Circulating Ficolin-2 and Ficolin-3 Form Heterocomplexes

Area of Science:

• Immunology
• Molecular Biology

Background:

• The complement system is crucial for innate immunity.
• Collectins and ficolins are pattern recognition molecules activating complement via the lectin pathway.
• Previous observations suggested potential interactions between ficolin-2 and ficolin-3.

Purpose of the Study:

• To investigate the hypothesis of stable ficolin-2/-3 heterocomplexes.
• To characterize the formation and presence of these complexes in human biological samples.
• To determine the relationship between heterocomplex concentration and individual ficolin levels.

Main Methods:

• ELISA assays using specific antibodies for ficolin-2 and ficolin-3.
• Coimmunoprecipitation and Western blot analysis for complex validation.
• Coexpression of recombinant ficolin-2 and ficolin-3 in CHO cells.
• Concentration measurements in 94 healthy individuals.

Main Results:

• Demonstrated the presence of ficolin-2/-3 heterocomplexes in human serum and plasma.
• Validated complex formation through coimmunoprecipitation and Western blot.
• Confirmed complex formation only upon coexpression, not simple mixing of recombinant proteins.
• Found significant correlations between heterocomplex concentration and ficolin-2 (ρ: 0.24) and ficolin-3 (ρ: 0.46) levels.

Conclusions:

• Described a novel protein complex formed by ficolin-2 and ficolin-3.
• This ficolin-2/-3 heterocomplex exists in human serum and plasma.
• The complex may possess distinct biological relevance beyond individual ficolin-2 and ficolin-3 molecules.