Resolution and analysis of 'native' and 'activated' properdin.

Area of Science:

• Immunology
• Complement System Biology

Background:

• Properdin is a key component of the alternative complement activation pathway.
• Understanding properdin's functional states is crucial for dissecting complement-mediated immune responses.

Purpose of the Study:

• To develop a method for resolving native and activated properdin forms.
• To investigate the conditions leading to properdin activation.
• To analyze the functional heterogeneity of native properdin.

Main Methods:

• Gel filtration chromatography using Fractogel TSK HW-55(S).
• Analysis of properdin forms in serum and in vitro conditions.
• Electron microscopy to characterize properdin structures.

Main Results:

• A reproducible method successfully separated native and activated properdin.
• Only native properdin was found in serum, even after complement activation.
• In vitro activation was induced by freeze-thawing, not by C3 convertase binding.
• Native properdin exhibited cyclic structures, while activated properdin formed aggregates.

Conclusions:

• Properdin activation is an artifact of protein isolation, not a physiological event in serum.
• The developed fractionation method allows for detailed analysis of native properdin's functional heterogeneity.