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Lymphokines inhibit macrophage RNA synthesis
Abstract:
The effects of lymphokine (LK) preparations on the incorporation of [3H]uridine into macrophage RNA were investigated. Supernatants from murine spleen cells activated in vitro by alloantigens or Con A, and shown to contain macrophage-activating factor (MAF), were used as the source of LK. It was observed that such LK preparations contain factor(s) causing a profound inhibition of [3H]uridine incorporation into the RNA of proteose-peptone-elicited peritoneal macrophages. Such RNA-labeling inhibitory factor (RIF) was absent in control supernatants from nonstimulated cultures, and showed activation curves similar to that of MAF. RIF activity was not due to altered permeability of macrophages to [3H]uridine nor to the changes in the specific activity of the pool of RNA precursors, but rather reflected an altered metabolism of RNA. The inhibition of RNA synthesis was dependent upon the presence of nanogram amounts of LPS as a costimulator. Moreover, the response to RIF appeared to be genetically controlled since macrophages from C3H/HeJ mice were not affected by RIF, while C3H/HeN mice were fully responsive. In parallel cultures of macrophages, LK were also tested for their MAF activity, and a strong similarity between the biological conditions in which MAF and RIF activities were expressed could be demonstrated. The assay for RIF provides a new and convenient parameter for measuring macrophage-sensitive LK activity that might be very useful for monitoring purification or for screening of T-cell hybridoma supernatants.
Insights
Lymphokine preparations contain a novel RNA-labeling inhibitory factor (RIF) that suppresses macrophage RNA synthesis. This factor
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Lymphokines (LK) are crucial signaling molecules in immune responses.
- Macrophage-activating factor (MAF) is a key lymphokine involved in macrophage activation.
- The precise mechanisms by which LKs influence macrophage metabolism are not fully understood.
Purpose of the Study:
- To investigate the effects of LK preparations on macrophage RNA synthesis.
- To identify and characterize a novel factor within LK preparations that inhibits RNA labeling.
- To explore the potential of this inhibitory factor as a tool for studying LK activity.
Main Methods:
- Investigated [3H]uridine incorporation into macrophage RNA using LK preparations from activated murine spleen cells.
- Assessed RNA-labeling inhibitory factor (RIF) activity in relation to macrophage-activating factor (MAF) activity.
- Evaluated the role of lipopolysaccharide (LPS) as a costimulator and genetic control of the response.
Main Results:
- LK preparations contained a potent RNA-labeling inhibitory factor (RIF) that significantly reduced [3H]uridine incorporation in macrophages.
- RIF activity was distinct from altered cell permeability or precursor pool specific activity, indicating direct RNA metabolism interference.
- RIF activity required LPS costimulation and showed genetic control, with C3H/HeJ macrophages being unresponsive.
- RIF expression correlated strongly with MAF activity, suggesting a shared biological pathway.
Conclusions:
- A novel RIF present in LK preparations inhibits macrophage RNA synthesis.
- RIF activity is dependent on LPS and genetic factors, offering insights into macrophage activation pathways.
- The RIF assay provides a valuable new method for quantifying macrophage-sensitive LK activity and aids in purification and screening.