| 1. |
- Björstad, Åse, 1976, et al.
(författare)
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Antimicrobial host defence peptides of human neutrophils – roles in innate immunity
- 2008
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Ingår i: Anti-Infective Agents in Medicinal Chemistry. - : Bentham Science Publishers Ltd.. - 1871-5214. ; 7:3, s. 155-168
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Forskningsöversikt (refereegranskat)abstract
- The innate immune system is an old defence mechanism that in primitive organisms consists mainly of humoral components like antimicrobial peptides. Many of these peptides share features such as size, cationicity, amphipathicity and kill microbes primarily by lysing the cell membrane. In more evolved organisms, humoral factors are supplemented by cellular components such as professional phagocytes, but the antimicrobial peptides are still important for host defence. Neutrophils are professional phagocytes that in humans contain two different classes of classical antimicrobial peptides belonging to the cathelicidin family and the α-defensin family, respectively. In addition to these two main groups of poly-peptides, neutrophils are also rich in antimicrobial proteins. It is becoming increasingly clear that the antimicrobial peptides of neutrophils not only contribute to phagosomal killing, but also function as regulators of immunity; therefore the alternative name host defence peptides is more appropriate. The question whether antimicrobial host defence peptides are primarily immunomodulatory or antimicrobial in vivo has not been conclusively determined. At some locations in the body, e.g. in a phagosome, their effect is likely directly antimicrobial, whereas their immunomodulatory functions are probably more important at other sites. This review will provide a background to the field of antimicrobial peptides including their common features, mechanisms of killing and availability in nature. It will focus on the antimicrobial peptides present in human neutrophils and special emphasis will be given to the functional dualism displayed by many peptides giving them the ability to modulate the immune response in addition to being directly antimicrobial
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| 2. |
- Björstad, Åse, 1976
(författare)
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Functional dualism of antimicrobial host defence peptides
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Antimicrobial host defence peptides are central to innate immunity and many possess direct antimicrobial actions on bacteria as well as indirect immunomodulatory functions on human leukocytes. Different variants of the bifunctional Helicobacter pylori peptide, Hp(2-20), were synthesised and inhibition zone assays and chemiluminescence systems were employed for determination of direct antimicrobial action and superoxide release (immunomodulatory) from human neutrophils, respectively. α-helically stabilised peptides displayed increased antimicrobial action, while destabilised peptides were impaired. Only native Hp(2-20) had the capability to induce superoxide production from neutrophils, this representing a sequence-specific feature. The well known chemokine interleukin-8 (IL-8) contains a C-terminal part with many similarities to α-helical antimicrobial peptides. The C-terminal part of IL-8 was synthesised and displayed antibacterial activity but was incapable of inducing neutrophil superoxide production and chemotaxis, prominent activities of the native protein. IL-8 could thus be viewed as a bifunctional molecule with the two effects residing in different parts of the molecule. A prominent example of a human host defence peptide exhibiting functional dualism is LL-37 that permeabilises microbial membranes. LL-37 also selectively permeabilised apoptotic human leukocytes leaving viable leukocytes intact, as measured by flow cytometry. The activity was reminiscent of its antimicrobial activity; it was rapid, independent of known surface receptors and/or active cell signalling. Selectivity was probably related to changes in membrane composition of apoptotic cells. Permeabilisation of apoptotic leukocytes by LL-37 was accompanied by leakage of cytoplasmic and intragranular molecules that may shift the balance between pro- and anti-inflammatory signals and by this be of importance for the termination of acute inflammation. LL-37 also interacted with different receptors present on viable leukocytes. Neutrophil- and monocyte NADPH-oxidase activation by LL-37 was studied and shown to depend on the FPRL1 receptor. Also, the rise of intracellular Ca2+ triggered by LL-37 was FPRL1 dependent, but the peptide was a rather weak FPRL1 agonist. However, L-selectin shedding from neutrophils was independent of FPRL1, suggesting the presence of another receptor on neutrophils for LL-37. The dual action of host defence peptides makes them especially important for handling infections; fighting the pathogen directly as well as indirectly by alarming the immune system.
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| 3. |
- Björstad, Åse, 1976, et al.
(författare)
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Interleukin-8-derived peptide has antibacterial activity
- 2005
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Ingår i: Antimicrobial agents and chemotherapy. - 0066-4804. ; 49:9, s. 3889-95
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Tidskriftsartikel (refereegranskat)abstract
- Chemokines are inflammatory mediators with effects on diverse processes associated with the immune response. Some of the proteins belonging to the CXC chemokine subfamily, one of four groups in the family, possess inherent antibacterial activity against a wide range of bacteria. The CXC chemokine interleukin-8 (IL-8) has not been ascribed any direct antibacterial activity, but the fact that several of the amino acids in the carboxy-terminal part of the protein are identical or similar to those in a bactericidal cecropin-like peptide [Hp(2-20)] from Helicobacter pylori suggests that processing of the cytokine might generate peptide fragments with antibacterial properties. Synthetic peptides representing the carboxy-terminal part of IL-8 were investigated for antibacterial activities. These fragments possessed an antibacterial activity absent in the full-length IL-8. The antibacterial effects were reduced at increasing salt concentrations whereas the activity was increased when the pH was lowered. The IL-8-derived peptide shared structural similarity with and was also functionally additive to the Hp(2-20) peptide. The IL-8-derived peptide lacked the proinflammatory effects of the full-length protein. We also showed that acid hydrolysis of IL-8 generated a major peptide fragment corresponding to the antibacterial carboxyl terminus of the protein. The results presented are of special interest when put in the context of the suggested importance of antimicrobial peptides for microbial colonization of the gastric mucosa.
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| 4. |
- Björstad, Åse, 1976, et al.
(författare)
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The host defense peptide LL-37 selectively permeabilizes apoptotic leukocytes.
- 2009
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Ingår i: Antimicrobial agents and chemotherapy. - 1098-6596. ; 53:3, s. 1027-38
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Tidskriftsartikel (refereegranskat)abstract
- LL-37 is a cationic host defense peptide that is highly expressed during acute inflammation and that kills bacteria by poorly defined mechanisms, resulting in permeabilization of microbial membranes. High concentrations of LL-37 have also been reported to have cytotoxic effects against eukaryotic cells, but the peptide is clearly capable of differentiating between membranes with different compositions (eukaryotic versus bacterial membranes). Eukaryotic cells such as leukocytes change their membrane composition during apoptotic cell death, when they are turned into nonfunctional but structurally intact entities. We tested whether LL-37 exerted specific activity on apoptotic cells and found that the peptide selectively permeabilized the membranes of apoptotic human leukocytes, leaving viable cells unaffected. This activity was seemingly analogous to the direct microbicidal effect of LL-37, in that it was rapid, independent of known surface receptors and/or active cell signaling, and inhibitable by serum components such as high-density lipoprotein. A similar selective permeabilization of apoptotic cells was recorded for both NK cells and neutrophils. In the latter cell type, LL-37 permeabilized both the plasma and granule membranes, resulting in the release of both lactate dehydrogenase and myeloperoxidase. Apoptosis is a way for inflammatory cells to die silently and minimize collateral tissue damage by retaining tissue-damaging and proinflammatory substances within intact membranes. Permeabilization of apoptotic leukocytes by LL-37, accompanied by the leakage of cytoplasmic as well as intragranular molecules, may thus shift the balance between pro- and anti-inflammatory signals and in this way be of importance for the termination of acute inflammation.
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| 5. |
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| 6. |
- Forsman, Huamei, et al.
(författare)
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The beta-galactoside binding immunomodulatory lectin galectin-3 reverses the desensitized state induced in neutrophils by the chemotactic peptide f-Met-Leu-Phe: role of reactive oxygen species generated by the NADPH-oxidase and inactivation of the agonist
- 2008
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Ingår i: Glycobiology. - : Oxford University Press (OUP). - 1460-2423 .- 0959-6658. ; 18:11, s. 905-12
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Tidskriftsartikel (refereegranskat)abstract
- Neutrophils interacting with a chemoattractant gradually become nonresponsive to further stimulation by the same agonist, a process known as desensitization. Receptor desensitization is a highly regulated process that involves different mechanisms depending on which receptor-ligand pair that is studied. Galectin-3, a member of a large family of beta-galactoside-binding lectins, has been suggested to be a regulator of the inflammatory process, augmenting or directly triggering the neutrophil functional repertoire. We show here that the desensitized state of neutrophils interacting with the chemotactic peptide fMLF is broken by galectin-3 and that this is achieved through an oxygen radical-mediated inactivation of the chemoattractant. The effect was inhibited by the competitor lactose and required the affinity of galectin-3 for N-acetyllactosamine, a saccharide typically found on cell surface glycoproteins. The latter was shown using a galectin-3 mutant that lacked N-acetyllactosamine binding activity, and this protein was not active. The mechanism behind the inactivation of the chemoattractant was found to depend on the ability of galectin-3 to induce a neutrophil generation/secretion of reactive oxygen species which in combined action with myeloperoxidase inactivated the peptides.
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| 7. |
- Fu, Huamei, 1979, et al.
(författare)
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A bactericidal cecropin-A peptide with a stabilized alpha-helical structure possess an increased killing capacity but no proinflammatory activity
- 2004
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Ingår i: Inflammation. - : Springer Science and Business Media LLC. - 0360-3997 .- 1573-2576. ; 28:6, s. 337-43
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Tidskriftsartikel (refereegranskat)abstract
- Antibacterial peptides are part of the innate immune system in a variety of different species including humans. Some of these peptides have also been shown to have effects on immune competent cells such as professional phagocytes. We have recently shown that a cecropin-like peptide from Helicobacter pylori, Hp(2-20), in addition to being bactericidal possesses proinflammatory effects and can recruit and activate neutrophils as well as monocytes. It is well established that cecropins have the ability to adopt amphipathic alpha-helices, which is thought to be required for their bactericidal activity. In this study we show the same structural requirements for Hp(2-20). Breaking the helical structure of Hp(2-20) reduced the antibacterial effect and abolished its proinflammatory activity. A C-terminal truncated cecropin A peptide that highly resembles Hp(2-20) failed to activate neutrophils and computer-based structural simulations revealed a difference between the two peptides in the stability of their helical structures. A hybrid peptide with amino acid substitutions stabilizing the alpha-helical structure of the truncated cecropin A peptide did not introduce any proinflammatory activity; the bactericidal activity was, however, increased. We thus conclude that the proinflammatory effect of Hp(2-20) is a unique sequence-specific feature of the peptide and the ability to adopt a stable amphipathic helix is a necessary but not sufficient criterion for the functional dualism of the peptide.
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| 8. |
- Granfeldt, Daniel, 1974, et al.
(författare)
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Neutrophil Secretion Induced by an Intracellular Ca(2+) Rise and Followed by Whole-Cell Patch-Clamp Recordings Occurs Without any Selective Mobilization of Different Granule Populations
- 2006
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Ingår i: Journal of biomedicine & biotechnology. - 1110-7243. ; 2006:2, s. 97803-97803
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated calcium-induced secretion in human neutrophils, using a whole-cell patch-clamp technique. Mobilization of subcellular granules to the cell membrane was followed as the change in membrane capacitance ( big up tri, openC(m)). Both the magnitude and the kinetics of the response differed between low and high concentrations of Ca(2+). A sustained secretion following a short lag phase was induced by high concentrations of Ca(2+) (100muM and higher). A stable plateau was reached after 5-7 minutes at big up tri, openC(m) values corresponding to values expected after all specific as well as azurophil granules have been mobilized. Capacitance values of the same magnitude could be obtained also at lower Ca(2+) concentrations, but typically no stable plateau was reached within the measuring time. In contrast to previous studies, we were unable to detect any pattern of secretion corresponding to a distinct submaximal response or selective mobilization of granule subsets specified by their Ca(2+)-sensitivity.
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| 9. |
- Karlsson, Anna, 1967, et al.
(författare)
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Galectin-3 functions as an opsonin and enhances the macrophage clearance of apoptotic neutrophils.
- 2009
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Ingår i: Glycobiology. - : Oxford University Press (OUP). - 1460-2423 .- 0959-6658. ; 19:1, s. 16-20
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Tidskriftsartikel (refereegranskat)abstract
- Galectin-3, a beta-galactoside binding, endogenous lectin, takes part in various inflammatory events and is produced in substantial amounts at inflammatory foci. We investigated whether extracellular galectin-3 could participate in the phagocytic clearance of apoptotic neutrophils by macrophages, a process of crucial importance for termination of acute inflammation. Using human leukocytes, we show that exogenously added galectin-3 increased the uptake of apoptotic neutrophils by monocyte-derived macrophages (MDM). Both the proportion of MDM that engulfed apoptotic prey and the number of apoptotic neutrophils that each MDM engulfed were enhanced in the presence of galectin-3. The effect was lactose-inhibitable and required galectin-3 affinity for N-acetyllactosamine, a saccharide typically found on cell surface glycoproteins, since a mutant lacking this activity was without effect. The enhanced uptake relied on the presence of galectin-3 during the cellular interaction and was paralleled by lectin binding to apoptotic cells as well as MDM in a lactose-dependent manner. These findings suggest that galectin-3 functions as a bridging molecule between phagocyte and apoptotic prey, acting as an opsonin. The process of clearance, whereby apoptotic neutrophils are removed by macrophages, is crucial for the resolution of acute inflammation and our data imply that the increased levels of galectin-3 often found at inflammatory sites could potently affect this process.
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| 10. |
- Li, H. N., et al.
(författare)
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Secondary necrosis of apoptotic neutrophils induced by the human cathelicidin LL-37 is not proinflammatory to phagocytosing macrophages
- 2009
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Ingår i: J Leukoc Biol. - 1938-3673 .- 1938-3673. ; 86:4, s. 891-902
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Tidskriftsartikel (refereegranskat)abstract
- Cathelicidins are CHDP with essential roles in innate host defense but also more recently associated with the pathogenesis of certain chronic diseases. These peptides have microbicidal potential and the capacity to modulate innate immunity and inflammatory processes. PMN are key innate immune effector cells with pivotal roles in defense against infection. The appropriate regulation of PMN function, death, and clearance is critical to innate immunity, and dysregulation is implicated in disease pathogenesis. The efferocytosis of apoptotic PMN, in contrast to necrotic cells, is proposed to promote the resolution of inflammation. We demonstrate that the human cathelicidin LL-37 induced rapid secondary necrosis of apoptotic human PMN and identify an essential minimal region of LL-37 required for this activity. Using these LL-37-induced secondary necrotic PMN, we characterize the consequence for macrophage inflammatory responses. LL-37-induced secondary necrosis did not inhibit PMN ingestion by monocyte-derived macrophages and in contrast to expectation, was not proinflammatory. Furthermore, the anti-inflammatory effects of apoptotic PMN on activated macrophages were retained and even potentiated after LL-37-induced secondary necrosis. However, this process of secondary necrosis did induce the release of potentially harmful PMN granule contents. Thus, we suggest that LL-37 can be a potent inducer of PMN secondary necrosis during inflammation without promoting macrophage inflammation but may mediate host damage through PMN granule content release under chronic or dysregulated conditions.
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