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Identification and characterization of a functional receptor for interferon-gamma on a megakaryocytic cell line
D Monté1, J Wietzerbin, V Pancré
1Centre d'Immunologie et de Biologie Parasitaire, Unité mixte INSERM 167-CNRS 624, Institut Pasteur de Lille, France.
Abstract:
We have previously shown that human interferon-gamma (Hu-IFN-gamma) induces platelets to become efficient effector cells, capable of killing young larvae of the parasite Schistosoma mansoni. Recently, binding sites for IFN-gamma on platelets have been characterized. We show here the presence of high-affinity receptors for IFN-gamma on the surface of the human megakaryocytic Dami cell line. Scatchard analysis indicated the presence of about 11,000 binding sites per cell, with a kd of 3 +/- 0.5 x 10(-10) mol/L; the apparent molecular weight of the receptor was 90 Kd. Receptor-bound 125I Hu-recombinant IFN-gamma was rapidly internalized and degraded when the temperature was increased from 4 degrees C to 37 degrees C. The half-life of this receptor was about 7 hours, and pretreatment of cells with IFN-gamma or phorbol myristate acetate had very little effect on the surface receptor number and no detectable effect on IFN-gamma receptor messenger RNA (mRNA) expression. The receptor was functional, because 24 hours of treatment with IFN-gamma led to the increase of HLA class I mRNA expression and to the initiation of HLA class II mRNA expression. These effects were selective because platelet glycoprotein Ib, IIb, or IIIa mRNA expression and cell proliferation were unaffected.
Insights
Human interferon-gamma (IFN-gamma) activates platelets to fight parasites. This study identifies high-affinity IFN-gamma receptors on megakaryocytic cells, demonstrating their role in immune response.
Area of Science:
- Immunology
- Cell Biology
- Parasitology
Background:
- Human interferon-gamma (Hu-IFN-gamma) previously shown to induce platelets as effector cells against Schistosoma mansoni.
- IFN-gamma binding sites on platelets have been recently characterized.
Purpose of the Study:
- To characterize high-affinity IFN-gamma receptors on the human megakaryocytic Dami cell line.
- To investigate the functional properties and regulation of these receptors.
Main Methods:
- Scatchard analysis to quantify IFN-gamma receptors.
- Radioligand binding assays using 125I Hu-recombinant IFN-gamma.
- Measurement of mRNA expression for HLA class I, HLA class II, and platelet glycoproteins.
- Assessment of cell proliferation.
Main Results:
- High-affinity IFN-gamma receptors (kd = 3 x 10(-10) mol/L, ~11,000 sites/cell, 90 Kd) were identified on Dami cells.
- Receptor-bound IFN-gamma was internalized and degraded at 37°C with a half-life of ~7 hours.
- IFN-gamma treatment increased HLA class I and initiated HLA class II mRNA expression, indicating receptor functionality.
- Receptor number and mRNA expression were largely unaffected by IFN-gamma or PMA pretreatment.
- Platelet glycoprotein mRNA expression and cell proliferation remained unaffected.
Conclusions:
- The Dami cell line expresses functional, high-affinity IFN-gamma receptors.
- These receptors mediate IFN-gamma-induced immune responses, specifically HLA class I and II expression.
- The findings provide insights into the mechanism of IFN-gamma-mediated platelet activation and immune modulation.