CD24 and Siglec-10 Selectively Repress Tissue Damage-Induced Immune Responses
ABSTRACT Patten recognition receptors, which recognize pathogens or components of injured cells (danger), trigger activation of the
innate immune system. Whether and how the host distinguishes between danger- versus pathogen-associated molecular patterns
remains unresolved. We report that CD24-deficient mice exhibit increased susceptibility to danger- but not pathogen-associated
molecular patterns. CD24 associates with high mobility group box 1, heat shock protein 70, and heat shock protein 90; negatively
regulates their stimulatory activity; and inhibits nuclear factor κB (NF-κB) activation. This occurs at least in part through
CD24 association with Siglec-10 in humans or Siglec-G in mice. Our results reveal that the CD24–Siglec G pathway protects
the host against a lethal response to pathological cell death and discriminates danger- versus pathogen-associated molecular
Full-textDOI: · Available from: Pan Zheng, May 05, 2015
- SourceAvailable from: Sergio Iván Valdés-Ferrer
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- "Accordingly, here we reasoned that MD-2 may similarly discriminate different HMGB1 isoforms to facilitate TLR4-dependent signaling. of ischemia/reperfusion (I/R; Tsung et al., 2005) or chemical toxicity (Antoine et al., 2013). HMGB1 can signal through a family of receptors, including RAGE (Huttunen et al., 1999), TLR4 (Yang et al., 2010), and cluster of differentiation 24 (CD24)/Siglec-10 (Chen et al., 2009), thereby functioning as a DAMP that alerts, recruits, and activates innate immune cells to produce a wide range of cytokines and chemokines. Thus, seemingly unrelated conditions such as infection and sterile injury can converge on a common process: inflammation , which is orchestrated by HMGB1 actively secreted from innate immune cells or passively released from damaged tissues (Zhang et al., 2010; Andersson and Tracey, 2011). "
ABSTRACT: Innate immune receptors for pathogen- and damage-associated molecular patterns (PAMPs and DAMPs) orchestrate inflammatory responses to infection and injury. Secreted by activated immune cells or passively released by damaged cells, HMGB1 is subjected to redox modification that distinctly influences its extracellular functions. Previously, it was unknown how the TLR4 signalosome distinguished between HMGB1 isoforms. Here we demonstrate that the extracellular TLR4 adaptor, myeloid differentiation factor 2 (MD-2), binds specifically to the cytokine-inducing disulfide isoform of HMGB1, to the exclusion of other isoforms. Using MD-2-deficient mice, as well as MD-2 silencing in macrophages, we show a requirement for HMGB1-dependent TLR4 signaling. By screening HMGB1 peptide libraries, we identified a tetramer (FSSE, designated P5779) as a specific MD-2 antagonist preventing MD-2-HMGB1 interaction and TLR4 signaling. P5779 does not interfere with lipopolysaccharide-induced cytokine/chemokine production, thus preserving PAMP-mediated TLR4-MD-2 responses. Furthermore, P5779 can protect mice against hepatic ischemia/reperfusion injury, chemical toxicity, and sepsis. These findings reveal a novel mechanism by which innate systems selectively recognize specific HMGB1 isoforms. The results may direct toward strategies aimed at attenuating DAMP-mediated inflammation while preserving antimicrobial immune responsiveness. © 2015 Yang et al.Journal of Experimental Medicine 01/2015; 212(1):5-14. DOI:10.1084/jem.20141318 · 12.52 Impact Factor
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- "CD24 was then shown to be able to bind HMGB1 and to function as an inhibitor of NF-B activation . CD24 though, doesn't have signalling capacities and it has to interact with siglec-10 (siglec-G in mice) as a co-receptor (Chen et al., 2009). CD24 and siglec-10, in turn, seem to have a very specific role in dampening only damage associated inflammation. "
ABSTRACT: The ability of the immune system to give rise to an effective response against pathogens while maintaining tolerance towards self-tissues has always been an object of keen interest for immunologist. Over the years, different theories have been proposed to explain if and how the immune system is able to discriminate between self and non-self, including the Infectious Non-self theory from Charles Janeway and Polly Matzinger's Danger theory. Nowadays we know Janeway's theory is largely true, however the immune system does respond to injured, stressed and necrotic cells releasing danger signals (DAMPs) with a potent inflammatory response. To avoid unwanted prolonged autoimmune reactions, though, danger-induced inflammation should be tightly regulated. In the present review we discuss how prototypic DAMPs are able to induce inflammation and the peculiarity of danger-induced inflammation, as opposed to a complete immune response to fight pathogen invasions.Molecular Immunology 12/2014; 63(2). DOI:10.1016/j.molimm.2014.06.037 · 2.97 Impact Factor
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- "Platelet TLR cross-linking by ligands can promote an inflammatory response. Furthermore, Siglec(s) form a complex with CD24, a glycosyl-phosphatidyl-inositol–anchored molecule expressed by immature hematopoietic cells, that recognizes DAMPs and reduces immune system-mediated damage . The platelet expression of Siglec-7 may thus be part of a complex mechanism of auto-regulation of pro-inflammatory platelets. "
ABSTRACT: Background Platelets participate in tissue repair and innate immune responses. Sialic acid-binding immunoglobulin-like lectins (Siglecs) are well-characterized I-type lectins, which control apoptosis. Methodology/Principal Findings We characterized the expression of Siglec-7 in human platelets isolated from healthy volunteers using flow cytometry and confocal microscopy. Siglec-7 is primarily expressed on α granular membranes and colocalized with CD62P. Siglec-7 expression was increased upon platelet activation and correlated closely with CD62P expression. Cross-linking Siglec-7 with its ligand, ganglioside, resulted in platelet apoptosis without any significant effects on activation, aggregation, cell morphology by electron microscopy analysis or secretion. We show that ganglioside triggered four key pathways leading to apoptosis in human platelets: (i) mitochondrial inner transmembrane potential (ΔΨm) depolarization; (ii) elevated expression of pro-apoptotic Bax and Bak proteins with reduced expression of anti-apoptotic Bcl-2 protein; (iii) phosphatidylserine exposure and (iv), microparticle formation. Inhibition of NAPDH oxidase, PI3K, or PKC rescued platelets from apoptosis induced by Siglec-7 recruitment, suggesting that the platelet receptors P2Y1 and GPIIbIIIa are essential for ganglioside-induced platelet apoptosis. Conclusions/Significance The present work characterizes the role of Siglec-7 and platelet receptors in regulating apoptosis and death. Because some platelet pathology involves apoptosis (idiopathic thrombocytopenic purpura and possibly storage lesions), Siglec-7 might be a molecular target for therapeutic intervention/prevention.PLoS ONE 09/2014; 9(9):e106239. DOI:10.1371/journal.pone.0106239 · 3.23 Impact Factor