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Complement factor I deficiency in a family with recurrent infections
M F Leitão1, M M Vilela, R Rutz
1Department of Pediatrics, State University of Campinas Medical School, SP, Brazil.
Immunopharmacology
|February 26, 1998
Summary
Factor I deficiency leads to uncontrolled complement activation and recurrent bacterial infections. Restoring factor I function in vitro corrected complement dysregulation and impaired immune functions in affected individuals.
Area of Science:
- Immunology
- Biochemistry
Background:
- Factor I deficiency results in uncontrolled alternative pathway activation, leading to complement component consumption.
- Clinical manifestations include recurrent bacterial infections, particularly in early infancy, such as meningitis and sepsis.
Observation:
- A Brazilian family with consanguinity presented with three children exhibiting complete factor I deficiency.
- Patients experienced chronic otitis, meningitis, respiratory infections, and one fatality due to sepsis.
- Reduced levels of C3, factor B, and properdin were observed, rendering the alternative pathway's hemolytic activity undetectable.
Findings:
- Factor I deficiency prevented C3b metabolism, leading to undetectable C3-derived split products.
- In vitro reconstitution with factor I restored regulatory function and C3b cleavage.
- Decreased and C3b-complexed factor H levels were observed, which normalized upon factor I addition.
- Complement-mediated functions like opsonization, chemotaxis, and phagocytosis were impaired.
Implications:
- This study highlights the critical role of factor I in complement regulation and host defense.
- Understanding factor I deficiency provides insights into managing recurrent infections in affected individuals.
- The findings underscore the importance of complement system analysis in diagnosing and treating primary immunodeficiencies.