The influence of natural and synthetic cationic substances on phagocytic activity of human polymorphonuclear cells. An alternative pathway of phagocytic enhancement

Augmentation of Urinary Lactoferrin Enhances Host Innate Immune Clearance of Uropathogenic Escherichia coli

Urinary tract infection (UTI) is a prominent global health care burden. Although UTI is readily treated with antibiotics in healthy adults, complicated cases in immune-compromised individuals and the emerging antibiotic resistance of several uropathogens have accelerated the need for new treatment strategies. Here, we surveyed the composition of urinary exosomes in a mouse model of uropathgenic Escherichia coli (UPEC) UTI to identify specific urinary tract defense constituents for therapeutic development. We found an enrichment of the iron-binding glycoprotein lactoferrin in the urinary exosomes of infected mice. In subsequent in vitro studies, we identified human bladder epithelial cells as a source of lactoferrin during UPEC infection. We further established that exogenous treatment with human lactoferrin (hLf) reduces UPEC epithelial adherence and enhances neutrophil antimicrobial functions including bacterial killing and extracellular trap production. Notably, a single intravesicular dose of hLf drastically reduced bladder bacterial burden and neutrophil infiltration in our murine UTI model. We propose that lactoferrin is an important modulator of innate immune responses in the urinary tract and has potential application in novel therapeutic design for UTI.

Human lactoferrin and peptides derived from a surface-exposed helical region reduce experimental Escherichia coli urinary tract infection in mice

Lactoferrin (LF) is a multifunctional immunoregulatory protein that has been associated with host defense at mucosal surfaces through its antibacterial properties. The antibacterial and anti-inflammatory properties of LF were further explored with an animal model of experimental urinary tract infection. Bovine LF (bLF), human LF (hLF), and synthetic peptide sequences based on the antibacterial region of hLF (amino acid residues 16 to 40 [HLD1] and 18 to 40 [HLD2]) were given orally to female mice 30 min after the instillation of 10(8) Escherichia coli bacteria into the urinary bladder. The control groups received phosphate-buffered saline or water. C3H/Tif mice were treated with hLF or bLF, and C3H/HeN mice were treated with bLF only. The numbers of bacteria in the kidneys and bladder of C3H/Tif and C3H/HeN mice were significantly reduced 24 h later by the LF treatments compared to the findings for the control group. The hLF-treated group showed the strongest reduction compared with the vehicle-treated-group (P values were 0.009 and 0.0001 for the kidneys and bladder, respectively). The urinary leukocyte response was diminished in the hLF-treated group. The hLF treatment also significantly reduced the urinary interleukin-6 (IL-6) levels at 2 h and the systemic IL-6 levels at 24 h after infection (P values were 0.04 and < 0.002, respectively). In the bLF-treated animals, no such strong anti-inflammatory effects were obtained. In another series of experiments, C3H/Tif mice perorally treated with HLD1 or HLD2 also showed reduced numbers of bacteria in the kidneys compared with the vehicle-treated mice, although the results were significantly different only for HLD2 (P < 0.01). Analysis of urine from hLF-fed C3H/Tif mice showed that hLF was excreted into the urinary tract at 2 h after feeding. Testing of the in vitro bactericidal activity of LF (1 mg/ml) or the peptides (0.1 mg/ml) in mouse urine against the E. coli bacteria revealed moderate killing only by HLD2. In conclusion, these results demonstrate for the first time that oral administration of hLF or peptides thereof is effective in reducing infection and inflammation at a remote site, the urinary tract, possibly through transfer of hLF or its peptides to the site of infection via renal secretion. The antibacterial mechanism is suggested to involve bactericidal capacities of LF, fragments thereof, or its peptides.

Bovine lactoferrin stimulates the phagocytic activity of human neutrophils: identification of its active domain

Bovine LF (bLF) at concentrations in the range of 50-250 micrograms/ml enhanced the phagocytic activity of human neutrophils as determined by measuring the incorporation of FITC-labeled latex beads by flow cytometry. The stimulatory effect of bLF was not abrogated by hydrolysis with pepsin. Bovine lactoferricin (bLFcin), which is a bactericidal fragment purified from a pepsin hydrolysate of bLF (bLFH), also enhanced the phagocytic activity, whereas, in contrast, the fraction of bLFH depleted of bLFcin showed no stimulatory effect. The phagocytosis-enhancing activity of bLF still remained after washing the neutrophils, following exposure to bLF. Also, bLF pretreatment of the latex beads stimulated their uptake. These results demonstrate that bLF is effective in promoting the phagocytic activity of human neutrophils. This activity appears to be due to its bLFcin domain and may involve dual mechanisms of direct binding to neutrophils and opsonin-like activity.

Transloading of tumor antigen-derived peptides into antigen-presenting cells

The discovery of a steadily growing number of tumor antigens (TAs) has made generic, cell-free, peptide-based cancer vaccines a possible alternative to cytokine-transfected autologous cellular cancer vaccines. The major drawback of peptide vaccines, however, is the poor immunogenicity of peptides. It is commonly thought that for the induction of an effective anticancer immune response, antigen-presenting cells (APCs) have to display TA-derived peptides to T lymphocytes. Polycationic amino acids have been employed in the past to enhance transport of proteins into cells. In a systematic study, the ability of different cationic polymers to transfer fluorescence-tagged peptides to APCs was investigated. We were able to show that several compounds enhance uptake of fluorescence-labeled peptides by APCs to different degrees. The most efficient compound identified, polyarginine (pArg), enhanced peptide delivery by more than 2 logs as compared with cells treated with peptide alone, whereas polylysine (pLys) treatment resulted in approximately 10-fold increased levels of fluorescence. Augmentation of peptide uptake was concentration-dependent, and the molecular weight of pArg or pLys also influenced peptide delivery. Furthermore, highly negatively charged peptides appear to be delivered with higher efficiency, although neutral peptides were also taken up at enhanced rates. Whereas peptide uptake mediated by pLys appears to be due to an at least transient permeabilization of cell membranes, peptide delivery in the presence of pArg may rely on endocytic processes. TA-derived peptides applied as cancer vaccines in conjunction with polycations afforded antitumor protection in animal models.

Cationic polyelectrolytes: potent opsonic agents which activate the respiratory burst in leukocytes

Bacteria and yeasts which are "opsonized" with cationic polyelectrolytes (poly-L-arginine, poly-L-histidine and arginine-rich histone) are avidly endocytosed by both "professional" and "non-professional" phagocytes. The cationized particles also strongly activate the respiratory burst in neutrophils and in macrophages leading to the generation of chemiluminescence, superoxide and hydrogen peroxide. On the other hand, lysine and ornithine-rich polymers are poor opsonic agents. Poly L-arginine is unique in its capacity to act synergistically with lectins, with chemotactic peptides and with cytochalasin B to generate large amounts of chemiluminescence and superoxide in human neutrophils. Unlike polyarginine, polyhistidine, in the absence of carrier particles, is one of the most potent stimulators of superoxide generations, known. Neutrophils treated with cetyltrimethylammonium bromide fail to generate superoxide, but generate strong luminol-dependent chemiluminescence which is totally inhibited by sodium azide and by thiourea. Neutrophils injured by cytolytic agents (saponin, digitonin, lysolecithin) lose their chemiluminescence and superoxide-generating capacities upon stimulation by a variety of ligands. These activities are however regained by the addition of NADPH. Lysolecithin can replace polyarginine in a "cocktail" also containing lectins and cytochalasin B, which strongly activate the respiratory burst. This suggests that polyarginine acts both as a cytolytic agent and as a ligand. Arginine and histidine-rich polyelectrolytes enhance the pathogenic effects of immune complexes in vivo (reversed Arthus phenomenon) presumably by "glueing" them to tissues. Polyhistidine complexed to catalase or to superoxide dismutase, markedly enhances their efficiency as antioxidants. On the other hand polyhistidine complexed to glucose oxidase markedly enhances injury to endothelial cells suggesting that the close association of the cationized enzyme with the plasma membrane facilitates the interaction of hydrogen peroxide with the targets. A variety of cationic agents (histone, polyarginine, polyhistidine, polymyxin B) and membrane-active agents (lysophosphatides, microbial hemolysins) act synergistically with glucose oxidase or with reagent hydrogen peroxide to kill target cells. The mechanisms by which arginine- and histidine-rich polyelectrolytes activate the respiratory burst in neutrophils might involve interaction with G-proteins, the activation of arachidonic acid metabolism and phospholipase A2, or the interaction with myeloperoxidase. Naturally-occurring cationic proteins might modulate several important functions of leukocytes and the course and outcome of the inflammatory process.

Influence of cationic superoxide generation enhancing protein (SGEP) on phagocytic and intracellular bactericidal activity of human polymorphonuclear cells

Cationic fraction III from the lysosomes of normal human peripheral blood polymorphonuclear cells (PMNs) was found to contain superoxide generation enhancing protein (SGEP). Herein, we report on the influence of partially purified SGEP obtained from fraction III (subfractions III-5 and III-6), on various phagocytic functions of human PMNs. SGEP markedly enhanced intracellular bactericidal activity of human peripheral PMNs. The enhancement was time and dose dependent. It also reduced adhesiveness of the PMNs. SGEP did not influence chemotaxis, phagocytosis or phagocytic index. These findings are compatible with our original observation regarding superoxide generation enhancement properties of SGEP.

Influence of neutrophil cationic proteins on generation of superoxide by human polymorphonuclear cells during phagocytosis

The cationic proteins from neutrophil lysosomes have been shown to modulate phagocytic activity of granulocytes. The present study reports the effects of the cationic protein fractions on the generation of O2- by human PMNs during phagocytosis. Human PMNs were reacted with different phagocytic stimuli in the presence and absence of lysosomal cationic proteins and the amount of O2- generated was determined by superoxide dismutase inhibitable reduction of cytochrome c. Total cationic protein extract from neutrophil lysosomes enhanced O2- generated by PMNs during the phagocytosis of IgG-coated latex beads and opsonized zymosan particles. The analysis of the fractions of cationic proteins obtained from a Sephadex G-75 column showed that the O2- generation-enhancing activity was associated with the proteins eluted in fractions III and IV. A protein fraction mainly eluted in void volume inhibited the cytochrome c reduction by O2- formed during phagocytosis. This was due to the presence of superoxide dismutase-like activity since O2- generated by the xanthine-xanthine oxidase system was also inhibited by this fraction. The cationic protein fractions III and IV from the Sephadex G-75 column were further subfractionated. Although the O2(-)-enhancing activity was eluted in the same fractions as chymotrypsin activity, there was no quantitative correlation between the amount of O2- generation and chymotrypsin activity. Moreover, commercial chymotrypsin did not enhance O2- generation. Electrophoretic analysis of the isolated protein fractions suggests that O2- generation enhancing protein (SGEP) is different from lysozyme or chymotrypsin and probably represents previously undescribed protein.

Protamine sulfate-induced enzyme secretion from rabbit neutrophils

Protamine sulfate induces enzyme secretion from rabbit neutrophils. Enzyme secretion is mainly due to exocytosis but, depending on the experimental conditions, a small amount of cytolysis may occur. As compared with stimulation of neutrophil functions by other activators, protamine sulfate-induced enzyme release by exocytosis is a relatively slow process and is not accompanied by a marked activation of the metabolic burst. For optimal exocytosis, extracellular Ca2+ is required, but there is still some enzyme release in its absence, and other metal ions (Sr2+, Ba2+, Mg2+) can partly mimic the effect of Ca2+. Positive charges on protamine are of primary importance because the polyanion heparin completely inhibits protamine sulfate-induced enzyme release. Protamine linked to agarose beads is able to induce enzyme release; thus the induction of exocytosis is due to an interaction of the positive charges on protamine with the plasma membrane. Sialic acid residues on the membrane, however, seem not to play an important role in this process.

Modulation of locomotor activity of polymorphonuclear cells by cationic substances and cationic lysosomal fractions from human neutrophils

Seven cationic substances--human and egg-white lysozyme, RNase, protamine, histone, poly-L-lysine and poly-L-arginine; five cationic lysosomal fractions from human polymorphonuclears (PMNs); RNA; poly-L-glutamic acid; DNA; heparin; endotoxin; mastocytotropic agent compound 48/80; and cytochalasin B were tested for the influence on chemotaxis and random migration of human PMNs using under-agarose migration and Boyden chambers with two filters and [51Cr]PMNs. The above substances were either preincubated with PMNs, added to chemoattractants, or used instead of chemoattractants. In under-agarose migration method chemotaxis was inhibited by 11-35% when egg-white lysozyme, protamine, heparin, endotoxin, or compound 48/80 was added to the cells. High concentration of cytochalasin B inhibited chemotaxis by 73%. Cationic fractions I and V and low concentration of cytochalasin B enhanced chemotaxis by 11%, 41%, and 30%, respectively. When human and egg-white lysozyme, DNA, or cytochalasin B was added to the chemoattractants, motility of PMNs was inhibited. Cationic fractions II and V from human PMNs, when used as chemoattractants, enhanced cellular motility by 143-167%. Random migration was enhanced by heparin and inhibited by cytochalasin B and by cationic fractions from human PMNs. These findings suggest that various cationic and anionic substances and cationic fractions from human PMNs have heterogeneous influence on random migration and chemotactic activity of human PMN. Analysis relating chemotaxis to phagocytosis and to intracellular bactericidal activity (ICBA) has shown several patterns. Protamine, poly-L-lysine, poly-L-arginine, and agent compound 40/80 all inhibit chemotaxis and enhance phagocytosis and ICBA; cationic fractions II and V enhanced all three functions, whereas cytochalasin B suppressed phagocytosis and ICBA and had concentration-dependent modulatory influence on chemotaxis. It implies diverse mechanisms of action and possible impact on inflammatory reactions.

Cytolytic effect of polylysine on rabbit polymorphonuclear leukocytes

The cationic polyamino acids polylysine and polyarginine cause a time and concentration dependent lysis of rabbit polymorphonuclear leukocytes. Lysis, measured as LDH release, is preceded by exocytosis, as can be deduced from a higher lysozyme release than LDH release, at short incubation time or with low concentrations of polylysine. The lytic effect of polylysine could be annihilated with the polyanion polyglutamic acid. Monomeric lysine or arginine, or low-molecular-weight polylysine, were not lytic. This indicates that positive charges on a polymeric molecule of sufficient chain length play a predominant role in the interaction. Substances that promote exocytosis cause an increase of lysozyme release and a reduction of LDH release, whereas inhibitors of exocytosis cause the reverse: less lysozyme release and more LDH release. Negatively charged sialic groups on the plasma membrane are not important for the interaction, because their removal does not affect the lytic effect of polylysine on the cell. The possibility that the lipid part of the plasma membrane is the point of attack for the polycations is discussed.

Chemiluminescence and superoxide generation by leukocytes stimulated by polyelectrolyte-opsonized bacteria. Role of histones, polyarginine, polylysine, polyhistidine, cytochalasins, and inflammatory exudates as modulators of oxygen burst

Human blood leukocytes generate intense luminol-dependent chemiluminescence (LDCL) following stimulation by streptococci and by Gram negative rods which had been preopsonized by cationic polyelectrolytes (histone, poly L-arginine-PARG, poly L-histidine-PHSTD). Streptococci but not Gram negative rods or hyaluronic acid-rich streptococci (group C) also induced intense LDCL following opsonization with the anionic polyelectrolytes-dextran sulfate or polyanethole sulfonate (liquoid) suggesting that the outer surfaces of different bacteria bound anionic polyelectrolytes to different extents. Both normal and immune serum, synovial fluids and pooled human saliva inhibited the LDCL responses induced by streptococci preopsonized with poly cations. On the other hand, bacteria which had been first preopsonized by the various body fluids and then subjected to a second opsonization by cationic ligands ("sandwiches"), induced a very intense LDCL response in leukocytes. Streptococci which had been preopsonized by PARG, histone or by PHSTD also triggered superoxide generation by blood leukocytes, which was markedly enhanced by a series of cytochalasins. PHSTD alone induced the formation of very large amounts of superoxide. Paradoxically, the same concentrations of cytochalasins B or C which markedly boosted the generation of superoxide following stimulation of leukocytes with soluble or particulate ligands, had a strong inhibitory effect on the generation of LDCL. On the other hand cycochalasins failed to inhibit LDCL which had been induced by phorbol myristate acetate (PMA). Peritoneal macrophages which had been harvested from C. parvum-stimulated mice, generated more LDCL and superoxide following stimulation by PARG than macrophages obtained from proteose peptone-stimulated mice. Macrophages which had been activated either by proteose peptone or by C. parvum and cultivated for 2 hours on teflon surfaces, generated much more LDCL than macrophages which had been cultivated for 24 hours on teflon surfaces. Both cationic and anionic polyelectrolytes mimic the effects of antibodies as activators of the oxygen burst in blood leukocytes and in macrophages. Such polyelectrolytes can serve as models to further study leukocyte-bacteria interactions in infectious and inflammatory sites.

Inhibition of bone resorption in vitro by compound 48/80

The mechanisms that control cycles of bone formation and bone resorption are not well understood. In this report we provide evidence that compound 48/80 is a potent inhibitor of bone resorption in vitro. Resorption was assessed by the release of calcium-45 from pre-labelled newborn mouse calvaria that were treated with compound 48/80 and/or parathyroid hormone (PTH) in organ culture. Our results demonstrate that co-incubation of calvaria with PTH plus compound 48/80 (concentrations 1-10 mcg/ml) produces a marked reduction of calcium-45 release compared to PTH alone. Furthermore, pre-incubation of calvaria with compound 48/80, for as little as three hours, inhibits resorption by subsequent treatment with PTH alone. Measurement of lactate dehydrogenase (LDH) released into the culture medium indicated that treatment with compound 48/80, at the doses and time periods studied, was not cytotoxic. This novel effect of compound 48/80 may provide a useful tool for studying the cellular mechanisms involved in the bone resorption process.

Purification and characterization of a phagocytosis-stimulating factor from phagocytosing polymorphonuclear neutrophils: comparison with granule basic proteins

Phagocytosis-stimulating factor (PSF) was purified by copper chelate chromatography and characterized in comparison with basic proteins in the granule of polymorphonuclear neutrophils. By copper chelate chromatography, PSF was eluted at pH 3.7; whereas cationic protein, lysozyme, and lactoferrin were eluted at pH 5.6, 5.1, and 4.0, respectively. Purified PSF has an approximate molecular weight of 16,000 and an isoelectric point at 8.7, which differ from those of basic proteins, such as cationic protein, lysozyme, and lactoferrin. Anionic substances such as DNA and heparin did not influence the phagocytosis-stimulating activity of PSF, whereas that of the granule basic protein fraction from resting polymorphonuclear neutrophils was abolished. PSF had little bactericidal activity against Escherichia coli and Staphylococcus aureus, whereas the granule basic protein fraction from resting PMNs had strong bactericidal activity against E. coli and weak activity against S. aureus. These results indicate that PSF is a basic protein which is distinguishable from cationic protein, lysozyme, and lactoferrin.

Opsonic activity of MCP-1 and MCP-2, cationic peptides from rabbit alveolar macrophages

MCP-1 and MCP-2, cationic peptides derived from rabbit alveolar macrophages, enhanced the ability of these cells to ingest Staphylococcus aureus, Klebsiella pneumoniae, Bordetella bronchiseptica, and Candida albicans in vitro. The opsonic effect of MCP-1 was potentiated by Ca++ and Mg++ and was associated with binding of the peptide to alveolar macrophages and microorganisms. MCP-1 and MCP-2 may contribute to the ability of alveolar macrophage to ingest microorganisms that gain entry to the lower respiratory tract.

Modulation of phagocytosis and intracellular bactericidal activity of polymorphonuclear and mononuclear cells by cationic proteins from human granulocytes: alternative pathway of phagocytic enhancement

Cationic lysosomal proteins from human polymorphonuclears (PMN) were isolated by column chromatography and divided into five fractions. On acrylamide gel electrophoresis, fraction I had four bands slower than lysozyme (LZM) mobility; fraction II had five or six bands slower than LZM; fraction III had at least seven bands slower and two bands faster than LZM; fraction IV contained LZM, two bands faster and a few faint bands slower than LZM; fraction V was composed of almost pure LZM. Partial characterization of the fractions showed presence of neutral protease in fractions I-IV, chymotrypsin in fraction III, lysozyme in fractions IV and V, and phospholipase A2 mainly in fractions II and III. Modulatory activity of fractions I-V were tested at concentrations up to 50 micrograms/ml. Enhancement of phagocytosis of Staphylococcus aureus was observed by fractions I, IV, and V, whereas phagocytic index was enhanced by all but the fraction II. Intracellular bactericidal activity (ICBA) was markedly enhanced by fractions I, II, and V. Addition of DNA or cytochalasine B inhibited or abolished phagocytosis-enhancing activity of cationic fractions. Their influence on ICBA was much less pronounced. Fraction III enhanced phagocytic index and phagocytosis of E. coli, whereas fractions I and II enhanced intracellular bactericidal activity against this bacteria. Enhancement of phagocytic activity of monocytes has also been observed. The data suggest that some cationic lysosomal fractions from human PMNs enhance phagocytosis and phagocytic index by human PMNs and monocytes and intracellular bactericidal activity of human PMNs. This alternative pathway of phagocytic enhancement is unrelated to the previously described enhancers of phagocytosis and may play a role in defense mechanisms against infection.

Synergy between acylureidopenicillins and immunoglobulin G in experimental animals

The interaction of a commercially available 7S modified immunoserumglobulin and beta-lactam antibiotics was studied in animal experiments (granuloma pouch model) as well as an ex vivo system (rat polyvinyl sponge model). Infections of the pouches were caused by gram-negative rods and gram-positive cocci, respectively. Therapy of pouches being infected with beta-lactamase-producing strains with beta-lactam antibiotics and immunoserumglobulin was as effective as beta-lactam antibiotic monotherapy of beta-lactamase-negative strains. This synergistic effect between immunoserumglobulin and beta-lactam antibiotics against beta-lactamase-producing bacteria is due to inactivation of enzymic beta-lactamase activity by specific antibodies against beta-lactamases. Immune phagocytosis was studied by adopting the in vivo and ex vivo models, respectively. Immune phagocytosis was most effectively stimulated by immunoserumglobulin whereas a pepsin-degraded product or a preparation obtained by pH4 treatment caused only minor effects. Furthermore, immunoserumglobulin stimulated phagocytosis and intracellular killing of gram-negative bacteria even in the absence of specific antibodies against these strains. Analogous effects were obtained with spermidine and albumin. These results indicate that immunoserumglobulin may stimulate phagocytosis nonspecifically, too. Thus, immunoserumglobulin may play a dual role in host defense mechanisms; in addition immunoserumglobulin acts as a beta-lactamase inhibitor, thus protecting beta-lactam antibiotics from hydrolysis.

Poly-L-arginine and an N-formylated chemotactic peptide act synergistically with lectins and calcium ionophore to induce intense chemiluminescence and superoxide production in human blood leukocytes. Modulation by metabolic inhibitors, sugars, and polyelectrolytes

Various cationic polyelectrolytes (poly-alpha-amino acids and histones), lectins, the chemotactic peptide, f-methionyl-leucyl-phenylalanine (fMLP), the calcium ionophore A23187, and phorbol myristate acetate (PMA) were investigated regarding their capacity to induce luminol-dependent chemiluminescence (LDCL) and superoxide production by human blood leukocytes. Although when tested individually, poly-L-arginine (PARG), phytohemagglutinin (PHA), concanavalin A (Con A), or fMLP induced only a low to moderate LDCL response, very intense synergistic CL reactions were obtained by mixtures of PARG + PHA, PARG + Con A, PARG + PHA + fMLP, Ca2 + ionophore + PARG + PHA + fMLP, and PARG + PMA. The sequence of addition of the various agents to WBC in the presence of luminol absolutely determined the intensity of the LDCL signals obtained, the highest reactions being achieved when the WBC were preincubated for 2-3 min with A23187 followed by the sequential addition of fMLP, PARG, and PHA. These "multiple hits" induced CL reactions which were many times higher than those obtained by each factor alone. On the other hand, neither poly-L-lysine, poly-L-ornithine, poly-L-histidine, nor poly-L-asparagine, when employed at equimolar concentrations, cooperated efficiently with PHA and fMLP to trigger synergistic LDCL responses in leukocytes. Concomitantly with the induction of LDCL, certain ligand mixtures also triggered the production of superoxide. The LDCL which was induced by the "cocktail" of agents was markedly inhibited by sodium azide (93% inhibition), but to a lesser extent by catalase (10% inhibition) or by superoxide dismutase (20%-60% inhibition). On the other hand, scavengers of singlet oxygen and OH (sodium benzoate, histidine) did not affect the synergistic LDCL responses induced by these multiple ligands. Cytochalasin B also markedly inhibited the LDCL responses induced either by soluble stimuli or by streptococci preopsonized either with histone or with polyanethole sulfonate. The LDCL responses which were induced by mixtures of PARG and concanavalin A were also strongly inhibited by mannose, alpha-methyl mannoside, and poly-L-glutamic acid. The data suggest that the LDCL responses induced by the soluble ligands involved a myeloperoxidase-catalyzed reaction. The possible employment of "cocktails" of ligands to enhance the bactericidal effects of PMNs, macrophages, and natural killer cells on microbial cells and mammalian targets is discussed.

Cationic polyelectrolytes, liquoid and leukocyte extract modulate the binding of IgG to group A streptococcal Fc-receptors

Various polyelectrolytes were investigated regarding their capacity to inhibit the binding of human IgG to Fc-receptors on group A streptococci, type M1. Of cationic substances, protamine and arginine-rich histone inhibited significantly, while lysine-rich histone, concanavalin A, lysozyme, polymyxin B, ribonuclease and tuftsin did not. Of anionic materials, liquoid was inhibitory, in contrast to chondroitin sulphate, dextran sulphate, DNA and heparin. Washing experiments showed that the inhibition was caused by binding of the polyelectrolytes to the streptococci. The finding that heated IgG inhibited the binding of histone to the streptococci also indicated a close relation between the binding sites for these compounds. Diffusion-in-gel experiments with alkaline extract of M1 demonstrated that the substances blocking the IgG Fc-receptor were bound to polyglycerophosphate, suggesting that the inhibition of the IgG uptake was due to interaction with lipoteichoic acid. Leukocyte and platelet extracts could modify the binding of IgG, probably by an enzymatic digestion of the receptors. The arginine-rich histone was also capable of inhibiting the binding of IgG to type M15 group A streptococci and to one group G strain. However, the polyelectrolytes had no effect on the binding of IgG to Staphylococcus aureus or of IgA to type 4 group A streptococci.

Phagocytic activity and hyperpolarizing responses in L-strain mouse fibroblasts

1. Fibroblastic L cells not only respond with a slow hyperpolarizing potential change to a mechanical or electrical stimulus but also show spontaneous, repetitive hyperpolarizations (i.e. membrane potential oscillation). 2. Almost all the cells can actively take up latex beads whose surfaces were treated by U.V. irradiation. 3. Non-phagocytic L cells hardly showed hyperpolarizing responses, while hyperpolarizing responses were obtained in all the phagocytic L cells. The exposure of the cell surface to beads, however, did not trigger the generation of hyperpolarizing responses. 4. Metabolic inhibitors, low temperature and cytochalasin B inhibited both the uptake of beads and the hyperpolarizing responses. 5. Increasing the external concentration of Ca2+ induced a remarkable stimulation of the phagocytosis of beads. Mg2+ and Ba2+, which inhibited hyperpolarizing responses due to competition for Ca2+ sites on the outer surface of the membrane, significantly suppressed the uptake of beads. 6. Verapamil, a Ca2+ channel blocker, inhibited not only hyperpolarizing membrane responses but also ingestion of beads. 7. It is concluded that the Ca2+ inflow on the hyperpolarizing membrane responses is closely associated with the phagocytic activity in L cells, probably through activation of the microfilament assembly.

Latex phagocytosis by polymorphonuclear leukocytes: role of sialic acid groups

Polystyrene latex particles are rapidly phagocytized by rabbit polymorphonuclear (PMN) leukocytes. The uptake is influenced by macromolecules which have the effect of altering the surface charge of the latex particle. The influence of polylysines of varying chain length on the surface charge of latex particles and of PMN cells was studied by micro-electrophoresis. Charge reversal at the latex surface was found to occur at concentrations considerably below that at which the surface charge of the PMN cells is reversed. Phagocytosis of latex by PMN cells is enhanced in the presence of low concentrations of long-chain polylysines. The enhancement of phagocytosis is strongly reduced if PMN cells are treated with neuraminidase. This suggests participation of sialic acid groups in a stage of particle-cell interaction which precedes engulfment.