Identification of haptoglobin as an alternative ligand for CD11b/CD18.
ABSTRACT 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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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.International journal of inflammation. 01/2013; 2013:980327.
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ABSTRACT: The present study was undertaken to investigate correlation between some hematological parameters, acute phase proteins and immunoglobulins in the experimentally infected goats with Besnoitia caprae from the time of infection till 360 days post infection (DPI). Six male goats, approximately 12–16 months old, were inoculated subcutaneously with approximately 1.3 × 108 bradyzoites of B. caprae and blood samples were collected at weekly intervals from the jugular vein of the goats. Total leukocyte count and differential leukocyte counts were determined. Acute phase proteins (APPs) including serum amyloid A (SAA), haptoglobin (Hp), fibrinogen and ceruloplasmin were undertaken at weekly intervals. We evaluated an enzyme-linked immunosorbent assay (ELISA) (using a somatic antigen of bradyzoite) to detect anti-B. caprae antibodies in caprine sera. Cysts were present in the skin biopsies of the distal parts of the leg of the infected goats from 28 DPI. From 30 to 360 DPI, results showed that the APPs concentrations including SAA, Hp, fibrinogen and ceruloplasmin were enhanced in the serum of infected goats. However, there were some variation in hematological parameters; the differences were not significant with those of the normal values. Some variations were seen in the levels of specific antibodies against this parasite and they had correlation with some hematological parameters and acute-phase proteins.Journal of parasitic diseases
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ABSTRACT: The onset of inflammatory response is associated with neutrophil recruitment into infected or injured tissues, whereas the resolution of inflammation, on the contrary, requires blockade of further recruitment and clearance of the recruited cells. Adhesion of circulating neutrophils to the endothelium represents a crucial step in their recruitment into the inflamed tissues. Previous studies have identified a number of proteins which can interfere with neutrophil-endothelial adhesive interactions and act as natural inhibitors of the leukocyte egress from the circulation. Essentially, these proteins are up-regulated in inflammation and, therefore, have potential pro-resolving activity. Knockout animals deficient in the anti-adhesive proteins demonstrated increased magnitude and duration of acute inflammation indicating that the proteins play a non-redundant role in dampening the inflammatory response. This paper is a review of the experimental data supporting the hypothesis that the up-regulation of the anti-adhesive proteins may represent an anti-inflammatory mechanism that contributes to the resolution of inflammation.Immunobiology 03/2013; · 2.81 Impact Factor