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Related Experiment Videos

The inhibitory effect of factor J on the alternative complement pathway

C González-Rubio1, M A Jiménez-Clavero, G Fontán

  • 1Unidad de Inmunología, Hospital la Paz, Madrid, Spain.

The Journal of Biological Chemistry
|October 21, 1994
PubMed
Summary

Factor J (FJ) regulates the alternative complement pathway by inhibiting C3 convertase generation and accelerating its decay. This glycoprotein modulates complement activation, similar to other highly charged inhibitory molecules.

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Area of Science:

  • Immunology
  • Complement System Biology

Background:

  • Factor J (FJ) is a cationic glycoprotein known to inhibit the classical complement pathway's C1 component.
  • The role of FJ in regulating the alternative complement pathway has not been fully elucidated.

Purpose of the Study:

  • To investigate the inhibitory activity of Factor J (FJ) on the alternative complement pathway.
  • To determine the mechanisms by which FJ modulates alternative pathway C3 convertase activity.

Main Methods:

  • Assays measuring C3 convertase generation and decay using sheep erythrocytes (EAC4b,3b) and complement components (B, D, P).
  • Fluid-phase assays assessing C3 cleavage by factor B.
  • Solid-phase binding assays to detect direct interaction of FJ with complement components.
  • Investigating the effect of polyanions (heparin) and surface interactions on FJ activity.

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Main Results:

  • FJ inhibits the formation of fluid-phase and cell-bound alternative pathway C3 convertase (C3b,Bb).
  • FJ accelerates C3 convertase decay, comparable to Factor H, with synergistic effects when combined.
  • FJ prevents alternative pathway initiation in stabilized systems but shows less efficiency with pre-formed convertases.
  • Direct binding of FJ to C3 convertase components was confirmed.
  • FJ's inhibitory activity is modulated by polyanions and surface interactions, with reversibility observed after heparin-Sepharose chromatography.

Conclusions:

  • Factor J (FJ) is a potent regulator of the alternative complement pathway, inhibiting C3 convertase formation and accelerating its decay.
  • FJ's activity is influenced by molecular charge and surface interactions, positioning it alongside other complement-inhibiting molecules like heparin.
  • These findings expand the understanding of complement regulation and identify FJ as a potential therapeutic target.