Which of the following is not a mechanism that triggers the complement system?

• A. C3b binding to the surface of invading microbes.
• B. Antibodies binding to antigens found in the surface of invading microbes.
• C. Mannose-binding lectins binding to mannose on the surface of invading microbes.
• D. C3 convertase binding to the surface of invading microbes.

Answer: (D)

Verified step by step guidance

1. Understand the complement system: The complement system is a part of the immune system that enhances the ability to clear microbes and damaged cells, promote inflammation, and attack the pathogen's cell membrane.
2. Identify the pathways: The complement system can be activated through three main pathways: the classical pathway, the lectin pathway, and the alternative pathway.
3. Classical pathway: This pathway is triggered by antibodies binding to antigens on the surface of invading microbes, leading to the activation of the complement system.
4. Lectin pathway: This pathway is initiated when mannose-binding lectins bind to mannose residues on the surface of pathogens, activating the complement cascade.
5. Alternative pathway: This pathway is activated by the spontaneous hydrolysis of C3 and the subsequent binding of C3b to microbial surfaces, not by C3 convertase binding. C3 convertase is an enzyme complex that forms during the complement activation process, not a trigger for it.