| 1. |
- Andréasson, Emil, et al.
(författare)
-
The Subcellular Localization of the Receptor for Platelet-Activating Factor in Neutrophils Affects Signaling and Activation Characteristics
- 2013
-
Ingår i: Clinical & Developmental Immunology. - : Hindawi Limited. - 1740-2522 .- 1740-2530.
-
Tidskriftsartikel (refereegranskat)abstract
- The localization in neutrophils, of the receptor for platelet-activating factor (PAFR), has been determined using subcellular fractionation and a receptor mobilization protocol. We show that the PAFR is expressed primarily in the plasma membrane. Although activation of neutrophils by PAF induces responses typical also of agonists that bind the formyl peptide receptors (FPR), known to be stored in mobilizable organelles, some quantitative as well as qualitative differences were observed when neutrophils were activated through these receptors. PAF is equipotent to fMLF (high affinity agonist for FPR1) to cleave off L-selectin and to induce granule/vesicle secretion but is more potent than fMLF to induce a rise in intracellular Ca2+. Similar to fMLF, PAF induced also a robust release of reactive oxygen species, but with higher EC50 value and was less sensitive to a PI3K inhibitor compared to the fMLF response. Despite the lack of a granule localized storage pool of receptors, the PAF-induced superoxide production could be primed; receptor mobilization was, thus, not required for priming of the PAF response. The desensitized PAFR could not be reactivated, suggesting that distinct signaling pathways are utilized for termination of the responses triggered through FPR1 and PAFR.
|
|
| 2. |
- Bergh Thorén, Fredrik, 1976, et al.
(författare)
-
The anionic amphiphile SDS is an antagonist for the human neutrophil formyl peptide receptor 1.
- 2010
-
Ingår i: Biochemical pharmacology. - : Elsevier BV. - 1873-2968 .- 0006-2952. ; 80:3, s. 389-95
-
Tidskriftsartikel (refereegranskat)abstract
- The anionic amphiphil sodium dodecyl sulfate (SDS) is commonly used to activate the superoxide-generating NADPH-oxidase complex in cell-free systems, but very little is known about the effects of SDS on intact cells. It was, however, recently shown that SDS causes a translocation and an activation of Rac (a small G-protein) in intact cells, but this signal is not in its own sufficient to activate the oxidase (Nigorikawa et al. (2004) [1]). We found that SDS acted as an antagonist for FPR1, one of the neutrophil members of the formyl peptide receptor family. Accordingly, SDS reduced superoxide anion production induced by the chemoattractant formylmethionyl-leucyl-phenylalanine (fMLF). The receptor specificity of SDS was fairly high, but the concentration range in which it worked was narrow. The length of the carbohydrate chain as well as the charge of the molecule was of importance for the antagonistic effects. Signaling through FPR2, a closely related receptor also expressed in neutrophils, was not inhibited by SDS. On the contrary, the response induced by the FPR2-specific agonist WKYMVM was primed by SDS. The precise mechanism behind the primed state is not known, but might be related to the effects earlier described for SDS on the small G-protein Rac, that is of importance for a proper transduction of the down-stream signals from the occupied receptor.
|
|
| 3. |
- Biswas, Amlan, et al.
(författare)
-
Negative regulation of Toll-like receptor signaling plays an essential role in homeostasis of the intestine.
- 2011
-
Ingår i: European journal of immunology. - : Wiley. - 1521-4141 .- 0014-2980. ; 41:1, s. 182-94
-
Tidskriftsartikel (refereegranskat)abstract
- A healthy intestinal tract is characterized by controlled homeostasis due to the balanced interaction between commensal bacteria and the host mucosal immune system. Human and animal model studies have supported the hypothesis that breakdown of this homeostasis may underlie the pathogenesis of inflammatory bowel diseases. However, it is not well understood how intestinal microflora stimulate the intestinal mucosal immune system and how such activation is regulated. Using a spontaneous, commensal bacteria-dependent colitis model in IL-10-deficient mice, we investigated the role of TLR and their negative regulation in intestinal homeostasis. In addition to IL-10(-/-) MyD88(-/-) mice, IL-10(-/-) TLR4(-/-) mice exhibited reduced colitis compared to IL-10(-/-) mice, indicating that TLR4 signaling plays an important role in inducing colitis. Interestingly, the expression of IRAK-M, a negative regulator of TLR signaling, is dependent on intestinal commensal flora, as IRAK-M expression was reduced in mice re-derived into a germ-free environment, and introduction of commensal bacteria into germ-free mice induced IRAK-M expression. IL-10(-/-) IRAK-M(-/-) mice exhibited exacerbated colitis with increased inflammatory cytokine gene expression. Therefore, this study indicates that intestinal microflora stimulate the colitogenic immune system through TLR and negative regulation of TLR signaling is essential in maintaining intestinal homeostasis.
|
|
| 4. |
|
|
| 5. |
- Björkman, Lena, 1965, et al.
(författare)
-
Data on the NADPH-oxidase activity induced by WKYMVm and galectin-3 in bone marrow derived and exudated neutrophils isolated from four different mouse strains.
- 2017
-
Ingår i: Data in brief. - : Elsevier BV. - 2352-3409. ; 10, s. 349-353
-
Tidskriftsartikel (refereegranskat)abstract
- Neutrophils are the key players in inflammatory reactions and the release of superoxide through the NADPH-oxidase upon neutrophil activation contributes to bacterial clearance and surrounding tissue damage. Here we describe data on the mouse neutrophil NADPH-oxidase activation induced by the mouse formyl peptide receptor (Fpr) agonist WKYMVm and galectin-3. Neutrophils isolated from bone marrow, peritoneal exudated, and in vitro TNFα primed bone marrow neutrophils from four different laboratory strains (C57BL/6, DBA/1, BALB/c and NMRI) were used. Both Fpr agonist and galectin-3 activated neutrophils to release superoxide. No differences were observed in the amounts of superoxide released from neutrophils derived from four different strains.
|
|
| 6. |
- Björkman, Lena, 1965, et al.
(författare)
-
Larixol is not an inhibitor of Gαi containing G proteins and lacks effect on signaling mediated by human neutrophil expressed formyl peptide receptors
- 2024
-
Ingår i: Biochemical Pharmacology. - 0006-2952 .- 1873-2968. ; 220
-
Tidskriftsartikel (refereegranskat)abstract
- Neutrophils express several G protein-coupled receptors (GPCRs) connected to intracellular Gαi or Gαq containing G proteins for down-stream signaling. To dampen GPCR mediated inflammatory processes, several inhibitors targeting the receptors and/or their down-stream signals, have been developed. Potent and selective inhibitors for Gαq containing G proteins are available, but potent and specific inhibitors of Gαi containing G proteins are lacking. Recently, Larixol, a compound extracted from the root of Euphorbia formosana, was shown to abolish human neutrophil functions induced by N-formyl-methionyl-leucyl-phenylalanine (fMLF), an agonist recognized by formyl peptide receptor 1 (FPR1) which couple to Gαi containing G proteins. The inhibitory effect was suggested to be due to interference with/inhibition of signals transmitted by βγ complexes of the Gαi containing G proteins coupled to FPR1. In this study, we applied Larixol, obtained from two different commercial sources, to determine the receptor- and G protein- selectivity of this compound in human neutrophils. However, our data show that Larixol not only lacks inhibitory effect on neutrophil responses mediated through FPR1, but also on responses mediated through FPR2, a Gαi coupled GPCR closely related to FPR1. Furthermore, Larixol did not display any features as a selective inhibitor of neutrophil responses mediated through the Gαq coupled GPCRs for platelet activating factor and ATP. Hence, our results imply that the inhibitory effects described for the root extract of Euphorbia formosana are not mediated by Larixol and that the search for a selective inhibitor of G protein dependent signals generated by Gαi coupled neutrophil GPCRs must continue.
|
|
| 7. |
- Björkman, Lena, 1965, et al.
(författare)
-
Neutrophil recruitment to inflamed joints can occur without cellular priming.
- 2019
-
Ingår i: Journal of leukocyte biology. - 1938-3673. ; 105:6, s. 1123-1130
-
Tidskriftsartikel (refereegranskat)abstract
- Recruitment of neutrophils from blood to tissues is a cardinal event in inflammation during which neutrophils switch from a resting, naive state to a preactivated, primed phenotype; the priming process is characterized by alterations in the composition of cell surface adhesins, for example, shedding of l-selectin and mobilization of granule-stored integrins to the cell surface. Ligation of chemotactic receptors and interactions with the endothelial lining are established triggers of neutrophil priming and in line with this, in vivo transmigrated neutrophils obtained from tissues are typically highly primed. We here characterize the priming of neutrophils brought about by in vivo recruitment from blood to inflamed joints by the analyses of synovial fluid and blood from patients with inflammatory arthritis. For comparisons, we used controlled in vivo models of neutrophil transmigration to skin of healthy subjects. In contrast to the residing view and in vivo transmigrated neutrophils from skin models, neutrophils from synovial fluid were often surprisingly resting and phenotypically very similar to naive cells isolated from peripheral blood; synovial fluid cells often retained l-selectin and had undergone minimal up-regulation of integrin receptors. In complete agreement with our in vivo findings, cell-free synovial fluid was potently chemotactic without triggering alteration of surface receptors also in vitro. We conclude that tissue recruitment of neutrophils does not by default trigger l-selectin shedding and granule mobilization, and the chemoattractant(s) guiding neutrophils to synovial fluid apparently operate without inducing cellular priming.
|
|
| 8. |
- Björkman, Lena, 1965, et al.
(författare)
-
The Neutrophil Response Induced by an Agonist for Free Fatty Acid Receptor 2 (GPR43) Is Primed by Tumor Necrosis Factor Alpha and by Receptor Uncoupling from the Cytoskeleton but Attenuated by Tissue Recruitment
- 2016
-
Ingår i: Molecular and Cellular Biology. - : Informa UK Limited. - 0270-7306 .- 1098-5549. ; 36:20, s. 2583-2595
-
Tidskriftsartikel (refereegranskat)abstract
- Ligands with improved potency and selectivity for free fatty acid receptor 2 (FFA2R) have become available, and we here characterize the neutrophil responses induced by one such agonist (Cmp1) and one antagonist (CATPB). Cmp1 triggered an increase in the cytosolic concentration of Ca2+, and the neutrophils were then desensitized to Cmp1 and to acetate, a naturally occurring FFA2R agonist. The antagonist CATPB selectively inhibited responses induced by Cmp1 or acetate. The activated FFA2R induced superoxide anion secretion at a low level in naive blood neutrophils. This response was largely increased by tumor necrosis factor alpha (TNF-alpha) in a process associated with a recruitment of easily mobilizable granules, but neutrophils recruited to an aseptic inflammation in vivo were nonresponding. Superoxide production induced by Cmp1 was increased in latrunculin A-treated neutrophils, but no reactivation of desensitized FFA2R was induced by this drug, suggesting that the cytoskeleton is not directly involved in terminating the response. The functional and regulatory differences between the receptors that recognize short-chain fatty acids and formylated peptides, respectively, imply different roles of these receptors in the orchestration of inflammation and confirm the usefulness of a selective FFA2R agonist and antagonist as tools for the exploration of the precise role of the FFA2R.
|
|
| 9. |
- Björnsdottir, Halla, et al.
(författare)
-
Phenol-soluble Modulin α Peptide Toxins from aggressive Staphylococcus aureus induce rapid Formation of neutrophil extracellular Traps through a reactive Oxygen species-independent Pathway
- 2017
-
Ingår i: Frontiers in Immunology. - : Frontiers Media SA. - 1664-3224. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Neutrophils have the ability to capture and kill microbes extracellularly through the formation of neutrophil extracellular traps (NETs). These are DNA and protein structures that neutrophils release extracellularly and are believed to function as a defense mechanism against microbes. The classic NET formation process, triggered by, e.g., bacteria, fungi, or by direct stimulation of protein kinase C through phorbol myristate acetate, is an active process that takes several hours and relies on the production of reactive oxygen species (ROS) that are further modified by myeloperoxidase (MPO). We show here that NET-like structures can also be formed by neutrophils after interaction with phenol-soluble modulin alpha (PSM alpha) that are cytotoxic membrane-disturbing peptides, secreted from community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). The PSMa-induced NETs contained the typical protein markers and were able to capture microbes. The PSMa-induced NET structures were disintegrated upon prolonged exposure to DNase-positive S. aureus but not on exposure to DNase-negative Candida albicans. Opposed to classic NETosis, PSMa-triggered NET formation occurred very rapidly, independently of ROS or MPO, and was also manifest at 4 degrees C. These data indicate that rapid NETs release may result from cytotoxic membrane disturbance by PSMa peptides, a process that may be of importance for CA-MRSA virulence.
|
|
| 10. |
- Björstad, Åse, 1976, et al.
(författare)
-
The host defense peptide LL-37 selectively permeabilizes apoptotic leukocytes.
- 2009
-
Ingår i: Antimicrobial agents and chemotherapy. - 1098-6596. ; 53:3, s. 1027-38
-
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.
|
|
