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Signal regulatory protein alpha is present in several neutrophil granule populations and is rapidly mobilized to the cell surface to negatively fine-tune neutrophil accumulation in inflammation
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Histology and Cell Biology.
Department of Rheumatology and Inflammation Research, Sahlgrenska Academy, University of Gothenburg, Gothenburg.
Department of Rheumatology and Inflammation Research, Sahlgrenska Academy, University of Gothenburg, Gothenburg.
Department of Rheumatology and Inflammation Research, Sahlgrenska Academy, University of Gothenburg, Gothenburg.
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2014 (English)In: Journal of Innate Immunity, ISSN 1662-811X, Vol. 6, no 4, 553-560 p.Article in journal (Refereed) Published
Abstract [en]

Signal regulatory protein alpha (SIRPα) is a cell surface glycoprotein with inhibitory functions, which may regulate neutrophil transmigration. SIRPα is mobilized to the neutrophil surface from specific granules, gelatinase granules, and secretory vesicles following inflammatory activation in vitro and in vivo. The lack of SIRPα signaling and the ability to upregulate SIRPα to the cell surface promote neutrophil accumulation during inflammation in vivo.

Place, publisher, year, edition, pages
2014. Vol. 6, no 4, 553-560 p.
Keyword [en]
Neutrophils, Inflammation, Signal regulatory protein alpha, Chemotactic factor, Skin window, Exudate
National Category
Other Basic Medicine
URN: urn:nbn:se:umu:diva-86668DOI: 10.1159/000357820ISI: 000337655900013PubMedID: 24516072OAI: diva2:700263
Available from: 2014-03-04 Created: 2014-03-04 Last updated: 2014-07-21Bibliographically approved
In thesis
1. Studies of SIRPα-mediated regulation of neutrophil functions
Open this publication in new window or tab >>Studies of SIRPα-mediated regulation of neutrophil functions
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Neutrophil granulocytes constitute the front line of defense in the innate immune response to invading microorganisms, but can also contribute to development of inflammatory disease and tissue destruction following e.g. myocardial infarction or stroke. During inflammatory activation, neutrophils leave the blood, interact with extracellular matrix proteins, and migrate into tissues in response to chemotactic factors to phagocytose and kill infectious agents by using toxic granule contents and reactive oxygen metabolites. The functional neutrophil response relies on exocytosis of cytoplasmic granules, each containing membrane proteins, which are thereby mobilized to the plasma membrane. Specific programmed cell death (apoptotic) pathways regulate neutrophil homeostasis, where an inflammatory milieu can prolong the life span of neutrophils to several days, whereas non-activated neutrophils are committed to constitutive/spontaneous apoptosis within hours.

Signal regulatory protein alpha (SIRPα) is a surface glycoprotein with two intracellular immunoreceptor-tyrosine-based inhibitory motifs (ITIMs), which is highly expressed in neutrophils and other myeloid cells. In other cell types, SIRPα has been shown to regulate cellular functions such as cell migration and phagocytosis. The aim of the present thesis was to investigate neutrophil SIRPα expression in response to inflammatory activation or apoptosis, and how this receptor can regulate neutrophil adhesion and cell migration.

Neutrophils contain several subcellular granule compartments, including primary (azurophilic), secondary (specific), tertiary (gelatinase) granules, and a fourth compartment called secretory vesicles. In resting neutrophils, SIRPα was found to be present in the plasma membrane and in all types of granules except for the azurophilic granules. Stimulation with the bacterial peptide fMLF in vitro, or inflammatory activation in vivo, was found to rapidly mobilize SIRPα to the neutrophil cell surface. In mice expressing a mutated form of SIRPα, where the cytoplasmic signaling domain was deleted, we found an enhanced accumulation of neutrophils in the peritoneal cavity in a peritonitis model. These findings therefore suggest that an increased amount of SIRPα on the surface of activated neutrophils could serve to negatively fine-tune neutrophil accumulation in inflammation.

Neutrophil priming means that the cell becomes partially activated, in a way that facilitates subsequent full activation. One part of the priming process is a moderate exocytosis of granules, mostly the secretory vesicles, which increases the density of certain receptors on the cell surface. It also involves the activation of adhesion receptors called integrins. We found that TNFα-induced priming involved an increased accumulation of SIRPα on the cell surface. When comparing wild-type and SIRPα-mutant neutrophils, we found a strongly reduced TNFα-stimulated and β2 integrin-dependent adhesion of mutant neutrophils to type I collagen or fibrinogen. This adhesion defect resulted in a reduced adhesion-dependent activation of the respiratory burst and an increased chemotactic response of SIRPα-mutant neutrophils in vitro.

During neutrophil apoptosis, several receptors are known to be shed from the cell surface (e.g. CD16 and CD43). We found that also SIRPα is shed from the surface during spontaneous as well as Fas-induced apoptosis. The shedding mechanism was found to involve matrix metalloproteinase (MMP) activity, mostly that of MMP-3 and MMP-8.

In conclusion, neutrophil cell surface SIRPα expression is regulated during neutrophil activation and seems to play an important role in stimulating β2-integrin-dependent adhesion. This way, SIRPα can negatively fine-tune neutrophil migration and accumulation in inflammation. During apoptosis, SIRPα is shed from the cell surface, which may be one mechanism contributing to the well-known down-regulation in the adhesiveness of apoptotic neutrophils.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2014. 55 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1630
neutrophils, SIRPα, inflammation, adhesion, chemotaxis, apoptosis
National Category
Immunology in the medical area
urn:nbn:se:umu:diva-86744 (URN)978-91-7459-808-7 (ISBN)
Public defence
2014-03-28, Biologihuset, BiA201, Umeå universitet, Umeå, 09:00 (Swedish)
Swedish Research Council, 2012-2702
Available from: 2014-03-07 Created: 2014-03-06 Last updated: 2014-03-07Bibliographically approved

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Stenberg, ÅsaVesterlund, LiselotteSehlin, JanoveOldenborg, Per-Arne
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