Membrane-anchored forms of lipopolysaccharide (LPS)-binding protein do not mediate cellular responses to LPS...

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Inflammatory responses to lipopolysaccharide (LPS) in myeloid cells are mediated by CD14, a receptor that binds LPS.
• The exact function of CD14 in LPS-induced cellular activation is unclear, as it does not traverse the plasma membrane and alternative anchoring forms still permit activation.

Purpose of the Study:

• To elucidate the specific role of CD14 in mediating cellular responses to LPS.
• To investigate whether LPS-binding protein (LBP), when membrane-anchored, can mediate LPS-induced activation independently of CD14.

Main Methods:

• Created Chinese hamster ovary (CHO) and U373 astrocytoma cell lines expressing either membrane-anchored LBP (mLBP) or membrane CD14 (mCD14).
• Assessed cellular responses, including NF-kappaB activation, ICAM, and IL-6 production, under serum-free conditions with varying LPS concentrations.
• Evaluated cell line responses in the presence of soluble CD14 to confirm LPS-induced activation capability.

Main Results:

• CHO and U373 cells expressing mCD14 responded to low concentrations of LPS (0.1 ng/ml) under serum-free conditions.
• mLBP-expressing cell lines and vector controls did not respond to LPS (even at >100 ng/ml) without soluble CD14.
• All cell lines responded to LPS in the presence of soluble CD14, confirming their capacity for LPS-induced activation.

Conclusions:

• Membrane-anchored LPS-binding protein (mLBP) does not mediate cellular responses to LPS independently of CD14.
• These findings indicate that CD14 plays a more specific role in LPS response mediation than simply facilitating LPS cell surface presentation.
• CD14 is essential for initiating cellular signaling pathways triggered by LPS.