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Human recombinant C5a enhances lipopolysaccharide-induced synthesis of interleukin-6 by human monocytes
Abstract:
The effect of human recombinant C5a (hrC5a) on the synthesis of interleukin-6 (IL-6) was studied in human monocytes. Monocytes incubated in the absence of hrC5a and of bacterial lipopolysaccharide (LPS) produced only low amounts (less than 100 U/2 x 10(6) cells/16 h) of IL-6 activity. LPS in concentrations from 10 pg ml-1 to 10 ng ml-1 greatly stimulated the synthesis of IL-6 to about 50.000 U/10(6) cells/16 h. When hrC5a was added to the monocyte media maximal IL-6 synthesis was reached at lower LPS concentrations, i.e. at 0.1 ng ml-1 LPS in the presence of 100 ng ml-1 hrC5a. Maximal IL-6 production was not significantly enhanced by hrC5a. Metabolic labelling with [35S]-methionine followed by immunoprecipitation of IL-6 showed that the increased IL-6 activity in the medium of hrC5a treated monocytes was due to a stimulation of the de novo synthesis of IL-6. Increased amounts of IL-6 mRNA were found in monocytes treated with LPS and hrC5a compared with monocytes stimulated only with LPS. HrC5a prolonged the elevation of IL-6 mRNA levels after stimulation of monocytes with LPS. HrC5a thus enhanced the LPS-induced synthesis of IL-6 by human monocytes.
Insights
Human recombinant C5a (hrC5a) enhances interleukin-6 (IL-6) synthesis in monocytes. This immune factor boosts IL-6 production, particularly when combined with bacterial lipopolysaccharide (LPS).
Area of Science:
- Immunology
- Cell Biology
Background:
- Interleukin-6 (IL-6) is a key cytokine in immune responses.
- Monocytes are crucial immune cells involved in inflammation.
- The role of complement component C5a in modulating monocyte cytokine production is of significant interest.
Purpose of the Study:
- To investigate the effect of human recombinant C5a (hrC5a) on interleukin-6 (IL-6) synthesis in human monocytes.
- To determine if hrC5a influences IL-6 production induced by bacterial lipopolysaccharide (LPS).
Main Methods:
- Human monocytes were cultured with varying concentrations of hrC5a and LPS.
- IL-6 activity in the cell culture supernatant was quantified.
- Metabolic labeling with [35S]-methionine and immunoprecipitation were used to assess de novo IL-6 synthesis.
- IL-6 mRNA levels were analyzed using quantitative methods.
Main Results:
- LPS significantly stimulated IL-6 synthesis in a dose-dependent manner.
- hrC5a enabled maximal IL-6 synthesis at lower LPS concentrations.
- hrC5a promoted de novo synthesis of IL-6 and increased IL-6 mRNA levels.
- hrC5a prolonged the elevation of IL-6 mRNA following LPS stimulation.
Conclusions:
- hrC5a enhances LPS-induced IL-6 synthesis in human monocytes.
- The mechanism involves stimulation of de novo IL-6 synthesis and prolonged IL-6 mRNA expression.
- C5a plays a role in modulating monocyte inflammatory responses through IL-6 production.