Monomeric C-reactive protein inhibits renal cell-directed complement activation mediated by properdin

Area of Science:

• Immunology
• Nephrology
• Cell Biology

Background:

• Complement activation on renal tubular cells contributes to interstitial fibrosis and cellular injury.
• The alternative pathway (AP) of complement, regulated by properdin, is implicated in initiating tubular cell damage.

Purpose of the Study:

• To investigate the inhibitory potential of C-reactive protein (CRP) in its monomeric (mCRP) and pentameric (pCRP) forms on properdin-mediated AP activation and renal tubular cell injury.
• To identify potential inhibitors of properdin in circulation.

Main Methods:

• Fluorescent microscopy, ELISA, and flow cytometry were used to assess properdin binding and complement activation.
• Experiments involved viable and necrotic renal tubular cells (PTECs) and Jurkat cells.

Main Results:

• Monomeric CRP (mCRP) inhibited properdin binding to viable PTECs and properdin-directed deposition of C3 and C5b-9.
• mCRP also inhibited properdin binding to necrotic Jurkat cells.
• Pentameric CRP (pCRP) showed no inhibitory effect.

Conclusions:

• mCRP acts as an inhibitor of properdin, preventing its binding to both necrotic and viable cells.
• mCRP regulates cell surface complement activation, potentially limiting tissue injury by controlling properdin-driven AP amplification.