PGG-Glucan activates NF-kappaB-like and NF-IL-6-like transcription factor complexes in a murine monocytic cell line

Sustainable production and pharmaceutical applications of β-glucan from microbial sources

β-glucans are a large class of complex polysaccharides found in abundant sources. Our dietary sources of β-glucans are cereals that include oats and barley, and non-cereal sources can consist of mushrooms, microalgae, bacteria, and seaweeds. There is substantial clinical interest in β-glucans; as they can be used for a variety of diseases including cancer and cardiovascular conditions. Suitable sources of β-glucans for biopharmaceutical applications include bacteria, microalgae, mycelium, and yeast. Environmental factors including culture medium can influence the biomass and ultimately β-glucan content. Therefore, cultivation conditions for the above organisms can be controlled for sustainable enhanced production of β-glucans. This review discusses the various sources of β-glucans and their cultivation conditions that may be optimised to exploit sustainable production. Finally, this article discusses the immune-modulatory potential of β-glucans from these sources.

β-Glucans Could Be Adjuvants for SARS-CoV-2 Virus Vaccines (COVID-19)

Waiting for an effective treatment against the SARS-CoV-2 virus (the cause of COVID-19), the current alternatives include prevention and the use of vaccines. At the moment, vaccination is the most effective strategy in the fight against pandemic. Vaccines can be administered with different natural biological products (adjuvants) with immunomodulating properties. Adjuvants can be taken orally, complementing vaccine action. Adjuvant compounds could play a key role in alleviating the symptoms of the disease, as well as in enhancing vaccine action. Adjuvants also contribute to an effective immune response and can enhance the protective effect of vaccines in immunocompromised individuals such as the elderly. Adjuvants must not produce adverse effects, toxicity, or any other symptoms that could alter immune system function. Vaccine adjuvants are substances of wide varying chemical structure that are used to boost the immune response against a simultaneously administered antigen. Glucans could work as adjuvants due to their immunomodulatory biological activity. In this respect, β-(1,3)-(1,6) glucans are considered the most effective and safe according to the list issued by the European Commission. Only glucans with a β-(1,3) bond linked to a β-(1,6) are considered modulators of certain biological responses. The aim of this review is to present the possible effects of β-glucans as adjuvants in the efficacy of vaccines against SARS-CoV-2 virus.

Development of an in vitro macrophage screening system on the immunomodulating effects of feed components

Background

While feed components capable of modulating the immune system are highly sought after and marketed, often little evidence is available to support functional immune response claims. Thus, a high-throughput in vitro cell screening system was developed to test these compounds for innate immune signaling effects, using Saccharomyces cerevisiae and its cell wall components in addition to lauric acid and its esters as models in two separate experiments. This screening system utilized RAW 264.7 murine macrophages to assess live S. cerevisiae cells and S. cerevisiae-derived cell wall components β-glucan, mannan, and zymosan (a crude cell wall preparation containing both β-glucan and mannan). D-mannose was also evaluated as the monomer of mannan. We also examined the effect of a saturated fatty acid (C12:0, lauric acid) and its esters (methyl laurate and glycerol monolaurate) on innate immune cell activation and cellular metabolism. RAW cells were transfected with a vector that drives expression of alkaline phosphatase upon promoter activation of nuclear factor κ-light-chain-enhancer of activated B cells (NFκB), a major inflammatory/immune transcription factor. RAW cells were incubated with 0.01, 0.1 or 1 mg/mL of yeast compounds alone or RAW cells were challenged with LPS and then incubated with yeast compounds. In a separate experiment, RAW cells were incubated with 0, 0.5, 2.5, 12.5, 62.5, and 312.5 μmol/L of lauric acid, methyl laurate, or glycerol monolaurate alone, or RAW cells were challenged with LPS and then incubated with fatty acid treatments.

Results

Treatment with zymosan or β-glucan alone induced NFκB activation in a dose-dependent manner, whereas treatment with D-mannose, mannan, or live S. cerevisiae cells did not. Post-treatment with mannan after an LPS challenge decreased NFκB activation, suggesting that this treatment may ameliorate LPS-induced inflammation. Slight increases in NFκB activation were found when fatty acid treatments were applied in the absence of LPS, yet substantial reductions in NFκB activation were seen when treatments were applied following an LPS challenge.

Conclusions

Overall, this cell screening system using RAW macrophages was effective, high-throughput, and sensitive to feed components combined with LPS challenges, indicating modulation of innate immune signaling in vitro.

Graphical abstract

The linear structure of β-glucan from baker's yeast and its activation of macrophage-like RAW264.7 cells

Yeast β-glucan has many formulations with different chemical structures, water solubility and purity. In particular, the purity of β-glucan in these formulations is variable and relatively low, contributing to different data on its biological activity. In this study, the major polysaccharide component in the crude Baker's yeast polysaccharides coded as BBG with high purity of 99% was obtained, and its chemical structure was determined to be a linear β-(1,3)-glucan. It was found that BBG interacted with complement receptor 3 (CR3) and toll-like receptor 2 (TLR2) on the surface of macrophage-like RAW264.7 cells, and initiated activation of RAW264.7 cells characterized by significant production of tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein 1 (MCP-1). Additionally, activation of the nuclear factor kappaB p65 (NF-κB p65), c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) induced by BBG, were also observed, further confirming the stimulation of RAW264.7 cells by BBG. All these findings provided important scientific evidences for better understanding the molecular mechanism of action for the linear β-(1,3)-glucan in cells.

Mitochondrial calcium uniporter inhibition attenuates mouse bone marrow-derived mast cell degranulation induced by beta-1,3-glucan

Mast cells are primary mediators of allergic inflammation. Beta-1,3-glucan (BG) protects against infection and shock by activating immune cells. Activation of the BG receptor induces an increase in intracellular Ca²⁺, which may induce exocytosis. However, little is known about the precise mechanisms underlying BG activation of immune cells and the possible role of mitochondria in this process. The present study examined whether BG induced mast cell degranulation, and evaluated the role of calcium transients during mast cell activation. Our investigation focused on the role of the mitochondrial calcium uniporter (MCU) in BG-induced degranulation. Black mouse (C57) bone marrow-derived mast cells were stimulated with 0.5 µg/ml BG, 100 µg/ml peptidoglycan (PGN), or 10 µM A23187 (calcium ionophore), and dynamic changes in cytosolic and mitochondrial calcium and membrane potential were monitored. BG-induced mast cell degranulation occurred in a time-dependent manner, and was significantly reduced under calcium-free conditions. Ruthenium red, a mitochondrial Ca²⁺ uniporter blocker, significantly reduced mast cell degranulation induced by BG, PGN, and A23187. These results suggest that the mitochondrial Ca²⁺ uniporter has an important regulatory role in BG-induced mast cell degranulation.

Improved antimicrobial host defense in mice following poly-(1,6)-β-D-glucopyranosyl-(1,3)-β-D-glucopyranose glucan treatment by a gender-dependent immune mechanism

Clinical trials with biological modifiers targeting specific inflammatory mediators associated with severe sepsis have shown no or limited survival benefit. The approach taken in studies reported here was to limit the point source of intra-abdominal infection by potentiating innate immune function, thereby lessening the severity of sepsis and improving survival. Soluble beta-glucans, glucose polymers of the fungal cell wall, have been shown to stimulate innate immune host defense in animal and human studies when administered prior to an infectious challenge. We evaluated the effects of poly-(1,6)-β-d-glucopyranosyl-(1,3)-β-d-glucopyranose glucan (PGG glucan) on overall survival when administered intraperitoneally after the onset of polymicrobial infection by cecal ligation and puncture (CLP). Since gender-dependent differences in host immune response to infection have been reported, male and female mice were prospectively stratified for PGG glucan treatment. Outbred CD-1 mice were administered 10 mg/kg of body weight PGG glucan or the polysaccharide control, dextran, 1 h after CLP. Six hours after CLP, blood samples were obtained for cytokine measurements. Surprisingly, a gender-dependent effect on the response to PGG glucan was revealed. PGG glucan enhanced survival in female mice over a 10-day period, but survival in males was improved for only 24 h. In female mice, PGG glucan reduced interleukin-6 (IL-6) and IL-10 levels and reduced the bacterial burden in the liver. Ovariectomy abrogated the response to PGG glucan. Together, the translational potential of these findings is the indicated use of PGG glucan given locally, rather than intravenously, for improved source control during the management of sepsis. This therapy does not require prophylactic beta-glucan administration.

Immunomodulatory beta-glucan from Lentinus edodes activates mitogen-activated protein kinases and nuclear factor-kappaB in murine RAW 264.7 macrophages

Lentinan, a cell wall β-glucan from the fruiting bodies of Lentinus edodes, is well known to be a biological defense modifier, but the signal transduction pathway(s) induced by Lentinan have not been elucidated. In this study, we extracted Lentinan (LNT-S) by ultrasonication from Lentinus edodes and report that, in murine RAW 264.7 macrophages, LNT-S glucan activated NF-κB p65 and triggered its nuclear translocation as determined by Western blotting. Moreover, LNT-S enhanced NF-κB-luciferase activity in the Dual-Luciferase gene system assay. Its upstream signaling molecules, MAPKs such as ERK1/2 and JNK1/2, were shown to be activated by assessing the level of phosphorylation in a time- and concentration-dependent manner, but its downstream proinflammatory enzyme, inducible NOS, was not observed. The data evaluated using a TNF-α ELISA kit and Griess reagent further demonstrated that no proinflammatory mediators such as TNF-α and NO were produced by LNT-S stimulation in RAW 264.7 cells. In contrast, LPS significantly induced inducible NOS expression and increased NO and TNF-α production, which are associated with activation of the NF-κB p65/p50 heterodimer complex. It is possible that LNT-S did not activate NF-κB p65/p50, and the activation of NF-κB p65 was not sufficient to stimulate cytokine production. These data demonstrate that LNT-S glucan carries out its immunomodulating activity by activating MAPK signaling pathways without secretion of TNF-α and NO.

Study of new ways of supplementary and combinatory therapy of rheumatoid arthritis with immunomodulators. Glucomannan and Imunoglukán®in adjuvant arthritis

We studied the anti-arthritic activity of glucomannan (GM) isolated from Candida utilis and of Imunoglukán®, a beta-(1,3/1,6)-d-glucan (IMG) isolated from Pleurotus ostreatus. Adjuvant arthritis (AA) was induced intradermally by the injection of Mycobacterium butyricum in incomplete Freund’s adjuvant to Lewis rats. Blood for biochemical and immunological analysis was collected on experimental days 1, 14, 21, and 28. A clinical parameter – hind paw volume (HPV) – was also measured. The detection of IL-1 alpha, IL-4, TNF alpha, and MCP-1 was done by immunoflowcytometry. On day 28 – the end of the experiment – we determined spectrophotometrically: the total anti-oxidant status (TAS) of plasma samples along with thiobarbituric acid-reacting substances (TBARS) levels in plasma and we assessed the activity of gamma-glutamyl transferase (GGT) in hind paw joint homogenate. The experiments included healthy animals, arthritic animals without treatment, and arthritic animals with administration of glucomannan (GM-AA) in the oral daily dose of 15 mg/kg b.w. and of IMG (IMG-AA) in the oral daily dose of 2 mg/kg b.w. The progress of AA was manifested by all parameters monitored. Both substances had beneficial effects on HPV, TBARS levels, GGT activity, and TAS levels. For cytokine assessment, only IMG-AA samples were selected, considering the significant HPV improvement accompanied with the observed anti-oxidant action. IMG administration had a positive immunomodulating effect on all cytokine plasma levels measured, changed markedly due to arthritis progression. Thus, IMG may be considered as a candidate for combinatorial therapy of rheumatoid arthritis.

Oral and systemic administration of beta-glucan protects against lipopolysaccharide-induced shock and organ injury in rats

beta-Glucans are glucose polymers with a variety of stimulatory effects on the immune system. The objective of this study was to determine the effect of prophylactic oral administration of soluble Saccharomyces cerevisiae-derived beta-1,3/1,6-glucan (SBG) on the outcome of experimental endotoxaemia and shock-associated organ injury. Male Wistar rats were pretreated with SBG orally (SBGpo, 20 mg/kg/day) for 14 days, subcutaneously (SBGsc, 2 mg/kg/day) for 3 days, or vehicle (placebo). Rats were anaesthetized and subjected to endotoxaemia by intravenous infusion of Escherichia coli lipopolysaccharide (LPS) (6 mg/kg) or saline infusion (sham). We observed significant levels of plasma beta-glucan in the SBGpo group (P<0 x 5), although the SBGsc group had levels approximately 40-fold higher despite a 10-fold lower dose. SBG prophylaxis caused enhanced blood pressure recovery following LPS-induced blood pressure collapse. Oral treatment with SBG attenuated the LPS-induced rise in plasma creatinine levels (P<0 x 05), indicating protection against renal injury. SBG also attenuated the plasma levels of aspartate aminotransferase and alanine aminotransferase (SBGpo, P<0 x 01; SBGsc, P<0 x 01), indicating protection against LPS-induced hepatic injury. A moderate increase in baseline interleukin (IL)-1beta levels was observed in the SBGsc group (P< 0 x 05). In the LPS-challenged rats, plasma levels of proinflammatory cytokines was moderately reduced in both SBG-treated groups compared to placebo. SBG treatment, particularly oral administration, had a striking effect on the haemodynamics of LPS-treated rats, although only a minute fraction of the orally administered beta-glucan translocated to the circulation. Enhanced organ perfusion may thus be responsible for the attenuated levels of indicators of kidney and liver injury seen in SBG-treated rats.

Beta-(1-->3)-D-glucan modulates DNA binding of nuclear factors kappaB, AT and IL-6 leading to an anti-inflammatory shift of the IL-1beta/IL-1 receptor antagonist ratio

BACKGROUND

Beta-1-->3-D-glucans represent a pathogen-associated molecular pattern and are able to modify biological responses. Employing a comprehensive methodological approach, the aim of our in vitro study was to elucidate novel molecular and cellular mechanisms of human peripheral blood immune cells mediated by a fungal beta-1-->3-D-glucan, i.e. glucan phosphate, in the presence of lipopolysaccharide (LPS) or toxic shock syndrome toxin 1 (TSST-1).

RESULTS

Despite an activation of nuclear factor (NF) kappaB, NFinterleukin(IL)-6 and NFAT similar to LPS or TSST-1, we observed no significant production of IL-1beta, IL-6, tumor necrosis factor alpha or interferon gamma induced by glucan phosphate. Glucan phosphate-treated leukocytes induced a substantial amount of IL-8 (peak at 18 h: 5000 pg/ml), likely due to binding of NFkappaB to a consensus site in the IL-8 promoter. An increase in IL-1receptor antagonist (RA) production (peak at 24 h: 12000 pg/ml) by glucan phosphate-treated cells positively correlated with IL-8 levels. Glucan phosphate induced significant binding to a known NFIL-6 site and a new NFAT site within the IL-1RA promoter, which was confirmed by inhibition experiments. When applied in combination with either LPS or TSST-1 at the same time points, we detected that glucan phosphate elevated the LPS- and the TSST-1-induced DNA binding of NFkappaB, NFIL-6 and NFAT, leading to a synergistic increase of IL-1RA. Further, glucan phosphate modulated the TSST-1-induced inflammatory response via reduction of IL-1beta and IL-6. As a consequence, glucan phosphate shifted the TSST-1-induced IL-1beta/IL-1RA ratio towards an anti-inflammatory phenotype. Subsequently, glucan phosphate decreased the TSST-1-induced, IL-1-dependent production of IL-2.

CONCLUSION

Thus, beta-1-->3-D-glucans may induce beneficial effects in the presence of pro-inflammatory responses, downstream of receptor binding and signaling by switching a pro- to an anti-inflammatory IL-1RA-mediated reaction. Our results also offer new insights into the complex regulation of the IL-1RA gene, which can be modulated by a beta-1-->3-D-glucan.

Dectin-1: a signalling non-TLR pattern-recognition receptor

Dectin-1 is a natural killer (NK)-cell-receptor-like C-type lectin that is thought to be involved in innate immune responses to fungal pathogens. This transmembrane signalling receptor mediates various cellular functions, from fungal binding, uptake and killing, to inducing the production of cytokines and chemokines. These activities could influence the resultant immune response and can, in certain circumstances, lead to autoimmunity and disease. As I discuss here, understanding the molecular mechanisms behind these functions has revealed new concepts, including collaborative signalling with the Toll-like receptors (TLRs) and the use of spleen tyrosine kinase (SYK), that have implications for the role of other non-TLR pattern-recognition receptors in immunity.

Immunomodulatory effects of beta-glucan on neutrophil function in fathead minnows (Pimephales promelas Rafinesque, 1820)

Stimulatory effects of yeast beta-1,3-1,6-glucans on neutrophils have long been recognized, but effects of glucans on degranulation of primary granules in fish neutrophils have not been previously reported. Neutrophil function was monitored during in vitro and in vivo application of glucans to non- (NS), acute- (AS) and chronically stressed (CS) fish. beta-Glucan proved to be a strong and quick (80%, 2 min) stimulant of degranulation. Dietary glucan increased degranulation in NS fish, and prevented a decrease in AS fish. Degranulation in CS fish returned to NS levels 3 days after the glucan diet was fed. Fathead minnows appear to be a useful model to investigate neutrophil degranulation in fish exposed to different environmental conditions and immunomodulators. Use of beta-glucans in fish diets prior to AS and during chronic stress can enhance neutrophil function, potentially increasing disease resistance and survival rates after transportation or exposure to poor water quality.

Immune recognition of fungal β-glucans

The recognition of conserved microbial structures is a key aspect of metazoan immunity, and beta-glucans are emerging as a major target for the recognition of fungal pathogens. A number of receptors for these carbohydrates have been identified, which upon recognition, trigger a variety of immune responses. In contrast to many other systems, there is little apparent conservation in these mechanisms between vertebrates and invertebrates. In this review, we will highlight all the known receptors for beta-glucans and will discuss the various immune responses they can initiate, with reference to fungal infection, in both vertebrates and invertebrates.

New synthetic peptides can enhance gene expression of key antioxidant defense enzymes in vitro and in vivo

Neurodegenerative, cardiovascular, and age-related disorders have been attributed to the cellular damage caused by elevated production of reactive oxygen species (ROS) and free radicals (FRs). These cannot be adequately defended by existing levels of key antioxidant enzymes. Two peptides, 8 and 14 amino acids long, were synthesized and found to up-regulate, at nanomolar concentrations, superoxide dismutase (SOD) and catalase (CAT) m-RNAs (9- to 12-fold) within 3 h, and then elevate by 5- to 10-fold the protein levels of SOD, CAT, and glutathione peroxidase (GPX) in rat primary cortical cultures. Kinetic studies showed that the peptide up-regulation of all three enzymes appears to be a coordinated process which occurs in vitro and in vivo. We also found that ischemia alone, without added drugs, can lead to enhanced gene expression of SOD, CAT, and GPX. This suggests that the CNS can initiate its own "defense" against ROS and FR. Thus, our peptides may activate such systems, as well as AP-1 transcription factor, reported in earlier findings to lead to "repair" (growth) of injured cells.

Microparticulate β-glucan upregulates the expression of B7.1, B7.2, B7-H1, but not B7-DC on cultured murine peritoneal macrophages

Beta-1,3-(D)-glucan from a variety of biological sources has been shown to enhance both humoral and cellular immune responses to a variety of antigens, infectious agents, and tumors. Nevertheless, its mode of action has not been fully defined. We sought to determine whether a 1-2 microm diameter microparticulate form of beta-glucan (MG) from the yeast Saccharomyces cerevisiae could regulate expression of B7 family glycoproteins on resident peritoneal macrophages from BALB/c mice. We discovered that MG uregulated B7.2 mRNA expression and enhanced the surface membrane expression of B7.2 glycoprotein. Although B7.1 mRNA was not upregulated above constitutive levels, MG treatment enhanced B7.1 glycoprotein expression on the macrophages, albeit to a lesser extent than B7.2. At the same time, the gene and cell surface expression of B7-H1, a putative negative regulator of T cell activity, was also upregulated by MG. The expression of B7-DC, another B7 family molecule with negative regulatory activity, was not affected by incubation with MG. This study has demonstrated that a microparticulate form of beta-glucan can enhance B7 co-stimulatory molecule expression on macrophages, thereby enabling these antigen-presenting cells to deliver the second signal to T-lymphocytes that express CD28. In addition, because MG also induces the expression of B7-H1, it may enable macrophages to provide a concomitant downregulatory signal to T-lymphocytes expressing PD-1 or related receptors.

Modulation of the Phosphoinositide 3-Kinase Pathway Alters Innate Resistance to Polymicrobial Sepsis

We examined the effect of modulating phosphoinositide 3-kinase (PI3K) activity in a murine model of cecal ligation and puncture-induced polymicrobial sepsis. Inhibition of PI3K activity with wortmannin increased serum cytokine levels and decreased survival time in septic mice. We have reported that an immunomodulator, glucan phosphate, induces protection in murine polymicrobial sepsis. We observed that glucan stimulated tissue PI3K activity, which positively correlated with increased survival in septic mice. We investigated the effect of PI3K inhibition on survival in septic mice treated with glucan. Treatment of mice with the PI3K inhibitors, wortmannin and LY294002, completely eliminated the protective effect of glucan, indicating that protection against septic mortality was mediated through PI3K. Inhibition of PI3K resulted in increased serum levels of IL1-beta, IL-2, IL-6, IL-10, IL-12, and TNF-alpha in septic mice. Apoptosis is thought to play a central role in the response to septic injury. We observed that inhibition of PI3K activity in septic mice resulted in increased splenocyte apoptosis and a change in the anatomic distribution of splenocyte apoptosis. We conclude that PI3K is a compensatory mechanism that suppresses proinflammatory and apoptotic processes in response to sepsis and/or inflammatory injury. Thus, PI3K may play a pivotal role in the maintenance of homeostasis and the integrity of the immune response during sepsis. We also observed that glucan phosphate decreased septic morbidity and mortality through a PI3K-dependent mechanism. This suggests that stimulation of the PI3K pathway may be an effective approach for preventing or treating sepsis and/or septic shock.

Fungal beta-glucans and mammalian immunity

Beta-glucans are structural cell wall polymers of many fungi which possess immunomodulatory activities. Although the therapeutic benefits associated with these compounds, particularly as anti-infective and antitumorigenic agents, have led to a large body of published research over the last five decades, it is still unclear how these carbohydrates mediate their effects. Recent studies, however, are starting to shed some light on the cellular receptors and molecular mechanisms involved, which also have direct relevance on the innate immune response to fungal pathogens.

Pneumocystis carinii cell wall beta-glucans initiate macrophage inflammatory responses through NF-kappaB activation

beta-Glucans are major structural components of fungi. We have recently reported that the pathogenic fungus Pneumocystis carinii assembles a beta-glucan-rich cell wall that potently activates alveolar macrophages to release pro-inflammatory cytokines and chemokines. Purified P. carinii beta-glucans predictably induce both cytokine generation and associated neutrophilic lung inflammation. Herein, we demonstrate that P. carinii beta-glucan-induced macrophage stimulation results from activation of NF-kappaB. Although analogous to macrophage activation induced by bacterial lipopolysaccharide (LPS), P. carinii beta-glucan-induced macrophage NF-kappaB activation exhibits distinctly different kinetics, with slower induction and longer duration compared with LPS stimulation. Macrophage activation in response to P. carinii beta-glucan was also substantially inhibited with the NF-kappaB antagonist pyrrolidine dithiocarbamate. In addition to different kinetics of NF-kappaB activation, P. carinii beta-glucan and LPS also utilize different receptor systems to induce macrophage activation. Macrophages from Toll-like receptor 4-deficient and wild type mice produced equivalent amounts of tumor necrosis factor alpha when stimulated with P. carinii beta-glucan. However, Toll-like receptor 4-deficient macrophages were refractory to stimulation with LPS. In contrast, MyD88-deficient macrophages exhibited a significant (though partial) blunted response to P. carinii beta-glucan. These data demonstrate that P. carinii beta-glucan acts as potent inducer of macrophage activation through NF-kappaB utilizing cellular receptors and signaling pathways distinct from LPS.

The effect of soluble beta-1,3-glucan and lipopolysaccharide on cytokine production and coagulation activation in whole blood

Soluble beta-1,3-glucan has been demonstrated to protect against infection and shock in rats and mice, and clinical studies suggest that administration of soluble glucans to trauma/surgical patients decreases septic complications and improves survival. However, little is known about the precise mechanisms by which glucans influence the state of activation of blood cells, which are responsible for the fulminant cytokine production and the activation of the coagulation system observed in serious gram-negative infection. We studied therefore the effect of an underivatized, soluble yeast beta-1,3-glucan and lipopolysaccharide (LPS), either alone or in combination, on tumor necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6), IL-8 and IL-10 secretion and monocyte tissue factor (TF) expression in human whole blood. As expected, LPS induced the secretion of substantial amounts of all measured parameters, whereas only minor amounts of TNFalpha, IL-6, and IL-10 were induced by beta-glucan itself. However, beta-glucan itself induced the production of significant amounts of IL-8 and TF. Soluble beta-1,3-glucan had a strong synergistic effect on the LPS-induced secretion of IL-8, IL-10, and on monocyte TF activity, but not on TNFalpha and 1L-6 production. On the other hand, soluble beta-glucan strongly primed LPS stimulation of all parameters, including TNFalpha and IL-6. beta-Glucan also induced detectable neutrophil degranulation within 15 min, whereas a response to LPS was first detected after 90 min. In conclusion, soluble beta-1,3-glucan upregulated leukocyte activity, both on its own and in concert with LPS.

In vitro and in vivo immunomodulatory effects of microdispersed oxidized cellulose

The immune system can be manipulated specifically by vaccination or nonspecifically by immunomodulation. Many of biological response modifiers (BRM) have polysaccharidic structure similar to that of microdispersed oxidized cellulose (MDOC). We have investigated the immunomodulatory activity of different inorganic MDOC salts (H, Na, Ca, Mg, Zn, Al, Co, Ca/Na) and organic MDOC derivatives (urea, gelatine, arginine) both in vitro and in vivo. A dose-dependent stimulation by a number of MDOC derivatives was observed with spontaneous and mitogen-induced proliferation of human peripheral blood leukocytes (PBLs) and mouse splenocytes in vitro. In both primary cultures, the most intensive proliferation was induced by a Ca/Na salt at a concentration of 1 mg/ml. We have also demonstrated stimulatory effects of MDOC Ca/Na salt on the mouse mixed leukocyte reaction (MLR). The stimulatory activity of MDOC towards the immune system was further supported by the fact that in vitro the product stimulates the release of Th1 cytokine TNF-alpha, but not IFN-gamma, IL-4 or IL-6. In vivo MDOC application increases more than 50% the number of colony-forming units spleen (CFU-s), i.e., stimulates the stem cells in bone marrow, and increases relative percentage of monocytes and B lymphocytes in the mouse peripheral blood.

Human Vascular Endothelial Cells Express Pattern Recognition Receptors for Fungal Glucans Which Stimulates Nuclear Factor κB Activation and Interleukin 8 Production

Fungal cell wall glucans nonspecifically stimulate various aspects of innate immunity via interaction with membrane receptors on macrophages, neutrophils, and natural killer cells. We investigated the binding of water-soluble glucans in primary cultures of normal human coronary or dermal vascular endothelial cells (VECs). Membranes from VECs exhibited saturable binding. Competition studies demonstrated the presence of at least two glucan binding sites on VECs. Glucan phosphate competed for all binding sites with a KD of 3.7 μm for coronary VECs and 11 μm for dermal VECs, respectively. Laminarin, a low molecular weight glucan, competed for 47 to 51 per cent of binding ( KD = 2.8–2.9 μm), indicating the presence of at least two binding sites. Glucan (1 μg/mL) stimulated VEC nuclear factor κB nuclear binding activity and Interleukin 8 expression—but not that of vascular endothelial growth factor—in a time-dependent manner. This is the first report of pattern recognition receptors for glucan on human VECs. It also provides the first evidence that glucans can directly modulate the functional activity of VECs by stimulating cytokine gene. These results provide new insights into the mechanisms by which the host recognizes and responds to fungal cell wall products and suggests that the response to glucans may not be confined to leukocytes.

Glucan stimulates human dermal fibroblast collagen biosynthesis through a nuclear factor-1 dependent mechanism

Glucan, an immunomodulator, has been reported to increase collagen deposition and tensile strength in experimental models of wound repair. Previous data suggest that glucan modulates wound healing via an indirect mechanism in which macrophages are stimulated to release growth factors and cytokines. However, recent data have shown the presence of glucan receptors on normal human dermal fibroblasts, suggesting that glucans may be able to directly stimulate fibroblast collagen biosynthesis. To test this hypothesis, we examined the effect of glucan on collagen biosynthesis in normal human dermal fibroblasts. We assessed nuclear factor-1 (NF-1) activation, procollagen mRNA expression, collagen biosynthesis, and whether there was a causal link between glucan treatment, NF-1 activation, and collagen expression. Glucan (1 microg/ml) increased NF-1 binding activity by 46% (8 hours), 64% (24 hours), 215% (36 hours), and 119% (48 hours) in cultured normal human dermal fibroblasts. Alpha 1(I) and alpha1 (III) procollagen mRNA were increased in glucan-treated normal human dermal fibroblasts when compared with the untreated fibroblasts. Collagen synthesis was increased at 24 hours and 48 hours following glucan treatment of normal human dermal fibroblasts. Down-regulation of NF-1 by pentifylline inhibited glucan-induced procollagen mRNA expression. These data indicate that glucan can directly stimulate human fibroblast collagen biosynthesis through an NF-1-dependent mechanism.

Differential mRNA expression of prostaglandin receptor subtypes in macrophage activation

Assessing the regulation of macrophage receptors for prostaglandin (PGE2) is essential to understanding the control which that potent lipid mediator has in modulating macrophage activities. The purpose of this study was to assess the differential mRNA expression of PGE2 receptor subtypes (EP) during macrophage exposure to activating and transducing agents. RAW 264.7 macrophages constitutively expressed mRNA for EP2,EP3 and EP4 receptor subtypes. Messenger RNA for EP4 was expressed at a much higher level when compared to EP2 in unstimulated macrophages as assessed by kinetic quantitative RT-PCR. When macrophages were stimulated with LPS, EP2 m RNA levels were 12-fold higher when compared to unstimulated macrophages, while EP4 m RNA remained unchanged. Conversely, mRNA levels of both EP2 and EP4 receptors were lower after macrophages were treated with IFN-gamma. Messenger RNA levels of both receptors were lower in macrophages after treatment with PGE2 or dibutyryl (db) cAMP Addition of the PKA inhibitor H89 reversed the effects of PGE2 and dbcAMP to varying degrees. Proteosome and p38 MAP kinase inhibitors blocked the LPS-stimulated increase in EP2 mRNA levels. Those inhibitors had no effect on EP4 mRNA.Thus, activating agents such as LPS and IFN-gamma may differentially regulate mRNAfor PGE2 receptor types in macrophages but the ligand and its associated signal transducing factors probably have similar regulatory effects.

CMX-8933, a peptide fragment of the glycoprotein ependymin, promotes activation of AP-1 transcription factor in mouse neuroblastoma and rat cortical cell cultures

An 8-amino acid peptide fragment (CMX-8933) of Ependymin, a glycoprotein component of the extracellular fluid and cerebrospinal fluid of goldfish brain, was synthesized and tested for its capacity to activate AP-1 transcription factor in cell cultures. Dose-response and time-course studies of AP-1's binding to DNA were carried out in neuroblastoma (NB2a/dl) and primary rat brain cortical cultures using an electrophoretic mobility shift assay (EMSA). A 13-14-fold increase in AP-1's DNA binding was obtained when NB2a cells were incubated for 4 h with 6-10 microg/ml CMX-8933. Primary rat brain cortical cultures were much more sensitive to the effects of CMX-8933 than transformed (NB2a) cultures; here a 26.7+/-5.2-fold increase in binding was observed following a 3-h treatment with as little as 10 ng/ml peptide. These findings are consistent with an activation of this transcription factor, a characteristic that has been previously correlated with functional aspects of full-sized neurotrophic factors (nerve growth factor and brain-derived nerve growth factor) in neuronal differentiation and regeneration. Such data suggest a role for Ependymin in transcriptional control.

A (1-->3)-beta-D-linked heptasaccharide is the unit ligand for glucan pattern recognition receptors on human monocytes

Glucans are fungal cell wall polysaccharides which stimulate innate immune responses. We determined the minimum unit ligand that would bind to glucan receptors on human U937 cells using laminarin-derived pentaose, hexaose, and heptaose glucan polymers. When U937 membranes were pretreated with the oligosaccharides and passed over a glucan surface, only the heptasaccharide inhibited the interaction of glucan with membrane receptors at a K(d) of 31 microM (95% CI 20-48 microM) and 100% inhibition. However, the glucan heptasaccharide did not stimulate U937 monocyte NFkappaB signaling, nor did it increase survival in a murine model of polymicrobial sepsis. Laminarin, a larger and more complex glucan polymer (M(w) = 7700 g/mol), only partially inhibited binding (61 +/- 4%) at a K(d) of 2.6 microM (99% CI 1.7-4.2 microM) with characteristics of a single binding site. These results indicate that a heptasaccharide is the smallest unit ligand recognized by macrophage glucan receptors. The data also indicate the presence of at least two glucan-binding sites on U937 cells and that the binding sites on human monocyte/macrophages can discriminate between glucan polymers. The heptasaccharide and laminarin were receptor antagonists, but they were not receptor agonists with respect to activation of NFkappaB-dependent signaling pathways or protection against experimental sepsis.

Normal human fibroblasts express pattern recognition receptors for fungal (1-->3)-beta-D-glucans

Fungal cell wall glucans nonspecifically stimulate various aspects of innate immunity. Glucans are thought to mediate their effects via interaction with membrane receptors on macrophages, neutrophils, and NK cells. There have been no reports of glucan receptors on nonimmune cells. We investigated the binding of a water-soluble glucan in primary cultures of normal human dermal fibroblasts (NHDF). Membranes from NHDF exhibited saturable binding with an apparent dissociation constant (K(D)) of 8.9 +/- 1.9 microg of protein per ml and a maximum binding of 100 +/- 8 resonance units. Competition studies demonstrated the presence of at least two glucan binding sites on NHDF. Glucan phosphate competed for all binding sites, with a K(D) of 5.6 microM (95% confidence interval [CI], 3.0 to 11 microM), while laminarin competed for 69% +/- 6% of binding sites, with a K(D) of 3.7 microM (95% CI, 1.9 to 7.3 microM). Glucan (1 microg/ml) stimulated fibroblast NF-kappaB nuclear binding activity and interleukin 6 (IL-6) gene expression in a time-dependent manner. NF-kappaB was activated at 4, 8, and 12 h, while IL-6 mRNA levels were increased by 48% at 8 h. This is the first report of pattern recognition receptors for glucan on human fibroblasts and the first demonstration of glucan binding sites on cells other than leukocytes. It also provides the first evidence that glucans can directly modulate the functional activity of NHDF. These results provide new insights into the mechanisms by which the host recognizes and responds to fungal (1-->3)-beta-D-glucans and suggests that the response to glucans may not be confined to cells of the immune system.

Glucans exhibit weak antioxidant activity, but stimulate macrophage free radical activity

Polymeric carbohydrates have been reported to modulate inflammatory responses in vitro and in vivo. Previous reports suggest that certain carbohydrate polymers, such as (1-->3)-beta-D-glucans, may possess free radical scavenging activity. If glucans are free radical scavengers then it might explain, in part, the ability of these ligands to modulate inflammatory responses. The present study examined the free radical scavenging activity of a variety of carbohydrate polymers and the effect of the polymers on free radical levels in a murine macrophage cell line. All of the carbohydrates exhibited concentration dependent antioxidant effects (EC(50) range = 807 to 43 microg/ml). However, the antioxidant activity for the carbohydrates was modest in comparison with PDTC (EC(50) = 0.13 microg/ml) and the carbohydrate concentration required for antioxidant activity was high (x EC(50) = 283 microg/ml). The antioxidant ability of the polymers was greater (p < .05) than their monosaccharide constituents, i.e., dextrose EC(50) = 807 vs. glucan sulfate EC(50) = 43 microg/ml. Coincubation of glucans with murine J774a.1 cells increased free radical levels when compared to controls. Therefore, the weak free radical scavenging activity of glucan polymers cannot explain their modulatory effect on inflammatory responses in tissue culture and/or disease models of inflammation.

Polysaccharide immunomodulators as therapeutic agents: structural aspects and biologic function

Polysaccharide immunomodulators were first discovered over 40 years ago. Although very few have been rigorously studied, recent reports have revealed the mechanism of action and structure-function attributes of some of these molecules. Certain polysaccharide immunomodulators have been identified that have profound effects in the regulation of immune responses during the progression of infectious diseases, and studies have begun to define structural aspects of these molecules that govern their function and interaction with cells of the host immune system. These polymers can influence innate and cell-mediated immunity through interactions with T cells, monocytes, macrophages, and polymorphonuclear lymphocytes. The ability to modulate the immune response in an appropriate way can enhance the host's immune response to certain infections. In addition, this strategy can be utilized to augment current treatment regimens such as antimicrobial therapy that are becoming less efficacious with the advent of antibiotic resistance. This review focuses on recent studies that illustrate the structural and biologic activities of specific polysaccharide immunomodulators and outlines their potential for clinical use.

Polysaccharide immunomodulators as therapeutic agents: structural aspects and biologic function

Polysaccharide immunomodulators were first discovered over 40 years ago. Although very few have been rigorously studied, recent reports have revealed the mechanism of action and structure-function attributes of some of these molecules. Certain polysaccharide immunomodulators have been identified that have profound effects in the regulation of immune responses during the progression of infectious diseases, and studies have begun to define structural aspects of these molecules that govern their function and interaction with cells of the host immune system. These polymers can influence innate and cell-mediated immunity through interactions with T cells, monocytes, macrophages, and polymorphonuclear lymphocytes. The ability to modulate the immune response in an appropriate way can enhance the host's immune response to certain infections. In addition, this strategy can be utilized to augment current treatment regimens such as antimicrobial therapy that are becoming less efficacious with the advent of antibiotic resistance. This review focuses on recent studies that illustrate the structural and biologic activities of specific polysaccharide immunomodulators and outlines their potential for clinical use.

The influence of glucan polymer structure and solution conformation on binding to (1-->3)-beta-D-glucan receptors in a human monocyte-like cell line

Glucans are (1-3)-beta-D-linked polymers of glucose that are produced as fungal cell wall constituents and are also released into the extracellular milieu. Glucans modulate immune function via macrophage participation. The first step in macrophage activation by (1-3)-beta-D-glucans is thought to be the binding of the polymer to specific macrophage receptors. We examined the binding/uptake of a variety of water soluble (1-3)-beta-D-glucans and control polymers with different physicochemical properties to investigate the relationship between polymer structure and receptor binding in the CR3- human promonocytic cell line, U937. We observed that the U937 receptors were specific for (1-->3)-beta-D-glucan binding, since mannan, dextran, or barley glucan did not bind. Scleroglucan exhibited the highest binding affinity with an IC(50)of 23 nM, three orders of magnitude greater than the other (1-->3)-beta-D-glucan polymers examined. The rank order competitive binding affinities for the glucan polymers were scleroglucan>>>schizophyllan > laminarin > glucan phosphate > glucan sulfate. Scleroglucan also exhibited a triple helical solution structure (nu = 1.82, beta = 0.8). There were two different binding/uptake sites on U937 cells. Glucan phosphate and schizophyllan interacted nonselectively with the two sites. Scleroglucan and glucan sulfate interacted preferentially with one site, while laminarin interacted preferentially with the other site. These data indicate that U937 cells have at least two non-CR3 receptor(s) which specifically interact with (1-->3)-beta-D-glucans and that the triple helical solution conformation, molecular weight and charge of the glucan polymer may be important determinants in receptor ligand interaction.

Activation of a rel-A/CEBP-beta-related transcription factor heteromer by PGG-glucan in a murine monocytic cell line

PGG-Glucan is a soluble beta-glucan immunomodulator that enhances a variety of leukocyte microbicidal activities without activating inflammatory cytokines. Although several different cell surface receptors for soluble (and particulate) beta-glucans have been described, the signal transduction pathway(s) used by these soluble ligands have not been elucidated. Previously we reported that PGG-Glucan treatment of mouse BMC2.3 macrophage cells activates a nuclear factor kappa-B-like (NF-kappaB) transcription factor complex containing subunit p65 (rel-A) attached to an unidentified cohort. In this study, we identify the cohort to be a non-rel family member: a CCAAT enhancer-binding protein-beta (C/EBP-beta)-related molecule with an apparent size of 48 kDa, which is a different protein than the previously identified C/EBP-beta p34 also present in these cells. C/EBP-beta is a member of the bZIP family whose members have previously been shown to interact with rel family members. This rel/bZIP heteromer complex activated by PGG-Glucan is different from the p65/p50 rel/rel complex induced in these cells by lipopolysaccharide (LPS). Thus, our data demonstrate that PGG-Glucan uses signal transduction pathways different from those used by LPS, which activates leukocyte microbicidal activities and inflammatory cytokines. We further show that heteromer activation appears to use protein kinase C (PKC) and protein tyrosine kinase (PTK) pathways, but not mitogen-activated protein kinase p38. Inhibitor kappa-B-alpha (IkappaB-alpha) is associated with the heteromer; this association decreases after PGG-Glucan treatment. These data are consistent with a model whereby treatment of BMC2.3 cells with PGG-Glucan activates IkappaB-alpha via PKC and/or PTK pathways, permitting translocation of the rel-A/CEBP-beta heteromer complex to the nucleus and increases its DNA-binding affinity.

Microfibrillar structure of PGG-glucan in aqueous solution as triple-helix aggregates by small angle x-ray scattering

The conformation of polysaccharide PGG-Glucan, isolated from yeast cell walls, in aqueous solution was investigated by small angle x-ray scattering (SAXS) and multidetector gel permeation chromatography coupled with postcolumn delivery (GPC/PCD) techniques in comparison with scleroglucan. It was shown that both polysaccharides exhibit a rigid rod-like conformation in aqueous solution by SAXS experiments. The mass per unit length (M/L) and radius (R) of rod cross section of PGG-Glucan were measured to be 6300 daltons/nm and 1.89 nm, while those of scleroglucan are 2300 and 0.83, respectively. Utilizing a GPC/light scattering technique, the average aggregation number of PGG-Glucan is 9, while that of scleroglucan is around 3. From the comparison of the M/L and R of the respective rod cross sections as well as their aggregation number data, it is concluded that PGG-Glucan is composed of triple helices, which tend to aggregate as triplets in solution, whereas scleroglucan is composed of a single triple helix. The aggregation number distribution of PGG-Glucan was found to range from 1 to about 25 determined by GPC/PCD. From the observation of a Debye-Scherrer ring type of peak in the macroscopic scattering cross section of PGG-Glucan by SAXS, the existence of a small amount of ordered clusters of PGG-Glucan can be deduced. The "lattice parameter" of these ordered fasces-like clusters is consistent with the radius of the individual triple-helical rods forming a microfibrillar superstructure. These results indicate that higher aggregated forms of PGG-Glucan containing up to 8 triple helices behave as ordered fasces-like clusters. We conclude that PGG-Glucan is triple-helix aggregates formed by rigid rods stacking together side by side. We propose a molecular structural model for PGG-Glucan conformations.

Inhibiting early activation of tissue nuclear factor-kappa B and nuclear factor interleukin 6 with (1-->3)-beta-D-glucan increases long-term survival in polymicrobial sepsis

BACKGROUND

Recent data implicate the activation of nuclear factor-kappa B (NF-kappa B) and nuclear factor interleukin 6 (NF-IL6) as important steps in the pathophysiologic mechanisms of adult respiratory distress syndrome and systemic inflammatory response syndrome.

METHODS

This study evaluated the effect of immunomodulating polysaccharides on transcription factor activation, cytokine expression, and mortality in a murine cecal ligation and puncture (CLP) model. ICR/HSD mice were treated with glucan (50 mg/kg) 1 hour before or 15 minutes after CLP. Liver and lung tissue were harvested at 3 hours and mortality trends were observed for 20 days.

RESULTS

CLP increased liver and lung NF-kappa B and NF-IL6 nuclear binding activity as well as tumor necrosis factor-alpha and interleukin 6 messenger RNA levels at 3 hours. Pretreatment or posttreatment with glucans inhibited tissue NF-kappa B and NF-IL6 nuclear binding activity and tissue cytokine messenger RNA levels. Prophylaxis with glucan phosphate or scleroglucan increased (P < .001) long-term survival (20% CLP vs 65% glucan phosphate, 75% scleroglucan). Posttreatment with glucan phosphate also increased (P < .05) long-term survival (20% vs 65%).

CONCLUSIONS

Pretreatment or posttreatment with biologic response modifiers decreased tissue transcription factor nuclear binding activity and cytokine message in liver and lung of septic mice. Inhibiting early transcription factor activation and cytokine message expression correlates with improved outcome in polymicrobial sepsis as denoted by increased long-term survival.

Promotion of Neutrophil Chemotaxis Through Differential Regulation of β1 and β2 Integrins

Migration of neutrophils requires sequential adhesive and deadhesive interactions between β1 and β2 integrins and components of the extracellular matrix. Prompted by reports that describe interaction of soluble β-glucan with the β2 integrin Mac-1, a role for β-glucan in regulation of integrin-mediated migration was investigated. Neutrophil migration in response to fMLP was assessed using an agarose overlay method with slides precoated with fibronectin (Fn) ± β-glucan. On Fn, random migration in excess of directed migration was observed. In contrast, migration on Fn + β-glucan was directional, with marked diminution of random migration. This conversion of random to directed migration was seen neither when Fn was supplemented with alternative polysaccharides nor when β-glucan was applied to other components of the extracellular matrix. This effect of β-glucan was shown to be cation dependent and to be effected by Arg-Gly-Asp-containing peptides consistent with an integrin-mediated event. mAb inhibition studies demonstrate that β-glucan effects this shift toward directed migration through suppression of migration mediated by Mac-1 and very late Ag 5 and enhancement of very late Ag 3-mediated migration. Adhesion assays suggest that the prochemotactic influence of β-glucan is due, in part but not entirely, to modulation of PMN adhesion to Fn. In summary, these data support a novel role for β-glucan in regulation of β1- and β2-mediated neutrophil migration on Fn.

PGG-glucan, a soluble beta-(1,3)-glucan, enhances the oxidative burst response, microbicidal activity, and activates an NF-kappa B-like factor in human PMN: evidence for a glycosphingolipid beta-(1,3)-glucan receptor

PGG-Glucan, a soluble beta-(1,6)-branched beta-(1,3)-linked glucose homopolymer derived from the cell wall of the yeast Saccharomyces cerevisiae, is an immunomodulator which enhances leukocyte anti-infective activity and enhances myeloid and megakaryocyte progenitor proliferation. Incubation of human whole blood with PGG-Glucan significantly enhanced the oxidative burst response of subsequently isolated blood leukocytes to both soluble and particulate activators in a dose-dependent manner, and increased leukocyte microbicidal activity. No evidence for inflammatory cytokine production was obtained under these conditions. Electrophoretic mobility shift assays demonstrated that PGG-Glucan induced the activation of an NF-kappaB-like nuclear transcription factor in purified human neutrophils. The binding of 3H-PGG-Glucan to human leukocyte membranes was specific, concentration-dependent, saturable, and high affinity (Kd approximately 6 nM). A monoclonal antibody specific to the glycosphingolipid lactosylceramide was able to inhibit activation of the NF-kappaB-like factor by PGG-Glucan, and ligand binding data, including polysaccharide specificity, suggested that the PGG-Glucan binding moiety was lactosylceramide. These results indicate that PGG-Glucan enhances neutrophil anti-microbial functions and that interaction between this beta-glucan and human neutrophils is mediated by the glycosphingolipid lactosylceramide present at the cell surface.

Modulation of endotoxin- and enterotoxin-induced cytokine release by in vivo treatment with beta-(1,6)-branched beta-(1,3)-glucan

Leukocytes activated by endotoxin or enterotoxins release proinflammatory cytokines, thereby contributing to the cascade of events leading to septic shock. In the present studies, we analyzed the effects of in vivo administration of a soluble immunomodulator, beta-(1,6)-branched beta-(1,3)-glucan (soluble beta-glucan), on toxin-stimulated cytokine production in monocytes and lymphocytes isolated from treated mice. In vitro stimulation of lymphocytes isolated from soluble beta-glucan-treated mice with lipopolysaccharide (LPS) resulted in enhanced production of interleukin-6 (IL-6) and suppressed production of tumor necrosis factor alpha (TNF-alpha), while stimulation of these cells with staphylococcal enterotoxin B (SEB) or toxic shock syndrome toxin 1 (TSST-1) resulted in enhanced production of gamma interferon (IFN-gamma) and suppressed production of IL-2 and TNF-alpha compared to that in cells isolated from untreated mice. In vitro stimulation of monocytes isolated from soluble beta-glucan-treated mice with LPS also resulted in suppressed TNF-alpha production, while stimulation of these cells with SEB or TSST-1 resulted in suppressed IL-6 and TNF-alpha production compared to that in cells isolated from untreated mice. Thus, the overall cytokine pattern of leukocytes from soluble beta-glucan-treated mice reflects suppressed production of proinflammatory cytokines, especially TNF-alpha. Taken together, our results suggest that treatment with soluble beta-glucan can modulate the induction cytokines during sepsis, resulting in an overall decrease in host mortality.

Enhanced clearance of a multiple antibiotic resistant Staphylococcus aureus in rats treated with PGG-glucan is associated with increased leukocyte counts and increased neutrophil oxidative burst activity

PGG-Glucan [Betafectin], a highly purified soluble beta-(1-6)-branched beta-(1 3)-linked glucan isolated from Saccharomyces cerevisiae, has broad in vitro and in vivo anti-infective activities unrelated to cytokine induction. Here we present in vivo results on the anti-infective activity of PGG-Glucan against a multiple antibiotic resistant Staphylococcus aureus. PGG-Glucan (0.25-4 mg/kg) was administered intramuscularly to male Wistar rats 48 h, 24 h, and 4 h before and 4 h after intraperitoneal implantation of a gelatin capsule containing 10(8)S. aureus colony forming units (CFU). Blood samples were collected at various times after challenge to determine CFU levels, leukocyte counts and neutrophil oxidative burst activity; serum TNF-alpha, and IL-1beta levels were also evaluated. The 0.25 mg/kg PGG-Glucan dose had no effect on reducing blood CFU levels; however, PGG-Glucan doses of 0.5 mg/kg, 1 mg/kg, 2 mg/kg or 4 mg/kg significantly reduced blood CFU levels by 48 h after challenge. Reduced CFU levels correlated with significantly elevated absolute monocyte counts, absolute neutrophil counts, and neutrophil oxidative burst activity in the absence of any effect on TNF-alpha or on IL-1beta levels. In additional studies, effects on mortality and blood CFU levels were evaluated in rats treated with ampicillin (an antibiotic to which the S. aureus was resistant), PGG-Glucan, or both agents. Mortality and blood CFU levels were reduced most in combination-treated rats compared to saline control rats or rats treated with either ampicillin alone or PGG-Glucan alone. We conclude that in vivo (1) PGG-Glucan can enhance clearance of an antibiotic resistant S. aureus, (2) that this clearance is accompanied by an increase in monocytes and neutrophils as well as a potentiation of neutrophil oxidative microbiocidal activity without alteration of the proinflammatory cytokine response, and (3) PGG-Glucan can enhance the effectiveness of traditional antibiotic treatment.

A novel carbohydrate-glycosphingolipid interaction between a beta-(1-3)-glucan immunomodulator, PGG-glucan, and lactosylceramide of human leukocytes

The immunomodulator Betafectin(R) PGG-glucan is a homopolymer of glucose derived from yeast cell walls which has been demonstrated to enhance leukocyte anti-infective activity in vitro and in vivo, without the induction of proinflammatory cytokines. We report here the purification of a PGG-glucan-binding element from human leukocytes and its identification as lactosylceramide, a major glycosphingolipid of neutrophils, which includes the CDw17 epitope. The binding of radiolabeled PGG-glucan to purified lactosylceramide was saturable, specific, and time- and temperature-dependent. Lactosylceramides from human leukocytes were fractionated by high performance liquid chromatography in order to analyze the effect of ceramide structure on binding. A variety of fatty acid chain lengths with varying degrees of unsaturation were found to support binding to radiolabeled PGG-glucan. However, DL-lactosylceramides containing dihydrosphingosine did not bind. Radiolabeled PGG-glucan bound several other neutral glycosphingolipids with a terminal galactose, including galactosylceramide, globotriaosylceramide, and gangliotetraosylceramide. The binding of radiolabeled PGG-glucan to lactosylceramide was not inhibited by glycogen, dextran, mannan, pustulan, laminarin, or a low molecular weight beta-(1-3)-glucan, but was inhibited by high molecular weight beta-(1-3)-glucans and by a monoclonal antibody to lactosylceramide. Although this glycosphingolipid has been shown in numerous reports to bind various microorganisms, this represents the first report of lactosylceramide binding to a macromolecular carbohydrate.

Ligand binding to the (1 --> 3)-beta-D-glucan receptor stimulates NFkappaB activation, but not apoptosis in U937 cells

Recent data suggest that sepsis stimulates macrophage apoptosis (Ao) with subsequent induction of macrophage dysfunction. Nuclear factor-kappaB (NFkappaB) activation has been linked to Ao in either a pro- or antiapoptotic role. Glucans are biological response modifiers which exert antisepsis activity. This investigation examined the effect of (1-3)-beta-D-glucan receptor binding by a high affinity ligand on Ao and NFkappaB activation in U937 cells in the presence or absence of LPS. A high affinity glucan ligand (IC50 = 23 nM) activated NFkappaB, but did not induce Ao or significantly alter LPS induced U937 Ao. These data indicate that: i) modulation of the macrophage (1-3)-beta-D-glucan receptor stimulates NFkappaB; ii) does not induce Ao or significantly diminish LPS induced Ao and iii) activation of the U937 FAS receptor does not alter the relative Ao responses in glucan and LPS treated cells.

C1q receptors: regulating specific functions of phagocytic cells

A C1q receptor that upregulates the phagocytic capacity of professional phagocytes, C1qRp, has been identified, and its primary structure determined by cDNA cloning and sequencing. Monoclonal antibodies that immunoprecipitate this 126,000 Mr polypeptide inhibit the enhancement of phagocytosis triggered not only by C1q but also by mannose binding lectin (MBL) and pulmonary surfactant protein A (SPA) providing critical evidence that this polypeptide is a functional receptor or component of the receptor that mediates this enhancement of phagocytosis. The amino acid sequence, deduced from the cloned cDNA coding for this receptor, indicates that this surface glycoprotein receptor is a novel type I membrane protein of 631 amino acid containing a region homologous to C-type lectin carbohydrate recognition domains, 5 EGF-like domains, a single transmembrane domain and a 47 amino acid intracellular domain. Expression of this receptor is limited to cells of myeloid origin, platelets and endothelial cells, consistent with a relatively selective function, and making it an attractive candidate for therapeutic modulation of function. A distinct C1q receptor that triggers superoxide in polymorphonuclear leukocytes has been functionally characterized and designated as C1qRO2-. Thus, the accumulated data that will be summarized here demonstrate that there are at least two C1q receptor/receptor complexes (C1qRp and C1qRO2-), each triggering distinct cellular responses, that multiple C1q receptors can be expressed on the same, as well as on different, cell types, and that at least one C1q receptor, C1qRp, is capable of responding to multiple ligands.

Effects of particulate and soluble (1-3)-beta-glucans on Ca2+ influx in NR8383 alveolar macrophages

Particulate and soluble (1-3)-beta-glucans are effective in preventing infections by enhancing macrophage and neutrophil functions. However, the mechanisms triggering these enhanced cellular responses are essentially unknown. We recently demonstrated that zymosan, a particulate (1-3)-beta-glucan receptor agonist, caused an influx of Ca2+ in NR8383 rat alveolar macrophages (AMs) and a resulting increase in intracellular Ca2+ (Zhang et al., J. Leukoc. Biol. 62 (1997) 341-348). Since Ca2+ is important in mediating leukocyte responses, we investigated whether other (1-3)-beta-glucans also alter Ca2+ mobilization in AMs. Particulate and soluble (1-3)-beta-glucans derived from Saccharomyces cerevisiae were used in these studies. Like zymosan, particulate (1-3)-beta-glucan (WGPs) caused a concentration-dependent increase in [Ca2+]i, which was inhibited by removal of extracellular Ca2+ and by SKF96365, an inhibitor of receptor-operated Ca2+ channels. When three different soluble (1-3)-beta-glucans, with molecular weights of approximately 11,000, 150,000, and 1,000,000 Da, were tested alone for effects on Ca2+ responses, the low molecular weight (1-3)-beta-glucan produced no effect and the intermediate and high molecular weight (1-3)-beta-glucans caused only a small increase in [Ca2+]i. Interestingly, however, all three soluble (1-3)-beta-glucans could significantly reduce the Ca2+ responses induced by a subsequent exposure to either WGPs or zymosan. These results demonstrate that: 1) particulate (1-3)-beta-glucan activates Ca2+ influx in NR8383 macrophages through receptor-operated Ca2+ channels; 2) soluble (1-3)-beta-glucans do not strongly activate Ca2+ influx in these cells; and 3) soluble (1-3)-beta-glucans significantly inhibit Ca2+ influx induced by WGPs or zymosan. Soluble (1-3)-beta-glucans are likely to prevent Ca2+ influx by competitively binding to the (1-3)-beta-glucan receptors recognizing zymosan and WGPs. The smaller Ca2+ influx induced by soluble (1-3)-beta-glucans may represent only a partial activation of post-receptor signal transduction pathways necessary for inducing Ca2+ influx.