Macrophage activation by muramyl dipeptide as measured by macrophage spreading and attachment

The in vitro effects of aflatoxin B1 on physiological functions of swine alveolar macrophages

The toxic effects of aflatoxin B₁ (AFB₁ ) on the physiological functions of swine alveolar macrophages (SAM) were investigated. Freshly isolated SAM were incubated with various AFB₁ concentrations (1.6 × 10^-1  - 1.6 × 10⁵  nmol/L) and time periods, and their phagocytic ability, synthesis of DNA, RNA and protein, and cell activation by lipopolysaccharide (LPS), were analysed. Results demonstrated that a significant (p < .05) reduction (60%) in Staphylococcus aureus uptaken by SAM appeared 3 hr after AFB₁ (>16 nmol/L) treatment. The synthesis of DNA, RNA and protein were markedly reduced, among which DNA and protein synthesis were affected more noticeably. The activation of SAM by LPS was significantly (p < .05) suppressed when the concentration of AFB₁ reached 1.6 × 10³  nmol/L. In general, most of the analysed effects were more prominent as AFB₁ concentration or incubation period increased. Taken together, AFB ₁ could elicit significant adverse effects on the physiological functions of SAM. Exposure of pigs to aflatoxin-contaminated feed may increase their susceptibility to various secondary infections.

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.

A monocyte-activation inhibitory factor produced by fibroblasts

Culture media from human fibroblasts pretreated with culture media from activated normal human monocytes partially inhibited the activation of monocytes. Molecular weight of the major inhibitory factor in these culture media was very close to that of human fibroblast interferon. However, an immunoadsorption experiment using monoclonal antibody to human fibroblast interferon failed to adsorb this inhibitory factor.

Immunological activation of rainbow trout macrophages induced in vitro by sperm autoantibodies and factors derived from testis sensitised leucocytes

Young cultures of rainbow trout macrophages were found to significantly increase in diameter following addition of muramyl dipeptide or of supernatants from testis/FCA sensitised leucocytes incubated with spermatozoa, or a testis extract. However, such supernatants caused little migration inhibition or increase in phagocytosis of spermatozoa by macrophages, whereas opsonization of spermatozoa with anti-sperm serum caused an almost six-fold increase in phagocytosis. These results suggest an interplay between humoral and cell-mediated immune reactions upon macrophages during experimental autoimmunity to the testis in trout.

Monocyte activating factor in sarcoidosis. I. Existence of the factor in sarcoidosis sera

Sarcoidosis sera were found to have the ability to induce normal human monocytes to spread. Gel filtration of sarcoidosis sera on Sephadex G-200 showed that the factor mainly responsible for this activity had a molecular weight of about 70,000. The spreading factor also possessed the ability to increase all cell size of normal human monocytes as well as to increase their phagocytosis and glucose consumption. Accordingly, the spreading factor seems to be considered as a monocyte activating factor. Sarcoidosis sera showed a macrophage migration inhibitory activity, as well. On Sephadex G-200 column chromatography of the sera, the most obvious inhibitory activity was eluted in the fraction with a molecular weight of about 45,000. The macrophage migration inhibitory factor had the ability neither to increase cell size of normal human monocytes nor to increase their phagocytosis and glucose consumption.

Production of macrophage activating factor by human leukemic T cell lines

Human leukemic T cell lines were tested for their ability to produce a macrophage activating factor. When mouse peritoneal macrophages were cultured for 48 hr in the presence of culture supernatants from cell lines HPB-ALL, CCRF-CEM, or MOLT-4, glucose oxidation via the hexose monophosphate pathway was enhanced by five to seven fold. Culture supernatants from cell line HPB-MLT stimulated the oxidation to a lesser extent. However, cell line CCRF-HSB-2 was essentially inactive as a producer. The active supernatants also stimulated the release of hydrogen peroxide from macrophages, whereas the inactive one did not. Since treatment of the cell lines with 12-o-tetradecanoyl phorbol acetate or phytohemagglutinin had little effect on the production of the factor except HPB-ALL, the cell lines seemed to secrete the factor constitutively. The stimulatory effect was dose-dependent and evident at a concentration as low as a 1/80 dilution. The factor was resistant to heat treatment at 100 C for 20 min, nondialysable and sensitive to protease digestion. The activating factor could be partially purified by anion exchange and gel filtration chromatographies.

Granuloma formation by muramyl dipeptide associated with branched fatty acids, a structure probably essential for tubercle formation by Mycobacterium tuberculosis

Muramyl dipeptide, which does not induce epithelioid granuloma when injected alone dissolved in phosphate-buffered saline, could induce extensive granulomas in guinea pigs when chemically conjugated with branched, but not linear, fatty acids. Peptidoglycan fragments of Staphylococcus epidermidis could evoke epithelioid granulomas when incorporated in a water-in-oil emulsion. These findings suggest the importance of a lipid bound to muramyl dipeptide for granuloma formation. In view of the fact that mycobacteria uniquely contain large amounts of branched fatty acids, it was proposed that the complex of muramyl dipeptide and branched fatty acids, mostly mycolic acids, is a structure in tubercle bacilli responsible for tubercle formation.

Synthetic lipid A with endotoxic and related biological activities comparable to those of a natural lipid A from an Escherichia coli re-mutant

A synthetic compound (506), beta (1-6) D-glucosamine disaccharide 1,4'-bisphosphate, which is acylated at 2'-amino and 3'-hydroxyl groups with (R)-3-dodecanoyloxytetradecanoyl and (R)-3-tetradecanoyloxytetradecanoyl groups, respectively, and has (R)-3-hydroxytetradecanoyl groups at 2-amino and 3-hydroxyl groups, exhibited full endotoxic activities identical to or sometimes stronger than those of a reference lipid A from an Escherichia coli Re-mutant (strain F515). Endotoxic activities tested include pyrogenicity and leukopenia-inducing activity in rabbits, body weight-decreasing toxicity in normal mice, lethal toxicity in galactosamine-sensitized mice and chicken embryos, and the preparation and provocation of the local Shwartzman reaction in rabbits. Compound 406, a synthetic counterpart of a biosynthetic precursor of lipid A molecule, showed by contrast only weak activities in all of the above assay systems except for the lethality in galactosamine-loaded mice. This finding strongly suggests that the presence of acyloxyacyl groups at the C-2' and C-3' positions of the disaccharide backbone is one of the most important determinant structures of the lipid A molecule for exhibition of strong biological activities characteristic of lipopolysaccharide and its lipid A moiety. The activities of the corresponding 4'-monophosphate (compound 504) and 1-monophosphate (505) analogs were considerably less than those of the parent molecule 506 and the reference F515 lipid A. Regarding other biological activities, not only compound 506 but also compounds 504, 505, and 406 showed definite activities, sometimes comparable to those of F515 lipid A and other reference natural products. These are the activation of Tachypleus tridentatus amoebocyte clotting enzyme cascade and human complement via the classical pathway, mitogenic and polyclonal B-cell activation of murine splenocytes, stimulation of peritoneal macrophages in a guinea pig, enhancement of migration of human blood polymorphonuclear leukocytes, and induction of a serum factor that is cytostatic and cytocidal to L-929 cells in Mycobacterium bovis BCG-primed mice. Relative potencies of test synthetic compounds depended on the assay systems and varied from one system to another. Dephospho-compound 503 lacked most of the biological activities that were definitely observed with phosphorylated compounds, probably because of its insolubility. This study demonstrates the successful chemical synthesis of an E. coli-type lipid A.

Enhancement of dengue virus infection in cultured mouse macrophages by lipophilic derivatives of muramyl peptides

Dengue virus multiplication in cultures of a murine myelomonocytic cell line (WEHI-3) as well as mouse peritoneal macrophages was enhanced by treatment of the cells with lipophilic derivatives of muramyl peptides for 2 or 3 days before virus inoculation, but not for 2 hr before virus inoculation or during the adsorption period. The infection-enhancing activity of the materials was dependent on their chemical structure, correlating with their immunoadjuvanticity. The infection enhancement in WEHI-3 cells was due primarily to an increase in the number of virus-infected cells which was accompanied by an increased cellular capacity to bind latex particles to their cell surfaces.

Inhibition of macrophage DNA synthesis by immunomodulators. II. Characterization of the suppression by muramyl dipeptide or lipopolysaccharide [3H]thymidine incorporation into macrophages

Guinea pig peritoneal exudate macrophages actively incorporated [3H]thymidine into trichloroacetic acid-insoluble fraction in vitro. The incorporation of [3H]thymidine was almost completely inhibited by aphidicolin, an inhibitor of DNA polymerase alpha and an autoradiograph showed heavy labeling in nuclei of 15% of macrophage populations. These results indicate that the observed thymidine incorporation was due to a nuclear DNA synthesis. The [3H]thymidine incorporation was markedly suppressed when macrophages were activated by immunoadjuvants such as muramyl dipeptide (MDP) or bacterial lipopolysaccharide (LPS). The suppression of [3H]thymidine incorporation by MDP was neither due to the decrease in thymidine transport through the cell membrane, nor due to dilution by newly synthesized "cold" thymidine. An autoradiograph revealed that MDP markedly decreased the number of macrophages the nuclei of which were labeled by [3H]thymidine. These results suggest that the suppression of [3H]thymidine incorporation by the immunoadjuvants reflects a true inhibition of DNA synthesis. The inhibition of DNA synthesis by MDP was also observed in vivo. Further, it was strongly suggested that the inhibition was not caused by some mediators, such as prostaglandin E2, released from macrophages stimulated by the immunoadjuvants but caused by a direct triggering of the adjuvants at least at the early stage of activation. Cyclic AMP appears to be involved in the inhibitory reaction.

Augmentation of the proliferative response of thymocytes to phytohemagglutinin by the muramyl dipeptide1

A synthetic N-acetylmuramyl-L-alanyl-D-isoglutamine or muramyl dipeptide (MDP) and adjuvant-active analogs, but not lipopolysaccharide (LPS), exhibited the augmenting effect on the proliferative response of thymocytes to phytohemagglutinin (PHA). MDP also had a comitogenic effect on PHA-stimulated T lymphocytes. It was shown that the thymocyte-stimulating effect of MDP is not through the production of the monikines by MDP-stimulated macrophages and that MDP has a direct action on lymphocytes.

Immunobiologically active lipid A analogs synthesized according to a revised structural model of natural lipid A

Synthetic lipid A analogs which have two amide-bound and two ester-bound (R)-3-hydroxytetradecanoyl groups at the C-2 and -2' and C-3 and -3' positions of beta(1-6)glucosamine disaccharide mono- or diphosphates showed high activities in most in vitro assays, and the lethality of a diphosphate derivative to galactosamine-treated mice was almost comparable to that of natural lipid A. The pyrogenicity and Shwartzman induction activity of the synthetic analogs, however, were much less than those of natural lipid A.

The effects of T-2 toxin on alveolar macrophage function in vitro

T-2 toxin, a metabolite of several Fusarium species, is a mycotoxin of the trichothecene family which occurs in a variety of grains. Previous work in our laboratory showed that T-2 toxin is highly toxic to rat alveolar macrophages in vitro at submicromolar concentrations. The present investigation was undertaken to study the basis of the cytotoxic effects observed. The following parameters of macrophage function were measured: macromolecular synthesis, release of 51Cr, cellular ATP, phagocytosis, and alveolar macrophage "activation." The incorporation of radiolabeled leucine into acid-precipitable molecules was significantly inhibited within 1 hr of treatment at sublethal concentrations, although amino acid uptake was unaffected. Cell volume and release of 51Cr was unaffected by 0.1 microM T-2 toxin after 6 hr but evidence of significant leakage was seen after 18 hr treatment. The capacity of alveolar macrophages to phagocytize Saccharomyces cerevisiae and 3H-Staphylococcus aureus was significantly reduced whereas binding of 3H-S. aureus to the macrophage was not. Macrophage activation with endotoxin (Escherichia coli lipopolysaccharide) and mitogen-generated lymphokines, as monitored by incorporation of [14C]glucosamine, was significantly altered at 0.01 microM T-2 toxin. Thus, the data clearly demonstrate that T-2 is toxic to alveolar macrophage function in vitro and suggest that the primary mechanism of this toxicity is related to the inhibition of protein synthesis.

An improved macrophage spreading assay--a simple and effective measure of activation

The development of a quantitative spreading assay of macrophage activation is described. The assay involved incubation of macrophages on glass coverslips for 1 hour and assessment of cell size using a microscope attached to a microcomputer-assisted digitising system which allowed the diameter of 200 cells to be assessed within 10 minutes. Mouse peritoneal macrophages were used in the development of the assay. Internal consistency of the assay was shown by minimal inter-observer, intra-observer and inter-animal variation. Validation of the assay as a measure of macrophage activation was confirmed by the use of in vivo and in vitro activating agents. Once validated the assay was used to detect activation in alveolar macrophages from rats exposed to airborne asbestos. The macrophage spreading assay described here is quick, reliable, consistent and easy to perform and has a potentially wide application in studies of macrophage function and dysfunction.

Stimulation of complement production in mice by N alpha-(N-acetylmuramyl-L-alanyl-D-isoglutamine)-N epsilon-stearoyl-L-lysine

N alpha-(N-acetylmuramyl-L-alanyl-D-isoglutamine)-N epsilon-stearoyl-L-lysine, a synthetic muramyl dipeptide analog, stimulated the production of the third component of complement (C3) in mice. The serum concentration of C3 was elevated significantly by subcutaneous treatment with a single dose (10 to 100 micrograms per mouse) of the adjuvant 24 h before assay of the serum. Thereafter, the concentration decreased gradually with time and returned to the normal level on day 4 to 5. Immunoelectrophoretic analysis of the serum revealed that the decrease in serum C3 could not be accounted for by the cleavage to C3a and C3b. By intermittent treatment with the adjuvant on every fifth day, a significant increase in serum C3 was repeated. However, no continuous retention of the serum level of C3 was established even during continuous treatment with the adjuvant once a day for 10 consecutive days. Instead, in this case, the level of C3 increased repeatedly at almost 5-day intervals.

Enhancement of dengue virus type 2 replication in mouse macrophage cultures by bacterial cell walls, peptidoglycans, and a polymer of peptidoglycan subunits

The effects of bacterial cell walls, peptidoglycans, and a water-soluble polymer of peptidoglycan subunits on dengue virus type 2 replication in cultured mouse peritoneal macrophages were studied. Pretreatment of macrophage cultures with all of test cell walls isolated from seven bacterial species for 3 days significantly enhanced the virus production in the cultures. Peptidoglycans prepared from four of the above cell walls also exerted the virus production-enhancing effects in a similar manner as the walls. A water-soluble polymer of peptidoglycan subunits which was prepared by treatment of Staphylococcus epidermidis wall peptidoglycan with an interpeptide bridge-splitting enzyme (endopeptidase) also definitely enhanced the virus production in macrophage cultures, although its activity was weaker than that of the original wall and peptidoglycan. Macrophage cultures from athymic nude mice, when treated with cell walls and peptidoglycans of S. epidermidis and Lactobacillus plantarum for 3 days, also showed an increased ability to support dengue virus type 2 replication. The infectious center assay demonstrated that the virus replication enhancement by S. epidermidis cell wall and peptidoglycan was primarily due to an increase in the number of virus-infected cells. This finding did not seem to be in conflict with the observation that macrophages treated with the above cell wall or peptidoglycan phagocytized more latex particles than did untreated macrophages. The conclusions based on the above experiments are that the treatment of mouse peritoneal macrophage cultures with bacterial cell walls and their components increases the take of dengue virus type 2 by macrophages and thus raises the virus production in the macrophage cultures.

Inhibition of macrophage DNA synthesis by immunomodulators. I. Suppression of [3H]thymidine incorporation into macrophages by MDP and LPS

Oil-induced guinea pig peritoneal exudate macrophages were found to incorporate actively [3H]thymidine without any tissue fluids such as conditioned medium, lymphokines or inflammatory tissue exudates. The [3H]thymidine incorporation was markedly suppressed by macrophage stimulants such as muramyl dipeptide (MDP) or bacterial lipopolysaccharide (LPS), while glucosamine incorporation was simultaneously increased by these stimulants. The degree of suppression of thymidine incorporation depended on the cell density, the concentrations of the stimulants, and sera or culture media used. The exposure of macrophages to MDP for 30 min was sufficient to cause significant suppression.

Muramyl dipeptides: prospect for cancer treatments and immunostimulation

The immunopharmacological activities of bacterial cell walls and muramyl peptides were collected in table form with a comprehensive literature. The past and present studies emphasizing the host-defense enhancing activities of muramyl peptides for antitumor immunotherapy were surveyed along three possible approaches: 1) the nonspecific enhancement of natural defense ability of host against tumor cells themselves; 2) the enhancement of nonspecific resistance of host to microbial infections which are frequently encountered and difficult to treat in the advanced stage of tumor patients; and 3) the stimulation of immunity against tumor-specific or tumor-associated immunogens. Finally, the prospects of successful antitumor immunotherapy with muramyl peptides and their derivatives was discussed.

Stimulation of migration of human monocytes by bacterial cell walls and muramyl peptides

Bacterial cell walls, water-soluble fragments of the wall peptidoglycan, N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP), and 6-O-acyl derivatives of MDP were examined for migration-stimulating activity on human peripheral blood monocytes by using a multiwell chemotaxis assembly. Cell walls isolated from 11 bacterial species caused a definite increase in monocyte migration, but the walls of Micrococcus lysodeikticus were scarely active. The migration-enhancing activity of Staphylococcus epidermidis cell walls was retained by a monomer as well as a polymer of disaccharide peptides which were prepared by digestion of the peptidoglycan with enzymes. It was finally revealed that the migration of monocytes was enhanced by MDP. 6-O-Octadecanoyl-MDP, 6-O-(2-tetradecylhexadecanoyl)-MDP, and 6-O-(3-hydroxy-2-docosylhexacosanoyl)-N-acetylmuramyl-L-seryl-D-isoglutamine were active, but to a lesser extent. A checkerboard assay demonstrated that the increased monocyte migration caused by S. epidermidis cell walls was directed toward a positive stimulus (chemotaxis).

Polymorphonuclear leukocyte activation by a synthetic muramyl dipeptide analog

N alpha-(N-Acetylmuramyl-L-alanyl-D-isoglutaminyl)-N epsilon -stearoyl-L-lysine, a synthetic derivative of muramyl dipeptide, stimulated the chemotactic mobility, phagocytic activity, and superoxide anion (O2-) productivity of peritoneal polymorphonuclear cells in mice. The chemotactic mobility of both cells preincubated with the adjuvant in vitro and those derived from the mice previously treated with the adjuvant was significantly enhanced. The phagocytic activity of cells preincubated in vitro with the adjuvant was also enhanced transiently, and that of the cells derived from the mice treated subcutaneously with the adjuvant 24 h before intraperitoneal inoculation with Escherichia coli was significantly greater than that of cells from the mice given phosphate-buffered saline instead of the adjuvant. The release of O2- from the cells derived from the adjuvant-treated mice was also greater than that from the cells of untreated control mice. However, the exposure of the cells derived from untreated mice to the adjuvant in vitro did not stimulate O2- generation by the cells.

Effect of L18-MDP(Ala), a synthetic derivative of muramyl dipeptide, on nonspecific resistance of mice to microbial infections

By subcutaneous treatment with an aqueous solution of 6-O-stearoyl-N-acetylmuramyl-L-alanyl-D-isoglutamine [6-O-CH3-(CH2)16-CO-MurNAc-L-Ala-D-isoGln] [referred to here as L18-MDP(Ala)], an augmentation of the resistance of mice to Escherichia coli, Pseudomonas aeruginosa. Staphylococcus aureus, and Candida albicans infections was observed, but not to infections with Klebsiella pneumoniae and Listeria monocytogenes. Against E. coli infections, L18-MDP(Ala) was highly protective, irrespective of the administration route. Bacteremia occurring at an early phase of such infections was almost completely prevented by subcutaneous treatment 1 day before infection. Single or multiple doses were also effective against C. albicans infection. The phagocytosis of E. coli by mouse peritoneal polymorphonuclear cells was enhanced by treatment with the adjuvant, and the phagocytosis of K. pneumoniae was also enhanced, but only when the mice were treated either with rabbit normal serum or with a specific immune serum. The growth of the fungus in the kidneys was significantly inhibited, and growth was eliminated from the kidneys by treatment with the adjuvant once a day for 4 consecutive days, starting 1 day before infection. However, no growth suppression of L. monocytogenes in the livers or spleens of infected mice was observed when they were treated with a single dose of the adjuvant. This difference may be ascribed to the differences in the effector mechanisms of defense and to the different degree of augmentation of each defense mechanism by L18-MDP(Ala).

Cellular responses of the mouse to the peptidoglycan of a gram-positive bacterium (Streptococcus pyogenes)

The cellular responses and the stimulation of the reticulo-macrophagic system induced in the mouse by a purified bacterial peptidoglycan (PGL) as previously described, were studied by the changes in the peritoneal cytology, the macrophage-migration-inhibition test and the clearance of colloidal carbon. PGL was submitted to chemical and immunochemical characterization and was shown to be substantially free of contamination by polysaccharides, phospholipids, teichoic acid and nucleic acids, but to contain a detectable amount of peptide contaminants; N-acetylglucosamine and the tetrapeptide (with terminal D-alanine) were shown to be the main antigenic determinants. This substance had no action on polymorphonuclear leucocytes but induced an inhibition of the migration of macrophages. This was due to an immunological reaction rather than to direct cytotoxicity, as shown by the negative cytotoxicity tests and the age and life-environment-dependence of the phenomenon. The reticulomacrophagic system was significantly stimulated after primary inoculation, and still more so after a booster. The possible mechanisms of these activities, which are therefore independent from toxic and/or inflammatory responses, are discussed.

Macrophage activation by muramyl dipeptide (MDP) without lymphocyte participation

An increase in the numbers of spread macrophages caused by macrophage stimulants was found to be a very sensitive measure for macrophage activation. Muramyl dipeptide (MDP), bacterial lipopolysaccharide (LPS), and lymphokines were found to activate macrophages dose-dependently as measured by this parameter. Macrophage activation by MDP was strictly dependent on its adjuvant-active stereochemically specific structures. Macrophage activation by MDP and LPS occurred without lymphocyte participation. It is suggested that LPS also activates macrophages via lymphocytes.

Effect of muramyldipeptide, a synthetic bacterial adjuvant, on enzyme release from cultured mouse macrophages

Monolayer cultures of macrophages obtained by peritoneal lavage of normal or thioglycollate-stimulated mice spontaneously secreted lysosomal enzymes into the culture medium. When the elicited macrophages were cultured in the presence of muramyldipeptide (MDP), a 20-30% increase in the release of beta-glucuronidase was consistently observed and the intracellular activity decreased to about 45% of that of control cells after 6-8 days' culture. A stimulatory effect of MDP on lysozyme secretion, though less profound, was also observed. In contrast, release of neither enzyme was stimulated in resident macrophages by the addition of MDP. A neutral alpha-glucosidase, which has recently been found to localize also in granules of macrophages, remained inside the cells and neither its activity nor its release was affected by the addition of MDP to either type of macrophages. A large amount of lactic dehydrogenase was released only when the resident, not the elicited, macrophages were cultured for 3-4 days and then phagocytosed zymosan.