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Related Experiment Videos

Complementary recognition of alternative pathway activators by decay-accelerating factor and factor H

D Kraus1, M E Medof, C Mold

  • 1Department of Molecular Genetics and Microbiology, University of New Mexico, Albuquerque 87131, USA.

Infection and Immunity
|February 7, 1998
PubMed
Summary

The alternative complement pathway distinguishes self from non-self using regulatory proteins. Bacterial lipopolysaccharide structure impacts complement activation and regulation by factor H and decay-accelerating factor.

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Area of Science:

  • Immunology
  • Microbiology
  • Biochemistry

Background:

  • The alternative complement pathway (ACP) is crucial for innate immunity, identifying and opsonizing pathogens like microorganisms.
  • Effective ACP function depends on distinguishing foreign (non-self) from host (self) components.
  • Key regulatory proteins, including factor H (H) and membrane decay-accelerating factor (DAF), control complement activation.

Purpose of the Study:

  • To investigate how lipopolysaccharide (LPS) structure from Salmonella Minnesota influences ACP activation.
  • To determine the susceptibility of LPS-bound C3b to regulation by factor H and DAF.
  • To assess the impact of LPS polysaccharide size on complement regulation.

Main Methods:

  • Liposomes containing wild-type and mutant Salmonella Minnesota LPS were incubated in serum to assess ACP activation.

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  • Bound C3b on LPS-liposomes was evaluated for regulation by factor H and DAF.
  • The cofactor activity of factor H on bound C3b was tested in the presence of varying LPS structures.

    • Main Results:

    • Re595 LPS (shortest mutant) did not activate the ACP, while R7 LPS (with an additional disaccharide) did.
    • ACP activation by R7 LPS was poorly regulated by DAF but inhibited by factor H.
    • Factor H's regulatory activity on C3b decreased with increasing LPS polysaccharide size.
    • Phosphatidylethanolamine-induced ACP activation was inhibited by DAF but poorly by factor H.

    Conclusions:

    • Bacterial LPS structure significantly modulates alternative complement pathway activation.
    • The size of LPS polysaccharide chains influences the effectiveness of complement regulatory proteins H and DAF.
    • Understanding these interactions is vital for developing strategies against complement-mediated immune evasion by pathogens.