Priming of macrophages for enhanced oxidative metabolism by exposure to proteolytic enzymes

The C-terminus of murine S100A9 inhibits hyperalgesia and edema induced by jararhagin

The effect of a synthetic peptide (H92-G110) identical to the C-terminus of murine S100A9 (mS100A9p) was investigated on hyperalgesia and edema induced by either jararhagin or papain in the rat paw. mS100A9p not only reverted hyperalgesia and edema induced by jararhagin, but also the highest concentration induced antinociception. Hemorrhage induced by jararhagin and its hydrolytic activity were inhibited by mS100A9p. These data suggest that mS100A9p might block jararhagin-induced hyperalgesia and edema by inhibiting jararhagin catalytic activity, since papain-induced hyperalgesia and edema were not inhibited by mS100A9p.

Somatostatin binds to murine macrophages through two distinct subsets of receptors

Somatostatin (SRIF) exerts anti-inflammatory effects, in part by deactivating monocytes/macrophages. Thus, the objective of this study was to characterize specific receptors for SRIF on these cells. Macrophages isolated from mouse peritoneal cells bound [125I]Tyr(0), D-Trp(8) SRIF(14) specifically. Scatchard analysis of saturation binding data revealed two classes of binding sites with an affinity of 0.44+/-0.13 and 2.58+/-0.56 nM, respectively. By sensitive and specific RT-PCR, the mRNAs for the five SRIF receptors (SSTR1 to SSTR5) could be detected. Evidence for the involvement of SSTR1 and SSTR2 in the binding of SRIF to the high and low affinity sites, respectively, was obtained by the demonstration that (1) only SSTR1 and SSTR2 subtype-specific agonists were active in competing for [125I]Tyr(0), D-Trp(8) SRIF(14) binding to high and low affinity sites, respectively, and (2) [125I]Tyr(0), D-Trp(8) SRIF(14) bound to high but not low affinity sites on macrophages isolated from SSTR2 knock-out mice. In conclusion, we have identified and characterized two different SRIF receptor subtypes in murine macrophages.

Reactive oxygen intermediates, nitrite and IFN-gamma in Indian visceral leishmaniasis

Reactive oxygen intermediates (ROI), nitrite and interferon-gamma (IFN-gamma) production were investigated at different times during treatment in 10 patients with visceral leishmaniasis (VL). Hydrogen peroxide (H2O2), superoxide (O2-) and IFN-gamma production by cultured monocytes from patients with active VL were significantly lower compared with the healthy controls. In contrast, nitrite levels in the supernatants from monocyte cultures of VL patients were comparable to healthy controls and increased significantly during antileishmanial therapy. On day 20 of treatment, a significant increase in the release of H2O2, O2- and IFN-gamma was observed. However, at follow-up, 4 months after the end of treatment, the production of H2O2, O2-, IFN-gamma and nitrite had declined significantly. Thus, the impairment in hydrogen peroxide and superoxide production suggests that down-regulation of these mediators may be involved in the reduced killing of parasites by monocytes of active VL patients. Furthermore, the monocytes regained respiratory burst activity as the antileishmanial therapy progressed, suggesting that an immune-based mechanism is involved in successful drug therapy.

Oral supplementation with whey proteins increases plasma glutathione levels of HIV-infected patients

HIV infection is characterized by an enhanced oxidant burden and a systemic deficiency of the tripeptide glutathione (GSH), a major antioxidant. The semi-essential amino acid cysteine is the main source of the free sulfhydryl group of GSH and limits its synthesis. Therefore, different strategies to supplement cysteine supply have been suggested to increase glutathione levels in HIV-infected individuals. The aim of this study was to evaluate the effect of oral supplementation with two different cysteine-rich whey protein formulas on plasma GSH levels and parameters of oxidative stress and immune status in HIV-infected patients. In a prospective double blind clinical trial, 30 patients (25 male, 5 female; mean age (+/- SD) 42 +/- 9.8 years) with stable HIV infection (221 +/- 102 CD4 + lymphocytes L-1) were randomized to a supplemental diet with a daily dose of 45 g whey proteins of either Protectamin (Fresenius Kabi, Bad Hamburg, Germany) or Immunocal (Immunotec, Vandreuil, Canada) for two weeks. Plasma concentrations of total, reduced and oxidized GSH, superoxide anion (O2-) release by blood mononuclear cells, plasma levels of TNF-alpha and interleukins 2 and 12 were quantified with standard methods at baseline and after therapy. Pre-therapy, plasma GSH levels (Protectamin: 1.92 +/- 0.6 microM; Immunocal: 1.98 +/- 0.9 microM) were less than normal (2.64 +/- 0.7 microM, P = 0.03). Following two weeks of oral supplementation with whey proteins, plasma GSH levels increased in the Protectamin group by 44 +/- 56% (2.79 +/- 1.2 microM, P = 0.004) while the difference in the Immunocal group did not reach significance (+ 24.5 +/- 59%, 2.51 +/- 1.48 microM, P = 0.43). Spontaneous O2- release by blood mononuclear cells was stable (20.1 +/- 14.2 vs. 22.6 +/- 16.1 nmol h-1 10-6 cells, P = 0.52) whereas PMA-induced O2- release decreased in the Protectamin group (53.7 +/- 19 vs. 39.8 +/- 18 nmol h-1 10-6 cells, P = 0.04). Plasma concentrations of TNF-alpha and interleukins 2 and 12 (P > 0.08, all comparisons) as well as routine clinical parameters remained unchanged. Therapy was well tolerated. In glutathione-deficient patients with advanced HIV-infection, short-term oral supplementation with whey proteins increases plasma glutathione levels. A long-term clinical trial is clearly warranted to see if this "biochemical efficacy" of whey proteins translates into a more favourable course of the disease.

Putting priming into perspective - from cellular heterogeneity to cellular plasticity

The concept of priming is widely used in cell biology and has come to mean the functional enhancement of a given cell by cytokines. 'Primed' cells have a number of other cellular alterations, although the relationship between functional and phenotypical diversity has not been established. Here, Claus Kroegel and colleagues discuss the dynamic nature of inflammatory-cell priming, which might be part of a broader means of comprehending cell function in disease.

Mechanism of antinephritic effect of proteinase inhibitors in experimental anti-GBM glomerulopathy

We have previously documented amelioration of rat autologous anti-GBM nephritis with the antiproteolytic drugs epsilon-aminocaproic acid (EACA) and aprotinin, given from the day of induction or later in the course of disease. In the present study we investigated potential mechanisms of this effect by assessing interactions of the drugs with proteinase-dependent generation of superoxide anion in glomeruli, and their influence on both GBM degradation in vitro and activity of glomerular proteolytic enzymes. Release of O2- by enzymatically disrupted glomeruli, isolated from nephritic control or EACA/aprotinin-treated rats, was measured with the ferricytochrome reduction method and its activity was correlated with proteinuria and glomerular cellularity at the early phase of the disease. The hydroxyproline release assay was used to quantitate degradation of rat GBM in vitro by leukocyte proteinases stimulated by phorbol myristate acetate (PMA), in the presence or absence of EACA and aprotinin. Finally, the activities of elastase, cathepsins B and L, and plasmin, together with collagenase-like activity, were assessed fluorimetrically in homogenates of glomeruli isolated from control and antiproteolytic-drug-treated nephritic rats. EACA and aprotinin notably inhibited production of superoxide by nephritic glomeruli (by 47% and 66%, respectively), and this effect was not significantly correlated with proteinuria or glomerular hypercellularity at the early stage of disease. On the other hand, generation of O2- by glomeruli of untreated nephritic rats was notably correlated with total glomerular cell counts and numbers of macrophages infiltrating glomeruli. PMA-stimulated neutrophils and macrophages caused degradation of isolated rat GBM in vitro, markedly attenuated in the presence of EACA (P<0.0005) and, to a lesser extent, by addition of aprotinin (P<0.01). The activity of elastase was significantly reduced in glomeruli of nephritic rats treated with EACA or aprotinin (both P<0.001), while activities of remaining proteinases were not appreciably affected. The beneficial influence of proteinase inhibitors on rat anti-GBM disease may be due, at least in part, to abrogation of superoxide generation in nephritic glomeruli. EACA and aprotinin also have potential to interfere with digestion of GBM, and both these effects may be related to suppression of glomerular elastase.

Ebola virus infection in guinea pigs: presumable role of granulomatous inflammation in pathogenesis

An approach combining virology with light and electron microscopy was used to study the organs of guinea pigs during nine serial passages of Ebola virus, strain Zaire. It was observed that the wild type of Ebola virus causes severe granulomatous inflammation in the liver and reproduces in the cells of the mononuclear phagocyte system (MPS). Based on morphological characterization, two types of virus-cell interactions were demonstrated. The obtained data evidenced for heterogeneity of the population of wild type of Ebola virus. The virus accumulated in the liver of the infected animals, and the lesions became more pronounced with passage. Degenerative changes appeared, and their severity was increased with passage in the other organs as well. The set of target cells diversified and, as a result, not only the MPS cells, but also hepatocytes, spongiocytes, endotheliocytes and fibroblasts became involved in the reproduction of Ebola virus. The possible role of granulomatous inflammation in the development of the adaptive mechanism of Ebola virus to guinea pigs is discussed.

Serine protease inhibitors block priming of monocytes for enhanced release of superoxide

Monocytes freshly isolated from human blood produced large amounts of superoxide when triggered by phorbol ester. After monocytes were cultured for 18-24 hr in endotoxin-free, non-adherent conditions, they produced low amounts of superoxide. Addition of lipopolysaccharide (LPS), interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), or platelet-activating factor (PAF) at the beginning of culture 'primed' the monocytes, causing them to maintain a high superoxide response for at least 96 hr. Also, in response to LPS, monocytes secreted TNF-alpha. The ability of LPS, IFN-gamma, TNF-alpha or PAF to maintain the high superoxide response was blocked by addition of inhibitors of serine proteases, either 4-(2-aminoethyl)-benzenesulphonyl fluoride (AEBSF) or 3,4-dichloroisocoumarin. AEBSF was most effective at 200 microns, and required 6 hr for maximum effect. AEBSF did not affect phorbol-triggered superoxide release by unprimed monocytes. AEBSF did not affect cell viability, nor did it interfere with the TNF-alpha secretion in response to LPS. An analogue of AEBSF that lacked ability to inhibit proteases did not affect monocyte responses. 3,4-Dichloroisocoumarin blocked priming at a low concentration, 1 microM. We conclude that activity of a monocyte serine protease is required to maintain the high superoxide response in monocytes primed with LPS, IFN-gamma, TNF-alpha, or PAF.

Respiratory burst of intestinal macrophages in inflammatory bowel disease is mainly caused by CD14+L1+ monocyte derived cells

Macrophages play a crucial role in intestinal mucosal defence, forming dense subepithelial aggregates, particularly in the colon. One of their important bactericidal mechanisms is production of oxygen radicals but this may damage the intestinal epithelium, perhaps as an early step in inflammatory bowel disease (IBD). The potential for release of oxygen radicals from mucosal macrophages in IBD was measured and whether a difference exists between newly arrived (CD14+L1+) monocyte-like cells and resident macrophages (CD14(-)L1-), without or with additional priming in vitro, was investigated. Lamina propria mononuclear cells from six patients with IBD and five with a normal intestine were isolated with an ethylenediaminetetra acetic acid/collagenase/dispase technique and cultured for three days. The cells were tested with or without interferon gamma (200 U/ml) priming in the presence or absence of lipopolysaccharide (1 microgram/ml) for the last 48 hours in cultures. Samples from inflamed IBD mucosa depleted of CD14+ cells by immunomagnetic beads were compared with their undepleted counterparts and with samples from virtually normal mucosa from the same patients. The production of oxygen radicals was measured as the amount of reduced cytochrome C 2.5 hours after triggering with phorbol 12-myristate 13-acetate. The oxygen radical production in macrophages from moderately or severely inflamed mucosa was reduced by median 69% (range 22%-79%, p < 0.027) after depletion of CD14+ cells, reaching a level similar to that found for virtually normal samples from the same IBD patients. Furthermore, this production did not increase significantly in mucosal macrophages from normal reference mucosa and from virtually normal or inflamed IBD mucosa after priming with interferon gamma with or without addition of lipopolysaccharide. Upregulation of a respiratory burst in subepithelial resident macrophages os not a likely pathogenetic step in IBD. The increased oxygen radical production shown by macrophages from IBD lesions can, however, be ascribed to recently extravasated CD14+L1+ monocyte-like cells. Inhibition of extravasation of these reactive cells may form part of a therapeutic approach in the future.

Zanvil Alexander Cohn 1926-1993

Zanvil Alexander Cohn, an editor of this Journal since 1973, died suddenly on June 28, 1993. Cohn is best known as the father of the current era of macrophage biology. Many of his scientific accomplishments are recounted here, beginning with seminal studies on the granules of phagocytes that were performed with his close colleague and former editor of this Journal, James Hirsch. Cohn and Hirsch identified the granules as lysosomes that discharged their contents of digestive enzymes into vacuoles containing phagocytosed microbes. These findings were part of the formative era of cell biology and initiated the modern study of endocytosis and cell-mediated resistance to infection. Cohn further explored the endocytic apparatus in pioneering studies of the mouse peritoneal macrophage in culture. He described vesicular inputs from the cell surface and Golgi apparatus and documented the thoroughness of substrate digestion within lysosomal vacuoles that would only permit the egress of monosaccharides and amino acids. These discoveries created a vigorous environment for graduate students, postdoctoral fellows, and junior and visiting faculty. Some of the major findings that emerged from Cohn's collaborations included the radioiodination of the plasma membrane for studies of composition and turnover; membrane recycling during endocytosis; the origin of the mononuclear phagocyte system in situ; the discovery of the dendritic cell system of antigen-presenting cells; the macrophage as a secretory cell, including the release of proteases and large amounts of prostaglandins and leukotrienes; several defined parameters of macrophage activation, especially the ability of T cell-derived lymphokines to enhance killing of tumor cells and intracellular protozoa; the granule discharge mechanism whereby cytotoxic lymphocytes release the pore-forming protein perforin; the signaling of macrophages via myristoylated substrates of protein kinase C; and a tissue culture model in which monocytes emigrate across tight endothelial junctions. In 1983, Cohn turned to a long-standing goal of exploring host resistance directly in humans. He studied leprosy, focusing on the disease site, the parasitized macrophages of the skin. He injected recombinant lymphokines into the skin and found that these molecules elicited several cell-mediated responses. Seeing this potential to enhance host defense in patients, Cohn was extending his clinical studies to AIDS and tuberculosis. Zanvil Cohn was a consummate physician-scientist who nurtured the relationship between cell biology and infectious disease.(ABSTRACT TRUNCATED AT 400 WORDS)

PMN-derived proteases enhance the affinity of Fc gamma receptor II on myeloid cells, but not on B cells

Treatment of monocytes or K562 cells with proteolytic enzymes like pronase or trypsin, increases both the affinity of the type II Fc receptor for IgG and the signaling via this receptor. In the present study we evaluated whether other proteases could similarly enhance Fc gamma RII affinity. We furthermore assessed whether all cell types expressing Fc gamma RII display this effect. Therefore, proteins from the coagulation system and PMN-derived enzymes were tested for effects on Fc gamma RII-mediated ligand binding. Enzymes of the coagulation system were tested both in fibrinogen-depleted plasma, as well as in purified form. No effects were found on Fc gamma RII-mediated rosette formation for both situations. In contrast, supernatant of stimulated granulocytes as well as leucocyte elastase were observed to be active in augmenting EA-hIgG rosette formation of thrombocytes and myeloid cell lines K562 and U937. The B cell lines Raji and Daudi, did not show enhanced rosette formation after enzyme treatment. The active component from granulocyte supernatant was partially characterized as a serine esterase with an apparent Mw of 30 kD. We tested whether the isotype specificity of Fc gamma RII on K562 cells changes upon enzyme treatment. It was found that all three tested murine subclasses gamma 1, gamma 2a, gamma 2b, bound equally well to this receptor, and interaction with all isotypes was enhanced to the same extent.

Measurement of macrophage adherence and spreading with weak electric fields

A new method to monitor macrophage attachment on protein-coated surfaces and spreading in response to activating agents is described. Murine macrophages were cultured on small gold electrodes coated with protein, and attachment and spreading were detected as electrical impedance changes. The rate of attachment of cells to fibronectin-coated electrodes was measured to be significantly greater than to other proteins tested. Activation agents used included interferon-gamma, lipopolysaccharide and heat killed Listeria monocytogenes. Addition of each agent to macrophages on electrodes resulted in characteristic patterns in the impedance time course with impedance changes as large as 40%.

Trypsin- and chymotrypsin-induced chemiluminescence by isolated rat glomeruli

We examined whether the generation of reactive oxygen metabolites (as quantified by measuring luminol-amplified chemiluminescence) by isolated rat glomeruli could be triggered enzymatically. No response was observed with thrombin (1 or 10 U/ml), collagenase (100, 200, or 400 U/ml), or plasmin (0.1 or 1 U/ml). In contrast, chymotrypsin and trypsin caused a dose-dependent (10-200 micrograms/ml) increase in chemiluminescence from glomeruli. The peak response with chymotrypsin (100 micrograms/ml) and trypsin (50 micrograms/ml) was as follows: resting, 16 +/- 2 X 10(3) cpm/mg protein, n = 17; chymotrypsin, 233 +/- 58 X 10(3) cpm/mg protein, n = 17; and trypsin, 221 +/- 38 X 10(3) cpm/mg protein, n = 10. Tubules had only a minor response. Soybean trypsin inhibitor and aprotinin caused marked inhibition, indicating the dependency of the chemiluminescence response on the protease enzyme activity. The chemiluminescence response was by glomeruli rather than by "contaminating" leukocytes, since a similar marked response (n = 6) was observed in glomeruli isolated from cyclophosphamide-treated leukopenic (leukocyte less than 1,000/mm3) rats. Superoxide dismutase, a scavenger of superoxide, and free-radical scavengers benzoate and tryptophan inhibited the glomerular chemiluminescence response to trypsin and chymotrypsin. Neutral proteases from infiltrating leukocytes and/or renal tissue have been shown to be released in glomerular diseases; our results, which show the generation of chemiluminescence in response to neutral proteases, suggest a potential mechanism for the production of reactive oxygen metabolites in glomerular diseases.

Comparison of wheat germ agglutinin- and phorbol myristate acetate-mediated triggering for macrophage H2O2 release: susceptibilities to various macrophage inhibitors

Murine peritoneal macrophages (M phi S) elicited by a single injection of zymosan A showed a higher responsiveness to the wheat germ agglutinin (WGA)-mediated triggering for H2O2 release than M phi S activated by double injections of the agent. On the contrary, the response to phorbol myristate acetate(PMA)-mediated triggering was higher in the latter M phi S than in the case of the former M phi S. Furthermore, PMA-triggered M phi H2O2 release was found to be inhibited by sarcoma 180 tumor cell-derived proteinaceous factor in a much more marked fashion than the WGA-triggered H2O2 release. These results indicate some significant differences between the cellular mechanisms of the WGA- and PMA-triggering for M phi oxidative burst. On the other hand, microfilament-inhibitors (cytochalasins B and E) and serine protease-inhibitors (tosyl-L-lysine-chloromethyl ketone and tosylamido-2-phenylethyl-chloromethyl ketone), but not microtubule-disrupting agents (colchicine, vinblastine, and vincristine), suppressed both the WGA- and PMA-triggerings for M phi H2O2 release to a similar degree, thereby indicating that the WGA- and PMA-triggerings for M phi oxidative burst have a common process which is dependent on microfilament and serine protease functions. In relation to this, the WGA- and PMA-triggerings for M phi spreading were also depressed by microfilament- and serine protease-inhibitors but not by microtubule-inhibitors, indicating a participation of common membrane functions in the signal transduction in cases of M phi oxidative burst, and cell spreading induced by the WGA- as well as PMA-triggering.

Macrophage membrane proteins: possible role in the regulation of priming for enhanced respiratory burst activity

Brief exposure of macrophages to the proteolytic enzymes papain, elastase, or trypsin primed them for enhanced production of superoxide anion (O2-) in response to stimulation by phorbol myristate acetate (PMA). Priming by trypsin was achieved at 0 degree C, at which temperature trypsin functions as a protease but is not internalized, supporting the concept that protease priming depends on modification of the plasma membrane. Analysis of external membrane proteins after radioiodination of intact cells and separation by gel electrophoresis indicated that papain treatment of macrophages resulted in the cleavage of a membrane protein with a molecular weight of approximately 305K. Membranes from macrophages primed by elicitation with Corynebacterium parvum also demonstrated a reduced amount of the membrane protein at approximately 305 kDa, as well as a reduction of a protein at about 270 kDa. Lipopolysaccharide-elicited macrophages showed a reduced amount of a protein at about 175 kDa. Continuous spectrophotometric assays of O2- release from adherent macrophages indicated that after exposure to a stimulus, protease-treated cells produced O2- more quickly than did control cells (reduced lag time). Inhibitors of protein synthesis augmented the priming effect of papain when added with the protease. These results suggest that protease-induced priming results from inactivation of a membrane protein (or proteins) that exerts a down-regulating effect on the respiratory burst.

Regulation of respiratory burst in murine peritoneal macrophages: differential sensitivity to phorbol diesters by macrophages in different states of functional activation

Activation of macrophages either in vivo or in vitro can modulate the capacity to generate and secrete reactive oxygen intermediates including H2O2 and O2-. Thus, the cellular and biochemical components requisite for execution of the respiratory burst must be regulated during the activation process. In the present report, we have examined murine peritoneal macrophages in different stages of activation for their sensitivity to stimulants of respiratory burst known to activate protein kinase c (i.e., phorbol dibutyrate or diacylglycerol). The results demonstrated that more highly activated macrophages showed, in addition to greater magnitude of H2O2 or O2- production, a two- to fourfold greater sensitivity to these stimuli. While more active macrophages also exhibited a higher rate of H2O2 secretion, the time at which secretion was measured did not account for or modulate the heightened sensitivity. The increased sensitivity to stimulation was dependent upon the stage of activation and not on the agent used to elicit the macrophages. Increased sensitivity of the more active macrophage populations was also seen when physiologic stimuli (i.e., insoluble immune complexes or unopsonized zymosan) were used. These findings indicate that macrophage activation for H2O2 secretion modulates the sensitivity to stimulation such that more H2O2 is produced in a shorter time and at a lower concentration of stimulus, thereby heightening the inflammatory response in several independent ways. Because all the stimuli employed in the present study have in common the ability to activate protein kinase c (either directly or indirectly), the data also suggest that this form of macrophage activation may involve, at least in part, modulation of the stimulus-response coupling mechanisms which utilize this enzyme.

Activation of mouse macrophages causes no change in expression and function of phorbol diesters' receptors, but is accompanied by alterations in the activity and kinetic parameters of NADPH oxidase

Mouse peritoneal macrophages activated in vivo by the injection of Corynebacterium parvum release larger amounts of superoxide anion (O2-) than macrophages from control mice when stimulated with phorbol myristate acetate (PMA). The biochemical bases for this enhanced response of activated macrophages have been investigated by studying the expression and function of receptors for the stimulant, and the activity of the enzyme NADPH oxidase which is responsible for the production of O2- in leucocytes. Studies of binding of phorbol dibutyrate, an agent closely related to PMA, showed that the affinity constants (Kds) and the number of binding sites were the same in resident and activated peritoneal macrophages. The activity of the NADPH oxidase was, however, different in the two macrophage populations which differ in their capacity to release O2-. NADPH oxidase activity was studied in macrophage monolayers after lysis with deoxycholate. The main features of this activity were as follows: stimulation of macrophages with PMA or zymosan caused an increase in NADPH-dependent O2- production; NADPH oxidase activity in the lysates followed the same dose-response curve for different concentrations of PMA as O2- release by intact macrophages; O2- release by intact macrophages could be fully accounted for by NADPH-dependent O2- production by macrophage lysates; activity was strictly substrate-specific, in that NADH could not substitute for NADPH; after stimulation with PMA or zymosan, NADPH oxidase activity was higher in lysates of C. parvum-activated macrophages than in lysates of resident macrophages; NADPH oxidase activities of activated and resident macrophages differed markedly in their kinetic parameters. The NADPH oxidase of macrophages activated by C. parvum or trehalose dimycolate of mycobacterial origin displayed a five to seven times lower Km compared to the enzyme in resident macrophages.

Priming of neutrophils for enhanced release of oxygen metabolites by bacterial lipopolysaccharide. Evidence for increased activity of the superoxide-producing enzyme

We investigated the capacity of bacterial endotoxin (lipopolysaccharide, LPS) to modify the oxidative metabolic response to membrane stimulation of human neutrophils. Neutrophils were pretreated for 60 min with LPS, 10 ng/ml, then stimulated by exposure to fixed immune complexes, the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (FMLP), or phorbol myristate acetate. Release of superoxide anion (O-2) was up to 7-times greater in cells preincubated with LPS, depending upon the stimulus used. Consumption of oxygen and release of hydrogen peroxide (H2O2) were similarly increased, using FMLP as stimulus. The enhancement was accompanied by a reduction in lag time and an increase in the rate of the response, but the duration of the oxidative events was not changed. The molecular basis for the augmented oxidative response of LPS-pretreated cells was investigated. Preincubation with LPS at 0 degrees C prevented priming, but preincubation in the presence of cycloheximide or chelation of extracellular calcium ion did not. Neutrophils preincubated with LPS had slightly decreased numbers of binding sites and equivalent binding affinity for radiolabeled FMLP. Possible changes in the enzyme responsible for the oxidative burst were analyzed by studying NADPH-dependent generation of O-2 by particulate fractions from cells preincubated with LPS or buffer, then stimulated before cell disruption. The fraction prepared from LPS-pretreated neutrophils exhibited greater release of O-2 over a wide range of concentrations of NADPH. The calculated apparent Km for NADPH was equivalent in the two fractions, but the Vmax was increased 2.5-fold in the subcellular fraction from LPS-pretreated cells. These results suggest that LPS could increase neutrophil-mediated host defense or the tissue damage associated with endotoxemia by enhancing the generation of oxygen metabolites by neutrophils. These results also support the concept that the neutrophil is not an end-stage cell in regard to function or metabolic activity.

Human monocyte chemiluminescence triggered by IgG aggregates. Requirement of phospholipase activation and modulation by Fc receptor ligands

Human mononuclear cells stimulated with soluble IgG aggregates generated chemiluminescence, a response attributable to monocytes. Some requirements of this reaction were examined by preincubation of the cells with a variety of inhibitors. The protease antagonists TPCK and TLCK, the phospholipase inhibitors quinacrine and BPB, and the calcium channel blocker verapamil were all inhibitory at micromolar concentrations. The oxygen metabolite scavengers SOD and catalase were less inhibitory. These findings are consistent with a major role for arachidonic acid metabolites in the generation of light. Modulation of monocyte Fc-mediated chemiluminescence also occurred by preincubation of the cells with Fc ligands. While IgG aggregates and monomeric IgG blocked Fc-dependent chemiluminescence, IgG Fc fragments were stimulatory of this response.

Monocyte superoxide anion production in rheumatoid arthritis: preliminary evidence for enhanced rates of superoxide anion production by monocytes from patients receiving penicillamine, sodium aurothiomalate and corticosteroids

In-vitro studies of superoxide (O-2) anion production by blood monocytes after stimulation with either serum treated zymosan (STZ), IgG treated zymosan (IgGTZ), or fluoride ion (F-) were performed on cells from normal controls (n = 22) and patients with classical or definite rheumatoid arthritis (RA) (n = 35). Twenty-two of the patients were on nonsteroidal anti-inflammatory drugs (NSAID) alone and 13 were on either sodium aurothiomalate, penicillamine, corticosteroids, or a combination. Monocytes from RA patients on 'second-line therapy' showed significantly increased rates of O-2 release in response to STZ compared with normal controls, but no increase was seen in monocytes from patients on NSAID alone. With IgGTZ as the stimulus, rates of O-2 release were increased in monocytes from patients on NSAID alone compared with normal controls (p less than 0.02), but were increased to a greater extent in monocytes from patients on second-line therapy (p less than 0.01). There were no differences in basal unstimulated O-2 production and no differences after stimulation with F-. The enhanced release of O-2 by monocytes from patients on second-line therapy could not be attributed to increased disease activity and may be an effect of therapy.

Dissociation of phagocytosis from stimulation of the oxidative metabolic burst in macrophages

We explored the relationship between phagocytosis and the triggering of oxidative metabolism using resident, lipopolysaccharide (LPS)-elicited, and bacille Calmette-Guérin (BCG)-activated murine peritoneal macrophages. Sheep erythrocytes (E) coated with IgG [E(IgG)], E coated with IgM and complement [E(IgM)C], and E treated with 1% glutaraldehyde (GE) were used as stimuli. All three types of macrophages released superoxide anion (O2-) during phagocytosis of E(IgG). All macrophage types phagocytosed E(IgM)C and GE but none were stimulated to release O2- during phagocytosis of these particles. Vigorous consumption of oxygen was also stimulated by the ingestion of E(IgG) but not by ingestion of E(IgM)C or GE. E(IgM)C did not scavenge the O2- released from macrophages during phagocytosis of E(IgG) or during exposure to phorbol myristate acetate, and further addition of IgG anti-E antibody to E(IgM)C or GE permitted optimal stimulation of macrophage O2- release by these particles. The capacity of macrophages to ingest E(IgM)C and GE without stimulating the respiratory burst raises the possibility that clearance of particulate matter not opsonized with specific IgG might be achieved without stimulation of the release of toxic oxygen metabolites, and, therefore, without the risk of oxidative damage to the phagocytic cell or surrounding tissue.

Superoxide release by peritoneal and bone marrow-derived mouse macrophages. Modulation by adherence and cell activation

Macrophages (M phi) activated by BCG and other immune stimuli differ from thioglycollate-elicited M phi (TPM) in releasing O-2 upon initial contact with a foreign substratum. During adherence and spreading, activated M phi release approximately 50% of O-2 levels triggered by phorbol myristate acetate (PMA). The response requires divalent cations (Ca++ or Mg++) and is sensitive to lignocaine, a reversible inhibitor of adhesion. These features distinguish this reaction from the response to PMA, which also triggers substantial release of O-2 from TPM, 60-80% of bacille Calmette--Guérin-activated peritoneal M phi (BCG-PM) activity. During prolonged cultivation as monolayers, peritoneal and bone marrow derived M phi (BMDM) progressively lose their ability to release O-2 in response to PMA and serum-treated zymosan (STZ), although the cells continue to secrete other products and to phagocytose STZ. This loss can be prevented by maintaining peritoneal and BMDM as non-adherent cells in teflon beakers or poly-(2-hydroxyethylmethacrylate) (poly HEMA) coated vessels. High levels of O-2 activity were observed after cultivating TPM on poly-HEMA (300 nmoles O-2/mg/hr after PMA), 10-fold more than adherent controls. BMDM could be induced to release four-fold more O-2, greater than 100 nmoles O-2/mg/hr, after cultivation as non-adherent cells in the absence of L cell-conditioned medium. Our results show that heterogeneity in M phi respiratory burst activity depends on (i) intrinsic differences between populations, (ii) differential responses by activated and non-activated M phi to selective surface stimuli and (iii) modulation by environmental factors which control adherence and growth.

Role of membrane lipids in the immunological killing of tumor cells: II. Effector cell lipids

Peritoneal macrophages (M phi) from mice become cytotoxic after incubation in lymphokine (LK)-rich supernatants of antigen-stimulated spleen cell cultures. Tumoricidal activity is evident with M phi treated with LK for 4 hr, becomes maximal after 8-12 hr incubation and decreases to control levels by 24-36 hr. To gain insight into LK-induced functional changes, the lipid composition of M phi cultured with LK for 0-36 hr was analyzed by high pressure liquid chromatography. LK induced marked changes in M phi lipid composition: cellular content of cholesterol (CHOL) and polyunsaturated fatty acids increased 2- to 3-fold after 8 hr when the cells showed maximal tumoricidal activity. Cellular lipid and fatty acid content returned to control levels by 24 hr when the M phi had lost tumoricidal activity. These changes were not observed with equal numbers of M phi cultured in control supernatants. To analyze further the role of CHOL and unsaturated fatty acids in M phi tumor cytotoxicity, M phi were enriched in CHOL or linolenic acid (18:3) and tested for their ability to kill 1023 tumor cells. Within 1 hr of culture, M phi showed a 3- to 4-fold increase in CHOL or 18:3 content. 18:3-enriched cells were markedly tumoricidal, whereas controls cultured in delipidized medium alone or enriched with saturated fatty acids were cytotoxic. CHOL-enriched M phi were not tumoricidal; indeed, these cells were inhibited in their killing after treatment with LK compared to M phi cultured in delipidized medium with LK alone. These results suggest that UFA aids, whereas CHOL negates, expression of M phi tumor cytotoxicity.

Effect of phorbol myristate acetate, a tumor-promoting agent, on the growth of Mycobacterium lepraemurium in the mouse footpad

Phorbol myristate acetate (PMA), a potent inflammatory agent with tumor-promoting activity, was examined for its effect on the growth of Mycobacterium lepraemurium (MLM) in the left hind footpad of mice. When the animals were infected with 10(4) MLM and received multiple injections of 3 micrograms of PMA in the infection site weekly during the first 2 months and biweekly thereafter, the growth of the bacilli was markedly enhanced. PMA injection in the infection site resulted in severe footpad swelling accompanied by inflammatory signs such as redness, edema, induration, and sometimes ulcer. Acetic acid, as potent an inflammatory and hyperplastic agent as PMA but without any appreciable tumor-promoting action, did not stimulate MLM growth when it was injected biweekly in the site of infection with MLM at a dose of 30 mumol per injection. When mice were infected with 10(8) MLM, proper elimination of bacilli from the infection site was observed during the first 3 months. In this case, multiple injections of PMA in the infection site resulted in the enhancement of the elimination of MLM by host defense mechanisms, although PMA caused as severe inflammation as that observed when MLM infection was produced with a small inoculum (10(4) MLM). In both cases, dexamethasone was synergistic with, but indomethacin and L-l-tosylamide-2-phenyl-ethylchloromethyl ketone were antagonistic to, the effect of PMA.

Role of macrophage lipids in regulating tumoricidal activity

Peritoneal macrophages (M phi) from mice became cytotoxic after incubation with lymphokine (LK); tumoricidal activity was evident with M phi treated with LK for 4 hr, became maximal after 8-12 hr of incubation, and decreased to control levels by 24-36 hr. LK induced marked changes in M phi lipid composition: cellular content of cholesterol (CHOL) and polyunsaturated fatty acid (UFA) content of cellular lipids (especially 18:3) increased two- to threefold after 8 hr when the cells showed maximal tumoricidal activity. Cellular lipid and fatty-acid content returned to control levels by 24 hr when the M phi had lost tumoricidal activity. These changes were not observed with equal numbers of M phi cultured in control supernatants. To analyze the role of CHOL and UFA in M phi tumor cytotoxicity, casein-induced peritoneal M phi were enriched in CHOL or linolenic acid (18:3) and then tested for their ability to kill 1023 tumor cells. The 18:3-enriched cells were markedly tumoricidal, whereas controls cultured in delipidized medium alone or enriched with saturated fatty acid (18:0) were not cytotoxic. CHOL-enriched M phi were not tumoricidal; indeed, these cells were inhibited in their killing after treatment with LK compared to M phi cultured in delipidized medium with LK alone. The effects of 18:3 and CHOL enrichment of the M phi on their metabolic status, inflammatory function, and tumor cell-binding capacity were tested. The 18:3-enriched M phi were depressed in their ability to synthesize protein and in phagocytic activity compared to controls; these cells showed a transient increase in superoxide release. M phi cultured with 18:3 for 48 hr were also cytotoxic for P815 tumor cells, but did not show an enhanced capacity for P815 binding compared to controls. CHOL-enriched M phi were similar to control cells in their protein synthesizing and phagocytic activities; these cells also showed an early transient increase in superoxide release. CHOL-enriched M phi were not cytotoxic for P815 cells, but bound the tumor cells more readily than did the 18:3-enriched M phi. The data suggest that endogenous levels of 18:3 and CHOL can regulate M phi tumor cytotoxicity, but not through regulation of M phi protein synthesis, oxidative metabolism, or augmented capacity for tumor target binding.

Heparin receptors on mouse macrophages

This study deals with the nature of the attachment between the macrophage cell membrane and heparin molecules. Treatments intended to remove or internalise macrophage receptors (trypsinisation and stimulation of phagocytosis respectively) were shown to considerably modulate the attachment of heparin. An excess of heparin fractions ranging in mean molecular weight from 8100 to 25700 all inhibited attachment of 35S heparin as did a mixed isomer chondroitin sulphate preparation. Our study provides evidence for the presence of receptors for sulphated glycosamino-glycans on the mouse macrophage cell membrane.

Digestion and resynthesis of receptors binding IgG-sensitized erythrocytes on rat macrophages

The proteinase sensitivity of rat macrophage Fc receptors (FcR) binding rabbit IgG-sensitized sheep erythrocytes (EA) was analysed by incubating alveolar macrophages with trypsin, alpha-chymotrypsin, pronase, granulocytic elastase and inhibitors of protein biosynthesis. Even under conditions at which enzymes alone did not bring about any receptor degrading effect, a reduction of cycloheximide. After a temporary blockade of protein biosynthesis by cycloheximide of macrophages which had lost their FcR through treatment with pronase, a rapid reappearance of EA-binding activity could be observed when the cells were washed and incubated in medium without drug or enzyme. On the other hand, the blockade induced by actinomycin D could not easily be reversed. The rate of reappearance of EA-binding activity of alveolar macrophages (AM psi) was faster than that of peritoneal macrophages (PM psi). Our results may suggest an alternative explanation for the apparent resistance of receptors to proteolytic digestion. The finally observed result may be caused by re-expression of FcR--either newly synthesized or from an intracellular pool--as well as by an inaccessibility of the receptor to the enzyme.

Macrophage functions in antimicrobial defense

In the present short review article, we discuss some recent findings regarding the role of macrophages in antimicrobial defense. Problems that are briefly considered include the production of monocytes and its modification in infectious diseases; the role of circulating monocytes and "fixed" macrophages in the blood stream; emigration of monocytes from the vascular bed and their accumulation at sites of microbial attack; role of macrophages in immune responses; stimulation and activation of these cells including secretory functions; attachment to their surface and phagocytosis of microorganisms; microbicidal activities of macrophages; their role in granuloma formation; inherited and acquired deficiencies of macrophage functions. Emphasis is placed on currently unresolved problems.

The human FcR. III. Effects of pronase on soluble immune complex binding by polymorphonuclear leucocytes, monocytes and pulmonary macrophages

The effect of Pronase incubation on the Fc receptors of human polymorphonuclear leucocytes (PMN), monocytes and pulmonary alveolar macrophages was evaluated by Scatchard analysis of the binding of soluble immune complexes at equilibrium. All three cell types, when preincubated with Pronase, demonstrated a significant increase in Fc receptor affinity. Maximum binding (which measures the number of Fc receptors) on polymorphonuclear leucocytes was reduced 45%-50% but was unchanged on monocytes and pulmonary macrophages. The changes in Fc receptor affinity and maximum binding of the PMN were reversible in short-term culture, an effect which was prevented by cycloheximide. These studies indicate that the affinity of the Fc receptor of human phagocytic cells may change significantly independent of changes in receptor number and that this effect can be caused by extracellular proteases. In addition, the human polymorphonuclear leucocyte demonstrates a subpopulation of Fc receptors which is decreased by Pronase and which recovers, in vitro, by a process requiring protein synthesis.