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PubMed1998

[Opsonin requirements for phagocytosis of Enterococcus spp. by human polymorphonuclear leukocytes].

BACKGROUND: Interaction of Enterococcus spp. and host defense mechanisms is not well known. Opsonic requirements of Enterococcus faecalis and Enterococcus faecium to be phagocyted by human polymorphonuclear leukocytes (PMN) were evaluated. METHODS: Twenty strains (10 E. faecalis and 10 E. faecium) were studied. Phagocytosis was determined by a radiometric assay. Bacterial cells were labelled with 3H-adenine and opsonized with: a) 10% of human pool sera (HPS); b) 10% of decomplemented HPS, and c) albumin and fibronectin. RESULTS: Phagocytosis of Enterococcus spp. by PMN in the presence of HPS was significantly higher than that in the absence of opsonins. The phagocytosis of E. faecium was higher than that of E. faecalis. A strain-dependent effect of complement in the phagocytosis of Enterococcus spp. was observed. Neither albumin nor fibronectin showed an opsonic activity on Enterococcus spp. CONCLUSIONS: A great heterogeneity in the opsonic requirements of Enterococcus spp. was observed. Serum opsonins show a critical role in the phagocytosis of E. faecalis and E. faecium by PMN, this effect being more relevant with E. faecium. A strain-dependent opsonic activity of complement was observed.

Adult↗
PubMed1999

Priming of blood neutrophils in children with cystic fibrosis: correlation between functional and phenotypic expression of opsonin receptors before and after platelet-activating factor priming.

Blood phagocyte opsonin receptor CR1 (CD35) and CR3 (CD11b) functions were examined in cystic fibrosis (CF) patients with endobronchial Staphylococcus aureus or Pseudomonas aeruginosa chronic infection, CF patients without infection, heterozygous, non-CF patients with chronic pulmonary infection, and healthy controls. Circulating and platelet-activating factor (PAF)-primed phagocyte luminol luminescence responses to complement-opsonized zymosan were increased in both groups of infected CF and non-CF children relative to uninfected CF children and healthy control children and adults. The ratio between circulating and PAF-primed phagocyte responses was significantly elevated in all children with CF, and in these, the ratio could serve as an indicator of response to antibiotic treatment. The ratios of circulating and PAF-primed phenotypic expression for CR1, CR3, and FcgammaRIII (CD16), but not FcgammaRII (CD32), correlated with the functional ratios. Phagocyte opsonin receptor response capacity might be used for evaluation of inflammation and infection in CF patients.

Adolescent↗
PubMedDate not supplied

Acute necrotizing pancreatitis reduces opsonin receptor expression on peritoneal exudative neutrophils in mice.

BACKGROUND/AIMS: Acute necrotizing pancreatitis is often complicated by pancreatic or peripancreatic infection. Since necrotizing pancreatitis may impair immune function, thereby increasing susceptibility to bacterial infection, we examined the expression of surface opsonin receptors (CD11b, complement receptor 3; CD32/CD16, immunoglobulin G Fc receptor) on local neutrophils in murine acute pancreatitis. METHODOLOGY: The necrotizing and edematous forms of acute pancreatitis were induced by seven subcutaneous injections of cerulein with and without intraperitoneal administration of lipopolysaccharide, respectively. Peritoneal exudative neutrophils were counted and assayed for receptor expression by flow cytometry, serially, from 1 to 24 hours after induction of pancreatitis. RESULTS: The peritoneal exudative neutrophil count was greater in edematous than in necrotizing pancreatitis. The number of CD11b-positive peritoneal exudative neutrophils was elevated in edematous pancreatitis, but the number was lower in necrotizing than in edematous pancreatitis at 6-24 hours. The mean fluorescence intensity of CD11b on neutrophils was comparable in both pancreatitis models. The cell count and mean fluorescence intensity indicated upregulated expression of CD32/CD16 on peritoneal exudative neutrophils in edematous pancreatitis, whereas the upregulation was attenuated in necrotizing pancreatitis. CONCLUSIONS: Opsonin receptor expression on local neutrophils was reduced in necrotizing pancreatitis, compared to edematous pancreatitis, and the difference may be responsible for the local septic complications in necrotizing pancreatitis.

Animals↗
PubMed1984

Opsonin-independent phagocytosis of surface-adherent bacteria by human alveolar macrophages.

Opsonin-independent mechanisms of phagocytosis may be important in host defense of certain body sites such as the lung. In this study, one such mechanism, "surface phagocytosis," was investigated by measuring the uptake of unopsonized [3H]-labeled Staphylococcus aureus and Pseudomonas aeruginosa adherent to a plastic surface by human alveolar macrophages (AM) and peripheral blood polymorphonuclear leukocytes (PMN). Efficient uptake of unopsonized bacteria by both cell types was observed. Electron microscopic studies suggested that the manner in which these cell types encounter adherent bacteria is different. While AM appear to gather in organisms at their periphery as they spread out upon the underlying substrate, PMN seem to sweep bacteria up as they move along the plastic surface. Bacterial killing determined by a fluorochrome microassay was decreased by AM compared to PMN. Although the precise mechanism whereby phagocytes recognize unopsonized bacteria adherent to a surface remains to be determined, this aspect of phagocytic cell function may prove to have clinical relevance.

Cell Membrane↗
PubMed1995

Recognition and clearance of liposomes containing phosphatidylserine are mediated by serum opsonin.

Liver uptake of liposomes containing phosphatidylserine was studied in a single pass liver perfusion system and found to be serum dependent. The effectiveness of serum in mediating liposome uptake by the liver depends on liposomes size. Large liposomes appeared to be opsonized more efficiently and, therefore, taken up more by the liver than the smaller ones. The effects of liposomes size on liver uptake did not occur in the absence of serum. Treatment of serum at 56 degrees C for 30 min abolished the serum activity, suggesting the involvement of complement components. Inhibition of the hemolytic activity of complement through the alternative pathway by PS-containing liposomes suggests that components in this pathway are responsible for liposome opsonization. Liposomes containing phosphatidic acid, phosphatidylglycerol, and dicetyl phosphate compete in different degrees for serum components which mediate the liver uptake of PS-containing liposomes. These results suggest that the opsonization of liposomes by serum opsonins are the determining factors for the recognition and clearance of liposomes by the RES. Complement components are most likely involved in this process. The results presented here are relevant to the use of liposomes as drug delivery vehicle in vivo and to the PS-mediated clearance of red blood cells from the blood circulation.

Animals↗
PubMed1992

Function of the lipopolysaccharide-binding protein of Periplaneta americana as an opsonin.

Previously, we reported the purification of an LPS-binding protein from the hemolymph of the American cockroach that was specific for E. coli LPS. In this study we found that this protein participated in the clearance of E. coli cells injected into the abdominal cavity of the cockroach, and that hemocytes ingested E. coli cells treated with this LPS-binding protein in vitro. These findings suggest that this LPS-binding protein acts as an opsonin.

Acute-Phase Proteins↗
PubMed1986

A colorimetric microassay for opsonins by reduction of NBT in phagocytosing bovine polymorphs.

The adaptation of the reduction of nitro blue tetrazolium (NBT) by phagocytes to the measurement of the opsonising capacity of serum or milk whey is described. A dose-response curve of the absorbance of solubilised reduced NBT to the concentration of opsonins, along with a close correlation (r = 0.94) between the colorimetric NBT assay and ingestion of group B streptococci (as measured by reduction of [3H]thymidine incorporation by extracellular bacteria), was established. This NBT reduction test, employing 96-well flat-bottom microtitre plates, is simple, semiautomated, requires a low number of PMN, and is applicable to a large number of samples, which renders it useful as a screening test for the opsonising capacity of sera or other biologic fluids.

Animals↗
PubMed1985

Chemiluminescence by peripheral blood phagocytes from channel catfish: function of opsonin and temperature.

The ability of the peripheral blood phagocytes from channel catfish, Ictalurus punctatus, to produce chemiluminescence (CL) following ingestion of the enteric pathogen Edwardsiella ictaluri was evaluated under a variety of opsonic and temperature conditions. The CL response was influenced by the concentration of immune serum used to opsonize the bacteria as well as the presence of nonspecific, heat labile opsonins. Peak light emissions were diminished and the time to peak response was increased with a reduction in temperature. Temperature-mediated changes in CL activity was accompanied by a corresponding change in intracellular killing. The addition of the metabolic inhibitors superoxide dismutase or sodium azide resulted in a reduction in CL and intracellular killing.

Animals↗
PubMed1988

The phagocytic activity of Lumbricus terrestris leukocytes is enhanced by the vertebrate opsonins: IgG and complement C3b fragment.

The effect of the vertebrates opsonins: IgG and complement C3 fragments on phagocytic activity of Lumbricus terrestris leukocytes towards sheep erythrocytes was studied. Sheep erythrocytes were previously sensitized with specific IgG or IgM and coated with one of the third component fragments (C3b, C3bi, C3d) of human complement. Our results show that leukocyte phagocytosis was enhanced by vertebrate IgG and C3b complement fragments but not by IgM and fragment C3d. Because opsonization in vertebrates is related to the presence of receptors on the surface of phagocyte membrane, our results suggest that similar receptors exist on earthworm leukocyte surfaces. These new data strengthen the arguments in favour of the presence of components in Lumbricus terrestris which partially share common structures and functions with components of vertebrate humoral immune reactions.

Animals↗
PubMed1989

Phagocytosis of yeast by Biomphalaria glabrata: carbohydrate specificity of hemocyte receptors and a plasma opsonin.

In vitro phagocytosis of yeast cells by hemocytes of the mollusc Biomphalaria glabrata can occur in the absence of plasma, but is enhanced by opsonization in plasma from certain snail strains. We have investigated the carbohydrate specificity of the hemocyte-bound receptor for phagocytosis and the free plasma opsonin using two dominant carbohydrate components of the yeast cell wall (laminarin and mannan). Phagocytic uptake in the absence of plasma of both untreated and opsonized yeast is strongly inhibited by laminarin, but is unaffected by mannan. In contrast, laminarin does not interfere with opsonization whereas mannan blocks the process, blocking the binding of a 57 kD plasma component as detected by Western immunoblot. These results suggest that the opsonic lectin in plasma is not simply a free form of the hemocyte-bound receptor for yeast phagocytosis.

Animals↗
PubMed1993

Antibody dependent haemolysin, complement and opsonin in sera of a major carp, Cirrhina mrigala and catfish, Clarias batrachus and Heteropneustes fossilis.

The present communication is a continuation of our earlier study on the natural serum haemagglutinin/lectins of Cirrhina mrigala, Clarias batrachus and Heteropneustes fossilis. Sera of Cirrhina mrigala, belonging to the major carp family, could not only agglutinate heterologous rabbit erythrocytes, but also lyse them spontaneously. This lysis of rabbit RBC by Cirrhina mrigala sera was calcium ion dependent and heat sensitive, indicating thereby that the haemolysis was mediated by the fish serum complement system via the classical pathway. Quantification of CH50 and APCH50 levels in the sera of Clarias batrachus and Heteropneustes fossilis as well as in the sera of amphibia, aves and mammals showed that lower vertebrates predominantly possessed an alternative pathway of the complement system, while on the other hand, in the higher vertebrates the major pathway of complement activation was classical. Furthermore sera of Clarias batrachus and Heteropneustes fossilis had opsonins, which could stimulate heterologous rat peritoneal macrophages to engulf Staphylococcus aureus with the production of superoxide anion. From this study we concluded that fishes have been armed with various powerful natural humoral defense systems for their protection against environmental pathogens.

Animals↗
PubMed2004

The opsonin MFG-E8 is a ligand for the alphavbeta5 integrin and triggers DOCK180-dependent Rac1 activation for the phagocytosis of apoptotic cells.

Opsonization of apoptotic cells facilitates recognition by phagocytes for the rapid clearance of potentially inflammatory cellular material. The secreted glycoprotein Milk Fat Globule Factor-E8 (MFG-E8) is a member of this family of bridging molecules and is believed to bind phosphatidylserine (PS) on the dying cell, linking it to integrin receptors on the phagocyte. Here we report the characterization of a functional signaling module involving MFG-E8, alphavbeta5 integrin, and DOCK180 for the activation of Rac1. We show that MFG-E8 and DOCK180 are both expressed in phagocytic-competent primary immature dendritic cells (DCs) and DC2.4 cells, and are potently down-regulated upon DC maturation, consistent with their role in phagocytosis and antigen capture. Coexpression of MFG-E8 with alphavbeta5 integrin potentiated integrin-mediated Rac1 activation, which was abrogated by mutagenesis in the RGD motif in MFG-E8. Moreover, expression of antisense DOCK180 abrogated MFG-E8-alphavbeta5-mediated Rac activation and impaired the phagocytosis of apoptotic cells. These data demonstrate a biochemical link between an opsonin of apoptotic cells, the alphavbeta5 integrin, and the Crk-DOCK180-Rac1 pathway, and importantly, show that MFG-E8 and DOCK180 are expressed according to the functional status of the phagocyte.

Amino Acid Motifs↗
PubMedDate not supplied

Activation and deposition of human breast-milk complement C3 opsonins on serum sensitive Escherichia coli 0111.

Little is known about the physiological roles and contribution of the human breast-milk complement system in the protection of both the maternal mammary gland and the nursing infant. The ability of a serum-sensitive Escherichia coli to activate the complement components of human breast-milk and colostrum was assessed in vitro. The consequent deposition of C3 fragments, C3b, iC3b and C3dg, on the bacteria was analysed, using a slight modification of a standard ELISA technique for the assessment of activated C3 fragments. The deposition C3 fragments from human milk were demonstrated on the killed bacteria, E. coli NCTC 8007, serotype 0111 K58(B4) H2, using buffers with and without detergent, supporting both the classical and alternative pathways of complement activation. The milk fat appears to competitively inhibit the deposition of these opsonins on the solid-phase bacteria. This study suggests that the complement system is able to contribute to the increased resistance of breast-fed infants against infections.

Breast↗
PubMed1986

Investigations on opsonin-independent antistaphylococcal activity of human neutrophilic granulocytes, monocytes and lymphocytes.

Using cells from 20 healthy human donors the opsonin-independent staphylococcal killing abilities of peripheral blood neutrophilic granulocytes, monocytes and lymphocytes were studied. S. aureus strains T 1 and T 14, S. sciuri strain S I, S. saprophyticus strain S III and S. simulans strain S V were selected for these experiments because of their differing cell wall composition, surface hydrophobicity, protein A content and extracellular enzyme activity spectrum. We could demonstrate a very individual activity range of these cells against staphylococci. On the other hand each staphylococcal strain examined behaved in a very typical way in its susceptibility against the killing by human phagocytes and lymphocytes. Repeated tests in monthly intervals showed that the staphylococcal killing activity range of phagocytes and lymphocytes of a certain healthy donor remains constant and stable.

Humans↗
PubMed1987

The role of plasmids in opsonin-independent Staphylococcus aureus-leukocyte interactions.

The opsonin-independent phagocytic and bactericidal activity of human polymorphonuclear leukocytes stimulated by two Staphylococcus aureus strains and their variants with differing plasmid patterns was investigated. Interactions between staphylococci and phagocytes were evaluated by chemiluminescence and intracellular killing tests. The results obtained indicate that the presence or absence of certain plasmids can modify staphylococcal phagocytosis and their susceptibility to intracellular killing. Pretreatment of the strains investigated with subinhibitory concentrations of mezlocillin and ofloxacin (10% MIC) influenced these parameters, too.

Humans↗
PubMed1988

Investigations on the opsonin-dependent interaction of Klebsiella bacteria and human polymorphonuclear leukocytes.

Encapsulated and nonencapsulated Klebsiella strains with different types of fimbriation were tested for their opsonin-dependent stimulation of human polymorphonuclear leukocytes (PMNs). Chemiluminescence (CL) of the PMNs was determined since CL-response can be used indirectly to quantitate phagocytosis. Apparently, the interaction between Klebsiella bacteria and human PMNs is dependent on the type of fimbration and on the presence of capsules. Evaluation of the bactericidal capacity of human PMNs against Klebsiella bacteria positively correlated with the chemiluminescence response demonstrating the importance of fimbriation and capsulation for this process, too.

Bacterial Adhesion↗
PubMed1999

Purification and characterization of a humoral opsonin, with specificity for D-galactose, in the colonial ascidian Botryllus schlosseri.

A humoral agglutinin from the hemolysate of the colonial ascidian Botryllus schlosseri was purified by affinity chromatography. This agglutinin does not require metal cations for its activity and is specific for derivatives of D-galactose. On SDS-PAGE analysis, it was resolved in two bands, of 17 and 19 kDa in reducing conditions and 15 and 16 kDa in non-reducing conditions. This behavior is due to the establishment of disulfide bridge between the thiols of cysteine, well represented in the molecule as revealed by amino acid analysis. The latter also indicated high percentages of hydrophilic residues, probably involved in sugar recognition. The lectin is an opsonin, as it increases both the phagocytic index and the number of phagocytized yeast cells. The hypothesis that this Botryllus agglutinin belongs to the galectin family of lectins is discussed.

Agglutinins↗
PubMed1998

Heparin binding protein (CAP37) is an opsonin for Staphylococcus aureus and increases phagocytosis in monocytes.

Heparin binding protein (HBP), also known as cationic antibiotic protein (CAP37) or azurocidin, is stored in azurophilic granules of neutrophils and is released to the extracellular space when granulocytes phagocytose Staphylococcus aureus. We investigated whether extracellular HBP also has the potential to increase phagocytosis of S. aureus by other phagocytes. We used flow cytometry to characterize the binding of HBP to S. aureus and to simultaneously measure phagocytosis and superoxide production of opsonized S. aureus in monocytes and granulocytes. Our results demonstrate that HBP is a strong opsonin for S. aureus, and that monocytes, but not granulocytes, increase phagocytosis of HBP-treated S. aureus. However, HBP-treated S. aureus increases the production of superoxide in both monocytes and granulocytes as compared with untreated S. aureus. These findings support the role of granulocytes in the afferent limb of inflammation and demonstrate that HBP, when released from activated granulocytes, potentiates bacterial uptake in monocytes and enhances the potential of microbial killing in monocytes and granulocytes.

Antimicrobial Cationic Peptides↗