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- Leffler, Jonatan, et al.
(författare)
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Annexin-II, DNA and histones serve as Factor H ligands on the surface of apoptotic cells.
- 2010
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 285:6, s. 3766-3776
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Tidskriftsartikel (refereegranskat)abstract
- Apoptotic cells are opsonized by complement components such as C1q and C3b, which increases their susceptibility to phagocytosis. Soluble complement inhibitors such as factor H (fH)b also recognise apoptotic cells to minimize the pro-inflammatory effects of downstream complement activation. We used four radiolabelled protein constructs that span different regions of the 20 CCP modules that make up fH, and found that fragments comprising CCPs 6-8, CCPs 8-15 and CCPs 19-20 but not CCPs 1-4, bound to apoptotic Jurkat T-cells. There are four possible ligand types on apoptotic cells that could recruit fH: proteins, carbohydrates, lipids and DNA. We found that CCPs 6-8 of fH bind to annexin-II, a trypsin-insensitive protein that becomes exposed on surfaces of apoptotic cells. The second ligand of fH, which interacts with CCPs 6-8 and 19-20, is DNA. Confocal microscopy showed co-localisation of fH with antibodies specific for DNA. FH also binds to histones devoid of DNA and CCPs 1-4, 6-8 and 8-15 mediate this interaction. Treatment of apoptotic cells with neuraminidase, chondroitinase, heparitinase and heparinase did not change fH-binding. Treatment of apoptotic cells with phospholipase A2 dramatically increased both binding of fH and cell-surface DNA. We also excluded the possibility that fH interacts with lysophospholipids using surface plasmon resonance and flow cytometry with lipid-coated beads. Identification of annexin-II as one of the fH ligands on apoptotic cells together with the fact that autoantibodies against annexin-II are found in systemic lupus erythematosus provides further insight into understanding of the pathogenesis of this disease.
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