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Related Experiment Videos

Differences in complement activation between complement-resistant and complement-sensitive Moraxella (Branhamella)

C M Verduin1, M Jansze, C Hol

  • 1Eijkman-Winkler Institute of Medical and Clinical Microbiology, Utrecht University Medical Faculty, University Hospital, The Netherlands.

Infection and Immunity
|February 1, 1994
PubMed
Summary

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Moraxella catarrhalis uses a protein to resist complement killing by interfering with membrane attack complex formation. This resistance mechanism does not inhibit complement pathway activation but targets later stages of the complement cascade.

Area of Science:

  • Immunology
  • Microbiology
  • Bacterial Pathogenesis

Background:

  • Moraxella catarrhalis is a human pathogen that can cause respiratory tract infections.
  • Resistance to the human complement system is a key factor in bacterial survival and pathogenesis.

Purpose of the Study:

  • To elucidate the mechanism by which Moraxella catarrhalis achieves resistance to complement-mediated killing.
  • To identify the specific stage of the complement cascade that resistant strains target.

Main Methods:

  • Comparison of complement-sensitive and complement-resistant Moraxella catarrhalis strains.
  • Functional bystander hemolysis assay to assess complement-mediated lysis.
  • Enzyme-linked immunosorbent assay (ELISA) for soluble terminal complement complexes.

Related Experiment Videos

  • Treatment with trypsin to evaluate the role of protein-mediated resistance.

    • Main Results:

    • Complement-resistant strains activated complement pathways similarly to or better than sensitive strains.
    • Resistance was linked to interference with membrane attack complex (MAC) formation, not initial complement activation.
    • Dose-response curves differed significantly: resistant strains showed optimum curves, while sensitive strains showed linear curves.
    • Trypsin treatment abolished resistance in a resistant strain, converting its curve to a linear one.

    Conclusions:

    • Moraxella catarrhalis resistance to complement is mediated by a bacterial protein that interferes with MAC formation.
    • This protein likely acts by directly binding or inactivating terminal complement components or MAC intermediates.
    • The identified protein may bind a serum-derived inhibitor, further contributing to complement resistance.