Article

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

Division of Clinical Immunology, Department of Medicine, University of Leuven, Belguim.
The Journal of Immunology (Impact Factor: 5.36). 05/1996; 156(7):2542-52.
Source: PubMed

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.

0 Followers
 · 
143 Views
  • [Show abstract] [Hide abstract]
    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 01/2013; DOI:10.1007/s12639-013-0304-7
  • [Show abstract] [Hide abstract]
    ABSTRACT: Haptoglobin (Hpt) is a plasma protein with hemoglobin-binding capacity. It is a well-known marker of hemolysis. Hpt is also an acute-phase protein that functions as a bacteriostatic agent, an inhibitor of prostaglandin synthesis and angiogenesis. However, the best-known biological function of Hpt is capture of hemoglobin (Hb).The identification of functional differences in haptoglobin molecules resulting from relatively common polymorphisms has further elucidated the importance of haptoglobin in iron homeostasis and in disease processes influenced by iron metabolism. In this review the effect of Hpt polymorphism on these different disease entities will be discussed.
    Clinica Chimica Acta 05/2004; DOI:10.1016/S0009-8981(04)00150-0 · 2.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The haptoglobin phenotypes of Sudanese patients with complicated and uncomplicated falciparum malaria, and those of uninfected randomly selected individuals, were determined by electrophoresis of sera on polyacrylamide gels followed by benzidine staining of the gels. Among 273 malaria patients, the proportions with haptoglobin phenotypes (1-1), (2-1) and (2-2) were 60·8%, 29·7% and 9·5%, respectively, and in 72 cerebral malaria patients the proportions were 63·9%, 29·2% and 6·9%. The distribution among 208 control individuals was 26·0%, 55·8% and 18·3%, respectively. The difference between patients and controls was highly significant (P < 0·001). The distribution of the different haptoglobin phenotypes among the randomly selected group of 208 Sudanese individuals was comparable to that in many other populations. The results suggest that the haptoglobin phenotype (1-1) is associated with susceptibility to falciparum malaria and the development of severe complications; alternatively, the other phenotypes may confer resistance.
    Transactions of the Royal Society of Tropical Medicine and Hygiene 05/1998; 92(3):309-311. DOI:10.1016/S0035-9203(98)91025-2 · 1.93 Impact Factor