Identification of haptoglobin as an alternative ligand for CD11b/CD18
| Autor: | S M, El Ghmati, E M, Van Hoeyveld, J G, Van Strijp, J L, Ceuppens, E A, Stevens |
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| Rok vydání: | 1996 |
| Předmět: |
Haptoglobins
Temperature Antibodies Monoclonal Fibrinogen Macrophage-1 Antigen In Vitro Techniques Ligands Monocytes Cell Line Adenosine Diphosphate Killer Cells Natural Kinetics T-Lymphocyte Subsets CD18 Antigens Humans Calcium Lymphocytes Fluorescein-5-isothiocyanate Fluorescent Dyes Granulocytes Protein Binding |
| Zdroj: | Journal of immunology (Baltimore, Md. : 1950). 156(7) |
| ISSN: | 0022-1767 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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