In vivo interaction between alveolar macrophages and Cryptococcus neoformans

In vivo interactions of rabbit alveolar macrophages (AM) and Cryptococcus neoformans, a yeast pathogenic for humans, were studied. As a control, inert silica particles of a similar diameter (5–6 μm) were used. Of 16 rabbits, 6 were instilled intratracheally with fluorescein-labelled heat-killed C. neoformans, 6 with fluorescein-labelled silica particles and 4 with saline only. After 24 h, the AM were collected by lung lavage, and phagocytosis, oxidative metabolism, phagolysosomal pH and morphology were studied. The accumulated number of yeasts attached to the AM was almost the same for C. neoformans as for the silica particles. The ingested fraction of C. neoformans was even higher than that of the silica particles. Quantitative NBT reduction by the AM, reflecting their oxidative metabolism, was markedly increased by exposure to C. neoformans for 24 h. The phagolysosomal pH was on the average lower in phagolysosomes with C. neoformans than with the silica particles, although approximately 2% of the phagolysosomes with C. neoformans had neutral pH. Phagolysosomes with neutral pH was not observed for silica particles. Electron microscopy showed presence of C. neoformans in phagolysosomes of AM. The conclusion of this study is that the phagocytic activity, oxidative metabolism and phagolysosomal pH AM against C. neoformans are significant 24 h after the exposure. This revised version was published online in June 2006 with corrections to the Cover Date.     

Activation of protein kinase C beta II by the stereo-specific phosphatidylserine receptor is required for phagocytosis of apoptotic thymocytes by resident murine tissue macrophages

We showed previously that protein kinase C (PKC) is required for phagocytosis of apoptotic leukocytes by murine alveolar (AM?) and peritoneal macrophages (PM?) and that such phagocytosis is markedly lower in AM? compared with PM?. In this study, we examined the roles of individual PKC isoforms in phagocytosis of apoptotic thymocytes by these two M? populations. By immunoblotting, AM? expressed equivalent PKC eta but lower amounts of other isoforms (alpha, betaI, betaII, delta, epsilon, mu, and zeta), with the greatest difference in betaII expression. A requirement for PKC betaII for phagocytosis was demonstrated collectively by phorbol 12-myristate 13-acetate-induced depletion of PKC betaII, by dose-response to PKC inhibitor Ro-32-0432, and by use of PKC betaII myristoylated peptide as a blocker. Exposure of PM? to phosphatidylserine (PS) liposomes specifically induced translocation of PKC betaII and other isoforms to membranes and cytoskeleton. Both AM? and PM? expressed functional PS receptor, blockade of which inhibited PKC betaII translocation. Our results indicate that murine tissue M? require PKC betaII for phagocytosis of apoptotic cells, which differs from the PKC isoform requirement previously described in M? phagocytosis of other particles, and imply that a crucial action of the PS receptor in this process is PKC betaII activation.     

The concurrent expression of Griffonia simplicifolia-IB4 binding and tumor necrosis factor-alpha differs between alveolar and peritoneal macrophages.

As a corollary to their anatomic location, alveolar macrophages (AM) have a lower threshold for generating some physiologic functions than peritoneal macrophages (PM). In this study, we examined both of these populations for their ability to bind the lectin Griffonia simplicifolia-IB4 (GSIB4) and to produce tumor necrosis factor (TNF)-alpha. The results showed that these two responses were concurrently expressed in activated macrophages, although they differed in magnitude when AM and PM were compared. Following in vitro incubation, AM from lipopolysaccharide-treated rats demonstrated a higher percentage of GSIB4 positivity and TNF production when compared with their respective PM. Since prostaglandin E2 can regulate the expression of some macrophage activities, experiments were conducted to determine whether this could also affect the ability of macrophages to bind the GSIB4 lectin. Neither the administration of indomethacin nor exogenous prostaglandin E2 altered the expression of this marker. Conversely, these treatments produced significant changes in TNF-alpha production in both alveolar and peritoneal macrophages. When the concurrent expression of GSIB4 lectin binding and TNF-alpha production was analyzed, AM from lipopolysaccharide-treated rats demonstrated both superior GSIB4 positivity and TNF-alpha production compared with all other macrophages examined. The results of this work show that AM and PM differ in their expression of GSIB4 binding and TNF-alpha production. These differential responses may be important in determining the level of activity of macrophages that are participating in an immune response.     

Effect of macrophage decay products on the incorporation of H3-thymidine into pulmonary cells in rats

3H-thymidine is injected to Wistar rats 60 min before their sacrifice, that is performed 24 h after intratracheal administration of isotonic solution of natrium chloride (control), and in the test animals--24 or 72 h after similar injection of macrophage decay products (MDP). The MDP are prepared by freezing-thawing of syngenic peritoneal macrophages repeated 5 times in the dose corresponding to 10(8) of the destroyed cells per 100 g of body mass. During the first period after MDP injection the labelling index of macrophages, histiocytes and cells of the alveolar epithelium increases up to 4.07 +/- 0.21%, during the second--up to 3.34 +/- 0.17% (in the control--1.90 +/- 0.18%). The results obtained are discussed according to modern ideas on the role of the interstitial cell pool as an immediate source for mobilization of alveolar macrophages, and together with the data previously accumulated, on the role of MDP in the autoregulatory control of various links of the macrophagal pulmonary reaction.     

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.     

Interleukin 1 production and accessory cell function of rat alveolar macrophages exposed to mineral dust particles

Immunostimulatory effects of respirable mineral dust particles on alveolar macrophages (AM) and T lymphocytes were tested in vitro. When rat AM were incubated with fibrogenic silica and asbestos particles, a significant interleukin 1 (IL-1) activity was generated into the culture supernatants, whereas neither AM alone nor AM incubated with non-fibrogenic titanium dioxide (TiO2) particles, however, produced a detectable amount of IL-1. Interleukin 2 (IL-2) activity, as tested with IL-2-dependent CTLL-2 assays, was not detectable from all of these cultures. It was also revealed that concanavalin A-induced proliferation of T lymphocytes was enhanced in autologous AM and nylon wool-passed spleen cell co-cultures incubated only with fibrogenic particles, but not with non-fibrogenic particles. Higher IL-1 activity was detected only from co-cultures exposed to fibrogenic particles, whereas IL-2 activity was almost similar among these co-cultures. These results indicate the differences in immunostimulatory effects on pulmonary macrophages and T lymphocytes among a variety of mineral dust particles.     

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.     

Activation of antitumor properties in alveolar macrophages from protein-calorie malnourished rats

Summary Protein-calorie malnutrition (PCM) was induced by feeding male F344 rats on a 5% casein diet for 7 weeks. At appropriate times, rats from control (20% casein diet) and PCM groups were killed and alveolar macrophages (AM) were obtained by bronchoalveolar lavage. The functional integrity of the AM was determined by measuring their ability to become tumoricidal on treatment with macrophage activators, such as muramyl dipeptide (MDP) or multilamellar liposomes containing MDP or its lipophilic analog, MTP-PE. After 5 and 7 weeks, the numbers of lavaged AM per gram body weight of rats were much higher in the PCM group than in the control group. In week 3, AM from the PCM group showed spontaneous tumoricidal activity against syngeneic tumor cells, but in weeks 5 and 7 they did not. However, AM from PCM rats behaved the same way as controls in their response to activation stimuli in vitro with multilamellar liposomes containing synthetic MDP or MTP-PE.These data show that PCM affects the number of AM, but that AM from rats in a state of PCM become tumoricidal in response to activation stimuli in vitro.     

Cathepsin B and D activity in stimulated peritoneal macrophages

Summary Highly sensitive and specific synthetic substrates were used to quantitate cathepsin B and D activity in peritoneal macrophages in response to stimulation in vivo with mineral oil and thioglycollate. After intraperitoneal instillation of mineral oil the activity of cathepsin B increased significantly (to 15 300 units/mg protein versus 7 340 in saline controls), reaching values approaching those found in alveolar macrophages (18 400 units/mg protein). Significantly greater stimulation of enzyme activity was obtained after intraperitoneal instillation of thioglycollate (23 600 units/mg protein). Cathepsin D activity also increased significantly after both mineral oil and thioglycollate. However, the increase was moderate (from 806 to about 1 200 units/mg protein), remaining still more than six times lower-than in alveolar macrophages. The data are the first to demonstrate that cathepsin B activity can be stimulated in vivo in peritoneal macrophages by instillation of agents that induce acute inflammation. They also point to a differential control of expression of cathepsin B and D activity in both peritoneal and alveolar macrophages in spite of the common lysosomal origin of the two enzymes.Abbreviations Cbz -N-benxyloxycarbonyl - 2NA 2-naphthylamine - EDTA ethylenediamine tetraacetate - DMSO dimethylsulfoxide - PBS phosphate-buffered saline - PM peritoneal macrophage - AM alveolar macrophage     

Tumoricidal activation of murine alveolar macrophages by muramyldipeptide substituted mannosylated serum albumin

Rat and mouse alveolar macrophages have almost no spontaneous tumoricidal activity and are only slightly activated by muramyldipeptide (MDP). When MDP was carried by serum albumin, the activation was higher than with free MDP but only at high concentration. When MDP was bound to a neoglycoprotein (mannosylated serum albumin) - which binds to the sugar binding receptor at the macrophage cell surface and is actively endocytosed - the activation of rat or mouse alveolar macrophages is dramatically enhanced even at very low concentration of neoglycoprotein -bound MDP. Furthermore, neoglycoprotein -bound MDP injected i.v. or i.p. was found to be able to activate alveolar macrophages, the activity of which was maximal after 48 hours in mice and 72 hours in rats. Such conjugates have so potential values as new immunostimulant agents in cancer and parasite therapy.     

Selective down-regulation of alveolar macrophage oxidative response to opsonin-independent phagocytosis

We have compared the oxidative response of alveolar macrophages (AM) during opsonin-dependent and independent phagocytosis by using multiparameter flow cytometry. The respiratory burst of AM during phagocytosis was quantitated by the intracellular oxidation of the nonfluorescent precursors dichlorofluorescin diacetate (DCFH) or hydroethidine (HE, a reduced precursor of ethidium) to their fluorescent (oxidized) counterparts. After loading freshly isolated normal hamster AM with DCFH or HE, red or green fluorescent beads, respectively, were added to the shaking cell suspensions. Ingestion of opsonized particles by AM caused a marked increase in oxidation of both DCFH and HE proportional to the number of beads ingested. In contrast, uptake of one to three unopsonized particles per cell led to inhibition of oxidative activity compared to control cells incubated without particles. AM ingesting four or more unopsonized particles showed some increase in oxidative metabolism, but far less than that with identical numbers of particles in opsonin-dependent ingestion. Similar results were obtained using fluorescent labeled staphylococcal bacteria. Using three-color flow cytometry to study cells ingesting both types of particles, cells first ingesting unopsonized beads were also found to have an inhibited oxidative response to subsequently ingested opsonized particles. The mitochondrial poison antimycin inhibited most of the intracellular oxidative response to either type of phagocytosis. The remaining antimycin-insensitive, membrane derived respiratory burst of AM was also substantially diminished after phagocytosis of unopsonized particles vs similar numbers of opsonized particles. The greatly increased mitochondrial respiration in AM during phagocytosis of opsonized particles may be related to bactericidal mechanisms. Killing of ingested Staphylococcus by AM was markedly impaired in the presence of antimycin. The results suggest that AM may ingest the numerous, unopsonized inert particles that are inhaled without generation of potentially toxic oxygen metabolites, while retaining the capacity to undergo a respiratory burst after ingesting opsonized particles and bacteria. The mechanism(s) for this distinct response may include generation of an inhibitor of intracellular oxidative metabolism.     

Inhibition of Macrophage Phagocytosis by Pseudomonas aeruginosa Rhamnolipids In Vitro and In Vivo

Patients with cystic fibrosis often have chronic and ultimately lethal pulmonary infections with Pseudomonas aeruginosa. In order to understand why these bacteria resist pulmonary clearance, we have investigated the interaction of P. aeruginosa and phagocytic cells. In an earlier study we reported that sub-lytic concentrations of two glycolipids produced by P. aeruginosa (the mono- and dirhamnolipids) caused structural changes in human monocyte-derived macrophages, and at lower concentrations inhibited the phagocytosis of Staphylococcus epidermidis by these cells. In the present study we demonstrate that rhamnolipids also inhibit the in vitro phagocytosis of both P. aeruginosa and Saccharomyces cerevisiae by thioglycollate-elicited mouse peritoneal macrophages. Using lucifer yellow to label the lysosomal compartments of macrophages, we determined that rhamnolipids interfere with the internalization of attached particles and reduce the level of phagosome-lysosome fusion of internalized targets within macrophages. We also demonstrate that physiologically relevant concentrations of rhamnolipids injected intratracheally into rat lungs inhibited the response of alveolar macrophages to a challenge of zymosan particles in vivo. These studies further demonstrate the profound inhibitory effects of P. aeruginosa rhamnolipids on macrophage function and are consistent with our hypothesis that the in situ production of these rhamnolipids directly contributes to the persistence of this pathogen in cystic fibrosis patient lungs. Received: 15 December 1995 / Accepted: 22 January 1996     

The protective action of disodium cromoglycate on alveolar macrophages in phagocytosis of fibrogenic silica.

Treatment of fibrogenic silica (DQ-12) with Disodium Cromoglycate (DSCG) prior to its in-vitro and in-vivo phagocytosis by alveolar macrophages prevents the destruction of the cells and the fibrosis of lung tissue which are a consequence of phagocytosis. However, the treatment of alveolar macrophages with DSCG before phagocytosis of the silica had no, or a negligible, protective effect on the cells. Acid phosphatase activity which was significantly enhanced above the control in cells phagocytosing the silica was returned to the range found in phagocytosis of inert dust when silica treated with DSCG was phagocytized. The inhibitor of DNA- dependent RNA synthesis actinomycin D caused an increase of acid phosphatase activity. DSCG did not depress the phagocytic ability of alveolar macrophages. It appears that the catabolic enzyme process predominant in cells phagocytosing DQ-12 was under control in cells phagocytosing DQ-12 treated with DSCG and that DSCG probably acted as a regulator of the factors permitting catabolism. From the results it is suggested that the equilibrium of the enzyme reactions which accompany phagocytosis was such that the integrity of the phagocytes was preserved.     

Comparison of particle clearance and macrophage phagosomal motion in liver and lungs of rats

Magnetic particles and magnetometry were used to noninvasively measure motion of particle-containing organelles in macrophages as well as to monitor the disappearance of particles from tissues. We compared these parameters in the liver (where macrophages are attached to the endothelium) and in the lungs (where macrophages were mobile on epithelial surfaces). Submicrometric magnetic particles were injected intravenously (1.5 mg/kg) into rats; 94% was taken up by the liver. Rats were also instilled intratracheally (1.0 mg/kg) with the same particles. Ultrastructural analyses showed that almost all particles were ingested by macrophages in both organs. Periodically, the retained particles were magnetized and aligned with an external magnet. After the magnet was removed, the decay of the resulting remanent field (relaxation) was followed for 25 min. Relaxation parameters (t1/2 and lambda 0) in the liver were constant from 30 min to 30 days after particle administration, but relaxation in lungs showed a time-dependent increase during the 1st day due to the slower rate of particle phagocytosis. Relaxation in both organs primarily reflects the motion of particle-containing organelles as they are rotated by the cytoskeleton. Relaxation in the lungs may also reflect cell translocation or even changes in alveolar shape. Clearance of particles from the lungs or liver was measured by following B0 (initial magnetic field strength). After correction for growth, the clearance t1/2 was 17.7 and 27.3 days for the lungs and liver, respectively. Bulk transport of particles is probably a more important clearance mechanism in the lungs than in the liver.     

Correlation between chemiluminescence response and rate of zymosan uptake by rat alveolar macrophages. Scanning electron microscope observations

The rate of particle uptake by rat alveolar macrophages (AM) exposed to zymosan (mean number of zymosan particles becoming bound to 100 cells at a fixed time interval) was determined with the aid of the scanning electron microscope (SEM). The intensity of the chemiluminescence (CL) emitted by the AM on addition of zymosan, was measured concomitantly. During the whole course of CL emission, all the particles were found to be either attached or engulfed, but not ingested by the AM. A good correlation was obtained between the time dependence of CL intensity and that of the rate of particle uptake, both reaching a peak value at about 5 min after exposure. It is therefore assumed that the CL emitted by AM exposed to zymosan reflects the attachment and engulfment stages of phagocytosis.     

Role of destruction products of tissue macrophages in regulating granulocytopoiesis]

Peripheral blood leukocytosis and an increase of mature forms of neutrophils and monocytes in the bone marrow, as well as an improvement of the oxygen supply of the bone marrow cells (by the data of polarographic studies) followed the intraperitoneal injections of rat peritoneal macrophage destruction products (MDP) to the recipient rats. Analogous changes were obtained in the bone marrow in case of intraperitoneal injection of the cytotoxic quartz dust particles. Having been injected intraperitoneally to donor CBA mice, the MDPs strikingly stimulated the glanulocytopoietic colonies formation in the spleen of the recipient CBA mice X-irradiated with a lethal dose and then injected intravenously with the bone marrow of spleen tissue suspensions obtained from the donors. The results obtained are discussed from the aspect of a possible role of the destroyed tissue macrophages in the formation of a colony-stimulating factor in the auto-control of the phagocytic responses.     

In vivo and in vitro activation of alveolar macrophages by recombinant interferon-gamma

In vivo administration of recombinant interferon-gamma (rIFN-gamma) was previously shown to result in activation of the microbicidal activities of peritoneal macrophages (PM phi). Because macrophages at different anatomical sites vary in their functional capacities, we considered it of interest to determine whether administration of murine rIFN-gamma, either in vitro or in vivo, can enhance the microbicidal activity of resident alveolar macrophages (AM phi) and to compare the effects of rIFN-gamma on AM phi and PM phi. After incubation in vitro with rIFN-gamma, the antimicrobial activities of both murine AM phi and PM phi were enhanced, as assessed by their ability to inhibit replication of the intracellular parasite, Toxoplasma gondii. This effect was dose dependent for AM phi over a range of 0.1 to 1 U/ml and for PM phi over a range of 0.5 to 1000 U/ml. In this assay, the minimum dosage required for in vitro activation of AM phi was one-half that required for activation of PM phi, suggesting a greater sensitivity of AM phi to the in vitro activity of rIFN-gamma. Macrophages from both anatomical sites were also activated when rIFN-gamma was administered in vivo. This effect was dose dependent over a range of 10(3) to 10(5) U/mouse. Freshly harvested AM phi and PM phi from mice injected 24 hr earlier with 10(4) U rIFN-gamma by either the i.v. or i.p. routes markedly inhibited intracellular multiplication of Toxoplasma. In contrast, AM phi and PM phi from control mice permitted fourfold to ninefold increases in numbers of intracellular Toxoplasma. The anti-toxoplasma activity of AM phi and PM phi gradually diminished over a period of 3 days when assayed at successive 24 hr periods after a single i.v. injection of rIFN-gamma. At 3 days after injection, a substantial loss of anti-toxoplasma activity was observed with PM phi as compared with controls; residual anti-toxoplasma activity was still demonstrable in AM phi at 3 days. These results demonstrate that in vitro as well as in vivo treatment with rIFN-gamma confers on AM phi an enhanced antimicrobial activity. These findings provide a rationale for evaluating rIFN-gamma in the treatment of pulmonary infections, especially those due to opportunistic pathogens against which AM phi play a major role in host defense.     

Synthetic prostacyclin analogs differentially regulate macrophage function via distinct analog-receptor binding specificities

PGI(2) (prostacyclin) is a lipid mediator with vasodilatory and antithrombotic effects used in the treatment of vasoconstrictive/ischemic diseases including pulmonary artery hypertension. However, emerging research supports a role for PGs, including PGI(2), in the regulation of both innate and acquired immunity. As PGI(2) is unstable, we sought to define the effects of various PGI(2) analogs on resident alveolar macrophage (AM) and peritoneal macrophage (PM) innate immune functions. The effects of iloprost, carbaprostacyclin, and treprostinil on the regulation of phagocytosis, bacterial killing, and inflammatory mediator production were determined in both macrophage populations from rats. Iloprost failed to suppress AM functions to the same degree that it did in PMs, a characteristic shared by carbaprostacyclin. This difference reflected greater expression of the G(alphas) protein-coupled I prostanoid receptor and greater cAMP generation in PMs than AMs. Treprostinil inhibited phagocytosis, bacterial killing, and cytokine generation in AMs to a much greater degree than the other PGI(2) analogs and more closely resembled the effects of PGE(2). Studies with the E prostanoid (EP) 2 receptor antagonist AH-6809 and EP2-null macrophages indicated that this was due in part to the previously unknown ability of treprostinil to stimulate the EP2 receptor. The present investigation for the first time identifies differences in immunoregulatory properties of clinically administered PGI(2) analogs. These studies are the first to explore the capacity of PGI(2) to regulate bacterial killing and phagocytosis in macrophages, and our findings may hold important consequences regarding the risk of infection for patients receiving such agents.     

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.     

Pulmonary surfactant obtained from starved rats enhances phagocytosis of alveolar macrophages

Phagocytic activity of alveolar macrophages (AM) was enhanced by pulmonary surfactant obtained from bronchoalveolar lavage fluid of rats starved for 2 days, as compared to fed. The enhanced activity of phagocytosis was dependent on the dose of surfactant. The prepared surfactant showed a different protein to phospholipid ratio of 0.108 in fed and 0.234 in 2 days starved, because of an increased ratio of protein in surfactant from 2 days starved rats. F(ab')2 anti-surfactant protein inhibited the enhanced AM phagocytosis by surfactant. These results suggested that the enhancement of AM phagocytosis in 2 days starved rats was on account of an increase of protein in their surfactant compared to fed.