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Differential inside-out activation of β2 integrins by leukotriene B4 and fMLP in human neutrophils
Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology . Linköping University, Faculty of Health Sciences.
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2004 (English)In: Experimental Cell Research, ISSN 0014-4827, Vol. 300, no 2, 308-319 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated how LTB4, an endogenous chemoattractant encountered early in the inflammatory process, and fMLP, a bacteria-derived chemotactic peptide emanating from the site of infection, mediate inside-out regulation of the β2-integrin. The role of the two chemoattractants on β2-integrin avidity was investigated by measuring their effect on β2-integrin clustering and surface mobility, whereas their effect on β2-integrin affinity was measured by the expression of a high affinity epitope, a ligand-binding domain on β2-integrins, and by integrin binding to s-ICAM. We find that the two chemoattractants modulate the β2-integrin differently. LTB4 induces an increase in integrin clustering and surface mobility, but only a modest increase in integrin affinity. fMLP evokes a large increase in β2-integrin affinity as well as in clustering and mobility. Lipoxin, which acts as a stop signal for the functions mediated by pro-inflammatory agents, was used as a tool for further examining the inside-out mechanisms. While LTB4-induced integrin clustering and mobility were inhibited by lipoxin, only a minor inhibition of fMLP-induced β2-integrin avidity and no inhibition of integrin affinity were detected. The different modes of the inside-out regulation of β2-integrins suggest that distinct mechanisms are involved in the β2-integrin modulation induced by various chemoattractants.

Place, publisher, year, edition, pages
2004. Vol. 300, no 2, 308-319 p.
Keyword [en]
β2-Integrins, Cell adhesion, Chemotactic factors, Eicosanoids, Inflammation, Leukotriene B4, Lipoxins, Human Neutrophils, Signal transduction
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-14629DOI: 10.1016/j.yexcr.2004.07.015OAI: oai:DiVA.org:liu-14629DiVA: diva2:24060
Available from: 2007-09-13 Created: 2007-09-13 Last updated: 2009-12-14Bibliographically approved
In thesis
1. Pro- and anti-inflammatory regulation of β2 integrin signalling in human neutrophils
Open this publication in new window or tab >>Pro- and anti-inflammatory regulation of β2 integrin signalling in human neutrophils
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The body is under constant attack from pathogens trying to slip by our immune defence. If the barrier is breached, invading pathogens enter the tissues and cause inflammation. During this process neutrophils, constituting the first line of defence, leave the bloodstream and seek out and kill the invading pathogens. The mechanisms leading to activation of receptors on neutrophils must be closely orchestrated. Pro- and anti-inflammatory substances can influence the outcome of the inflammation process by affecting the involved players. If not well balanced, inflammatory diseases, such as atherosclerosis and rheumatoid arthritis, can be the outcome.

The aim of this thesis was to elucidate the effect of pro- (fMLP, Leukotriene B4, and Interleukin-8) and anti- (lipoxins, aspirin and statins) inflammatory substances on the β2 integrins, mediating adhesion of neutrophils both under “normal” conditions and during coronary artery disease. More specifically, the effect of these substances on the β2 integrins were studied in regard to: i) the activity (i.e. affinity and avidity) of β2 integrins, ii) the signalling capacity of β2 integrins (i.e. detected as release of arachidonic acid, and the production of reactive oxygen species, and iii) the signal transduction mediated by the β2 integrins (i.e. phosphorylation of Pyk2).

The pro-inflammatory substances belong to the family of chemoattractants that induces transmigration and chemotaxis. A hierarchy exists between the different family members; the end-target chemoattractants (e.g. fMLP) being more potent than intermediary chemoattractants (e.g. IL-8 and LTB4). It was found that intermediary chemoattractants regulate β2 integrins by mainly affecting the avidity of β2 integrins. End-target chemoattractants on the other hand, affected the β2 integrins by increasing the avidity and the affinity, as well as their signalling capacity.

The anti-inflammatory substances used in this study were the exogenous aspirin and statins, and the endogenous lipoxins. In the presence of aspirin, stable analogues of lipoxin (i.e. epi-lipoxins) are formed in a trans-cellular process. Lipoxin inhibited the signalling capacity of β2 integrins mediated by intermediary chemoattractants, as well as the signal transduction induced by end-target chemoattractants. Moreover, the signalling capacity of β2 integrins in neutrophils from patients suffering from coronary artery disease (CAD) was impaired. Arachidonic acid, the precursor for both pro- and anti-inflammatory eicosanoid, induced an increase in the β2 integrin activity (both affinity and avidity), but had no effect on the signal transduction.

In conclusion, different “roles” were observed for end-target and intermediary chemoattractants in the regulation of β2 integrins. The inhibitory effects of the anti-inflammatory lipoxins support earlier studies suggesting that these agents function as “stop signals” in inflammation. This is also confirmed by our findings in CAD patients, who have elevated levels of epi-lipoxins due to aspirin treatment. Moreover, Pyk2 was identified as a possible target for the inhibitory effect of anti-inflammatory drugs.

Place, publisher, year, edition, pages
Linköping: Institutionen för biomedicin och kirurgi, 2007. 75 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 996
Keyword
inflammation, neutrophils, signalling, integrins
National Category
Cell Biology
Identifiers
urn:nbn:se:liu:diva-9661 (URN)978-91-85715-22-0 (ISBN)
Public defence
2007-05-16, Berzeliussalen, Hälsouniversitetet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2007-09-13 Created: 2007-09-13 Last updated: 2010-01-14
2. Leukocyte responses to pathogens: integrins, membrane rafts and nitric oxide
Open this publication in new window or tab >>Leukocyte responses to pathogens: integrins, membrane rafts and nitric oxide
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During microbial invasion, leukocytes of the innate immunity are rapidly recruited to the site of infection where they internalize (phagocytose), kill and digest the invaders. To aid this process, leukocytes express surface receptors such as Toll-like receptors, β2-integrins and Fc-receptors. The β2-integrins are also used for attachment to the extracellular matrix and are important for migration. When pro- vs. anti-inflammatory regulation of β2-integrins was investigated, it was found that chemotactic factors modulate neutrophil adhesion through altered affinity and/or avidity of β2-integrins. A bacteria-derived chemoattractant evoked a large increase in affinity as well as in mobility and clustering, while an early, host-derived chemotactic factor induced increased clustering and surface mobility, but only a slight increase in affinity. Anti-inflammatory lipoxin affected β2-integrin avidity, but not affinity.

The leukocyte membrane is composed of lipids and proteins, which are inhomogeneously distributed. Specific domains in the membrane, membrane rafts, are enriched in signaling proteins and receptors. It was found that lipophosphoglycan (LPG) a virulence factor and membrane component of the parasite Leishmania donovani, accumulated in macrophage rafts during infection, inhibited PKCα translocation to the membrane and halted phagosomal maturation. Membrane rafts were instrumental for LPG to exert its effect. We further showed that nitric oxide (NO) rescued phagosomal maturation halted by Leishmania donovani parasites, possibly through effects on actin dynamics. NO did not affect parasite virulence per se. Moreover, lipoarabinomannan (LAM), a virulence factor on Mycobacterium tuberculosis (Mtb) bacteria, also inserted itself into macrophage membrane rafts. LAM from a less virulent strain (PILAM) was less efficiently inserted. Insertion could to some extent be inhibited by phosphatidylinositol mannoside (PIM), another structural molecule from Mtb. LAM did not activate the p38 MAPK signaling pathway nor did LAM interfere with TLR 2 or 4 signaling. In neutrophil leukocytes we observed a simultaneous, calciumdependent up-regulation of membrane rafts and secretion of azurophilic granules at the site of phagocytosis. Rafts were also found in the phagosome membrane. Wild type Streptococcus pyogenes bacteria, which can survive phagocytosis, modulated raft delivery.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2008. 63 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1058
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:liu:diva-43383 (URN)73683 (Local ID)978-91-7393-921-8 (ISBN)73683 (Archive number)73683 (OAI)
Public defence
2008-05-28, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2015-11-19Bibliographically approved

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Patcha Brodin, VeronikaWigren, JaneRasmusson, BirgittaSärndahl, Eva

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