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Complement factor I in health and disease

Sara C Nilsson1, Robert B Sim, Susan M Lea

  • 1Department of Laboratory Medicine, Medical Protein Chemistry, Lund University, Sweden.

Molecular Immunology
|May 3, 2011
PubMed

Insights

Factor I (FI) regulates complement pathways by degrading C3b and C4b. FI deficiency causes severe infections, autoimmune diseases, or atypical hemolytic uremic syndrome.

Area of Science:

  • Immunology
  • Biochemistry

Background:

  • Factor I (FI) is a key regulator of all complement pathways.
  • It degrades activated complement proteins C3b and C4b with cofactor assistance.

Purpose of the Study:

  • To summarize the role of Factor I in complement regulation.
  • To describe the clinical consequences of Factor I deficiency.
  • To detail the structure and enzymatic activity of Factor I.

Main Methods:

  • Literature review of Factor I function and deficiency.
  • Structural analysis of the Factor I heterodimer.
  • Enzymatic activity assessment with natural and synthetic substrates.

Main Results:

  • Complete FI deficiency leads to complement consumption, causing severe infections, glomerulonephritis, and autoimmune diseases.
  • Incomplete FI deficiency is linked to atypical hemolytic uremic syndrome.
  • FI is an 88kDa heterodimer with specific structural domains and cofactor-dependent enzymatic activity.

Conclusions:

  • Factor I is essential for preventing complement-mediated pathology.
  • FI deficiency has significant clinical implications, ranging from infections to severe systemic diseases.
  • Understanding FI structure and function is crucial for managing complement-related disorders.

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