High-affinity interaction between gram-negative flagellin and a cell surface polypeptide results in human monocyte...

Area of Science:

• Immunology
• Microbiology
• Molecular Biology

Background:

• Gram-negative bacterial flagella stimulate cytokine production in human monocytes.
• Flagellin is the primary structural protein of bacterial flagella.

Purpose of the Study:

• To identify the specific components of flagellin responsible for inducing TNF-alpha production.
• To elucidate the mechanism by which flagellin activates monocytes.

Main Methods:

• Purification of flagellin proteins from Salmonella and Pseudomonas aeruginosa.
• Treatment of THP-1 myelomonocytic cells with purified flagellins and mutants.
• Mutagenesis studies to analyze flagellin domains.
• Trypsin treatment of THP-1 cells to assess receptor involvement.

Main Results:

• Purified flagellin is a potent inducer of TNF-alpha production in human monocytes and THP-1 cells.
• The central hypervariable region of flagellin is essential for TNF-alpha induction.
• This region contains two active TNF-alpha-inducing domains.
• Conserved amino- and carboxy-terminal regions are inactive.
• Monocyte response to flagellin is mediated by high-affinity cell surface receptors.

Conclusions:

• Flagellin's cytokine-inducing activity is mediated by specific domains within its central hypervariable region.
• These domains interact with high-affinity polypeptide receptors on monocytes.
• This interaction triggers the production of TNF-alpha and potentially other cytokines.