Pulmonary macrophages are attracted to inhaled particles through complement activation

Area of Science:

• Pulmonary immunology
• Inorganic particle toxicology
• Complement system biology

Background:

• Pulmonary macrophages are crucial for clearing inhaled particles from the lungs.
• Previous research demonstrated asbestos fibers activate complement, recruiting macrophages to deposition sites.

Purpose of the Study:

• To investigate complement activation by various inorganic particles in vitro.
• To correlate in vitro complement activation with in vivo macrophage accumulation.
• To determine if complement activation is a mechanism for macrophage detection of inhaled particles.

Main Methods:

• In vitro testing of inorganic particles (asbestos, fiberglass, iron, zymosan) for complement activation in rat serum and lavaged proteins.
• In vivo exposure of rats to particle aerosols.
• Assessment of macrophage accumulation at particle deposition sites (alveolar duct bifurcations) at 48 hours and over 8 days post-exposure.

Main Results:

• Chrysotile/crocidolite asbestos, iron-coated asbestos, fiberglass, wollastonite, carbonyl iron, and zymosan activated complement.
• Mt. St. Helens ash did not activate complement.
• All tested particles, except ash, induced significant macrophage accumulation at deposition sites within 48 hours.
• Carbonyl iron induced a rapid macrophage response, with clearance of particles and macrophages within 8 days.

Conclusions:

• Particles with diverse physical characteristics can activate complement and attract pulmonary macrophages.
• Complement activation is a likely mechanism for macrophages to detect inhaled particles on alveolar surfaces.
• This process facilitates the clearance of inhaled foreign materials from the lungs.