Comparison of live human neutrophil and alveolar macrophage elastolytic activity in vitro. Relative resistance of macrophage elastolytic activity to serum and alveolar proteinase inhibitors.

Elastin is an extracellular matrix protein critical to the normal structure and function of human lung. Recently reported data indicate that live human alveolar macrophages can degrade purified elastin in vitro. In this study, we directly compared the elastolytic activity of alveolar macrophages with that of human neutrophils. In the absence of proteinase inhibitors, human neutrophils degrade much more elastin than do human alveolar macrophages. However, macrophages cultured in 10% human serum and in contact with purified 3H-elastin degraded 4.7 micrograms elastin/10(6) cells per 24 h, as compared to less than 1 microgram/10(6) cells/24 h for neutrophils. We observed a similar pattern when the two cells were cultured in human alveolar fluid. We determined that the relative resistance of macrophage elastolytic activity to serum or alveolar proteinase inhibitors was not simply due to phagocytosis of substrate by the larger macrophages. Live macrophages as well as neutrophils degrade 125I-elastin coupled to noningestible sepharose beads. Again in serum-free media, neutrophils degraded eight-fold more elastin than macrophages but only macrophages degraded sepharose-coupled elastin in the presence of 10% serum. Because of these findings, we compared the enzymatic mechanisms of elastin breakdown by macrophages with that of neutrophils. Macrophage elastolytic activity is largely (65-80%) due to a cysteine proteinase(s), at least part of which is Cathepsin B. Approximately half of the cysteine proteinase activity appeared to be expressed at or near the cell surface. These experiments defined two enzymatically distinct pathways of elastin breakdown by human inflammatory cells: the classic, neutrophil derived soluble elastase(s) that is sensitive to serum and alveolar proteinase inhibitors, and a macrophage-mediated pathway that is largely cell associated and relatively resistant to inhibitors. The function of the two pathways depends on the relative excess or deficiency of soluble inhibitors. At inflammatory sites rich in proteinase inhibitors, tissue macrophages may degrade more extracellular matrix elastin than neutrophils. In smokers without antiproteinase deficiency, pulmonary macrophages, which are known to be increased in number, may be the more important cause of elastin breakdown and emphysema.

Degradation of fibrin and elastin by intact human alveolar macrophages in vitro. Characterization of a plasminogen activator and its role in matrix degradation.

Fibrin deposition is prominent in the histopathology of a number of inflammatory lung diseases. Plasmin, activated locally in the lung, can degrade not only this fibrin but potentially structural proteins important to normal lung architecture. Because alveolar macrophages are prominent in inflammatory processes of the lung, we examined the plasminogen activator (PA) activity of human alveolar macrophages. Intact alveolar macrophages from each of 10 healthy subjects expressed PA activity. There was no difference in activity between smoking and nonsmoking individuals. The activator activity was largely cell-associated, but under certain culture conditions, macrophages released a soluble activator into the culture medium. The membrane-bound activator had an apparent molecular mass of 52-55 kD in nonreduced sodium dodecyl sulfate (SDS) gels, and monospecific antibody to urokinase neutralized the enzyme activity. Immunoprecipitation of [35S]methionine-labeled cells showed that human alveolar macrophages actually synthesize the PA in vitro. SDS-gel analysis of the immunoprecipitated material revealed the predominant species of PA to be structurally similar to reduced, active urokinase. We also examined the role of PA in the degradation of both insoluble fibrin and elastin matrices by live macrophages. Cells degraded an insoluble fibrin matrix in the presence of plasminogen whether or not the macrophages contacted the fibrin as long as proteinase inhibitors were not in the culture medium. In the presence of serum proteinase inhibitors, macrophages still degraded a fibrin matrix, but only if they were in contact with the fibrin. Live macrophages also degraded insoluble elastin only when in contact with the elastin but could do so even in the presence of serum proteinase inhibitors. In matrices containing a mixture of fibrin and elastin, cells did not degrade elastin unless plasminogen was added to the medium. These results indicate that normal alveolar macrophages synthesize and express, probably at the cell surface, a PA. The PA is physically and immunochemically similar to urokinase but is membrane bound. The PA is critical to the degradation of fibrin matrices by normal alveolar macrophages. Under tissue conditions where elastin is embedded within other structural proteins, the activator may be rate-limiting in elastin degradation as well. The findings also suggest that live macrophage proteolytic activity is relatively insensitive to the presence of serum proteinase inhibitors, suggesting a mechanism for proteolytic lung injury even in the presence of proteinase-proteinase inhibitor balance in the soluble phase.

Human alveolar macrophages synthesize factor VII in vitro. Possible role in interstitial lung disease.

Both fibrin and tissue macrophages are prominent in the histopathology of chronic inflammatory pulmonary disease. We therefore examined the procoagulant activity of freshly lavaged human alveolar macrophages in vitro. Intact macrophages (5 X 10(5) cells) from 13 healthy volunteers promoted clotting of whole plasma in a mean of 65 s. Macrophage procoagulant activity was at least partially independent of exogenous Factor VII as judged by a mean clotting time of 99 s in Factor VII-deficient plasma and by neutralization of procoagulant activity by an antibody to Factor VII. Immunoprecipitation of extracts of macrophages metabolically labeled with [35S]methionine by Factor VII antibody and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a labeled protein consistent in size with the known molecular weight of blood Factor VII, 48,000. The addition of 50 micrograms of unlabeled, purified Factor VII blocked recovery of the 48,000-mol wt protein. In addition, supernatants of cultured macrophages from six normal volunteers had Factor X-activating activity that was suppressed an average of 71% after culture in the presence of 50 microM coumadin or entirely by the Factor VII antibody indicating that Factor VII synthesized by the cell was biologically active. Endotoxin in vitro induced increases in cellular tissue factor but had no consistent effect on macrophage Factor VII activity. We also examined the tissue factor and Factor VII activities of freshly lavaged alveolar cells from nine subjects with clinical and/or histologic evidence of sarcoidosis. Four of the nine subjects expressed increased tissue factor and seven of nine had increased Factor VII activity over the normal range (P less than 0.01). We estimate the mean Factor VII associated with the cells of sarcoid patients to be 4.7 ng/10(6) cells (range 0.4-20) as compared to a mean of 0.74 ng/10(6) cells (range 0.2-2) for that of normal subjects. Along with previous data showing synthesis of plasminogen activator, these findings indicate that human alveolar macrophages normally synthesize and express measurable amounts of the initial enzymes of proteolytic reactions regulating both fibrin deposition and fibrin resorption. Abnormalities in Factor VII activity in a small group of patients with sarcoidosis raise the possibility that modulation of fibrin turnover by macrophages may contribute to the pathology of this and perhaps other interstitial lung diseases.

The effects of hyperthermia on DNA replication in HeLa cells.

The extent of heat-induced inhibition of DNA replication in HeLa cells was assayed at temperatures between 43 and 48 degrees C. During hyperthermic exposure replicon initiation, as well as elongation of replicons into larger replicative fragment sizes, was rapidly inhibited. Elongation of nascent DNA into replicons continued at a normal rate for up to 45 min at 45 degrees C. Heated cells, replaced at 37 degrees C, elongated nascent DNA at a reduced rate and elongation was incomplete for up to 36 hr. Nascent DNA, not fully elongated 24 hr after hyperthermic exposure, was observed in replicative fragment sizes as small as replicons. The extent of heat-induced inhibition of DNA elongation increased with increasing time-temperature exposure with an activation energy of 122 kcal/mole of DNA. When pulsed cells were incubated at 37 degrees C for various times prior to heating, the extent of heat-induced inhibition of DNA elongation decreased with a half-time of 20-25 min, suggesting that the heat-sensitive structure is associated with replicative fragments having sizes less than 140-150S.

Macromolecule synthesis in HeLa cells after thermal shock.

The incorporation of radioactivity into HeLa cell polypeptides and DNA after exposure to 45 degrees C heating for 15 min was measured by continuous exposure to radiolabeled precursors. Both polypeptide and DNA synthesis were inhibited by thermal shock. The rate of incorporation of radiolabeled amino acids into whole cell, nuclear, or histone protein recovered to control levels by 5 to 8 hr after thermal shock. The rate of incorporation of radiolabeled thymidine into DNA did not recover to a control level within the first 8 hr after thermal shock. Thermal effects on amino acid and nucleotide precursor pools could not explain the inhibition of either protein or DNA synthesis. Since histone protein synthesis recovers prior to DNA synthesis, we conclude that the inhibition of histone protein synthesis after thermal shock is not responsible for the depression in synthesis of cellular DNA.

The sedimentation coefficient and buoyant density of nucleosomes from replicating chromatin in heated cells.

The sedimentation coefficient and buoyant density of mononucleosomes from the replicating chromatin of heated (45 degrees) and unheated HeLa cells were determined. It was observed that both physical parameters were the same (S = 10.8 and p = 1.165 g/cm3) for nucleosome particles from replicating and mature chromatin in heated and unbeated cells. The size of DNA in the nascent and mature nucleosome from heated or unheated cells was observed to be 145 base pairs of double-stranded DNA. A significant fraction of nucleosomal DNA from heated cells was observed at subnucleosomal sizes, principally at 125 base pairs of DNA. It is concluded that 45 degrees thermal shock does not alter appreciably the subunit structure of chromatin at the replication fork.

Co-operation between plasmin and elastase in elastin degradation by intact murine macrophages.

Intact, thioglycollate-stimulated murine macrophages cultured on an insoluble [3H]-elastin substratum progressively hydrolysed the elastin. Cell lysates had little activity. We compared the effect of various proteinase inhibitors on elastinolysis by either live cells or cell-free, elastase-rich conditioned medium. Only known inhibitors of macrophage elastase blocked the activity of elastase-rich cell-conditioned medium whereas inhibitors of cathepsin B also suppressed intact cell activity. Serum proteinase inhibitors blocked cell-derived soluble elastase activity but not intact cell elastolytic activity. We also observed that plasminogen added to the cell cultures markedly increased elastinolysis by live macrophages or cell-free elastase-rich medium. Purified plasmin alone had no measurable effect on native elastin. Additional experiments indicated that the plasmin enhancement was due to elastin-dependent activation of latent macrophage elastase. These results indicate that live macrophage elastinolysis is a co-operative process involving multiple proteinases, especially a cysteine proteinase(s) and elastase. Plasmin may be a physiological activator of latent macrophage elastase.

Characterization of a macrophage-derived plasminogen-activator inhibitor. Similarities with placental urokinase inhibitor.

Human and mouse macrophages release a fibrinolytic inhibitor after stimulation by endotoxin in vitro. The released mouse inhibitor was indistinguishable in size by molecular-sieve chromatography from an intracellular form (approx. 50 kDa), and both inhibitors blocked urokinase directly as judged by a 125I-plasminogen conversion assay. The intracellular inhibitor was found mostly to dissociate from 125I-urokinase during sodium dodecyl sulphate/polyacrylamide-gel electrophoresis under reduced conditions, but a dodecyl sulphate-stable complex at 65-67 kDa was observed. Because of similarities in the reported size, stability and urokinase-binding properties of a placental urokinase inhibitor, the kinetic properties of the two inhibitors were compared. Under the reaction conditions employed (37 degrees C at pH7.4 in the presence of 0.2% Triton X-100), the association rate constants and equilibrium dissociation constants of the two inhibitors were indistinguishable, 3 X 10(5) M-1 X s-1 and 4 X 10(-10) M respectively. These data show that peritoneal macrophages contain a plasminogen-activator very similar to a previously recognized placental inhibitor. Although the inhibitor appears to be a trace protein in macrophages, placental macrophages may account for the accumulation of the inhibitor in placental tissue.

Histone protein and DNA synthesis in HeLa cells after thermal shock.

Exposure of suspension-cultured HeLa cells to a 45 degrees thermal shock resulted in cell inactivation and inhibition of both protein and DNA synthesis. DNA synthesis was inhibited in a biphasic manner with a more sensitive (Do = 7 min) and a less sensitive (Do = 20 min) phase. The less sensitive process was demonstrated to be DNA chain elongation. Transport of thymidine into intracellular pools was significantly less sensitive to thermal shock (Do in excess of 200 min). When HeLa cells were heated at 45 degrees for 15 min there was an 80% inhibition of incorporation of precursors into both DNA and protein with little effect on precursor transport into cellular pools. While the rate of synthesis of whole cell and histone protein (H2a, H2b, H3, and H4) and DNA chain elongation recovered by 6 h after cell heating, total precursor incorporation into DNA was only 0.4 of control levels. The long-term depression of the DNA synthetic rate could not be explained by a cell cycle redistribution, a depression in the total fraction of S phase cells synthesizing DNA, or by a depression in the rate of DNA chain elongation. We conclude that thermal shock results in a long-term depression in the fraction of cell replicons involved in DNA replication.

A fibrinolytic inhibitor of human alveolar macrophages. Induction with endotoxin.

Alveolar macrophages are intimately involved with fibrin during the course of acute and chronic inflammatory processes in the lung. In this study, the capability of macrophages to impede fibrinolysis was investigated. Human alveolar macrophages obtained by lavage from normal volunteers released a fibrinolytic inhibitor during the first 24 h of in vitro culture but only inconsistently and in some cases (7 of 15) not at all. Lysates of freshly lavaged cells had no activity. Endotoxin, 5 to 100 ng/ml, consistently induced intracellular accumulation and extracellular release of a fibrinolytic inhibitor by cultured macrophages. Induction required protein synthesis. The intracellular and secreted forms of the inhibitor were true plasminogen activator (PA) inhibitors, as judged by their ability to block urokinase-mediated conversion of 125I-plasminogen. On average, 10(7) endotoxin-stimulated macrophages secreted sufficient PA inhibitor during a 24-h culture in vitro to neutralize 2 picomoles urokinase (16 international units). Analysis of the interaction of the human macrophage PA inhibitor with 125I-urokinase (apparent size, 33 kilodaltons) by SDS-gel electrophoresis showed that the enzyme and inhibitor mostly dissociated in SDS, but a stable complex occurred at 60 to 65 kilodaltons and a broad band of enzyme or enzyme-inhibitor complexes between 33 and 40 kilodaltons. Either heat treatment of the inhibitor or active site inhibition of urokinase with p-nitrophenylguanidinobenzoate blocked both types of interaction. The pattern of interaction was virtually indistinguishable from that of a partially purified human placental urokinase inhibitor but different from that of serum protease inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities in pathways of alveolar fibrin turnover among patients with interstitial lung disease.

Fibrin deposition is prominent in the histopathologic features of chronic interstitial lung disease. Human alveolar macrophages can potentially modulate this process because normal macrophages synthesize and express the initial enzymes of both coagulation and fibrinolytic pathways. In the present study, we examined the cell-associated procoagulant activity of macrophages lavaged from patients with sarcoidosis (n = 14) or idiopathic pulmonary fibrosis (n = 13) and compared the enzyme activities with that of a group of normal volunteers (n = 16). Cells from sarcoid patients had a mean (+/- 1 SD) tissue factor activity of 1,491 +/- 2,160 units/5 X 10(5) cells, as compared with a mean of 480 units (range, 140 to 1,000 units) for normal control subjects. The same cells had a mean plasma Factor VII equivalent of 4.7 ng/10(6) cells, as compared with 0.81 ng/10(6) cells (range, 0.2 to 2.0 ng) for the normal control subjects. The enhanced activity correlated with disease activity as judged by radiographic stage: only patients with Stage II or Stage III disease had consistently elevated procoagulant activity. There was no correlation of procoagulant activity with the percentage of lymphocytes in the alveolar fluid. Cells from patients with idiopathic pulmonary fibrosis also had increased tissue factor (mean, 2,980 +/- 2,619 units) but less consistently elevated Factor VII. There was considerable variation in both procoagulant activity and cell differentials between lavage sites in 10 patients in whom 2 separate lobes were studied concurrently. In addition, we examined the plasminogen activator (PA) activities of lavaged cells and concentrated alveolar fluids.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the enhanced susceptibility of paroxysmal nocturnal hemoglobinuria erythrocytes to complement-mediated hemolysis initiated by cobra venom factor.

When whole serum C is activated by cobra venom factor complexes (CoFBb), paroxysmal nocturnal hemoglobinuria (PNH) III E (the most C-sensitive type) are hemolyzed, but normal and PNH II E (the intermediately sensitive type) are not. Previous studies have shown that after exposure to CoFBb and serum, PNH III E bind relatively large amounts of the trimolecular C complex, C5b67, whereas normal and PNH II E bind virtually none. In the studies reported herein, we have observed that when normal and PNH III E are incubated with isolated C5, C6, and 125I-C7 in the presence CoFBb, the normal E bind more C5b-7 than the PNH cells. When C7-deficient serum is included in the reaction mixture, however, the PNH E are once again observed to bind much greater amounts of C5b-7. These observations suggest that plasma and membrane factors act in concert to restrict the assembly of the trimolecular C5b-7 complex on human E. PNH III E appear to be deficient in the membrane component of this inhibitory system.

Vitronectin (S protein) is associated with platelets.

Vitronectin is a plasma glycoprotein that has regulatory activity in the complement and the coagulation systems, in cell-cell and cell-substrate interactions, and in monocyte/macrophage function. Because of its potential to participate in several of the processes of inflammation and repair, the association of vitronectin with platelets was investigated. Immunochemical studies demonstrated that the majority of the platelet associated vitronectin was intracellular, while a relatively modest amount was localized to the ectoplasmic portion of the plasma membrane. Analysis by Western blot showed that the electrophoretic mobility of platelet associated vitronectin was indistinguishable from that of vitronectin isolated from plasma. In response to thrombin, approximately 1 microgram of vitronectin was released into the supernate of 10(9) platelets, while somewhat less than one-half of the total platelet vitronectin remained cell associated. The binding of vitronectin to platelets was investigated by comparing the capacity of unlabelled vitronectin and fibronectin to inhibit binding of radiolabelled fibronectin to thrombin stimulated platelets. On a weight basis, inhibition by the two proteins was equivalent, suggesting that vitronectin competes with fibronectin for binding to platelet glycoprotein IIb/IIIa. These results demonstrate that vitronectin is a platelet specific protein which, because of its multifunctional properties, may participate in physiological and pathophysiological events associated with thrombosis and haemostasis.