Bacterial lipopolysaccharide can enter monocytes via two CD14-dependent pathways

Area of Science:

• Immunology
• Cell Biology
• Microbiology

Background:

• Lipopolysaccharide (LPS) is a key Gram-negative bacterial molecule recognized by host cells.
• Glycosylphosphatidylinositol (GPI)-anchored CD14 is a primary receptor for LPS.
• Intracellular processing of LPS is crucial for host immune response.

Purpose of the Study:

• To investigate the initial cellular entry pathways of LPS mediated by CD14.
• To differentiate LPS internalization routes from those of other molecules like transferrin.
• To understand the role of CD14 anchoring in LPS uptake.

Main Methods:

• Utilized THP-1 cells and normal human monocytes expressing CD14.
• Employed hypertonic medium to inhibit clathrin-dependent endocytosis.
• Applied immunogold electron microscopy and confocal microscopy to track LPS and transferrin.
• Investigated LPS internalization in cells expressing a modified CD14 receptor.

Main Results:

• CD14-mediated LPS internalization occurred independently of clathrin-coated pits.
• LPS primarily entered cells via non-coated plasma membrane invaginations, forming distinct intracellular vesicles.
• Internalized LPS did not significantly colocalize with transferrin in early endosomes.
• LPS aggregation enhanced its uptake via the non-clathrin pathway.

Conclusions:

• CD14-dependent LPS internalization predominantly utilizes non-clathrin pathways.
• LPS is directed to intracellular compartments separate from the transferrin endocytic pathway.
• The GPI anchor of CD14 influences the internalization route of LPS.