Legionella pneumophila mediated activation of dendritic cells involves CD14 and TLR2

Area of Science:

• Immunology
• Microbiology

Background:

• Dendritic cells (DCs) are key immune cells that bridge innate and adaptive immunity.
• Activation of DCs by bacterial components is critical for initiating immune responses.
• The role of CD14 and Toll-like receptors (TLRs) in DC activation by Legionella pneumophila is not fully understood.

Purpose of the Study:

• To investigate the role of CD14 in the activation of bone-marrow derived dendritic cells (BMDCs) by Legionella pneumophila.
• To identify the specific Toll-like receptors (TLRs) involved in this activation process.

Main Methods:

• BMDCs from mice lacking the cd14 gene were stimulated with purified L. pneumophila lipopolysaccharide (LPS) and viable or formalin-killed L. pneumophila.
• BMDCs from mice lacking functional TLR2 and/or TLR4 molecules were used to assess receptor involvement.
• Flow cytometry and other immunological assays were employed to measure DC activation.

Main Results:

• Low concentrations of L. pneumophila LPS and bacteria required CD14 for BMDC activation.
• Higher LPS concentrations could activate BMDCs lacking CD14, suggesting alternative pathways.
• BMDCs from TLR4-deficient mice responded to L. pneumophila LPS and bacteria, but BMDCs from TLR2-knockout mice did not.
• Both purified L. pneumophila LPS and the bacteria itself activate BMDCs via TLR2, dependent on CD14.

Conclusions:

• CD14 is essential for optimal activation of BMDCs by L. pneumophila at infection-relevant doses.
• TLR2 is the primary receptor mediating BMDC activation by L. pneumophila components and the bacteria itself.
• These findings elucidate the intricate interplay between CD14 and TLR2 in sensing L. pneumophila and activating dendritic cells.