Complement levels and activity in the normal and LPS-injured lung

Area of Science:

• Immunology and Molecular Biology
• Respiratory Medicine

Background:

• The complement system is crucial for host defense, with known activity in serum and the lung.
• Understanding lung complement regulation is vital for addressing respiratory infections and inflammation.

Purpose of the Study:

• To characterize complement system components and function in normal and inflamed lungs.
• To investigate the impact of lipopolysaccharide (LPS) exposure on lung complement activity.

Main Methods:

• Western blot analysis of bronchoalveolar lavage (BAL) fluid.
• Reverse transcription polymerase chain reaction (RT-PCR) for gene expression in lung tissue.
• Functional assays measuring C3b deposition on bacteria.

Main Results:

• Specific complement proteins (C5, C6, factor I, C2) were detected in BAL fluid at varying levels compared to serum.
• LPS exposure significantly altered complement protein levels in human and animal BAL fluid and gene expression in lung tissue.
• LPS-exposed rat BAL demonstrated enhanced bacterial C3b deposition, indicating increased complement-mediated opsonization.

Conclusions:

• Complement levels, gene expression, and function are dynamically altered in the lung during acute inflammation.
• Lung complement appears regulated to enhance pathogen opsonization while potentially limiting excessive inflammation.