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Serum bactericidal activity against Haemophilus influenzae.
1Department of Clinical Microbiology, Flinders Medical Centre, Adelaide.
Pathology
|April 1, 1988
Summary
An intact thiolester bond in complement component 3 (C3) is essential for bacterial killing via the alternative pathway. This bond enables C3 to activate the complement system, but antibody presence is crucial for bactericidal activity against Haemophilus influenzae.
Area of Science:
- Immunology
- Biochemistry
- Microbiology
Background:
- The complement system is vital for innate and adaptive immunity.
- Complement component 3 (C3) plays a central role in complement activation.
- The thiolester bond in C3 is critical for its function.
Purpose of the Study:
- To investigate the role of the C3 thiolester bond in complement-mediated bactericidal activity.
- To determine the necessity of antibody for alternative pathway-mediated killing of Haemophilus influenzae.
Main Methods:
- Used potassium bromide-treated serum deficient in C3 and C4.
- Reconstituted serum with native C3 (intact thiolester bond) or NH3.C3 (disrupted thiolester bond).
- Assessed bactericidal activity against Haemophilus influenzae b strains.
Main Results:
- Native C3, but not NH3.C3, supported significant bactericidal activity against H. influenzae b.
- Bactericidal activity was observed only in the presence of specific antibodies.
- Alternative pathway-mediated killing was antibody-dependent, even with native C3.
Conclusions:
- An intact C3 thiolester bond is required for C3 to function as a C5 convertase and mediate bactericidal activity.
- Antibody is absolutely essential for alternative pathway-mediated killing of H. influenzae.
- The biochemical structure of C3 dictates its functional capabilities in bacterial killing.