Properdin and factor h: opposing players on the alternative complement pathway "see-saw"

Area of Science:

• Immunology
• Molecular Biology

Background:

• Properdin and factor H are key regulators of the alternative complement pathway.
• Properdin stabilizes the C3bBb complex, up-regulating the pathway.
• Factor H promotes C3b degradation, down-regulating the pathway.

Purpose of the Study:

• To discuss the significance of local synthesis of properdin and factor H.
• To highlight novel, non-complement roles of these proteins.

Main Methods:

• Literature review and synthesis of existing research on properdin and factor H synthesis and function.

Main Results:

• Factor H is primarily produced in the liver but also in numerous extrahepatic tissues.
• Properdin is mainly produced by neutrophils, but also by monocytes, T cells, and endothelial cells.
• Diverse extrahepatic synthesis sites suggest localized importance for both proteins.

Conclusions:

• Local synthesis of properdin and factor H is vital for their functions.
• Emerging evidence suggests roles beyond complement regulation, underscoring the importance of tissue-specific production.