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Complement activation by tubular cells is mediated by properdin binding.

Hilde Gaarkeuken¹, Machiel A Siezenga, Kim Zuidwijk

¹Department of Nephrology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA, Leiden, The Netherlands.

American Journal of Physiology. Renal Physiology

|August 30, 2008

Summary

This summary is machine-generated.

Properdin initiates complement activation on kidney tubules, contributing to proteinuric kidney disease. Targeting properdin binding may offer a new treatment strategy for this condition.

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Area of Science:

Nephrology
Immunology
Complement System Biology

Background:

Proteinuria-induced tubulointerstitial injury involves complement activation on tubular epithelial cells.
The precise mechanism of complement activation within renal tubules remains incompletely understood.
Properdin is increasingly recognized for its role in initiating the alternative complement pathway.

Purpose of the Study:

To investigate the role of properdin in complement activation on proximal tubular epithelial cells (PTEC).
To determine if properdin acts as a focal point for complement activation in proteinuric kidney disease.

Main Methods:

Immunohistochemical staining for properdin in kidney biopsies from proteinuric patients.
In vitro experiments assessing properdin binding to PTEC and endothelial cells.
Complement activation assays using normal human serum, properdin-deficient serum, and properdin-depleted serum with PTEC.

Main Results:

Strong properdin staining was observed on the luminal surface of tubules in proteinuric kidney disease.
Properdin dose-dependently bound to PTEC but not to endothelial cells.
Complement activation (C3 deposition, C5b-9 generation) on PTEC was dependent on properdin, and could be restored by adding properdin to properdin-depleted serum.

Conclusions:

Properdin plays a crucial role in initiating alternative complement pathway activation on the surface of renal tubular cells.
Filtered properdin may bind to PTEC in proteinuric conditions, driving tubular complement activation and injury.
Interfering with properdin binding presents a potential therapeutic target for proteinuric renal diseases.