Enhanced superoxide anion release from phagocytes by muramyl dipeptide or lipopolysaccharide

Dynamic aspect of reactive oxygen and nitric oxide in oral cavity

Oral mucosa is a critical protective interface between external and internal environments. Therefore, it must serve as a barrier to a huge number of microbial species present in the environment. Saliva is an important factor that provides for the environment in the oral cavity, and it is indispensable to the host defense reaction in this manner. Oral neutrophils are also important contributors to maintaining the balance between health and disease in this complex environment. These produce reactive oxygen species, nitric oxide, and several antimicrobial peptides, and enzymes. Neutrophils and saliva all contribute to the maintaining the health of the oral cavity in overlapping but independent ways. In addition to production by neutrophils and macrophage, some bacteria can also generate superoxide, hydrogen peroxide, and nitric oxide. Dietary intake of nitrate-enriched vegetables might play important roles in the protection of the oral and stomach against hazardous pathogens via the gastro-intestinal-salivary cycle of nitric oxide (NO) and related metabolites. This review will focus on defense system of the human oral cavity and metabolism of reactive oxygen and NO.

Experimental enteropathy in athymic and euthymic rats: synergistic role of lipopolysaccharide and indomethacin

The aim of this study was to investigate the immunologic and microbiological bases of indomethacin enteropathy. Athymic nude and euthymic specific pathogen-free (SPF) rats were reared under conventional or SPF conditions. In each group, indomethacin was given intrarectally for 2 days. Indomethacin enteropathy was evaluated using a previously described ulcer index and tissue myeloperoxidase activity. Both euthymic and athymic nude rats developed intestinal ulcers to the same degree under conventional conditions but no or minimal ulcer under SPF conditions. Pretreatment of conventional rats with intragastric kanamycin sulfate, an aminoglycoside antibiotic, attenuated indomethacin enteropathy in a dose-dependent fashion. Interestingly, when lipopolysaccharide was injected intraperitoneally in kanamycin-pretreated rats, it fully restored enteropathy in these rats in a dose-dependent manner. We confirmed that kanamycin decreased the number of gram-negative bacteria and endotoxin concentration of the small intestine in a dose-dependent fashion. These results indicate that indomethacin enteropathy is bacteria dependent and does not require a T cell function. Synergy between indomethacin and bacterial lipopolysaccharide may play a major role in this enteropathy.

Side-effects of peptidoglycan monomer (PGM) treatment in mice

The influence of single (4 mg/mouse) and multiple (1 mg/mouse per day for 5 consecutive days) injections of PGM on some hepatic enzymes, lipid peroxide generation in serum and liver, sialic acid concentration in serum and spleen and hepatic lysosomal membrane permeability was investigated. The studies performed showed that a single injection of PGM in vivo changed temporarily the permeability of lysosomal membranes, lipid peroxidation products and sialic acid concentration, and when administered in vitro modulated superoxide anion production and did not affect the activity of lysosomal membrane enzymes. Multiple injections of PGM did not cause significant changes in the examined parameters. Although the metabolic changes were time-limited and from the toxicological point of view, provoked transient effects, the results obtained may be of importance when using PGM in combined chemo-immunotherapy.

Modulation of the intracellular survival of Brucella abortus by tuftsin and muramyl dipeptide

Tuftsin, a physiologic bioactive peptide of animal origin, and muramyl dipeptide, a synthetic bioactive glycopeptide of microbial origin, are known to enhance several recognized macrophage functions and increase non-specific resistance of the host against a number of pathogens. The influence of these two bioactive peptides was studied in permissive bovine mammary macrophages that were unable to control the intracellular replication of Brucella abortus and restrictive bovine mammary macrophages that were able to effectively reduce the intracellular survival of B. abortus. Addition of tuftsin (Thr-Lys-Pro-Arg) or muramyl dipeptide significantly (P < 0.03) enhanced the ability of the permissive macrophages to control the intracellular replication of B. abortus strain 2308 and resulted in the functional conversion of the permissive macrophages into restrictive macrophages. Addition of tripeptide tuftsin fragment (Lys-Pro-Arg), a natural inhibitor of tuftsin, to the medium completely abrogated the effect of tuftsin (P < 0.03). No additive effect on the ability of the macrophages to control the survival of B. abortus resulted from the combination of tuftsin and muramyl dipeptide.

Suppression of the development of tumoricidal function in gamma interferon-treated human peripheral blood monocytes by lipopolysaccharide: the role of cyclooxygenase metabolites

Bacterial lipopolysaccharide (LPS) is generally regarded as one of the most potent macrophage activators. Thus, LPS has been used as an obligatory second signal to stimulate macrophage cytotoxic function against a wide array of bacterial and neoplastic targets. In this study, however, we define conditions under which LPS can suppress the development of cytotoxic function in normal human peripheral blood monocytes. When monocytes were treated with a priming dose of gamma interferon (gamma-INF), followed 18-24 hr later by a triggering dose of LPS, significant cytotoxic function developed. However, when monocytes were treated with even minimal amounts of LPS during priming with interferon, the development of cytotoxic function following stimulation with a second, triggering dose of LPS was virtually abolished. This effect could be produced from 0 to 14 hr following the addition of gamma-INF. The inhibition of monocyte cytotoxicity which was produced by LPS treatment during priming was dose dependent and could not be overcome by modifying either the priming dose of gamma-IFN or the triggering dose of LPS. The suppression was largely overcome, however, by treatment with the cyclooxygenase inhibitor, indomethacin. The possibility that LPS-induced suppression of monocyte cytotoxicity was mediated by products of the cyclooxygenase pathway was supported further in this study by demonstrating that LPS stimulated the production of significant amounts of prostaglandin E2 (PGE2) from monocytes and that this was facilitated by gamma-IFN. In kinetics studies, it appeared that LPS suppression of monocyte activation was correlated temporally with a heightened sensitivity to suppression by exogenously added PGE2, a condition which was reduced greatly by the end of the priming phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Selection of a muramyl peptide based on its lack of activation of nuclear factor-kappa B as a potential adjuvant for AIDS vaccines

Activation of the cellular transcription factor nuclear factor-kappa B (NF-kappa B) by cytokines and other immunostimulants has been tightly linked with enhanced replication of human immunodeficiency virus-type 1 (HIV-1) in infected cells. Various immunomodulators are currently being examined in animal and human trials for their suitability as adjuvants in potential vaccines against acquired immunodeficiency syndrome (AIDS). It may prove to be beneficial to select adjuvants that do not induce NF-kappa B activation and particularly if the vaccines are to be aimed at seropositive individuals. We have examined a battery of synthetic immunostimulants of the muramyl peptide family for their ability to activate NF-kappa B in human and mouse cell lines. In this report, we demonstrate selective activation of NF-kappa B in different cell lines and by different muramyl peptides possessing immunostimulatory activities. The mechanism of such activation is apparently via production of reactive oxygen intermediates (ROI) since pretreatment of cells with antioxidants blocked subsequent activation of NF-kappa B. However, among all the molecules tested only one lipophilic, non-pyrogenic adjuvant active muramyl peptide showed a complete lack of NF-kappa B activation in all cell lines tested. This molecule could well become the adjuvant of choice in future AIDS vaccines.

Species dependency of in vitro macrophage activation by bacterial peptidoglycans

The effect of various bacterial cell wall components on in vitro biological function of murine peritoneal exudate macrophages was evaluated. We examined four different parameters of metabolic activity and monokine secretion. Peritoneal exudate macrophages from rats and guinea pigs, all of the strains tested, were stimulated by whole bacterial cell wall preparations, purified bacterial cell wall peptidoglucans, its water-soluble peptidolglycan fragments, muramyl dipeptides and amphipathic substances. Murine peritoneal exudate macrophages were activated by amphipathic substances of gram-positive bacteria. However, macrophages from mice, irrespective of strains, were not stimulated in the in vitro assay systems by purified bacterial cell wall peptidoglycan, water-soluble bacterial peptidoglycan fragments or muramyl dipeptides. These results suggest that macrophage activation by bacterial peptidoglycan in vitro is animal species specific.

Host mediators in gingival crevicular fluid: implications for the pathogenesis of periodontal disease

During the past few years, a considerable number of studies have examined different aspects of the host response in gingival crevicular fluid (GCF), including the relationship of specific markers to the active phases of periodontal disease. Various indicators of the acute inflammatory response (the lysosomal enzymes beta-glucuronidase and collagenase, the cytoplasmic enzyme aspartate aminotransferase, and the arachidonic acid metabolite PGE2) have been shown to be associated with clinical attachment loss in chronic adult periodontitis in man and experimental periodontitis in animal models. In contrast, the relationship of indicators of the humoral immune response in GCF to active periodontal disease is equivocal. Furthermore, a number of indicators of the cellular immune response have been identified recently in GCF (i.e., Interleukin-1 alpha, IL-1 beta, tumor necrosis factor-alpha), but their relationship to active phases of periodontal disease have not been studied. The polymorphonuclear leukocyte (PMN) is the cellular hallmark of acute inflammation. Evidence from the GCF studies suggests that hyperreactivity of these cells plays a critical role in the active phases of some forms of periodontal disease. Metabolic activation of PMN can be associated with a number of potentially destructive reactions. The major effector mechanism for tissue destruction that can be specifically identified with the PMN is the synergistic effect of the release of PMN proteases and the generation of reactive oxygen metabolites by these cells. Priming of the PMN, where the PMN response is enhanced by agents that do not initiate the response, may be an important mechanism for PMN activation in the crevicular environment; for example, cytokines such as IL-1 beta and TNF-alpha, and lipopolysaccharides released from subgingival Gram-negative bacteria, can serve this function. The hypothesis proposed here argues that in addition to the severe forms of periodontal disease that have been associated with qualitative or quantitative PMN defects, tissue destruction in the periodontum can be observed with hyperreactivity of these cells. These differing conclusions do not create a dilemma, but may represent opposite ends of a balance that is no longer in equilibrium.

Priming of human alveolar macrophages and blood monocytes for superoxide anion release by interferons and lipopolysaccharide

Biological agents such as the interferons (IFNs) or lipopolysaccharides (LPSs) can prime phagocytic cells to generate increased amounts of oxygen metabolites upon exposure to various stimuli. The priming of human peripheral blood monocytes and alveolar macrophages (AM) by recombinant IFN-beta ser (rIFN-beta ser) and rIFN-gamma for an enhanced respiratory burst was compared. Both rIFN-beta ser and rIFN-gamma increased phorbol myristate acetate-stimulated superoxide anion generation by AM in a dose-dependent fashion. rIFN-beta ser was capable of priming AM for an enhanced superoxide anion release nearly as well as rIFN-gamma. In contrast, rIFN-beta ser was much less effective as a priming agent for monocytes when compared to either its effect on AM or to the priming effect of rIFN-gamma on monocytes. The respiratory burst of IFN-exposed AM was not inhibited by co-incubation with low concentrations of LPS. However, the ability of IFN to augment superoxide anion release by cells simultaneously exposed to LPS in comparison to superoxide anion generation by cells exposed to LPS only was attenuated.

The electron microscopic immunolocalization of a copper-zinc superoxide dismutase in association with collagen fibers of periodontal soft tissues

Periodontal soft tissues were cleaved from freshly extracted human teeth. Tissues were then prepared for subsequent biochemical and morphological studies according to the following plan: 1) immediate immersion in liquid nitrogen for the biochemical assay of superoxide dismutase (SOD); 2) immediate fixation prior to routine preparation for routine transmission electron microscopy; 3) immediate fixation prior to preparation for electron microscopic immunohistochemistry. Biochemical analysis showed that the human periodontal ligament contained about twice as much SOD activity as human skin (dermis), but considerably less enzyme activity than that seen in red blood cells. Interestingly, periodontal SOD activity appeared to decrease with age. Immunohistochemistry localized enzyme activity to the periphery of matrix collagen fibrils and to the glycocalyx of tissue fibroblasts. The pathophysiology of this enzyme regarding inflammatory diseases such as periodontitis is discussed.

Bacterial lipopolysaccharide enhances polymorphonuclear leukocyte function independent of changes in intracellular calcium

Bacterial lipopolysaccharide (LPS) enhanced expression of C3bi receptors (CR3), phagocytosis of opsonized bacteria, and subsequent hydrogen peroxide (H2O2) production by human polymorphonuclear leukocytes (PMNs). The role of changes in intracellular calcium concentration ([Ca2+]i) in LPS-induced priming was examined by determining the effect of modulators of intracellular calcium on enhanced PMN function, determining the ability of calcium ionophores to reproduce the effects of LPS, and measuring PMN [Ca2+]i following addition of LPS. Inhibition of intracellular calcium-dependent processes with TMB-8 or quin-2 blocked all three measures of LPS-induced priming. LPS did not stimulate an increase in [Ca2+]i, and calcium ionophores failed to reproduce the effect of LPS. Maintenance of [Ca2+]i is necessary for LPS priming, but an increase in [Ca2+]i is not a component of the signal transduction pathway leading to PMN priming by LPS.

Recombinant granulocyte colony-stimulating factor and lipopolysaccharide maintain the phenotype of and superoxide anion generation by neutrophils

Superoxide anion (O2-) generation by human blood neutrophils induced by phorbol myristate acetate, formyl-methionyl-leucyl-phenylalanine, and monoclonal antibody YI51 was measured 24 h after incubation in medium alone, medium with recombinant human granulocyte colony-stimulating factor (rG-CSF), and medium with lipopolysaccharide (LPS). Monoclonal antibody YI51 was able to bind to neutrophils and induce O2- generation after the addition of anti-mouse immunoglobulin antibody as a cross-linking agent. In the 24-h culture, there was no significant difference in neutrophil survival among the three cultures. The amount of O2- generated by neutrophils in control medium markedly decreased compared with that before culture. However, cells in medium with rG-CSF or LPS maintained the ability to generate O2- well or moderately, respectively. Thus, the activity maintained by rG-CSF and LPS was neutralized by the anti-G-CSF serum. Furthermore, significant amounts of G-CSF were detected in supernatants of neutrophils cultured with LPS for 24 h. It was not detectable, however, in control supernatants. To examine whether the phenotype of the plasma membrane of cells changed in the 24-h culture, expression of CD16 (FcR III) and YI51 antigens was analyzed by flow cytometry. The expression of CD16 and YI51 antigens on cells cultured with rG-CSF or LPS was maintained compared with that of control cells. These observations thus indicate that G-CSF is one of the factors essential to maintain the functioning and phenotype of mature neutrophils.

Macrophages are stimulated by muramyl dipeptide to induce polymorphonuclear leukocyte accumulation in the peritoneal cavities of guinea pigs

N-Acetylmuramyl-L-alanyl-D-isoglutamine (muramyl dipeptide [MDP]) injected intraperitoneally significantly increased the number of cells entering the peritoneal cavity of guinea pigs primed with liquid paraffin or thioglycollate. There was a close relationship between peritoneal polymorphonuclear leukocyte (PMN) accumulation and the uptake of glucosamine by macrophages in guinea pigs treated with a variety of bacterial cell surface components such as cell wall peptidoglycan subunits and bacterial or synthetic lipid A. The PMN accumulation was also facilitated by the intraperitoneal transfer of the peritoneal macrophages that had been stimulated by MDP in vitro. Furthermore, cell-free lavage fluids taken from the peritoneum of MDP-treated guinea pigs also initiated the influx of PMNs when introduced into the peritoneal cavities of liquid paraffin-pretreated guinea pigs. These results suggest that a soluble factor which attracts neutrophils is produced by MDP-treated macrophages. Partial characterization of the factor is described.

Role of intracellular calcium in priming of human peripheral blood monocytes by bacterial lipopolysaccharide

To determine the role of intracellular calcium ([Ca2+]i) in the priming of monocytes (M phi) by bacterial lipopolysaccharide (LPS), the membrane expression of two functional proteins and phagocytosis and respiratory burst were examined by microfluorimetry. LPS induced a significant increase in HLA-DR and C3bi receptor (CR3) expression within 2 h of its addition to whole blood. The enhanced expression of both antigens by LPS was dose-dependent, with concentrations as low as 0.1 ng/ml producing a response. The involvement of [Ca2+]i was demonstrated by loading isolated M phi with the intracellular calcium chelator quin-2 or the inhibitor of intracellular calcium redistribution TMB-8 prior to addition of LPS. Both compounds inhibited the LPS-induced increase in HLA-DR and CR3 expression. No role for extracellular calcium, for calcium slow channel flux, or for the calcium-calmodulin complex in LPS priming was demonstrated when LPS was added in the presence of EGTA, trifluperazine (TFP), or verapamil. The addition of the calcium ionophores A23187 or ionomycin failed to increase expression of either antigen. Prior exposure to LPS primed M phi for enhanced phagocytosis and respiratory burst activity. These functions were inhibited by TMB-8, but not by TFP or verapamil. Addition of LPS to isolated M phi increased [Ca2+]i by 23% at 30 sec and 42% at 5 min, as measured by the calcium-sensitive, intracellular probe indo-1. These results suggest that intracellular Ca2+ mobilization is necessary, but not sufficient, for LPS-induced priming of human peripheral blood monocytes.

Phorbol myristate acetate modulates calcium ion-dependent superoxide anion generation induced by a monoclonal antibody raised against polymorphonuclear leukocytes

We used a monoclonal antibody, YI 51, raised against human polymorphonuclear leukocytes (PMN) to induce superoxide anion (O2-) generation in cells. Although YI 51 alone played only a small part in inducing O2- generation in PMN, the amount of O2- generation induced in 5 X 10(5) PMN was 3.7 to 5.5 nmol/min when F(ab')2 fragments of rabbit anti-mouse immunoglobulin antibody were added as a cross-linking agent. This O2- -inducing activity was high compared with that of wheat germ agglutinin (WGA), insoluble immunoglobulin G immune complexes (IC), or phorbol myristate acetate (PMA). The binding of YI 51 and soluble immunoglobulin G IC to PMN was not reciprocally inhibitory, indicating that YI 51 does not interfere with ligand binding to the Fc receptor-binding site. In the absence of calcium ion (Ca2+), O2- generation induced by YI 51 decreased to 10 to 20% of that in the presence of Ca2+. In contrast, O2- generation in response to WGA, IC, or PMA under Ca2+-free conditions was not affected. When PMN were pretreated with low concentrations of PMA (10(-10) to 10(-9) M), the amount of O2- generation by the cells in response to YI 51 in Ca2+-free buffer was enhanced in a concentration-dependent manner. It also equaled the O2- generated by the cells in buffer containing Ca2+. In cells pretreated with PMA, the amount of O2- induced by WGA was enhanced two- to threefold over that in untreated cells. In contrast, there was no augmentation over untreated cells with stimulation by IC. These results suggest that YI 51, IC, and WGA induce O2- generation in human PMN in different manners.

Macrophage-produced oxygen radical generating activities for polymorphonuclear leukocytes

Guinea pig peritoneal macrophages were stimulated in vitro by bacterial lipopolysaccharide. After incubation, the supernatants of macrophage cultures were collected and tested for O2- production on guinea pig peritoneal polymorphonuclear leukocytes. The supernatants of macrophage cultures stimulated by lipopolysaccharide had significantly higher levels of O2- -generating activities in polymorphonuclear leukocytes, and these activities appeared in the macrophage cultures within 2 h after stimulation by lipopolysaccharide. However, the supernatants obtained from the nonstimulated cultures could not produce these activities. These activities disappeared with heating or trypsin and were not produced in macrophage cultures by incubation with cycloheximide.

Different effects of bacterial lipopolysaccharide on superoxide anion production by macrophages from normal and tumor-bearing rats

Bacterial endotoxins or lipopolysaccharides (LPS) exhibit a wide range of modulatory activities on immunocompetent cells. Among the numerous effects of LPS on macrophages, an enhancement of superoxide anion (O2-) release has been reported. In previous studies carried out on tumor-bearing rats, it was found that several functions of peritoneal macrophages such as phagocytic, microbicidal and antiviral activities were depressed. In this paper we evaluated the spontaneous or phorbol myristate acetate (PMA)-induced production of superoxide anion by macrophages from tumor-bearing rats with respect to controls. Moreover, the effect of in vitro priming with LPS on O2- production by the same cells was studied. It was found that the pattern of superoxide release by macrophages from tumor-bearing rats is significantly different from controls. Preincubation of macrophages from normal rats with LPS enhanced the spontaneous and PMA-induced production of O2-. In contrast, the same concentrations of LPS did not prime macrophages from tumor-bearing rats.

Glucosaminylmuramyl dipeptide-induced changes in murine macrophage metabolism

The purpose of the study was to investigate influence of glucosaminyl muramyl dipeptide (GMDP) and its derivatives on adenosine deaminase (ADA, CE 3.5.4.4.) and 5'-nucleotidase (5-N, CE 3.1.3.5) activity in murine macrophages in vitro. The intensity of superoxide radicals (O2-) formation by these cells has been also studied. GMDP incubated with macrophages was found to inhibit substantially the activity of 5-N, without affecting the activity of ADA in these cells. The maximal effect on 5-N activity was noted following 24 h of co-culture and was accompanied by a higher intensity of O2- formation. GMDP added in doses ranging from 0.01 to 1 microgram/ml induced a gradual decrease in 5-N activity, with an increase in activity of the O2- -generating system. The GMDP analog with double dipeptide link GM(DP)2 has demonstrated the same activating effect as GMDP. The presence of dipeptide alanyl-D-isoglutamine in the GMDP structure is necessary for realization of the drug activating effect, as N-acetylglucosaminyl-N-acetylmuramyl failed to influence macrophage activity. Neither D-D nor L-L isomers of the drug affect the 5-N activity and O2- formation in macrophages. The mechanism of macrophages activation induced by GMDP may include the inhibition of 5-N activity and the stimulation in production of superoxide radicals.

Guinea pig Kupffer cells can be activated in vitro to an enhanced superoxide response. I. Comparison with peritoneal macrophages

Guinea pig Kupffer cells were obtained by partial digestion of the liver with pronase and collagenase and purified by centrifugal elutriation. Cells were kept in monolayer culture and their capacity to secrete superoxide anion in response to phagocytosis of zymosan was determined by the cytochrome c method. Compared to resident peritoneal macrophages, Kupffer cells produced somewhat less superoxide (60% +/- 30%). Both cell types were activated by 24 h preincubation with lipopolysaccharide from Salmonella minnesota or muramyl dipeptide to give twice as high a superoxide response to zymosan. The same effect was achieved when Kupffer cells in vitro were incubated for 3 days with supernatants from phytohaemagglutinin-activated peripheral T lymphocytes or recombinant gamma-interferon. These data demonstrate that the resident macrophages of the liver, the Kupffer cells, are able to increase their capacity to secrete reactive oxygen intermediates after proper activation; this fact is possibly important in the pathogenesis of hepatocyte damage upon inflammatory reactions in the liver.

Phagocytic and postphagocytic activities of bovine neutrophils for pure and mixed bacterial cultures

A comparative study of phagocytosis and postphagocytic oxidative metabolic activity of bovine blood neutrophils incubated with pure and mixed cultures of Escherichia coli, Staphylococcus aureus, and Streptococcus agalactiae was preformed. Most neutrophils when incubated with mixed cultures showed preferential phagocytosis for one species and a smaller number phagocytized both species of microorganisms. Percent phagocytosis for E. coli in pure culture was similar to that of Strep. agalactiae in pure culture and higher than that for Staph. aureus in pure culture. Neutrophils incubated with mixed cultures of E. coli and Staph. aureus or E. coli and Strep. agalactiae showed greater than expected phagocytosis of each microorganisms alone and reduced phagocytosis of both microorganisms together. Postphagocytic oxidative metabolic activity of neutrophils, measured by percent nitroblue tetrazolium reduction, did not differ following phagocytosis of these three microorganisms in pure cultures. In comparison, a synergistic effect on nitroblue tetrazolium reductive activity was seen in mixed cultures as evidenced by higher percent nitroblue tetrazolium reduction following phagocytosis of both E. coli and Staph. aureus or E. coli and Strep. agalactiae. These observations indicate that the phagocytic and metabolic activities of neutrophils for bacteria in mixed cultures may not be identical to those in pure cultures.

The superoxide-forming enzymatic system of phagocytes

The formation of oxygen-derived free radicals by the phagocytes (neutrophils, eosinophils, monocytes and macrophages) is catalysed by a membrane-bound NADPH oxidase which is dormant in resting cells and becomes activated during phagocytosis or following interaction of the cells with suitable soluble stimulants. This enzyme is under investigation in many laboratories but its molecular structure remains to be clarified. Possible components such as flavoproteins, cytochrome b558, and quinones have been proposed on the basis of enzyme purification studies, effects of inhibitors, kinetic properties and analysis of genetic defects of the oxidase. An extensive discussion of the evidence for the participation of these constituents is reported. On the basis of the available information on the structure and the catalytic properties of the NADPH oxidase, a series of possible models of the electron-transport chain from NADPH to O2 is presented. Finally, the triggering mechanism of the respiratory burst is discussed, with particular reference to the stimulus-response coupling and the final modification(s) of the oxidase (phosphorylation, assembly, change of lipid environment, etc.) which are involved in its activation.

Biochemical basis of HLA-DR and CR3 modulation on human peripheral blood monocytes by lipopolysaccharide

The biochemical events leading to enhanced membrane expression of HLA-DR and CR3 by human peripheral blood monocytes (MO) following exposure to bacterial lipopolysaccharide (LPS) were examined. In a previous study we demonstrated that an increase in intracellular calcium was necessary, but not sufficient, for MO to increase membrane expression of both antigens within 1 hr of addition of LPS. The present study was initiated to examine the other biochemical requirements which lead to the MO response to LPS. Enhanced expression of both antigens following addition of LPS was dependent on microfilament function, but independent of microtubule function and of protein synthesis. Inhibition of formation of cyclooxygenase or lipoxygenase metabolites of arachidonic acid had no effect on HLA-DR or CR3 modulation by LPS. A role for phosphatidylinositol metabolism was suggested by the inhibition of the MO response to LPS by dibutyryl cAMP and theophylline and by the enhanced expression of both antigens following addition of phorbol diesters. However, H-7, a putative inhibitor of protein kinase C, did not alter the MO response to LPS or phorbol diesters. These results suggest that LPS enhances expression of HLA-DR and CR3 by inducing redistribution of these antigens from an intracellular pool. The data also support a role for the generation of hydrolysis products of phosphatidylinositol, leading to calcium redistribution and activation of protein kinase C or other kinases, in the MO response to LPS.

Enhanced oxidative burst without interleukin 1 production by normal human polymorphonuclear leukocytes primed with muramyl dipeptides

Purified polymorphonuclear (PMN) cells were obtained from human blood leukocytes by centrifugation on colloidal silica gradients. PMNs could be primed for PMA-triggered oxidative burst by muramyl peptide molecules (MDP) and two of its adjuvant active nonpyrogenic derivatives. The priming effect of MDP could be demonstrated after a 1-h incubation period, whereas monocytes needed an 18-h incubation to produce an enhanced response in the NBT reduction test. Only the monocyte-enriched population was able to produce IL-1 activity after muramyl peptide stimulation. Under such conditions, PMNs neither produced nor secreted IL-1-like activity, and no IL-1 inhibitor was present in the supernatant fluids. In conclusion, muramyl peptides were able to prime PMNs for oxidative burst but not to stimulate IL-1-like factor production.

RU-41740 (K. pneumoniae glycoprotein) enhances resistance to experimental candidiasis and stimulates phagocytic functions

RU-41740, a purified glycoprotein extract from Klebsiella pneumoniae, (which is an efficient non-specific immune activator in a broad spectrum of in vitro and in vivo reactions) was administered either orally or parenterally in the mouse. It enhanced the resistance of mice to candidiasis, both in terms of survival rate and a decrease in viable yeast cell recovery in kidneys. The drug administered at 0.1 mg or 1 mg/kg augmented 4-fold the mean survival time (MST) of animals infected with 1 to 2 X 10(6) Candida albicans, both by the intraperitoneal and the intravenous route. The effect of the orally administered drug was less striking but nonetheless present. At 10 mg/kg, the MST of infected animals increased about 2-fold. In vitro, in the presence or absence of zymosan, the drug at 10 or 100 micrograms/ml was able to stimulate the phagocytic process of elicited mouse peritoneal cells (65% polymorphonuclear cells, 35% macrophages) and human peripheral blood cells (95% polymorphonuclear cells, 5% monocytes) in terms of activated oxygen species production. The involvement of polymorphonuclear cells in the mechanisms of natural resistance to C. albicans infection led us to discuss the role of these cells as targets for the drug.

Effect of lipopolysaccharide on intracellular killing of Leishmania enriettii and correlation with macrophage oxidative metabolism

The effect of lipopolysaccharide (LPS) on the lymphokine (LK)-dependent activation of murine peritoneal macrophages for intracellular killing of Leishmania enriettii parasites was investigated. Exposure to LPS alone did not induce macrophages to kill the parasite. In the presence of LK or recombinant interferon-gamma, however, which by themselves rendered the macrophages only weakly cytotoxic, considerable stimulation of intracellular parasite killing was achieved already at a LPS concentration of 1 ng/ml. The response to LPS was of the same magnitude in macrophages tested for intracellular killing as in parallel assays of extracellular cytolysis of target cells. Acquisition of leishmanicidal activity by macrophages exposed to LK and LPS correlated with stimulation of the respiratory burst, as shown by increased hexose monophosphate shunt levels, and priming for elevated chemiluminescence and O2- and H2O2 production. Polymyxin B blocked both this LPS-dependent metabolic activity and intracellular parasite destruction. Intracellular killing was, however, not solely dependent on oxidative metabolism of macrophages since in the absence of LK, LPS stimulated respiratory burst activity, yet no intracellular killing was observed, and triggering of the respiratory burst by phorbol myristate acetate or zymosan did not affect intracellular parasite survival. These results suggest that, in this experimental model, efficient intracellular parasite killing depends both on increased production of oxygen metabolites and on the availability of so far unidentified factor(s), the synthesis of which requires exposure of macrophages to both LK and LPS.

Anthrax toxin blocks priming of neutrophils by lipopolysaccharide and by muramyl dipeptide

We studied the pretreatment of human polymorphonuclear neutrophils (PMN) with purified preparations of the anthrax toxin components--protective antigen (PA), edema factor (EF), and lethal factor (LF)--and their effects on release of superoxide anion (O-2) after stimulation with the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP). PMN isolated in the absence of lipopolysaccharide (LPS) (less than 0.1 ng/ml) released only small amounts of O-2 after FMLP stimulation; pretreatment with anthrax toxin had little effect. The release of O-2 was increased fivefold by prior treatment with 3 ng/ml LPS for 1 h at 37 degrees C, an effect referred to as priming. PMN were primed to an equivalent extent by treatment with 100 ng/ml N-acetyl-muramyl-L-alanyl-D-isoglutamine (muramyl dipeptide [MDP]). Pretreatment of PMN with anthrax toxin components PA plus EF or PA plus LF inhibited priming by LPS or MDP, as shown by the reduction in the release of O-2 up to 90% relative to controls not treated with toxin; single toxin components were inactive. The inhibition was markedly reduced when priming with LPS or MDP was carried out before exposure to toxin. O-2 release after stimulation by phorbol myristate acetate was not increased by priming, and pretreatment with toxin did not inhibit O-2 release after this stimulus. Evidently, anthrax toxin inhibits the priming that is normally induced in PMN by bacterial products and is necessary for the full expression of antimicrobial effects.

Abolishment of inhibitory effects of 3'-deazaadenosine on superoxide generation of guinea pig phagocytes by pre-exposure to phorbol myristate acetate

Superoxide generation by guinea pig macrophages and polymorphonuclear leukocytes induced by wheat germ agglutinin, immune complexes or formyl-methionyl-leucyl-phenylalanine was inhibited considerably by 3'-deazaadenosine. The pre-exposure of the 3'-dezazaadenosine-treated cells to a small amount of phorbol myristate acetate abolished the inhibitory effect of 3'-deazaadenosine on the generation of superoxide.

The reduction of inflammatory responses in lipopolysaccharide-tolerant eyes

The development of tolerance induced by subcutaneous or intraocular injections of lipopolysaccharide (LPS, Escherichia coli) in rat eyes has been studied. In addition, the ocular inflammatory responses to the reversed passive Arthus (RPA) reaction in the tolerant eyes were investigated. The tolerance in the eye after a single injection of LPS persisted for at least 42 days. Up to 42 days, vasodilatation, disruption of the blood-aqueous barrier, and leukocyte accumulation in the anterior chamber after a second injection of LPS were inhibited. Unilateral intraocular injection of LPS produced local tolerance, which was not observed in the contralateral eyes. The inflammatory reactions in response to RPA in the LPS-tolerant eyes were also significantly attenuated. It was also found that inflammatory reactions induced by RPA or 16,16-dimethyl prostaglandin E2 had no inhibitory effect on the responses to subsequent RPA or LPS administration, which indicated that initial inflammatory reactions do not render the tissues refractory to the response to a second stimuli. The results of this study suggest that some, as yet unknown, local changes in the ocular tissues caused by LPS may be involved in the development of tolerance.

Depressed chemiluminescence response by influenza virus is enhanced after conjugation of viral subunits to muramyl dipeptide

The effect on respiratory burst of murine spleen cells after in vitro exposure to influenza virus, subunits, or subunits conjugated to muramyl dipeptide (MDP) was studied by luminol-dependent chemiluminescence (CL) in response to stimulation by zymosan. CL induced by infectious influenza A virus was depressed but could be elevated to normal levels when MDP was added together with a low, but not with a high, dose of the virus. Profound depression of CL was induced by high doses of influenza A/Brazil, A/Bangkok, and B/Singapore subunits. The same amounts of viral subunits conjugated to MDP restored or even enhanced the CL responses of spleen cells from BALB/c and C57BL/6 mice. Splenic cells from BALB/c mice generated higher levels of CL than did cells from C57BL/6 mice.

Fc receptor-mediated desensitization of superoxide (O2-) generation response of guinea-pig macrophages and polymorphonuclear leucocytes

Guinea-pig macrophages were pretreated with soluble immune complexes (1 hr, at 37 degrees). By this procedure, the capacity of the cells to produce superoxide anions (O2-) upon stimulation with wheatgerm agglutinin (WGA) was inhibited by as much as 80% (desensitization). However, the receptors for WGA were still available on the cell surfaces as determined by the binding of 125I-labelled WGA to both the pretreated and control cells. This inhibition of O2- generation was also observed when opsonized zymosan (Op-zymosan) was used as the stimulus for O2- generation. In contrast, the inhibition by soluble immune complexes was less than 25% of the control levels when the desensitized cells were stimulated with N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP) or phorbol myristate acetate (PMA). The same procedure was also used to desensitize guinea-pig polymorphonuclear leucocytes (PMN). In this case, the O2- generation of the PMN was suppressed to 50-55% of the control level when WGA or fMLP was used as stimulus. However, the PMA-induced O2- generation was far less affected by this treatment, as was the case with the macrophages. The activity of the desensitized macrophages for O2- generation recovered gradually to a normal level 24 hr after removal of the immune complexes from the medium. These results suggest that (i) some regulatory mechanisms which suppress the activation of NADPH oxidase are accentuated by prolonged exposure of guinea-pig macrophages and PMN with soluble immune complexes; (ii) the mechanism for O2- generation mediated by WGA or Op-zymosan may be different from that for O2- generation mediated by PMA, and (iii) the mechanism for O2- generation mediated by fMLP differs between macrophages and PMN.

Oxidative metabolic response and microbicidal activity of human milk macrophages: effect of lipopolysaccharide and muramyl dipeptide

Mouse macrophages can be primed by exposure in vitro to the bacterial products lipopolysaccharide and muramyl dipeptide (MDP) or in vivo by injection of MDP, so that they produce more of the bactericidal agent superoxide anion (O2-) when stimulated by phagocytosis or by contact with phorbol myristate acetate (PMA). Because little is known about the physiology of human tissue macrophages, we examined release of O2- by milk macrophages obtained from 45 normal women for the ability to undergo priming for greater O2- release. In samples from the same individuals, PMA-stimulated O2- release was similar from colostrum (0 to 3 days postpartum) or from transitional milk (5 to 8 days). Release of O2- by milk macrophages was almost identical to that by blood monocytes from the same women. Milk macrophages phagocytized and killed Candida albicans relatively effectively. Incubation with lipopolysaccharide activated the macrophages in that they were primed for greater PMA-stimulated O2- release. Incubation with the adjuvant MDP or its analog 6-O-(2-tetradecylhexadecanoyl)-MDP did not prime, but incubation with a second analog, 6-O-(stearoyl)-MDP, primed the macrophage for greater O2- release. These results indicated that human tissue macrophages can be primed for greater oxidative response by exposure to bacterial products. Potential exists for the therapeutic use of such immunomodulating agents in the enhancement of host defense.

Superoxide anion generation by polymorphonuclear leukocytes enhanced in a patient with colony-stimulating activity-producing lung cancer

We examined superoxide (O-2)-generating activity of polymorphonuclear leukocytes (PMN) from a patient with lung cancer in whom there was a marked granulocytosis. There was a high level of colony-stimulating activity (CSA) in both the serum and the supernatant of the culture of the primary tumor. The PMN from the patient produced almost three times more O-2 than did the PMN from healthy donors and other patients with lung cancers but with no granulocytosis. The binding of wheat germ agglutinin (WGA), used as a stimulus for O-2 generation, to the surface membrane of cells and the protein content in the cells were about double that noted in the case of healthy donors. Following total extirpation of the tumor, the level of CSA in the serum decreased, as did activity of PMN for O-2 generation, and the binding of WGA to the cells reverted to normal levels.

Serum factor requirement for reactive oxygen intermediate release by rabbit alveolar macrophages

Alveolar macrophages (AM) from pathogen-free rabbits were unable to release reactive oxygen intermediates (ROI) unless they were conditioned in serum for 24-48 h before triggering with membrane-active agents. The degree of serum conditioning of AM depended upon the concentration of serum used; optimal ROI release was obtained at or above 7.5% fetal bovine serum (FBS). FBS, autologous rabbit serum, pooled rabbit serum, and pooled human serum were each capable of conditioning AM for release of ROI. Serum conditioning of AM requires synthesis of new protein(s); and the enzyme required for ROI production, NADPH oxidase, was only detectable in serum-conditioned cells. Moreover, serum-conditioned cells lost their ability to release ROI after transfer to serum-free medium, while cells maintained in serum-free medium acquired the capacity to release ROI after their transfer to serum-containing medium, demonstrating the reversibility of the phenomenon. Initial purification data indicate that conditioning is mediated by a discrete serum constituent, which precipitates 40-80% saturated ammonium sulfate, does not bind to Cibacron Blue columns, and has a molecular weight of 30,000 to 50,000, as determined by molecular exclusion chromatography. Unlike gamma interferon, which also enhances ROI release by macrophages, our serum-conditioning factor is not acid labile, retaining 67% of its activity after 120 min incubation at pH 2.0. Moreover, it does not appear to be a contaminating endotoxin, since LPS neither conditioned AM for ROI production, nor triggered ROI production by serum-conditioned AM. We propose that such a conditioning requirement may normally protect the lung against ROI-mediated tissue injury. However, during a pulmonary inflammatory reaction initiated by other mediator systems, the resulting transudation of plasma proteins into the alveolar spaces may condition AM in situ for ROI production.

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.

Phorbol myristate acetate-induced modulation of antibody-dependent cellular cytotoxicity by human polymorphonuclear leukocytes

The effect of phorbol myristate acetate (PMA) on the antibody-dependent cellular cytotoxicity (ADCC) of human polymorphonuclear leukocytes (PMNs) against human erythroleukemic K562 cells was studied by the use of a 3-h 51Cr-release assay. Pretreatment of PMNs with PMA (10 ng/ml) for 60 min resulted in inhibition of subsequent ADCC. This inhibition was dependent on doses of PMA. The effect of pretreatment of PMNs with PMA on O2- generation of the cells was also studied. The ability of the cells to generate O2- was not suppressed, and the expression of Fc receptors on the cell membrane was well preserved. In contrast, the addition of PMA to the ongoing ADCC (5 to 30 min after the start of the ADCC assay) enhanced the activity of the cells for ADCC. This augmentation was abolished by catalase, whereas ADCC itself was not affected by the agent. These results imply divalent effects of PMA on the ADCC of PMNs. The suppression of ADCC activity of PMNs by pretreatment with PMA is not due to inhibition of the reactive oxygen burst of the cells. The augmentation of ongoing ADCC by the addition of PMA is due to secretion of hydrogen peroxide from the cells induced by PMA, and this augmentation occurs only when the interaction between effector and target cells exists through Fc receptor.

Enhanced killing of Candida albicans by cultured peritoneal exudate cells treated with SM-1213, a synthetic immunomodulator

The effect of SM-1213 [1,2-O-isopropylidene-3-O-3'-(N', N'-dimethylamino-n-propyl)-D-glucofuranose] on the candidastatic and candidacidal capacity of guinea pig peritoneal exudate cells was investigated. Phagocytes treated with SM-1213 demonstrated an enhanced ability to inhibit intracellular hyphal formation and elongation of Candida albicans cells as well as to reduce the percentage of viable cells remaining after phagocytosis. Significant drug-induced anticandidal effects were also observed when peritoneal exudate cells were preincubated with SM-1213 and washed before infection with C. albicans. SM-1213 had no direct anticandidal effect against the yeast or hyphal form of the fungus, suggesting that the observed candidastatic and candidacidal effect of this drug was due to the enhancement of antimicrobial functions of phagocytes.

Biphasic effects of muramyl dipeptide or lipopolysaccharide on superoxide anion-generating activities of macrophages

The superoxide anion (O2-)-generating activity of guinea pig macrophages stimulated by wheat germ agglutinin (WGA), immune complexes, or phorbol myristate acetate (PMA) was studied after short- and long-term exposures of the cells to muramyl dipeptide (MDP) or lipopolysaccharide (LPS). Neither MDP nor LPS alone induced O2- release in macrophages. Short-term (30 min) exposure to these agents caused the enhanced release of O2- in response to WGA or immune complexes, though the PMA-induced O2- generation was not affected. On the other hand, long-term exposure (more than 24 h) to MDP or LPS progressively enhanced O2- generation of the cells induced by WGA, immune complexes, or even PMA. These results suggest that the mechanism for O2- generation of macrophages stimulated by WGA or immune complexes differs from that stimulated by PMA and that the differences also exist between short- and long-term exposure to MDP or LPS.

Activation of human monocytes by free muramyl dipeptide (MDP)

Activation of human monocytes with MDP (N-acetylmuramyl-L-alanyl-D-isoglutamine) 1-100 micrograms per ml for 48 h in vitro enhanced the cytostatic activity against the target cell line K-562, while cytolysis remained unchanged. Catalase, 600 SU per ml, had no inhibitory effect on the cytostasis mediated by MDP-activated monocytes. The optimal MDP concentration for activation was in the range 3-10 micrograms per ml. Supernatants from monocytes activated with MDP 1-30 micrograms per ml for 48 h exerted no cytostatic activity. MDP 1-100 micrograms per ml had no direct cytostatic or cytolytic effect on the target cells in a 24 h assay. When added to monocytes cultured in vitro for four days immediately prior to the chemiluminescence (CL)-assay, MDP 10-100 micrograms per ml enhanced both the zymosan and phorbol myristate acetate-triggered lucigenin-dependent CL. Monocytes pre-activated with MDP for 48 h did not demonstrate any enhanced CL-response. MDP-activation 30 micrograms per ml for 48 h increased the zymosan-triggered generation of H2O2 moderately. The enhanced cytostatic activity induced by MDP-activation is probably not mediated by hydrogen peroxidase or production of cytostatic factors.

Oxygen radical production by peritoneal macrophages and Kupffer cells elicited with Lactobacillus casei

BALB/c mice were injected intraperitoneally (i.p.) or intravenously (i.v.) with Lactobacillus casei YIT9018 (LC 9018). The i.p. injected LC 9018 augmented oxygen radical (OR) production by peritoneal macrophages (PM) and suppressed the production of prostaglandin E2 by PM. The growth of i.p. inoculated Meth A fibrosarcoma was also inhibited by an i.p. injection of LC 9018. i.v. injection of LC 9018 stimulated OR production by fixed macrophages and inhibited the growth of Listeria monocytogenes in the liver. Furthermore, glucose-6-phosphate dehydrogenase activity in the liver was significantly increased (10 to 20 times) by LC 9018 i.v. injection. A significant correlation was observed between the augmentation of OR production by PM or fixed macrophages in the liver and inhibition of growth of Meth A or L. monocytogenes. The augmentation of OR production by LC 9018 was more marked and was maintained for a longer period of time than that by other bacterial immunostimulants.

Qualitative detection of muramic acid in normal mammalian tissues

Rat tissues were extracted with 8% trichloroacetic acid, and the products were hydrolyzed with hydrochloric acid and purified. Fluorescamine derivatives were made and subjected to thin-layer chromatography; material with an Rf corresponding to the authentic muramyl derivative was obtained. It was oxidized with periodate, and the resulting formaldehyde was identified fluorimetrically. Alternatively, treatment with base released D-lactate (beta-elimination), which was identified fluorimetrically by reduction of NAD to NADH with D-lactate dehydrogenase. The data indicate that small muramyl compounds, presumably peptides of bacterial origin, are normally present in rat liver, brain, and kidney. The functions of muramyl compounds are suggested by much recent work.

Muramyl peptides. Variation of somnogenic activity with structure

Sleep-promoting activities of muramyl dipeptide (MDP) (NAc-Mur-L-ala-D-isogln) and the naturally occurring muramyl peptide(s), factor S, have recently been demonstrated. We now have amplified our understanding of structural requirements for somnogenic activity. The effects of several analogs of MDP on rabbit slow-wave sleep are presented and these results are compared to the dose-response relationship for MDP. Some tentative conclusions as to structural requirements for somnogenic activity are presented; most notably, amidation of the free gamma-carboxyl of MDP and several of its analogs resulted in the loss of somnogenic activity. MDP also can induce febrile and immunostimulatory responses. In the present paper, we show that some analogs possess immunostimulatory and pyrogenic activity but not somnogenic activity, thus suggesting that these biological activities of muramyl peptides may, in part, be mediated by separate mechanisms.