Identification of haptoglobin as an alternative ligand for CD11b/CD18. J Immunol

Division of Clinical Immunology, Department of Medicine, University of Leuven, Belguim.
The Journal of Immunology (Impact Factor: 4.92). 05/1996; 156(7):2542-52.
Source: PubMed


Haptoglobin is an acute phase protein with presumed anti-inflammatory activities. We report that purified fluorescein-labeled haptoglobin 1-1 binds to THP1 and U937 promonocytic cell lines, to monocytes, to granulocytes, and to a subset of CD8+ T cells and to NK cells. Studies with radioiodinated haptoglobin on THP1 cells were consistent with specific binding to one class of receptors with a density of 1.7 x 10(5) binding sites per cell and a low affinity of 6.5 x 10(-6) Kd. Binding was increased by Ca2+ and by Ca2+ and ADP. Binding to THP1 and U937 cells could be inhibited by preincubation with nonfluoresceinated haptoglobin and by fibrinogen, but not by albumin, transferrin, or alpha1-acid glycoprotein. Fibrinogen binds to the CD11b/CD18 integrin. We therefore examined whether haptoglobin has the same receptor. The anti-CD11b mAb44 indeed inhibited the binding of fluoresceinated haptoglobin to THP1 and U937 cell lines, and haptoglobin inhibited the binding of the anti-CD11b mAb anti-Leu15 and mAb44 to both cell lines. An anti-CD18 mAb partly inhibited the binding of fluoresceinated haptoglobin to THP1 and U937, indicating that the beta-chain of MAC-1 is also involved in haptoglobin binding. There was no interference between the binding of anti-CD4, anti-CD11a, or anti-CD11c mAb and haptoglobin binding to THP1 cells. Binding of haptoglobin to purified CD11b/CD18 indicates that it binds directly to the receptor. Haptoglobin is an alternative low affinity ligand for the CD11b/CD18 integrin, suggesting that this acute phase protein might regulate MAC-1-dependent cell function in vivo.

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    • "Alternative receptor mechanisms and endotoxin contamination were excluded as confounding sources of intracellular signals. Mac-1 was eliminated as a possible alternative candidate receptor for haptoglobin [30]. Endotoxin levels in all cell cultures were below 5 pg/mL and inhibition of IL-10 secretion by phagocytic inhibitors also ruled out endotoxin as a possible trigger. "
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    ABSTRACT: Intraplaque hemorrhage causes adaptive remodelling of macrophages towards a protective phenotype specialized towards handling iron and lipid overload, denoted Mhem. The Mhem phenotype expresses elevated levels of hemoglobin (Hb) scavenger receptor, CD163, capable of endocytosing pro-oxidant free Hb complexed to acute phase protein haptoglobin (Hp). It is notable that individuals homozygous for the Hp 2 allele (a poorer antioxidant) are at increased risk of cardiovascular disease compared to the Hp 1 allele. In this study, we examined whether scavenging of polymorphic Hp:Hb complexes differentially generated downstream anti-inflammatory signals in cultured human macrophages culminating in interleukin (IL)-10 secretion. We describe an anti-inflammatory signalling pathway involving phosphatidylinositol-3-kinase activation upstream of Akt phosphorylation (pSer473Akt) and IL-10 secretion. The pathway is mediated specifically through CD163 and is blocked by anti-CD163 antibody or phagocytosis inhibitor. However, levels of pSer473Akt and IL-10 were significantly diminished when scavenging polymorphic Hp2-2:Hb complexes compared to Hp1-1:Hb complexes ( P < 0.05 ) . Impaired anti-inflammatory macrophage signaling through a CD163/pAkt/IL-10 axis may thus represent a possible Hp2-2 disease mechanism in atherosclerosis.
    04/2013; 2013(24):980327. DOI:10.1155/2013/980327
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    • "Another down-regulated protein, haptoglobin (Hp), is a positive acute phase protein. It strongly binds hemoglobin and has anti-inflammatory activities and binds to CD11b/CD18 integrins representing major receptors on the cell membranes of leukocytes [19]. Haptoglobin also has a role in stimulating angiogenesis and has been identified as an angiogenic factor in sera from patients with systemic vasculitis [20]. "
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    ABSTRACT: Classical swine fever virus (CSFV) belongs to the genus Pestivirus within the family Flaviviridae. Virulent strains of classical swine fever virus (CSFV) cause severe disease in pigs characterized by immunosuppression, thrombocytopenia and disseminated intravascular coagulation, which causes significant economic losses to the pig industry worldwide. To reveal proteomic changes in swine serum during the acute stage of lethal CSFV infection, 5 of 10 pigs were inoculated with the virulent CSFV Shimen strain, the remainder serving as uninfected controls. A serum sample was taken at 3 days post-infection from each swine, at a stage when there were no clinical symptoms other than increased rectal temperatures (≥ 40 °C). The samples were treated to remove serum albumin and immunoglobulin (IgG), and then subjected to two-dimension differential gel electrophoresis. Quantitative intensity analysis revealed 17 protein spots showing at least 1.5-fold quantitative alteration in expression. Ten spots were successfully identified by MALDI-TOF MS or LTQ MS. Expression of 4 proteins was increased and 6 decreased in CSFV-infected pigs. Functions of these proteins included blood coagulation, anti-inflammatory activity and angiogenesis. These proteins with altered expression may have important implications in the pathogenesis of classical swine fever and provide a clue for identification of biomarkers for classical swine fever early diagnosis.
    Virology Journal 03/2011; 8(1):107. DOI:10.1186/1743-422X-8-107 · 2.18 Impact Factor
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    • "The exact mechanism underlying the beneficial role of Hp in ICH is not entirely clear. Even though neutralization of Hb appears to offer logical explanation for Hp benefit in ICH, Hp has also been proposed to act as extracellular chaperon (Yerbury et al., 2005), inhibitor of cathepsin B activity (Snellman and Sylven, 1967), or ligand for CD11b/CD18 and CD22 (El Ghmati et al., 1996; El-Ghmati et al., 2002). As such, it raises the possibility that Hb could protect cells by improving generalized resistance of neurons to Hb-mediated injury. "
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    ABSTRACT: After intracerebral hemorrhage (ICH), the brain parenchyma is exposed to blood containing red blood cells (RBCs) and consequently to its lysis products. Iron-rich hemoglobin (Hb) is the most abundant protein in RBCs. When released into the brain parenchyma during hemolysis, Hb becomes a central mediator of cytotoxicity. Our study indicates that haptoglobin (Hp), an acute-phase response protein primarily synthesized in the liver and known to bind and neutralize Hb in the bloodstream, is also expressed in brain in which it plays an important role in defending neurons from damage induced by hemolytic products after ICH. We demonstrate that the Hb-induced hypohaptoglobinemia aggravates ICH-induced brain damage while pharmacologic intervention with sulforaphane to induce brain Hp is linked to a reduction in brain damage. In agreement with these findings, Hp deficiency worsens whereas Hp overexpression alleviates ICH-mediated brain injury. We also identified that oligodendroglia are the primary source of brain-derived Hp among brain cells and that oligodendroglia-released Hp plays protective roles against Hb-mediated toxicity to neurons and oligodendrocytes. We conclude that Hp, particularly the brain-derived Hp, plays cytoprotective roles and represents a potential therapeutic target for ICH treatment.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 12/2009; 29(50):15819-27. DOI:10.1523/JNEUROSCI.3776-09.2009 · 6.34 Impact Factor
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