Which of the complement pathways employs properdin?

• A. Alternative pathway
• B. Terminal pathway
• C. Classical pathway
• D. Lectin pathway

Answer: (A)

Verified step by step guidance

1. Understand that the complement system consists of three main pathways: Classical, Lectin, and Alternative, each initiating complement activation differently.
2. Recall that properdin is a positive regulator protein that stabilizes certain complement complexes, enhancing the activity of one specific pathway.
3. Identify that properdin specifically binds to and stabilizes the C3 convertase complex in the Alternative pathway, prolonging its activity on microbial surfaces.
4. Recognize that the Classical pathway is initiated by antibody-antigen complexes, and the Lectin pathway is initiated by mannose-binding lectin binding to pathogen surfaces, neither involving properdin.
5. Conclude that the pathway employing properdin is the Alternative pathway, as it uniquely uses properdin to stabilize its C3 convertase and amplify the complement response.