Endotoxemia elicits increased circulating beta 2-IFN/IL-6 in man

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Interleukin-6 (IL-6), also known as beta 2-interferon or hepatocyte stimulating factor, is a cytokine with broad biological functions.
• IL-6 is produced by various cells, including monocytes, fibroblasts, and endothelial cells.
• Its known activities include stimulating acute-phase protein synthesis and immunomodulation.

Purpose of the Study:

• To investigate the circulating levels of IL-6 in humans following bacterial lipopolysaccharide (endotoxin) administration.
• To understand the temporal dynamics of IL-6 release and its bioactivity in response to endotoxin.
• To explore the relationship between IL-6 levels and acute-phase protein response.

Main Methods:

• Administration of a single intravenous bolus of endotoxin (20 U/kg) to human subjects.
• Measurement of circulating immunoreactive IL-6 and IL-6 bioactivity using specific assays.
• Assays included hepatocyte stimulation and B cell differentiation.
• Monitoring of circulating C-reactive protein levels over time.

Main Results:

• A single endotoxin dose induced a rapid, monophasic increase in both IL-6 levels and bioactivity.
• Peak IL-6 concentrations were observed 2 to 4 hours post-endotoxin challenge, ranging from 4.1 to 27.5 ng/ml.
• A subsequent rise in C-reactive protein was detected approximately 20 hours after endotoxin administration.

Conclusions:

• IL-6 is a significant endogenous mediator rapidly activated in humans by bacterial endotoxin.
• The surge in IL-6 likely plays a crucial role in the host's metabolic and immune responses to bacterial infection.
• IL-6 is implicated in the acute-phase response observed during infection.