Double-stranded RNA-mediated TLR3 activation is enhanced by CD14

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• CD14 is a key pattern-recognition receptor in the innate immune system.
• Toll-like receptor 3 (TLR3) recognizes double-stranded RNA (dsRNA), a viral component.
• The precise role of CD14 in TLR3-mediated immune responses remains to be fully elucidated.

Purpose of the Study:

• To investigate the role of CD14 in dsRNA-induced TLR3 activation.
• To determine if CD14 directly interacts with dsRNA and influences its cellular uptake.
• To elucidate the mechanism by which CD14 enhances TLR3 signaling.

Main Methods:

• Utilized CD14 knockout (CD14-/-) mice and bone marrow-derived macrophages (BMDMs).
• Stimulated cells and mice with polyinosine-polycytidylic acid (pIpC), a dsRNA analog.
• Employed radiolabeled pIpC fragments (pIpCsf) to track binding and uptake.
• Performed immunofluorescence microscopy to analyze the subcellular localization of CD14 and TLR3.

Main Results:

• CD14-/- BMDMs and mice showed impaired responses to pIpC, including reduced inflammatory cytokine production.
• CD14 directly bound to pIpC fragments and mediated their cellular uptake.
• TLR3 was found to be intracellular and co-localized with CD14 and internalized pIpC within lysosomes.
• Uptake of pIpC led to the lysosomal localization of both CD14 and TLR3.

Conclusions:

• CD14 plays a critical role in enhancing TLR3 activation by dsRNA.
• CD14 facilitates the uptake of dsRNA and its subsequent interaction with intracellular TLR3.
• These findings reveal a novel mechanism for CD14 in innate immune signaling against viral RNA.
• CD14 is essential for efficient TLR3-mediated immune responses to dsRNA, impacting cytokine production and innate immunity.