemic AKI. Since macrophage activation and chemokine production are key events in the development of acute lung injury (ALI), these data provide further evidence that AKI may cause ALI.     

Exogenous surfactant changes the phenotype of alveolar macrophages in mice

Alveolar macrophages are essential for the maintenance of surfactant homeostasis. We asked whether surfactant treatment would change alveolar macrophage number and whether the alveolar macrophage phenotype would become activated or apoptotic when challenged in vivo with exogenous surfactant. Surfactant pool size in mice was increased by repetitive surfactant treatments containing 120 mg/kg (110 micromol/kg) saturated phosphatidylcholine. The number of alveolar macrophages recovered by alveolar lavage decreased after the first dose by 49% and slightly increased after the second and third doses. Up to 28.5% of the macrophages became large and foamy, and their appearance normalized within 12 h. Surfactant treatment did not increase the percent of apoptotic or necrotic cells. The alveolar macrophages were not activated as indicated by no change in expression of CD14, CD16, CD54, CD95, and scavenger receptor class A types I and II after surfactant treatment. Surfactant treatment in healthy mice transiently changed the phenotype of alveolar macrophages to large and foamy without indications of changes in the surface markers characteristic of activation.     

Alveolar macrophages contribute to alveolar barrier dysfunction in ventilator-induced lung injury

In patients requiring mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ARDS), tidal volume reduction decreases mortality, but the mechanisms of the protective effect have not been fully explored. To test the hypothesis that alveolar macrophage activation is an early and critical event in the initiation of ventilator-induced lung injury (VILI), rats were ventilated with high tidal volume (HV(T)) for 10 min to 4 h. Alveolar macrophage counts in bronchoalveolar lavage (BAL) fluid decreased 45% by 20 min of HV(T) (P < 0.05) consistent with activation-associated adhesion. Depletion of alveolar macrophages in vivo with liposomal clodronate significantly decreased permeability and pulmonary edema following 4 h of HV(T) (P < 0.05). BAL fluid from rats exposed to 20 min of HV(T) increased nitric oxide synthase activity nearly threefold in na?ve primary alveolar macrophages (P < 0.05) indicating that soluble factors present in the air spaces contribute to macrophage activation in VILI. Media from cocultures of alveolar epithelial cell monolayers and alveolar macrophages exposed to 30 min of stretch in vitro also significantly increased nitrite production in na?ve macrophages (P < 0.05), but media from stretched alveolar epithelial cells or primary alveolar macrophages alone did not, suggesting alveolar epithelial cell-macrophage interaction was required for the subsequent macrophage activation observed. These data demonstrate that injurious mechanical ventilation rapidly activates alveolar macrophages and that alveolar macrophages play an important role in the initial pathogenesis of VILI.     

Surfactant protein D regulates the cell surface expression of alveolar macrophage beta(2)-integrins

The beta(2)-integrin receptors (CD11a/CD18, CD11b/CD18, and CD11c/CD18) are expressed on the surface of alveolar macrophages and are important for the phagocytic clearance of pathogens. In the present study, we demonstrate that surfactant protein D (SP-D) modulates surface expression of CD11b and CD11c, but not CD11a or CD18, on alveolar macrophages. While cell surface receptors were reduced, CD11b and CD11c mRNAs were increased by SP-D deficiency. CCSP-rtTA(+)/(tetO)(7)-rSPD(+)/SP-D(-/-) mice, which conditionally express SP-D in the lung, were used to study the kinetics and reversibility of beta(2)-integrin receptors in response to changes in alveolar SP-D. Surface CD11b and CD11c were reduced on the alveolar macrophages within 3 days of SP-D deficiency and were restored with 3 days for CD11b and 7 days for CD11c of repletion of SP-D. SP-D deficiency caused a loss of cellular CD11b and CD11c content, indicating that the decrease in total cell content of the receptors was related to degradation rather than to redistribution of the receptor within the macrophage. CD11b and CD11c staining colocalized with Lamp-1 during SP-D deficiency, supporting the concept that reduced macrophage receptor levels resulted from increased lysosomal trafficking. Hydroxychloroquine, a lysomotropic agent, prevented the reduction of cellular and surface CD11b and CD11c. SP-D regulates surface CD11b and CD11c levels on the alveolar macrophage by modulating receptor trafficking, providing a mechanism by which SP-D mediates phagocytic activity in the alveolar macrophage.     

A Study of the influence of the ambient microflora on the structure of lung alveolar macrophages and an ultrastructural comparison of lung and peritoneal macrophages in germ-free and conventionally reared mice

In order to investigate quantitatively and objectively the influence of the normal microbial flora on the ultrastructure of the alveolar macrophage, three groups of mice were studied stereologically: germ-free (GF), conventionally reared under non sterile isolation conditions (IC), and conventionally reared in an open environment (OC). The alveolar macrophages of GF mice possess a smaller mitochondrial compartment, possibly with fewer organelles, than the macrophages of conventional mice. Other influences of the normal microflora on alveolar macrophage substructure are obscured by the effects of nonmicrobial stimuli such as droplets of lung surfactant. No previous comparison exists of alveolar and peritoneal macrophage ultrastructure. Lung macrophages are larger than the phagocytes of the peritoneum, but the difference in size is much less than is commonly believed. Alveolar macrophages are rounder than peritoneal macrophages, and exhibit much less rough endoplasmic reticulum (RER) as well as differences in mitochondrial morphometry. No difference in mitochondrial volume fraction exists between the two types of macrophage even though alveolar macrophages represent the extreme of aerobic adaptation in the mononuclear phagocyte system. Phagosomes occupy a significant fraction of cellular volume only in the alveolar macrophages. Moreover alveolar phagocytes contain fewer but larger lysosome-like granules than are found in peritoneal macrophages. The results represent the first objective, quantitative structural evidence confirming the common belief that alveolar macrophages experience greater physiological stimulation than peritoneal macrophages. The normal microflora accounts for only a small proportion of the differing degree of stimulation exerted on the two types of macrophage.     

Augmentation of impaired tumoricidal function in alveolar macrophages from lung cancer patients by cocultivation with allogeneic, but not autologous lymphocytes

 It has been reported that the in vitro development of tumoricidal function in alveolar macrophages from lung cancer patients is reduced significantly when compared to that in peripheral blood monocytes from the same patients or alveolar macrophages from control patients. In the present investigation, a method for potentiating the development of tumoricidal function in alveolar macrophages from lung cancer patients is described. This method, which relies on priming the macrophages with purified, allogeneic peripheral blood lymphocytes from normal donors, could not be demonstrated when autologous lymphocytes from lung cancer patients were used in the priming coculture. The augmentation of tumoricidal function appears to be mediated by one or more soluble factors, since supernatants from cocultures of alveolar macrophages and allogeneic peripheral blood lymphocytes could enhance the cytotoxic function of freshly obtained alveolar macrophages. Furthermore, it appears that NK cells are necessary for this effect, since depletion of CD56⁺/CD57⁺ cells from allogeneic lymphocytes eliminated their capacity to enhance alveolar macrophage cytotoxic function. The augmentation of cytotoxic function elicited in alveolar macrophages by this method was not associated with changes in the secretion of tumor necrosis factor α, or interleukin 1β. Received: 15 March 1997 / Accepted: 11 June 1997     

Influenza virus-induced immune complexes suppress alveolar macrophage phagocytosis

Immune complexes in the lungs are capable of inducing adverse responses. Herein we have detailed the formation of immune complexes in the lungs of influenza virus-infected mice and examined their effect on alveolar macrophage defenses. On days 3, 7, 10, 15, and 30 after aerosol infection with influenza A/PR8/34 virus, the acellular pulmonary lavage fluid was tested for viral antigen, specific viral antibody, and immune complexes by immunoassays. Whereas peak viral antigen (day 3) diminished to undetectable levels by day 10, specific viral antibody remained at a low concentration until day 10, after which it rapidly increased. Immune complex concentrations increased through day 7, peaked at day 10, and gradually returned to the control level by day 30. These data demonstrate that immune complexes of detectable size are induced by influenza virus infection during the interface between antigen excess and antibody excess conditions. Since alveolar macrophages are the pivotal phagocytic defense cells in the lung, the ability of normal alveolar macrophages to ingest opsonized erythrocytes was quantitated in the presence of immune complexes from lavage fluid. Immune complexes from day 10 virus-infected lungs caused a dose-dependent suppression of antibody-mediated phagocytosis to 30% of control values. In contrast, although these immune complexes also markedly decreased the phagocytosis of antibody-coated yeast cells, they did not significantly impair the antibody-independent ingestion of unopsonized yeast cells by macrophages. the suppressive effects of immune complexes on alveolar macrophages may, in part, explain the phagocytic dysfunction that occurs 7 to 10 days after influenza virus pneumonia.     

Characterization of proinflammatory cytokine production and CD14 expression by murine alveolar macrophage cell lines

Summary Alveolar macrophages, which play a central role in lung defense, produce cytokines that help orchestrate local inflammatory responses. In sepsis and other pathological conditions, bacterial lipopolysaccharide endotoxin can induce alveolar macrophages (AM) to release proinflammatory cytokines, including tumor necrosis factor-alpha, interleukin-1, and interleukin-6. Studying the mechanisms that control alveolar macrophage cytokine production may lead to better therapies for conditions involving inflammatory lung injury. We and others have noted significant differences between alveolar macrophages and peritoneal macrophages, but large numbers of human or murine alveolar macrophages are rarely available for detailed mechanistic studies. We have obtained three murine alveolar macrophage cell lines (AMJ2C8, AMJ2C11, and AMJ2C20) and have begun to characterize their cytokine responses to proinflammatory stimuli. We measured the effects of endotoxin, interferon gamma, and the combination of the two on production of tumor necrosis factor, interleukin-1 beta, and interleukin-6 in each line. We also studied the expression of the endotoxin receptor CD14 by these cells, and investigated the effect of serum on their endotoxin responsiveness. We show here that all three of the cell lines responded in a manner comparable to that of primary murine alveolar macrophages. Observed variations between these lines may reflect the documented heterogeneity seen in populations of primary alveolar macrophages. These cell lines should expand the repertoire of tools available to investigators studying regulation of murine alveolar macrophage responses.     

Pneumocystis carinii enhances soluble mannose receptor production by macrophages

Phagocytosis of extracellular organisms in the alveolar spaces of the lungs represents the first-line of host defense against pulmonary pathogens. Disruption of this process is likely to interfere with the generation of appropriate specific immune responses, and lead to a delayed or inefficient clearance of the pathogen. Pneumocystis carinii, an opportunistic pathogen in immunodeficient individuals, is cleared from the lung by alveolar macrophages. In the absence of specific anti-Pneumocystis antibodies, phagocytosis is dependent on the non-opsonic macrophage mannose receptor (MR). Recent studies have demonstrated that alveolar macrophage MR activity is downregulated in individuals infected with HIV, and that functional MR is shed from the macrophage cell surface. Here we report that P. carinii enhances the formation of soluble MR by macrophages in vitro. Soluble MR was detected in cell-free alveolar fluid from humans infected with HIV and/or P. carinii, but not in alveolar fluid from healthy controls. Soluble MR was found in association with extracellular clumps of P. carinii in the lungs of mice with P. carinii pneumonia, and was associated with P. carinii organisms purified from these mice. When purified P. carinii organisms were incubated with soluble MR-containing supernatants, they were phagocytosed less readily by alveolar macrophages than were control organisms. Our results suggest that P. carinii organisms enhance the shedding of MR from the surface of alveolar macrophages, and that the resultant soluble MR binds to intra-alveolar organisms, thereby interfering with their non-opsonic uptake via the macrophage cell surface MR.     

Pulmonary pharmacodynamics of an anti-GM-CSFRα antibody enables therapeutic dosing that limits exposure in the lung

Pulmonary alveolar proteinosis is associated with impaired alveolar macrophage differentiation due to genetic defects in the granulocyte macrophage colony-stimulating factor (GM-CSF) axis or autoantibody blockade of GM-CSF. The anti-GM-CSFRα antibody mavrilimumab has shown clinical benefit in patients with rheumatoid arthritis, but with no accompanying pulmonary pathology observed to date. We aimed to model systemic versus pulmonary pharmacodynamics of an anti-GM-CSFRα antibody to understand the pharmacology that contributes to this therapeutic margin. Mice were dosed intraperitoneal with anti-GM-CSFRα antibody, and pharmacodynamics bioassays for GM-CSFRα inhibition performed on blood and bronchoalveolar lavage (BAL) cells to quantify coverage in the circulation and lung, respectively. A single dose of 3 mg/kg of the anti-GM-CSFRα antibody saturated the systemic cellular pool, but dosing up to 10 times higher had no effect on the responsiveness of BAL cells to GM-CSF. Continued administration of this dose of anti-GM-CSFRα antibody for 7 consecutive days also had no inhibitory effect on these cells. Partial inhibition of GM-CSFRα function on cells from the BAL was only observed after dosing for 5 or 7 consecutive days at 30 mg/kg, 10-fold higher than the proposed therapeutic dose. In conclusion, dosing with anti-GM-CSFRα antibody using regimes that saturate circulating cells, and have been shown to be efficacious in inflammatory arthritis models, did not lead to complete blockade of the alveolar macrophages response to GM-CSF. This suggests a significant therapeutic window is possible with GM-CSF axis inhibition.     

Incorporation of [3H]palmitate and [14C]choline into disaturated phosphatidylcholines in rat alveolar macrophages

We studied the synthesis of disaturated phosphatidylcholines in rat alveolar macrophages and, in some cases, compared it with that which occurs in isolated alveolar type II cells. Alveolar macrophages suspended in phosphate-buffered medium incorporate palmitate, choline and glycerol into disaturated phosphatidylcholines. The time-course for incorporation of palmitate into disaturated phosphatidylcholines is linear for 20-30 min and reaches a maximum in 2-3 h. Incorporation is dependent on extracellular palmitate with a Vmax (at 1 mM) of 1.53 nmol palmitate incorporated into disaturated phosphatidylcholines per 5 X 10(5) cells per 2 h and a K 1/2 of 0.19 mM palmitate. Exposure of the cells to zymosan particles increases incorporation of palmitate disaturated phosphatidylcholines by almost 2-fold, while cholinergic and beta-adrenergic agonists have no effect. On a per cell basis, alveolar macrophages incorporate only one-third to one-half as much palmitate into disaturated phosphatidylcholines as do type II cells isolated by centrifugal elutriation. The following results suggest there is extensive remodeling of disaturated phosphatidylcholines in alveolar macrophages: (1) palmitate- and choline-labeled disaturated phosphatidylcholines are catabolized by the cells; (2) the products of catabolism are palmitate and water-soluble choline products; (3) addition of unlabeled palmitate and choline to the medium enhances catabolism of the labeled phospholipid. Addition of oleate also enhances catabolism, suggesting that modification of phospholipids is not specific for the saturated variety. Some of the recently labeled disaturated phosphatidylcholines is released from alveolar macrophages into the extracellular space. Several possible functions of alveolar macrophage disaturated phosphatidylcholines are discussed.     

Novel cell surface antigens expressed on mouse alveolar macrophages.

Two new cell surface antigens expressed on mouse alveolar macrophages were defined by rat monoclonal antibodies. One marker, AVM-1, was detected on mouse alveolar macrophages, but it was undetectable on resident peritoneal cells, thioglycollate medium-induced peritoneal cells, and splenic macrophages. Splenic lymphocytes, thymocytes and bone marrow cells were also AVM-1 negative. Anti-AVM-1 monoclonal antibody immunoprecipitated a single polypeptide with a molecular weight of 200,000. Of particular interest was the finding that the anti-AVM-1 antibody could inhibit the formation of EA and EAC rosette on macrophage line cells. A second antigen (AVM-2) was also present on alveolar macrophages, and its molecular weight was 38,000.