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Expression of functional receptors for interleukin-6 by human polymorphonuclear leukocytes. Downregulation by
R Henschler1, A Lindemann, M A Brach
1Department of Hematology and Oncology, University of Freiburg Medical Center, Germany.
Abstract:
Surface interleukin-6 receptors were identified on human polymorphonuclear leukocytes (PMNL) by monoclonal anti p80-chain antibody MT 18 Cytoplasmic RNA harvested from PMNL also contained IL-6-R transcripts. Binding of recombinant human (rh) interleukin-6 (IL-6) to IL-6-R bearing PMNL was identified by flow cytometry using phycoerythrin (PE)-conjugated ligand. Treatment of PMNL with rh granulocyte-macrophage colony-stimulating factor (GM-CSF) led to the inability of PMNL to bind MT 18 monoclonal antibody (moAb) and to display binding sites for PE-conjugated rh IL-6. Levels of IL-6-R transcripts in PMNL exposed to GM-CSF were about 5-fold below those of PMNL cultured in medium only. Though a definitive role for IL-6 to modulate the function of PMNL was not found, treatment of PMNL with rh IL-6 clearly resulted in an enhancement of transcript levels of the early response genes c-fos and c-jun in these cells, thus indicating that IL-6 binding is followed by signal transduction.
Insights
Human polymorphonuclear leukocytes (PMNL) express interleukin-6 receptors (IL-6-R). Granulocyte-macrophage colony-stimulating factor (GM-CSF) reduces IL-6-R expression on PMNL, but IL-6 binding still triggers early gene responses.
Area of Science:
- Immunology
- Molecular Biology
Background:
- Interleukin-6 (IL-6) is a key cytokine involved in immune responses.
- Polymorphonuclear leukocytes (PMNL) play critical roles in innate immunity.
- The presence and function of IL-6 receptors (IL-6-R) on PMNL are not fully understood.
Purpose of the Study:
- To investigate the expression and function of IL-6 receptors on human PMNL.
- To determine the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on IL-6-R expression in PMNL.
- To explore the signaling consequences of IL-6 binding to PMNL.
Main Methods:
- Identification of surface IL-6 receptors on human PMNL using monoclonal antibody MT 18.
- Detection of IL-6-R transcripts in PMNL via RNA analysis.
- Assessment of recombinant human IL-6 (rh IL-6) binding to PMNL using flow cytometry with PE-conjugated ligand.
- Evaluation of GM-CSF treatment on IL-6-R expression and IL-6 binding.
- Quantification of early response gene (c-fos, c-jun) transcript levels following rh IL-6 treatment.
Main Results:
- Surface IL-6 receptors and IL-6-R transcripts were identified on human PMNL.
- Treatment with rh GM-CSF significantly reduced MT 18 antibody binding and rh IL-6 binding to PMNL.
- GM-CSF exposure led to a 5-fold decrease in IL-6-R transcript levels in PMNL.
- rh IL-6 treatment enhanced the transcript levels of c-fos and c-jun in PMNL, indicating signal transduction.
Conclusions:
- Human PMNL express functional IL-6 receptors.
- GM-CSF downregulates IL-6 receptor expression and binding capacity on PMNL.
- IL-6 binding to PMNL initiates intracellular signaling pathways, evidenced by the induction of early response genes.