Human monocytes represent a competitive source of interferon-alpha in peripheral blood

Area of Science:

• Immunology
• Virology
• Cell Biology

Background:

• Interferon-alpha (IFN-alpha) is crucial for antiviral immunity.
• Plasmacytoid dendritic cells (pDCs) are known as the primary IFN-alpha producers following Toll-like receptor (TLR) 7 and 9 stimulation.
• The contribution of pDC-independent IFN-alpha sources in human peripheral blood remains under-investigated.

Purpose of the Study:

• To investigate pDC-independent sources of IFN-alpha production in human peripheral blood.
• To compare the efficacy of different pathogen-associated molecular patterns (PAMPs) in stimulating IFN-alpha production.
• To identify the specific cell types responsible for IFN-alpha generation.

Main Methods:

• Stimulation of peripheral blood mononuclear cells (PBMCs) with various PAMPs, including Poly(I:C)/Dotap, R848 (TLR7 agonist), and TLR9 agonists.
• Cell sorting to isolate specific immune cell populations.
• Enzyme-linked immunosorbent spot (ELISpot) assays to quantify IFN-alpha production at the cellular level.

Main Results:

• Poly(I:C)/Dotap was a potent stimulus for IFN-alpha production in PBMCs, second only to TLR9 stimulation.
• Dotap significantly enhanced Poly(I:C)-induced IFN-alpha production, highlighting its role in cellular uptake.
• Monocytes, rather than myeloid dendritic cells, were identified as the primary IFN-alpha producers following Poly(I:C)/Dotap stimulation.
• While pDCs produced higher IFN-alpha levels per cell, monocytes contributed significantly to overall IFN-alpha production due to their higher frequency.

Conclusions:

• Monocytes represent a significant, previously underappreciated source of IFN-alpha in human peripheral blood.
• The findings necessitate a re-evaluation of immune cell contributions to IFN-alpha-mediated antiviral responses.
• Targeting monocyte-derived IFN-alpha may offer new therapeutic strategies for viral infections.